The history of Coulomb-excitation measurements with AGATA dates back to the very first physics experiment with this array, which took place in April 2010 and aimed at investigation of a highly-deformed structure in $^{42}$Ca [1,2]. The measurement provided magnitudes and relative signs of numerous E2 matrix elements coupling the low-lying states in $^{42}$Ca. The shape parameters obtained for the 0$^+_2$ and 2$^+_2$ states confirm that the excited structure possesses a strikingly large elongation, similar to that established for superdeformed bands in this mass region, and a slightly non-axial character. In contrast, those for the ground state are consistent with large fluctuations about a spherical shape.
During the AGATA campaign at GANIL, Coulomb-excitation data were collected as a by-product of experiments performed at near-barrier beam energies. Notably, the analysis of slightly "unsafe" Coulomb-excitation data on $^{106}$Cd, collected during an experiment aiming at lifetime measurements in $^{106,108}$Sn [3], provides information on the collectivity of the presumably oblate structure built on the 0$^+_3$ state, as well as on the role of octupole correlations in this nucleus [4].
In the recent months, three Coulomb-excitation measurements were performed with AGATA at LNL, aiming at verification of the multiple shape-coexistence scenario in $^{110}$Cd and $^{74}$Se, and that of the type-II shell evolution in $^{96}$Zr. The status of the on-going analysis will be briefly presented.
[1] K. Hadyńska-Klęk et al., Phys. Rev. Lett. 117, 062501 (2016).
[2] K. Hadyńska-Klęk et al., Phys. Rev. C 97, 024326 (2018).
[3] M. Siciliano et al., Phys. Lett. B 806, 135474 (2020).
[4] D. Kalaydjieva, PhD thesis, Université Paris-Saclay, 2023.
Away from the valley of stability, the imbalance between the number of protons and neutrons serves as a magnifying lens for specific components of the nuclear interaction that cannot be studied otherwise. In such regions of the nuclear chart, new phenomena as appearance or disappearance of magic numbers, shape coexistence or transitions, are examples of the manifestation of the influence of those terms, whose understanding is of fundamental importance. The nuclei in the A∼100 region show one of the most remarkable example of sudden nuclear shape transition between spherical and well deformed nuclei, associated with a shape-coexistence phenomenon [1].
This presentation reports on new spectroscopic measurements for the neutron-rich odd-even Br nuclei, lying one proton bellow the low-Z boundary of this island of deformation. The analysis is done from the combination of two experiments : the first one from a transfer- and fusion-induced fission experiment at GANIL using the combination of the large acceptance VAMOS++ spectrometer [2] and the new generation γ-ray tracking array AGATA [3], providing a unique opportunity to obtain an event-by-event unambiguous (A, Z) identification of one of the fission fragments, and the prompt γ-rays emitted in coincidence with unprecedented resolution. The second one is a thermal neutron induced fission experiment at ILL using the FIPPS spectrometer [4], allowing for high gamma fold coincidences measurements.
The level schemes from 87,89Br have been extended, and new level schemes are proposed for the first time for 91,93Br. These new spectroscopic information are compared to state of the art Large Scale Shell Model (LSSM) calculations and the recently developed Discrete Non Orthogonal shell model (DNO-SM) approaches [5]. A very good agreement between experiment and LSSM results is obtained and the DNO-SM results suggest an unexpected shape evolution in Br isotopes from N=52 to N=58.
[1] Paul E. Garrett, Magda Zielińska, and Emmanuel Clément. Prog. Part. Nucl. Phys., 124 :103931, 2022.
[2] M. Rejmund et al. Nucl. Inst. Methods Phys. Res. A, 646(1) :184–191, aug 2011.
[3] S. Akkoyun et al. Nucl. Inst. Methods Phys. Res. A, 668 :26–58, mar 2012.
[4] Michelagnoli, Caterina et al. EPJ Web Conf., 193 :04009, 2018.
[5] D. D. Dao and F. Nowacki. Phys. Rev. C, 105 :054314, May 2022.
Exotic nuclei, far from stability, are a perfect laboratory to probe the specific components of the nuclear interaction. The imbalance between the number of protons and neutrons can lead to the appearance of phenomena such as sudden shape transitions and shape coexistence. The nuclei with Z and N around 40 and 60, respectively, show one of the most remarkable examples of sudden nuclear shape transition between spherical and well deformed nuclei.
This work reports on new spectroscopic measurements for the neutron-rich Nb isotopes, produced in transfer and fusion-induced fission reactions at GANIL from two different experiments. The combination of the large acceptance VAMOS++, the new generation gamma tracking array AGATA along with the EXOGAM gamma- ray spectrometer provide a unique opportunity to obtain an event-by-event unambiguous (A, Z) identification of one of the fission fragments, with the prompt and delayed gamma-rays emitted in coincidence with unprecedented resolution.
The level scheme of $^{99, 102, 104, 105, 106}$Nb have been significantly updated and a level scheme is presented for the first time for the $^{107}$Nb nucleus. The analysis of a newly observed spherical/deformed shape coexistence in $^{99}$Nb will be presented, as the evolution of the nuclear deformation with the increasing neutron number. These results contribute to a better understanding of the nuclear structure of neutron-rich Niobium isotopes and provide very useful experimental data to constrain nuclear models in this complex island of deformation region.
The region of neutron-rich nuclei around $N= 60$ has attracted interest in the late eighties, and even until now, its unique features continue to be of great importance in our understanding of shape evolution far from stability. First indirect evidence of shape coexistence in the region comes from a substantial increase in the two-neutron separation energy together with the difference in mean-square charge radius in nuclei from rubidium to zirconium at $N=60$ [1], [2]. The observation of low-lying $0^+$ states in even-even strontium and zirconium isotopes and the inversion between the spherical and intruder configuration at $N=60$ and above supports the shape transition hypothesis. Such an inversion can be explained by a polarization mechanism introduced by P. Federman and S. Pittel [3], in which the addition of neutrons to the $g_{7/2}$ orbital can cause the promotion of protons in its spin-orbit partner orbital, $g_{9/2}$, which in turn can cause the promotion of more neutrons to $g_{9/2}$. Correlations between neutrons in $g_{9/2}$ and protons in $g_{7/2}$ lead to deformation and the mutual polarization causes the $Z=40$ gap to be reduced, and the lowering of the energy of the $0^+$ intruder configurations towards $N=60$. The most direct way to study these low-lying $0^+$ states in even-even nuclei is via conversion electron spectroscopy, to observe electric monopole transition to the ground state.
An experiment was conducted in October 2022 at ALTO, to investigate neutron-rich strontium and zirconium isotopes up to mass 100 through $\beta$ decay of a rubidium ISOL beam. The beam was then collected in the newly developed COeCO [4] decay station to measure the E0 decay strength in $^{98}$Sr and both $^{98}$Zr and $^{100}$Zr but also to look for a low-lying $0^+$ state, predicted but not yet discovered, in $^{100}$Sr. I will present the results of this experiment, which led to several re-measurements of half-lives of states in $^{96, 97, 100}$Zr, $^{97}$Sr as well as a new value for the half-life of the first $0^+$ excited state in $^{98}$Zr. This new half-life value allows to determine the strength of the E0 transition, which in turn gives a value of the difference in mean-square charge radius between the ground state and the first excited $0^+$ state. These results expand on our knowledge of shape transition in the region and open up new perspectives for conversion electron studies in neutron-rich nuclei produced at ALTO.
[1] U. Hager et al., Phys. Rev. Lett. 96, 042504 (2006)
[2] P. Campbell et al., Phys. Rev. Lett. 89, 082501 (2002)
[3] P. Federman and S. Pittel, Phys. Rev. C 20, (1979)
[4] G. Tocabens, PhD thesis, defended December 2022
The search for chargeless nuclei consisting only of neutrons has been a long-lasting challenge in nuclear physics, dating more than six decades back (see Ref. [1] for a recent review). The tetraneutron, in particular, has attracted a lot of experimental and theoretical attention. Most models agree that nuclear forces cannot bind four neutrons together without destroying many of the other successful predictions for light nuclei. The theoretical models, however, struggle to provide reliable and consistent predictions regarding the possibility of four neutrons forming a resonance system. On the other hand, no solid experimental information on possible correlations between four neutrons was available until recently as experiments suffered from low statistics and/or large background. The possibility of the tetraneutron forming a resonance state is still an open and fascinating question, which can now be probed theoretically with state-of-the-art ab-initio calculations and studied experimentally by employing new techniques in the upgraded, high-intensity, radioactive-ion beam facilities. In this talk, I will present a brief overview of this long-standing quest and discuss some recent, high-quality results from a novel experiment that was performed at the SAMURAI setup in RIKEN, Japan. This experiment probes the correlation energy between the four remaining neutrons after the quasi-elastic removal of alpha cluster from 8He projectiles and has provided for the first time a notably clean experimental signature. The results have been recently published in Nature [2]. The quest now continues with renewed interest as theoretical models attempt to reproduce the experimental result and new experiments aim to confirm and refine the measurement; hence, this talk will conclude with a brief discussion of these new perspectives.
[1] Marqués, F. M. & Carbonell, J. The quest for light multineutron systems. Eur. Phys. J. A 57, 105 (2021).
[2] Duer, M., Aumann, T., Gernhäuser, R., Panin, V., Paschalis, S., Rossi, D. M., et al. Observation of a correlated free four-neutron system. Nature 606, 678–682 (2022). https://doi.org/10.1038/s41586-022-04827-6
Light proton-unbound nuclei, $^8$C, $^7$B, $^6$Be and $^5$Li, were investigated by the missing mass method. By using this method, we can measure resonances independently of their decay channels. This is efficient especially for the four-proton unbound nucleus $^8$C. Decay channels can be also investigated by the coincidence detection.
We performed the experiment with an N=3 isotone secondary beam containing $^9$C, $^8$B, $^7$Be and $^6$Li produced by the LISE spectrometer. The beam was bombarded on a liquid hydrogen target of 1.5 mm in thickness. Resonances in proton-unbound N=2 isotones were systematically populated via the one-neutron transfer ($p,d$) reaction. An array of MUST2 telescopes was used to detect recoil deuterons from the target and decay fragments. We will report on the experimental results on newly observed resonances.
In the shell model framework, the two-body nuclear force can be divided into a central, spin-orbit (SO) and tensor parts. The vast majority of studies performed so far in the chart of nuclides shows that the amplitude of the SO splitting scales with the function presented by G.Mairle [1], from systematics of nuclei studied so far in the valley of stability. Two exceptions to this trend have been found so far for the $^{133}$Sn [2,3] and $^{35}$Si [4] nuclei. As for the first, deviation to the trend has been attributed to the effect of the continuum, while the second to the effect of the central proton depletion that induces a strong reduction of the SO splitting of orbits probing the interior of the nucleus [5,6]. There is not so far striking evidence of the effect of the tensor force that should induce a change in the SO splittings that depends on its strength.
An experiment has been recently performed using the R³B setup at GSI, within the FAIR Phase-0 program. One of the scientific goals of is to study the role of the tensor force when approaching the neutron drip-line. During this experiment a “cocktail” of nuclei, among which $^{22}$O and $^{21}$N, was sent on a 5 cm LH2 target surrounded by tracking detectors and the CALIFA calorimeter [7]. This calorimeter allows to detect $\gamma$-rays and light particles from the QFS reactions in inverse kinematics. To study the spectroscopy of unbound states with an unprecedented energy resolution, this new setup includes the high resolution and granularity neutron detector NeuLAND [8].
In this work, the $^{22}$O($p,2p$) and $^{21}$N($p,pn$) QFS knockout reactions provide us information on the tensor force contribution to the $0p_{1/2}$-$0p_{3/2}$ SO splitting in the N isotope chain, from N=8 to N=14 shell closure, when the neutron $0d_{5/2}$ orbital is filled. The first reaction gives access to the $1/2^-$ and $3/2^-$ states in $^{21}$N, and the second allows to check that 6 neutrons are indeed populating the $0d_{5/2}$ orbital in $^{21}$N.
Preliminary results from this study will be presented.
$[1]$ G. Mairle, Phys. Lett. B $\textbf{304}$, (1993) 39.
$[2]$ K. L. Jones et al., Nature $\textbf{465}$, (2010) 454.
$[3]$ R. Orlandi et al., Phys. Lett. B $\textbf{785}$, (2018) 615.
$[4]$ G. Burgunder et al., Phys. Rev. Lett. $\textbf{112}$, (2014) 042502.
$[5]$ O. Sorlin et al., Phys. Lett. B $\textbf{809}$, (2020) 135740.
$[6]$ A. Mutschler et al. Nature Phys. $\textbf{13}$, (2017) 152.
$[7]$ A. Knyazev et al., Nucl. Instr. and Meth. A $\textbf{940}$, (2019) 393-404.
$[8]$ K. Boretzky et al., Nucl. Instr. and Meth. A $\textbf{1014}$, (2021) 165701.
Proton-removal reactions along the Be-Li chain close to the drip-line have been investigated with the aim of establishing the role of the Geometrical Mismatch Factor (GMF) and NN effects [1] in lowering the cross sections, as observed previously in He-Li nuclei [2].
The experiment was performed at GANIL using 10Be and 12Be beams at 30 AMeV impinging a CD2 target, with an intensity of 3 · 10⁵ pps and 2 · 10⁴ pps respectively. The angle and energy of the light recoil were detected by using 8 MUST2 telescopes [3], and a zero-degree detector consisting of an ionization chamber and a plastic scintillator that permitted the identification of the heavy recoil.
The missing-mass technique was used to reconstruct the excitation energy spectrum, from which cross sections can be extracted. Particular attention has been paid to the 12Be(d, 3He)11Li transfer reaction, but also to the 12Be(d, t)11Be channel as it enables a further constrain to the GMF of 12Be [4].
Preliminary results of the excitation energy for 11Li and 11Be will be presented and an overview of the status of the analysis for 10Be reactions will be depicted
References
[1] N. K. Timofeyuk, J. Phys. G Nucl. Partic. 41, 094008 (2014).
[2] A. Matta et al., Phys. Rev. C 92, 041302 (2015).
[3] E. Pollacco et al., Eur. Phys. J. A 25, 287–288 (2005).
[4] F. Nunes et al., Nucl. Phys. A 609, 43–73 (1996)
The pygmy dipole resonance (PDR) is a vibrational mode described as the oscillation of a neutron skin against a core symmetric in number of protons and neutrons. The PDR has been the subject of numerous studies, both experimental and theoretical [1,2,3]. Indeed, the study of the PDR has been and still is of great interest since it allows to constrain the symmetry energy, an important ingredient of the equation of state of nuclear matter that describes the matter within neutron stars [4]. Moreover, the PDR is predicted to play a key role in the r-process via the increase of the neutron capture rate [5]. However, despite numerous experiments dedicated to the study of the PDR, a consistent description is still discussed. In this context, we propose to study the PDR using a new probe: the neutron inelastic scattering reaction (n,n’g).
An experiment to study the pygmy resonance in 140Ce using the (n,n’g) reaction has been carried out in September 2022. This experiment has been made possible thanks to the high-intensity proton beam of the new accelerator SPIRAL2 at GANIL and the NFS (Neutron For Science) facility. The experimental setup consisting of the new generation multi-detectors PARIS [6], for the detection of gammas coming from the de-excitation of the PDR, and MONSTER [7], for the detection of scattered neutrons, was used. In this talk, preliminary results will be presented.
[1] D. Savran, T. Aumann, A. Zilges, Prog. Part. Nucl. Phys. 70, 210-245 (2013)
[2] A. Bracco, E.G. Lanza, A. Tamii, Prog. Part. Nucl. Phys. 106, 360-433 (2019)
[3] E. G. Lanza, L. Pellegri, A. Vitturi, M. V. Andrés, Prog. Part. Nucl. Phys. 129, 104006 (2023)
[4] A. Carbone et al., Phys. Rev. C 81, 041301(R) (2010)
[5] S. Goriely, E. Khan, M. Samyn, Nucl. Phys. A 739, 331-352 (2004)
[6] A. Maj et al., Acta Phys. Pol. B40, 565 (2009)
[7] A. R. Garcia et al., JINST 7, C05012 (2012)
Since 2016, while PARIS array has been in its initial development phase, one cluster of phoswich detectors has been available for tests and experiments at IJCLab. Hence there has been an excellent synergy between the IJCLab facility and the PARIS detector in its development phase. In 2018, 33 PARIS phoswich detectors (almost 4 clusters) were coupled to the ν−ball1 gamma-ray spectrometer hosted by IJCLab. It was used to study the giant resonance gamma-ray decay in coincidence with low-lying deformed structures. After successful ν−ball1 campaign, in 2022, ν−ball2 started to collect data. PARIS 8 clusters (72 phoswiches) in ‘wall’ configuration were mounted at IJCLab in October 2022.
In the talk I will present analysis results from the PARIS@ν−ball1 campaign, as well as preliminary results of experiments performed with use of PARIS@ν−ball2 since November 2022 till July 2023.
An experimental campaign of measurements of the γ decay from states excited in nuclei using proton inelastic scattering reaction have been performed at CCB facility of IFJ PAN. The main goal of the experiments was to study the decay to the ground state of isoscalar giant quadrupole resonance (ISGQR) via γ-ray emission. Previously such phenomenon was observed only once, in 1980s [1].
The experiment was performed at Cyclotron Centre Bronowice (CCB) of IFJ PAN Kraków, Poland, a facility dedicated mainly to the proton radiotherapy. The experimental setup consisted of eight large-volume BaF2 γ -ray detectors of the HECTOR (High Energy deteCTOR) array [2] and 16 triple telescopes of the KRATTA (KRAków Triple Telescope Array) array [3] together with fast plastic scintillators for light charged particle identification and energy measurement. In the experiment the inelastic scattering of 85 MeV proton beam on 208Pb target has been employed and the scattered protons were measured in coincidence with γ transitions.
As a result the measurement of the ISGQR γ-decay has been confirmed and the branching ratio between ISGQR gamma decay to ground state and neutron emission was obtained [4]. During the talk I will present the experimental method, the used equipment as well as the obtained results. In addition, the outlook for the continuation of such studies will be discussed.
[1] J.R. Beene, et al., Phys. Rev. C 39, 1307 (1989);
[2] A. Maj et al., Nucl. Phys. A 571, 185 (1994);
[3] J. Łukasik et al., Nucl. Instrum. Methods Phys. Res., Sect. A709, 120 (2013);
[4] B. Wasilewska et al., Phys. Rev. C 105, 014310 (2022).
The fabrication of nanoporous PAA-g-PVDF membranes is based on the selective chemical etching of Swift Heavy Ions (SHI) tracks in a polymer thin film followed by AA radiografting inside the etched ion-tracks. PAA functionalized nanopores have demonstrated to efficiently trap and preconcentrate metal ions presents in water at open circuit. This passive metal adsorption at solid-liquid interface at the nanopore walls generally follows a Langmuir law. A Square-Wave Anodic Stripping Voltammetry (SW-ASV) protocol for accurate metal analysis at ppb level is established. After the presorption step, the prototyped probe connecting the nanoporous membrane-electrode is immersed in an appropriate buffer electrolyte for analysis. An accumulation potential (-1.2V / -0.8V for a maximum of 120s without stirring) is then performed to electrodeposit presorbed metal ions trapped inside the polymer porosity. The following stripping step reveals the redox potential of each electrodeposited metals (Ag/AgCl pseudo-reference). Multiple measurements in synthetic waters close to the composition of contaminated natural waters exhibited a decreasing precision with the number of readings R (1.65% (R=2) and 6.56% (R=3)) due to the diminution of trapped metal content in the porosity after each measurement. These membrane-electrodes should be used as disposable (one measurement per membrane). The intra-batch mean precision was 14% (n=3) while inter-batches precision was 20% (n=15). Linear and linear-log calibrations allow exploitation of metal concentrations in industrial wastes ranging from 10 to 500 g.L-1 and 100 to 1000 g.L-1 respectively. The LOD depends of the metal ion complexation ability with the functionalized entities grafted inside the nanoporosity. For example, it was found equal to 0.1 g.L-1 for Hg (II) [1] and 4.2 g.L-1 (3S/N) for Zn(II) [2].
[1] U. Pinaeva, D. Lairez, O. Oral, A. Faber, M-C. Clochard, T.L. Wade, P. Moreau, J-P. Ghestemc, M. Vivier, S. Ammor, R. Nocua, A. Soulé “Early warning sensors for monitoring mercury in water” Journal of Hazardous Materials 376 (2019) 37–47
[2] M-C. Clochard, O. Oral, O. Cavani, M. Castellino, L. Medina Legiero, T. Elan “Zinc detection in oil-polluted marine environment by stripping voltammetry with mercury-free nanoporous gold electrodes” Scientific Reports (2022) 12:15721 https://doi.org/10.1038/s41598-022-20067-0
The study of ion collision with biologically relevant molecules in the gas phase has received increasing interest in recent years in parallel with the development of ion beam therapy. Indeed, these studies help understanding the fundamental mechanisms involved at the molecular level such as fragmentation and electron emission. To study such processes, we have recently built an experimental set-up where the molecular target beam of biomolecules produced with a two-stage effusion cell crosses perpendicularly the projectile ion beam provided by the different GANIL beamlines (ARIBE, IRRSUD or SME). The charged particles (either electrons or fragment cations) emitted in the collision are extracted by a Velocity Map Imaging (VMI) spectrometer and detected with microchannel plates coupled to a phosphor screen. The electrode arrangement of the VMI spectrometer acts as an electrostatic lens focusing particles with the same initial velocity vector into the same position on the detector regardless of their initial position (within the small interaction volume). The 2D image observed on the detector is then processed using an inverse Abel transform algorithm in order to deduce the number of particles (electrons or ionic fragments) emitted as a function of their energy and their emission angle. In this presentation, recent measurements of absolute cross sections for electron emission from the nucleobases uracil and adenine upon collision with carbon ions (0.98MeV/u-C4+ and 13.7MeV/u-C5+) will be presented. Moreover, preliminary data on ion-induced fragmentation processes will be discussed along with the future improvement of the set-up.
Nuclear materials define a class of solid of interest for the nuclear industry with the specificity of being submitted to intense irradiation fields. Nuclear fuels and transmutation matrices deserve special attention due to their location at the core of the reactor, and due to the complexity of irradiation sources to which they are subjected, leading to both physical (radiation damage, atomic and electronic displacements, structural transformations) and chemical modifications (incorporation of new elements with their own chemistry in the solid matrix fuel). Ion beams delivered by accelerator facilities are unique tools to simulate the behavior of irradiated solids due to their flexibility: the various relevant parameters can be monitored selectively (e.g., ion, energy, fluence, flux, irradiation temperature) in single or (sometimes) in dual beam conditions. In particular, swift heavy ions delivered by the GANIL facility are unvaluable probes to examine extreme irradiation condition provided by electronic stopping power, giving clues to extrapolate the fuel behavior for future nuclear reactors. Selected examples of irradiation condition for nuclear fuels and transmutation matrices and their consequences for their structural evolution upon ion bombardment will be discussed.
Fission at low excitation energy has shown over the past decades to be an ideal playground for studying fundamental nuclear properties, in general, and dynamical aspects of nuclear reactions, in particular. While the importance of structural effects in the nascent fragments has been established through numerous studies, the VAMOS campaigns performed during the last few years definitively confirmed the so-far elusive, but clearly dominant, role of specific proton configurations in driving the fission decay of actinides. In addition, the innovative approach implemented at VAMOS made it possible to address the competition between the influence of neutrons and protons with the accurate measurement of elaborate observables such as the fragment N/Z ratio and odd-even effects as a function of excitation energy. Most recently, the enhancement of the set-up permitted to apply the approach to fission of pre-actinides around lead, giving access for the first time in this region to bright new information on fragment isotopic information, N/Z ratio and prompt neutron multiplicity. The unexpected leading role of the proton subsystem with atomic number between the Z=28 and Z=50 characterized by very specific deformations at scission was revealed. Combined with the previously identified stabilizing forces, this finding demonstrates the striking connection between the "old" (actinide) and "new" (pre-actinide) islands of asymmetric fission. This connection is crucial to steer the strive for an unified theory of fission over the nuclear chart.
The recent results obtained at VAMOS are presented, and the “en route” campaigns and projects are discussed. The insight provided by the GANIL approach within the international context of fission studies is finally emphasized.
D. Doré1), D. Ramos2), E. Berthoumieux1), J.-E. Ducret2),
X. Ledoux2), P. Marini2,3), S. Oberstedt4), J. Pancin2),
M. Ballu1), P. Herran1), G. Kaur1), A. Letourneau1), T. Materna1), P. Miriot-Jaubert1),
B. Mom1), L. Thulliez1), M. Vandebrouck1), A.-M. Frelin2), P. Sharma2), I. Jangid2),
A. Cheboubbi5), O. Litaize5), O. Serot5), A. Porta6), M. Estienne6), M. Fallot6),
E. Bonnet6), J. Pépin6), L. Matthieu3), T. Kurtukian-Nieto3)
1) DPhN/Irfu, CEA/Saclay, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
2) GANIL, Caen,14000, France
3) Univ. Bordeaux, CNRS, LP2I, UMR 5797, F-33170 Gradignan, France
4) European Commission, Joint Research Centre (JRC), 2440 Geel, Belgium
5) CEA, DES, IRESNE, DER, SPRC, Cadarache, 13108 St. Paul lez Durance, France
6) Laboratoire Subatech, University of Nantes, CNRS/IN2P3, Institut Mines Telecom Atlantique, 44307 Nantes, France
diane.dore@cea.fr
Abstract: Nowadays the fission process still presents a great interest from both theoretical and experimental points of view. New developments on microscopic calculations and expected improvements of nuclear reactors are among the main motivations for new experimental programs devoted to the study of nuclear fission. The FALSTAFF spectrometer aims at providing constraining data that may significantly contribute to an accurate description of the fission process. In its future two-arm configuration, the goal of the FALSTAFF program will be to determine the evolution of prompt neutron multiplicity and the fragment characteristics (mass, charge and kinetic energy) as a function of the compound nucleus excitation energy, by studying neutron-induced fission of specific actinides in the MeV range. Recently FALSTAFF in its one-arm configuration was used in an experiment dedicated to the study of 235U(n,f) at NFS (Neutrons for Science, SPIRAL2/GANIL).
The white energy spectrum of incident neutron beam provided by reactions of deuterons on a thick 9Be production target at NFS allows us to study 235U post-neutron evaporation fission fragments over the incident neutron energy range from 0.5 to 40 MeV. The fragment velocities were measured thanks to two MWPC-SED detectors giving access to the time and position of the fragments crossing an emissive foil while an axial ionization chamber measured the residual energy and the energy loss profile of fragments. LaBr3 detectors were coupled to FALSTAFF to provide an absolute time reference point allowing the determination of the incident neutron energy. The evolution of the fragment characteristics can then be studied as a function of the incident neutron energy.
In this paper, the motivations for the FALSTAFF@NFS experiment will be detailed and the experimental setup will be described. Preliminary results for the fragment velocity, energy, mass and charge distributions will be presented. Foreseen experiments at NFS will be discussed.
Nuclear fission is a complex, dynamical process involving a dramatic re-arrangement of nuclear matter. Even after much experimental and theoretical investigations over many years this fascinating nuclear reaction is stil not fully understood due to the large number of degrees of freedom and final multitude of final states which can be populated. The gamma rays emitted in nuclear fission contain valuable information about both the fission process itself and the structure of exotic neutron-rich nuclei. In this presentation I will address ongoing work to perform gamma-ray spectroscopy of nuclear fission with state-of-the art hybrid deterction systems to learn more about open questions such as excitation energy and angular momentum sharing, high energy gamma-ray emission and barriers in the fission potential energy landscape. The presentation will focus on ongoing and future work at the ALTO and NFS facilties.
Fission of atomic nuclei is often affected by quantum effects leading to asymmetric mass splits. These shell effects can be investigated at the mean-field level with single particles level densities, indicating that several proton and neutron shell effects are usually at play prior to scission [1]. In addition to shell effects in the compound nucleus, quantum shells stabilising fission fragments with octupole shapes have been invoked as a factor determining the distribution of nucleons between the fragments at scission, explaining the fact that the centroid of the heavy fragment charge distribution is found around Z ≃ 54 in actinide fission [2].
Shell effects have also been identified in the quasifission process [3]. Quasifission occurs in fully damped heavy-ion collisions following a significant mass transfer from the heavy to the light fragment, without formation of a compound nucleus. Microscopic calculations recently showed that similar shell effects were to be expected in both fission and quasi-fission [4,5].
Here, we use static and time-dependent mean-field approaches to investigate and compare the shell effects affecting fragment formation in both fission and quasifission. In particular, we discuss the possibility to use quasifission to obtain some information on fission modes in superheavy nuclei, which would benefit from the fact that quasifission cross-sections are much larger than for fusion-fission.
[1] R.N. Bernard, C. Simenel, G. Blanchon, EPJA 59, 51 (2023)
[2] G. Scamps, C. Simenel, Nature 564, 382 (2018)
[3] M. Morjean, D.J. Hinde, C. Simenel et al., Phys. Rev. Lett. 119, 222502 (2017)
[4] C. Simenel, P. McGlynn, A. S. Umar, K. Godbey, Phys. Lett. B 822, 136648 (2021)
[5] P. McGlynn and C. Simenel, arXiv2302.06938
Neutron star (NS) is believed to be created as a remnant of supernova explosion. The property of neutron star can be described with the thermodynamical character (Equation of State, EoS) of nuclear matter.
For the determination of outer core NS-EoS, we have performed a series of measurements using heavy ion accelerator of RIKEN Radio Isotope Beam Factory (RIBF).
An international collaboration, named SPiRIT has been formed for the experimental study of the density dependence of symmetry energy term in nuclear EoS. One of the main devices of experimental setup is a Time Projection Chamber (TPC) which will be installed into the SAMURAI dipole magnet at RIBF. The TPC will measure charged pions, protons and light ions simultaneously in heavy RI collisions of neutron rich Sn reactions,
Sn-132 + Sn-124, and neutron deficient Sn reactions, Sn-108 + Sn-112, at Ebeam=270MeV/u.
In this talk, highlights of experimental result will be presented in addition to overview of SPiRIT device.
Heavy-ion collisions in the intermediate energy regime (20-100 MeV/nucleon) are a widespread tool to probe the properties of nuclear matter far from equilibrium: among other topics, they allow to investigate isospin transport phenomena, which can be interpreted in the framework of the Nuclear Equation of State (NEoS), i.e. the thermodynamic description of nuclear matter.
The INDRA-FAZIA apparatus, operating in GANIL, is particularly well suited to investigate such kind of phenomena, exploiting the best characteristics of INDRA and FAZIA: twelve FAZIA blocks cover the forward polar angles (from 1.4° to 12.6°) providing good charge and mass identification for the heavy quasi-projectile residue and for most of the reaction products, while twelve INDRA rings provide a large angular coverage (from 14° to 176°). The coupling of the two apparatuses was completed in 2019, and the first experiment was devoted to the study of isospin diffusion in $^{64,58}$Ni+$^{58,64}$Ni at 32 and 52 MeV/nucleon.
In this talk the most recent results from the INDRA-FAZIA apparatus will be presented, focusing on its first experiment. The identification capability of the apparatus allowed us to highlight the isospin transport effects on the neutron content of light and heavy fragments belonging to the QP phase space, obtaining coherent indications of the evolution towards isospin equilibration. Moreover, the high granularity of FAZIA makes it suitable to study the isospin content of the two heavy fragments produced in the quasi-projectile breakup, which in most cases can be simultaneously detected and mass identified. An in-depth analysis of this exit channel of semiperipheral collisions has been carried out, leading to novel results that add valuable information for a comprehensive view of the process.
The experimental results are also compared to the predictions of the antisymmetrized molecular dynamics (AMD) model, coupled with GEMINI++ as afterburner, in order to validate the event selection procedure and to inspect the dynamical features of the reactions. More specifically, the AMD calculations have been used to extract the information on the relevant timescales of the interaction process, thus helping with the interpretation of experimental observations.
The understanding of neutron star properties from fundamental physics is still far from being completed. One of the reasons is that the theory for strong force, QCD, does not apply simply to neutron star matter at a few times the nuclear saturation density. At low density, chiral effective field theory is fixing a limit which can be incorporated in the description of the crust of neutron stars. Above saturation density, the question of phase transition(s) and the onset of new degrees of freedom are extremely important since it impacts the properties of the core of neutron stars. Astrophysical observations (gravitational wave, x-rays, radio) and nuclear physics experiments can be employed to constrain the equation of state for neutron stars, including the symmetry energy. Prospects for future detections will also be discussed.
We present the first triaxial beyond-mean-field studies of super-heavy nuclei. They include the restoration of the particle-number and angular-momentum symmetries and the mixing of different shapes using the generator coordinate method. The importance of the $\gamma$ degree of freedom is highlighted by comparing the triaxial to axial-symmetric calculations performed within the same framework. In the calculations, the effective finite-range density-dependent Gogny force is used.
Calculations for the even Flerovium isotopes towards the supposed $N$=184 neutron shell closure were performed [1] .
For the three even Fl isotopes between the prolate $^{288}$Fl and the oblate $^{296}$Fl triaxial ground-state shapes are predicted, whereas axial-symmetric calculations suggest a sharp
prolate-oblate shape transition between $^{290}$Fl and $^{292}$Fl. A novel type of shape coexistence, namely that between two different triaxial shapes, is predicted to occur in $^{290}$Fl.
Finally, the existence of a neutron shell closure at $N$=184 is confirmed, while no evidence is found for $Z$=114 being a proton magic number.
In the same framework, we present the study of the excitation spectra of super-heavy nuclei. As representative examples, we have chosen the members of the $\alpha$-decay chains of $^{292}$Lv and $^{294}$Og [2,3],
the heaviest even-even nuclei which have been synthesized so far using $^{48}$Ca-induced fusion-evaporation reactions.
Rapidly varying characteristics are predicted for the members of both decay chains, which are further accentuated when compared to the predictions of simple collective models. The calculations will be compared to the available experimental data [2] and the prospect of observing $\alpha$-decay fine structures in future experiments discussed. Additionally, the excitation spectra along the $\alpha$-decay chains of the odd-A nucleus $^{289}$Fl is discussed [4]. \
[1] J. Luis Egido and Andrea Jungclaus, Phys. Rev. Lett. 125, 192504 (2020)
[2] A. S\r{a}mark-Roth, Phys. Rev. Lett. 126, 032503 (2021)
[3] J. Luis Egido and Andrea Jungclaus, Phys. Rev. Lett. 126, 192501 (2021)
[4] D. M. Cox at al, Phys. Rev. C107, L021301(2023)
The excitation functions for producing isotopes of super-heavy nuclei with charge numbers 108-116 are computed and compared to experimental data for $^{48}Ca$ and $Ra$/actinide-based complete fusion reactions.
The estimated production cross sections suggest that the Ds nucleus marks the boundary between the island of stability of super-heavy nuclei and the mainland, which contains a relatively large number of neutrons [1].
Comparing the calculated production cross-section of the Cn isotope in the Ca+U hot fusion reaction with the experimental data from the Zn+Pb cold fusion reaction, it is evident that the fusion probability correlates strongly with asymmetry in the entrance reaction channel.
This correlation suggests the possibility of bridging the gap between isotopes of super-heavy nuclei synthesized in opposite (cold and hot) reaction scenarios [2].
REFERENCES
[1] J. Hong, G. G. Adamian, N.V. Antonenko, M. Kowal, P. Jachimowicz,
Physical Review C bf 106 (1), 014614 (2022).
[2] J. Hong, G.G. Adamian, N.V. Antonenko, M. Kowal, P. Jachimowicz,
The European Physical Journal A 58 (9), 180 (2022).
One of the long-standing topics in nuclear physics is the competition between the symmetric and asymmetric modes of quasi-fission in collisions of heavy and very heavy nuclear systems. The separation of these modes from the excited compound nucleus fission is quite difficult experimentally. Theoretical calculations may give valuable insight into ascertaining contributions from these various processes. And may be used to evaluate fusion probabilities for the synthesis of super-heavy elements.
In this talk, a new method for predicting quasi-fission and fusion-fission yields will be presented. The approach uses a random walk algorithm, in which the shape evolution is governed by the density of states above the multidimensional potential energy surface (PES). The PESs were calculated within the latest version of the Warsaw macroscopic-microscopic model [1], with rotational energy taken into account.
Three cold fusion reactions will be discussed in detail: $^{208}$Pb+$^{48}$Ca, $^{208}$Pb+$^{50}$Ti and $^{208}$Pb$+^{54}$Cr. The influence of angular momentum and excitation energy on ratios of symmetric and asymmetric divisions will be demonstrated. The absorbing nature of the second minimum, leading to a very symmetric mode, will also be shown.
[1] P. Jachimowicz, M. Kowal, and J. Skalski, At. Data. Nucl. Data. Tables. 138, 101393 (2021).
DNA origami nanostructures represent a unique substrate for in singulo experiments with biomolecules, nanotechnology and medicine. In our recent experiments at GANIL, we used these nanostructures as nano-dosimeters to observe damage to DNA. Patterning of the surface deposited DNA origami as well as damage to nanostructures placed in bulk water will be described with focus on physico-chemical effects near the track, which could not be easily studied using other methods.
New accelerators are being developed, either for medical applications (X-ray radiotherapy, hadrontherapy, radiotherapy by synchrotron radiation and "flash" therapies), or for nuclear physics. These developments create the need for very precise beam monitoring with fast counting in a highly radiative environment. An important issue is the adaptation to the temporal beam structures, which vary greatly depending on the type of accelerators (cyclotrons, synchro-cyclotrons or synchrotrons), in terms of duty cycle or peak intensity. A recent tendency to increase the intensity of the beams, for example in a clinical setting, for flash therapy, poses new challenges for the detection of secondary radiation (adapting the counting capacity of the detectors, electronics and data acquisition). The intrinsic qualities of diamond (fast timing, low leakage current, excellent signal-to-noise ratio, radiation hardness, equivalence to human tissue) make this semiconductor a perfect candidate to meet the monitoring requirements of such accelerators and the detection of particles.
The objectives of our multidisciplinary projects are the development of innovative diamond detectors for beam monitoring based either on single or poly-crystalline Chemical Vapor Deposition (CVD) and dedicated front-end electronics readout designed at laboratory. Diamonds are used as solid-state ionization chambers. Their charge collection properties were investigated with various ionizing particles to evaluate the capability of diamond to be a position sensitive detector. Detectors were exposed to 68 MeV proton (ARRONAX) and 95 MeV/u carbon ion beams (GANIL), short-bunched 8.5 keV photons from the European Synchrotron Radiation Facility (ESRF) and 30 keV electron beams at Institut Néel to perform charge collection 2D mapping. Our ultimate scientific objective is to demonstrate that diamond can become a “standard detector” for particle detection, particle counting, time stamps through the design of beam monitors operating with temporal resolutions of 100 ps or less and a high-count rate (from a single particle up to bunches of thousand particles) over a wide dynamic range of beam intensities (fraction of pA up to µA).
Glioblastoma (GBM) are brain tumors resistant to conventional therapies, in particular to radiotherapy based on X-rays. Therefore, the use of hadrontherapy appears as very appealing strategy thanks to their finite dose deposition to spare normal brain tissue but also to their greater biological efficacy toward radioresistant tumor cells and their low sensitivity to hypoxia, a well know factor of radioresistance.
Here, we evaluated in vitro the effects of high-LET particles, especially carbon ions on hypoxia induced radioresistance. Hypoxia-induced radioresistance was studied in two human GBM cells (U251, GL15) exposed to X-rays or to carbon ion beams with various LET (28, 50, 100 keV/µm). Cell survival, radiobiological parameters and cell cycle, were assessed under those conditions. These results demonstrate that, although CIRT is more efficient than X-rays in GBM cells, hypoxia can limit CIRT efficacy in a cell-type manner that may involve cell-specific pathways. These results also confirm that other mechanisms in parallel to hypoxia are involved in radioresistance.
Glioma stem cells (GSC) are suspected to be the most radioresistant cells due to their quiescent state and high efficacy in DNA repair pathways. The number of GSC increases after radiotherapy and is associated with the risk of recurrence. This increase in GSC could result from dedifferentiation of tumor cells after X-ray irradiation. The impact of hadrontherapy on tumor cell dedifferentiation is less documented. We therefore studied the effect of different radiation modalities on this dedifferentiation capacity in human GBM cells (U87-MG). Interestingly, our results show that protons and in a less manner carbon ions decrease the formation of sphere contrary to X-rays. We are now conducting experiments to test whether the combination of radiation and hypoxia targeting agents could improve the effects of radiation alone.
Lastly, while hadrons appear of main interest to spare normal tissue due to ballistic properties, the effects on non-tumor tissues remain to be determined. It is important to question the potential effects of these new treatment modalities on cerebral cells. Preliminary results on various cells derived from normal brain will also be presented.
In conclusion, our study shows while targeting HIF pathways could rather be interesting in presence of X-rays. The use of hadrons limits the dedifferentiation ability of GBM. Thus, hadrontherapy seems to be a promising therapy to limit resistance and thus target the recurrence of GBM.
Exploiting closed-path ion trajectories in an electrostatic ion trap, the multi-reflection time-of-flight mass spectrograph (MRTOF-MS) [1] is one of the most promising techniques for precise mass measurements of short-lived isotopes. Exotic ions produced at radioisotope facilities are stored in an electrostatic trap at kinetic energies on the order of a few keV, reflected back and forth between two electrostatic ion mirrors, and ultimately ejected to a detector for time-of-flight (TOF) determination. By comparison of precise TOF data obtained from ions of well-known mass, the mass of an unknown ion can be calculated with relative uncertainties reaching $\Delta m/m < 5 \cdot 10^{-8}$ using state-of-the-art technology.
At the RIBF/BigRIPS facility of RIKEN (Wako, Japan) the new ZD-MRTOF system [2,3] located downstream of RIBF's ZeroDegree (ZD) spectrometer has been put into operation. The precision mass spectrometer is coupled to a cryogenic helium-gas filled ion catcher [4], where the initially relativistic reaction products are stopped, thermalized, and extracted as ions to be forwarded to the MRTOF-MS.
Since autumn 2020 exotic ion beams are provided to our new setup, and previously unknown radioactive isotope masses, or those with high mass uncertainty, have been determined with high precision and accuracy. This contribution will focus on the success of this setup and the recent achievements for nuclear mass measurements. The physics results and an outlook for the near future program will be presented.
Furthermore, new efforts have been made to improve the wideband mass accuracy of the system, and I will discuss about the presently known causes of uncertainties for wideband mass measurements in MRTOF-MS and our present state of knowledge for possible solutions and technical challenges.
[1] H. Wollnik and M. Przewloka, Int. J. Mass Spectrom. Ion Proc. 96, 267 (1990)
[2] M. Rosenbusch et al., Nucl. Instr. Meth A (under review), arXiv:2110.11507
[3] M. Rosenbusch et al., Nucl. Instr. Meth B 463, 184 (2019)
[4] A. Takamine et al., Acc. Prog. Rep. 52, 139 (2019)
The existence and stability of heavy nuclei is a forefront topic in physics. Modern laser spectroscopy techniques provide a unique tool to study nuclear shell effects by measuring isotope shifts to infer mean-square charge radii and hence deduce nuclear size and shape. Laser spectroscopy measurements of the isotope shift of an atomic transition of the actinide element fermium (Z=100) have been recently carried out covering isotopes across the N=152 shell gap. On-line and off-line laser spectroscopy experiments with direct and indirect production schemes and offline production methods were combined and methodologically pushed forward to measure isotope shifts in fermium isotopes. Previously non-accessible isotopes, short and long-lived, were covered, enabling experiments at atom-at-a-time quantities through newly developed detection concepts. Changes in the mean-square charge radii were extracted for the longest chain of isotopes investigated in the region of the heavy actinides revealing information on the deformation around the N=152 shell gap.
The Super Separator Spectrometer-Low Energy Branch (S$^3$-LEB) is a low-energy radioactive ion beam experiment under commissioning as part of the GANIL-SPIRAL2 facility [1-3]. It will be used for the production and study of exotic nuclei by in-gas laser ionization and spectroscopy (IGLIS), decay spectroscopy, and mass spectrometry.
Development work has been ongoing at the S$^3$-LEB setup [2-5]. It uses in-gas-jet laser ionization, to resonantly ionize the neutralized atoms, and ion guides to send them to the Piège à Ions Linéaire du GANIL pour la Résolution des Isobares et la mesure de Masse (PILGRIM), a Multi-Reflection Time Of Flight Mass Spectrometer (MR-TOF-MS), or to a decay spectroscopy study station, SEASON. A buffer gas cell with 400 ms extraction time is now coupled to the ion transport ensemble and a de-Laval nozzle of Mach number M ~ 8 (developed at KU Leuven) has been installed at the gas cell aperture, which can create a hypersonic jet of narrow velocity distribution in a reduced collision environment. The hypersonic jet environment reduces the Doppler and pressure broadening by at least an order of magnitude compared to the gas cell [6,7]. Laser spectroscopy with suitable atomic transition schemes at S3-LEB thus offers improved spectral resolution (≤ 300 MHz) while maintaining high efficiency. It is an efficient technique giving access to isotope shifts and hyperfine constants measurements and thus to nuclear structure such as nuclear spin, moments and difference in nuclear charge radii for the exotic nuclei.
Here, we present ongoing technical developments including development of a continuous wave Ti:sapphire laser system for high resolution laser spectroscopy. The results from the offline commissioning of S3-LEB with first in-gas-jet high-resolution laser spectroscopy results of erbium will be presented. Measurements of the isotope shifts and hyperfine constants in the hypersonic gas jet will be presented and compared with literature and measurements in an Atomic Beam Unit (ABU)[8]. Characterization of the pressure-broadening effects in the gas cell will be reported. Additionally, the first optimization of the overall transport efficiency for the setup with laser-produced ions will be presented.
References:
[1] Grand Accélérateur National d'Ions Lourds, URL: https://www.ganil-spiral2.eu/en/
[2] F. Déchery., et al., Eur. Phys. J. A 51, 66 (2015)
[3] F. Déchery., et.al., NIMS B, 376125 (2016)
[4] J. Romans., et al., Atoms, 10, 21 (2022)
[5] J. Romans., et.al., NIM B, 536, 102 (2023)
[6] R. Ferrer., et.al., NIMS B, 317570 (2013)
[7] R. Ferrer., et.al., Nat. Comm. 8, 14520 (2017)
[8] A.Ajayakumar., et.al.,NIM B, 539, (2023)
Optical spectroscopy of superheavy elements is an experimental challenge. The production yields of the elements are about one atom per second or even less, the half-lives are extremely short, and the atomic structure is uncharted experimental territory. Conventional spectroscopy techniques based on fluorescence detection are no longer suitable because they lack the sensitivity required to study superheavy elements. Resonance ionization spectroscopy has proven sensitive enough to study the atomic structure of the element nobelium (No, element number 102) [1] and is now being continuously developed to probe the next heavier element, lawrencium (Lr, element number 103).
Recently proposed laser resonance chromatography (LRC) [2] could remedy this situation by providing sufficient sensitivity for the study of superheavy ions and overcoming the difficulties associated with other methods. The novel method combines the element selectivity and spectral precision of laser spectroscopy with the cutting-edge technology of ion mobility spectrometry. Its successful application in the realm of superheavy elements would not only improve our understanding of the existence and functioning of such synthetic and exotic atoms, but also provide valuable data for astronomers searching for possible production sites of such elements in the universe.
In my talk, I will introduce the LRC technique and setup and show initial results from inauguration experiments before presenting prospects for the spectroscopy of Lr+ cations.
This work is supported by the European Research Council (ERC) (Grant Agreement No. 819957).
References:
[1] M. Laatiaoui et al., Nature 538 (2016) 495.
[2] M. Laatiaoui et al., PRL 125 (2020) 023002.
The Z=6 shell gap in neutron-rich carbon isotopes has been a subject of debate, with recent studies claiming its prevalence in this region of the nuclear chart [1], in contradiction with recent measurements [2] and shell model predictions [3].
In order to shed more light into this subject, the structure of $^{19}$N was investigated through the proton-removal d($^{20}$O, $^{3}$He) reaction using the active target ACTAR TPC [4].
In 2022, the GANIL facility provided a pure $^{20}$O beam which was selected by the LISE3 spectrometer at 35A MeV with an intensity of 2$\cdot 10^{4}$ pps. The beam was delivered to the ACTAR TPC setup, filled with a 90/10 mixture of $D_{2}$ and $C_{4}H_{10}$ at 1 bar. The energy of the particles leaving the volume was measured in the Si pad detectors while the angle was obtained from the reconstruction of the tracks in the gas. The $E_{x}$ spectrum was built with the missing mass technique. The obtained results demonstrate the potential of the ACTAR TPC setup for future transfer reaction experiments.
The low-lying structure of $^{19}$N revealed multiple $p$-hole states with l=1 determined from the differential cross section. The location of the states that carry the largest 0p$_{1/2}$ and 0p$_{3/2}$ strength allowed for the determination of the ($\pi 0 p_{1/2}$-$\pi0p_{3/2}$) spin-orbit splitting in $^{20}$O. Our results support a reduction of the Z=6 shell gap due to the tensor force in agreement with theoretical predictions from [3] using state-of-the art interactions in this region such as YSOX and SFO-tls.
References:
[1] D.T. Tran et al., Nature Communications, 9, (2018),1594.
[2] I. Syndikus et al., Physics Letters B, 809, (2020), 135748.
[3] T. Otsuka et al. Phys. Rev. lett. 95, (2005), 232502
[4] B. Maus et al. Nucl. Instrum. Meth. Phys. Res. A 940, (2019), 01689002.
Coulomb barrier scattering of the proton halo nucleus 17Ne
I. Martel(a), J. Díaz-Ovejas(b), D. Dell’Aquila(c,d),L. Acosta(e), J. L. Aguado(a), G. de Angelis(f), M. J. G. Borge(b), J. A. Briz(b), A. Chbihi(g), G. Colucci(h), C. Díaz-Martín(a), P. Figuera(d), D. Galaviz(i), C. García-Ramos(a), J. A. Gómez-Galán(a), C. A. Gonzales(a), N. Goyal(g), N. Keeley(j), K. W. Kemper(k), T. Kurtukian-Nieto(l), D. J. Malenica(m), M. Mazzocco(n,o), D. Nurkic(p), A. K. Orduz(g), A. Ortiz(g), L. Palada(m), C. Parascandolo(q), A. Di Pietro(d), A. M. Rodriguez(a), K. Rusek(h), F. Salguero(a), A. M. Sánchez-Benítez(r), M. Sánchez-Raya(a), J. Sánchez-Segovia(a), N. Soic(m), F. Soramel(n,o), M. Stanoiu(s), O. Tengblad(b), N. Vukman(m), M. Xarepe(i)
(a) Science and Technology Research Centre, University of Huelva, 21071 Huelva, Spain.
(b) Instituto de Estructura de la Materia, CSIC, 28006 Madrid, Spain.
(c) Dipartimento di Chimica e Farmacia, Universitá degli Studi di Sassari, Sassari, Italy .
(d) INFN-Laboratori Nazionali del Sud, 95123 Catania, Italy.
(e) Instituto de Física, UNAM, México.
(f) INFN-National Laboratories of Legnaro, 35020 Legnaro (PD), Italy.
(g) Grand Accélérateur National d’Ions Lourds, BP 55027-14076 Caen, Cedex 05, France.
(h) Heavy Ion Laboratory, University of Warsaw, ul. Pasteura 5a, 02-093 Warsaw, Poland.
(i) LIP, Av. Prof. Gama Pinto 2, PT-1649-003, Lisboa, Portugal.
(j) National Centre for Nuclear Research, ul. Andrzeja Sołtana 7, 05-400 Otwock, Poland.
(k) Department of Physics, The Florida State University, Tallahassee, Florida 32306, USA.
(l) Centre d’Etudes Nucléaires de Bordeaux Gradignan, Gradignan F-33175, France.
(m) Rudjer Boskovic Institute, Bijenicka cesta 54, HR-10000 Zagreb, Croatia.
(n) Dipartimento di Fisica e Astronomia, Universitá di Padova, I-35131 Padova, Italy.
(o) INFN-Sezione di Padova, via F. Marzolo 8, I-35131 Padova, Italy.
(p) Department of Physics, Faculty of Science, University of Zagreb, Zagreb, Croatia.
(q) INFN-Naples, Italy.
(r) Centro de Estudios Avanzados en Física, Matemáticas y Computación, University of Huelva, 21071 Huelva, Spain.
(s) IFIN-HH PO-BOX MG-6, 76900 Bucharest Magurele, Romania.
Abstract
17Ne is a proton drip-line nucleus and a candidate for a Borromean two-proton halo with a 15O core. Elastic scattering and the inclusive 15O production on a 208Pb target were measured for the first time at the SPIRAL1 facility at GANIL [1]. The experiment was carried out using the GLORIA detector array [2], a compact DSSSD array able to provide a continuous angular distribution of relevant reaction channels in the angular range from 20° to 120° Lab. The new data reveal the suppression of the Coulomb rainbow peak in 17Ne scattering, a surprising result since the rainbow peak persists in the scattering of the proton-halo 8B [3]. The angular distribution of the cross-section for inclusive 15O production seems compatible with the inelastic excitation of 17Ne. In this contribution the experimental details will be given, and the results discussed in the framework of the Optical Model and Coupled Channel Calculations [4].
References
[1] I. Martel et al., proposal E788S to the GANIL PAC, 2018.
[2] G. Marquínez-Durán, Nucl. Inst. Meth. A755 (2014) 69.
[3] R. Spartá et al., Physics Letters B 820 (2021) 136477.
[4] J. Díaz-Ovejas et al., Physics Letters B (2023), submitted.
MUGAST [1] is a state-of-the-art silicon array combining trapezoidal and square shaped double-sided silicon strip detectors (DSSD) to four MUST2 [2] telescopes. Coupled to a gamma-ray spectrometer, the excellent angular coverage and compacity of the MUGAST array make it an ideal tool for the study of transfer reactions. It is a first step toward the development of the new generation of silicon arrays using PSA for particle identification, such as the future GRIT array [3] developped by our collaboration.
In recent years, MUGAST has been widely used at GANIL. First with the AGATA gamma-ray spectrometer and the VAMOS large acceptance spectrometer for the study of ISOL beams from the SPIRAL1 facility. It is now coupled to the EXOGAM gamma-ray spectrometer and to a new zero degree detection system at the end of the LISE fragmentation beamline.
In this talk, a summary of previous results from the 2019-2021 MUGAST-VAMOS- AGATA campaign will be presented, followed by a description of the newly installed experimental setup at LISE, the opportunities it opens up and its performance.
References
[1] M. Assie et al., Nucl.Instrum.Meth.A, 1014, (2021)
[2] Y.Blumenfeld et al., Nucl.Instrum.Meth.A, 421, (1999) [3] M.Assie et al., Eur. Phys. Jour. A51, 11, (2015)
We have thoroughly investigated the influence of entrance channel effects on the spin distribution and angular momentum in heavy ion collisions, employing three-dimensional dissipative dynamics. The microscopically derived Langevin equations were numerically solved using the distance, neck, asymmetry and the three angular macroscopic variables, which allow for an adequate description of the fusion process, as it was done in Ref. [1]. Our analysis showed that, unlike what was done in Ref.~[1], a special handling of the boundary conditions is necessary to describe the correct asymptotic shape of the spin distributions. Moreover, by considering the full range of the asymmetry variable, rather than freezing it, we provide a comprehensive understanding of its impact on dissipative dynamics.
Different systems, involving various asymmetry entrance channels were studied using a Yukawa-plus-exponential folding $+$ Coulomb potential, and we will present results for the following heavy-ion reactions: $^{64}$Ni+$^{92,96}$Zr, and the asymmetric systems $^{16}$O+$^{152}$Sm and $^{48}$Ca,$^{50}$Ti,$^{54}$Cr on $^{208}$Pb.
Our analysis considers factors such as friction, mass tensor parameters, diffusion strength, potential energy, and stochasticity in a complete three-dimensional picture. We observe significant variations in the spin distribution by considering various target-projectile combinations with the same excitation energy and compound system. This underscores the crucial role of entrance channel asymmetry in shaping the spin distribution, as it strongly influences the hindrance mechanism and in turn, plays a vital role as a weight for subsequent processes such as splitting.
This investigation enhances our understanding of the intricate relationship between entrance channel effects and the resulting spin distribution, contributing to a broader understanding of dissipative dynamics in heavy ion collisions. Our ultimate aim is the inclusion of shell effects in the potential surface to give a fully microscopic-macroscopic description of the dissipative process.
Heavy-ion collisions at Fermi energies allow to investigate various phenomena, such as the isospin transport phenomena. These can be interpreted in the framework of the Nuclear Equation of State (NEoS), which describes the properties of nuclear matter in terms of thermodynamic variables.
In this talk we will show the preliminary results of the study of the $^{58}$Ni+$^{58}$Ni reaction at three different energies 32, 52 and 74 AMeV. These reactions were measured during the E789 and E818 experiments performed with FAZIA-INDRA apparatus [1,2] at GANIL (Caen, France). The large angular coverage of the coupled detectors (2°-176°) allows the characterization of events. Moreover FAZIA, covering the forward polar angles (1.5°-14°), provides an optimal charge and mass identification of the fragments (up to Z=25) [3].
The $^{58}$Ni+$^{58}$Ni reaction was measured at 32 and 52 AMeV in 2019 and partially already analysed [4], while the set of measurements was completed during the E818 experiment (May 2022) with the same reaction at 74 AMeV. These measurements are particularly interesting because they offer the possibility to investigate the isospin transport phenomena [5] in a wide energy range. Moreover, the measure at 74 AMeV allows to study how the cross section of the reaction channels changes at high energy where the vaporization channel could be important.
References
[1] R. Bougault et al., Eur. Phys. J. A 50, 47 (2014)
[2] J. Pouthas et al., Nucl. Instr. and Meth. in Phys. Res. A 357, 418 (1995)
[3] N. Le Neindre et al., Nucl. Instr. Meth. A 701, 145–152 (2013)
[4] C. Ciampi et al., Phys. Rev. C 106, 024603 (2022)
[5] S. Piantelli et al., Phys. Rev. C 103, 014603 (2021)
Collisions of heavy ions are the best tools at our disposal to probe nuclear matter. It allows us to reach extreme densities, giving us the possibility to constrain transport models. In particular, at incident energies around 100 MeV/nucleon a participant zone is formed by a part of projectile and target nuclei.
The aim of this work is to characterize the participant zone. We will focus on the characteristics of cluster production (chemical composition, energy, angular distributions, multiplicities, and their correlations). These analyses reveal the neutron richness of the emitted particles, and their yield provides an insight on the mixing of target and projectile contributions. Furthermore, a systematic analysis of the transverse energy of the emitted clusters shows a link between incident energy, compression energy, and density during the reaction.
For this study, INDRA datasets for 124,129Xe+112,124Sn collisions at 100 AMeV have been used to study the effect of neutron richness on the production of light particles. The kinematic study has been done using the datasets for 129Xe+124Sn at 65, 80, 100 and 150 AMeV collisions, and using the 136Xe+124Sn collision dataset for 32 and 45 AMeV.
The results of this analysis were compared to the semi-classical event generator ELIE. This work has been done with the goal of expanding it to a lighter system, 58,64Ni+58,64Ni, measured at 32 and 52 AMeV during the E789 INDRA-FAZIA campaign.
The development and improvement in terms of performances of accelerator facilities and detectors has paved the way for extending the study of nuclear structure towards more exotic nuclei and experimental quantities that have been, until now, less accessible.
In parallel, theoretical methods have advances in precision and prediction capabilities.
In recent years, \textit{ab-initio} calculations in particular have proven to be powerful tools to address open questions in nuclear structure; one example is the role of three-body forces in the evolution of nuclear structure far from stability.
The importance of their contribution is evident in the case of the oxygen isotopic chain.
In fact, only by including these forces in the calculations it is possible to correctly reproduce the neutron dripline in correspondence of $^{24}$O, instead of $^{28}$O as predicted by standard calculations.
However, in order to quantify the contribution of these forces, spectroscopic information is crucial.
In this context, the $^{20}$O nucleus is a perfect playground for these measurements; in fact, the properties of the $2^+_2$ and $3^+_1$ states of this nucleus are expected to be influenced by three-body forces.
By measuring the spectroscopic properties of these nuclei, such as the excitation energy, the branching ratio and the lifetime, and comparing them to theoretical calculations, it is possible to understand the depth of their influence.
For these reasons, an experiment aimed at studying the $^{20}$O was performed in GANIL. The radioactive beam of $^{19}$O, provided by the SPIRAL1 complex, impinged on a deuterated target, populating the nucleus of interest by means of a $(d,p)$ reaction.
The target was deposited on a layer of gold in order to measure the lifetime of the states by using the Doppler-Shift Attenuation Method.
The recoils of the binary reaction were detected using the MUGAST array and the VAMOS++ magnetic spectrometer, while the $\gamma$ rays emitted were detected using AGATA.
The nucleus was first investigated via particle-$\gamma$ spectroscopy to reconstruct the level scheme and measure the branching ratios.
Then the lifetimes of the $2^+_2$ and $3^+_1$ states were measured. To do so, the experimental lineshapes were compared to realistic Monte Carlo simulations and the lifetimes were extracted by using the least-$\chi^2$ method.
Finally the reduced transition probabilities, B(E2) and B(M1) deduced from the lifetime measurements, were compared to \textit{ab-initio} calculations.
In this contribution, the results of the particle-$\gamma$ spectroscopy and the lifetime measurements of the $2^+_2$ and $3^+_1$ states are reported.
An interpretation of the nature of the excited states of $^{20}$O is presented as well as the future perspectives for further investigation in this region.
Shell evolution in the region around the magic numbers $N=28$ and $Z=20$ is of great interest in nuclear structure physics. Moving away from the doubly-magic isotope $^{48}$Ca, in the neutron-rich direction there is evidence of an emergent shell gap at $N=34$ [1], and in the proton-deficient direction, the onset of shape deformation suggests a weakening of the $N=28$ magic number [2]. The $^{47}$K(d,p)$^{48}$K reaction is uniquely suited to investigating this region, as the ground state configuration of $^{47}$K has an exotic proton structure, with an odd proton in the $\pi(1s_{1/2})$ orbital, below a fully occupied $\pi(0d_{3/2})$ orbital [3]. As such, the selective neutron transfer reaction (d,p) will preferentially populate states in $^{48}$K arising from $\pi(1s_{1/2}) \otimes \nu(fp)$ cross-shell interactions. The implications of this extend both down the proton-deficient $N=28$ isotonic chain, where these interactions are expected to dominate the structure of the exotic, short-lived $^{44}$P nucleus [4], and across the neutron-rich region, where the relative energies of the $\nu(fp)$ orbitals is the driving force behind shell evolution.
The first experimental study of states arising from the interaction between $\pi(1s_{1/2})$ and the orbitals $\nu(1p_{3/2})$, $\nu(1p_{1/2})$ and $\nu(0f_{5/2})$ has been conducted, by way of the $^{47}$K(d,p) reaction in inverse kinematics. A beam of radioactive $^{47}$K ions was delivered by the GANIL-SPIRAL1+ facility, with a beam energy of 7.7 MeV/nucleon. This beam was estimated to be $>99.99$\% pure, with a typical intensity of $5\times10^{5}$ pps, and was impinged upon a 0.3 mg/cm$^2$ CD$_2$ target. The MUGAST+AGATA+VAMOS detection setup [5] allowed for triple coincidence gating, providing a great amount of selectivity. An analysis based both on excitation and gamma-ray energy measurements has revealed a number of previously unobserved states in $^{48}$K, and preliminary differential cross sections for the most strongly populated of these states will be presented. Spectroscopic factors for these states will be discussed in the context of shell model calculations, with regard to the N=28, 32 and 34 shell gaps. Additionally, results for positive and negative parity states in $^{46}$K, measured simultaneously via the $^{47}$K(d,t) reaction, will also be presented.
[1] D. Steppenbeck et al., Nature 502, 207 (2013).
[2] O. Sorlin and M.-G. Porquet, Prog. Part. Nucl. Phys. 61, 602 (2008).
[3] J. Papuga et al., Phys. Rev. C, 90 034321 (2014).
[4] L. Gaudefroy, Phys. Rev. C, 81, 064329 (2010).
[5] M. Assié et al., Nucl. Instrum. Methods A 1014, 165743 (2021).
The evolution of the N = 50 single-particle gap size from β stability towards the exotic 78Ni, at the origin of the magic nature of the N = 50 isotones, is still poorly understood. Experimental data indicate that the size of the effective N = 50 gap continuously decreases from stability down to Z = 32 [1]. This reduction must certainly be followed by a stabilization around Z = 30, a phenomenon that has still not received any theoretical explanation.
In 2018, the ν-Ball campaign took place at the ALTO facility of Orsay [2]. The γ-spectrometer was made of 34 HPGe detectors to perform high resolution γ-spectroscopy, coupled to 20 LaBr3 scintillators enabling the realization of fast-timing measurements. During this campaign, medium-spin yrast and near-yrast states of neutron-rich nuclei were successfully populated in the fission of a 232Th target exposed to the quasi-mono-energetic fast-neutron flux generated by LICORNE. Among all the reaction products, the N = 50 nucleus 82Ge have been identified. In this presentation, I will show results focusing on the new spectroscopic data obtained for the nucleus 82Ge [3]. Indeed, using double and triple γ coincidences in the HPGe of ν-Ball, we were able to add two new transitions and one excited state in its level scheme. The latter is interpreted as the 7+ state originating from the N = 50 core-breaking configuration ν(1g$_{9/2}$)$^{−1}$ν(2d$_{5/2}$)$^1$, and we discuss the relationship between its observed excitation energy and the effective N = 50 shell gap amplitude at Z = 32. This new information is used to quantify the evolution of the N = 50 gap from Z = 38 down to Z = 32. According to our analysis, the gap slope is almost three times as high as the one obtained in Ref. [1]. We propose for the first time to explain this
evolution by the effect of the isospin asymmetry of the pseudo-spin symmetry in this region [4].
In the future, at GANIL, there will be the opportunity to study N = 50 isotones on the neutron deficient side at the DESIR facility. The possibility to study nuclei close the N = Z line, near the doubly magic 100Sn nucleus, will allow to further study the role of the isospin asymmetry of the pseudo-spin symmetry in the evolution of the nuclear orbitals.
Références
[1] M.-G. Porquet and O. Sorlin, Evolution of the N = 50 gap from Z = 30 to Z = 38 and extrapolation toward 78Ni., Phys. Rev. C 85, 014307 (2012)
[2] M. Lebois et al., The ν-ball γ- spectrometer, NIM A 960, 163580 (2020)
[3] D. Thisse et al., Article submitted to EPJ A in January 2023
[4] H. Liang et al., Hidden pseudospin and spin symmetries and their origins in atomic nuclei, Phys. Rep. 570, 1-84 (2015)
The main subject of this study is the experimental investigation of the nuclear structure of exotic neutron-rich nuclei in the vicinity of shell closures in order to constrain the description of the nucleon-nucleon interaction, and in particular its tensor term. Previous studies have shown that a deformation region develops along the N=28 isotonic chain between the doubly magical and spherical $^{48}$Ca nucleus (20 protons/28 neutrons) and the $^{42}$Si nucleus which is extremely deformed in spite of its semi-magical character (14 protons/28 neutrons). It has been shown that this deformation results from neutron excitations above N=28 and proton excitations above Z=14, both made possible by the reduction of these shell closures under the effect of the tensor component of the nuclear interaction. The goal is now to follow the evolution of the deformation along the Si isotopic chain, between $^{34}$Si (N=20) and $^{42}$Si (N=28) by measuring for the first time and in a simultaneous way through experiments at GANIL (Grand Accelerator National d'Ions Lourds):
The contribution of neutrons to the excitation of the 2$^{+}$ state of $^{34-36-38}$Si nuclei by inelastic proton scattering.
The contribution of protons and neutrons to the excitation of the 2$^{+}$ state of $^{34-36-38}$Si nuclei by Coulomb excitation on a gold target.
The experiments has been set up during the 2022 campaign of LISE spectrometer (Line d'Ions Super Epluchés) at GANIL. This spectrometer allowed to produce and select $^{34}$Si, $^{36}$Si and $^{38}$Si nuclei. In order to measure the proton and neutron contributions, the experimental setup was composed of two independent experiments on the same beamline with the same radioactive beam.
The first experiment was perfomed with ACTAR-TPC detector (ACtif TARget-Time Projection Chamber). The purpose of this experiment was to measure the inelastic scattering of $^{A}$Si(p,p')$^{A}$Si* reactions, with $(A=34,36,38)$. The analysis of this part is in progress by one of the thesis students of the ACTAR collaboration.
The second experiment was the CoulEx part (Coulomb Excitation). The goal of this experiment was to measure the effective cross section of coulomb excitations. Several types of detectors composed the CoulEx setup. The work of this thesis is mainly based on the analysis of this experiment.
Reactor antineutrino energy spectra are the subject of active experimental researches nowadays, one of them being dedicated to nuclear physics measurements of the properties of the fission products. Some of these measurements were motivated by two observed anomalies in the antineutrino spectra. The reactor anomaly (RAA), first, was observed in 2011 as a deficit in the reactor antineutrino flux with respect to the conversion model which relies on measurements of integral beta spectra and a conversion approach to predict the antineutrino energy spectra. Then a distortion between 5 and 7 MeV of the measured antineutrino spectra with respect to the conversion model, called the shape anomaly, was observed and still remains unexplained up to now. In 2017, the Daya Bay experiment measured the evolution of the antineutrino flux with the fuel content of the reactor core. The collaboration observed that the deficit of the detected flux compared with the predictions of the conversion model was almost totally explained by the data arising from the fissions of 235U which called into question the measurements of its integral beta spectra.
Summation calculations, based on nuclear data of the fission products, are a unique alternative to the converted spectra. They have the advantage of being predictive for innovative fuels and also of giving access to the main nuclei contributing to the spectra in the various ranges of energy. However some of the beta decay data of interest suffer from the Pandemonium effect, a strong bias which can affect high resolution data coming from experiments with HPGe detectors. The TAGS measurements allow one to overcome this systematic error and thus to correct nuclear data from it as well as the predictions of antineutrino energy spectra. The TAGS collaboration has carried out three experimental campaigns during the last fifteen years at the JYFLTRAP of Jyväskylä (Finland) measuring a large set of data in order to improve the quality of the predictions of our summation method. The impact of these measurements on the predicted antineutrino energy spectrum and flux using our summation calculations will be presented and discussed as well as some on-going activity on studies dedicated to the shape of the antineutrino spectra.
The DESIR low-energy beam facility is dedicated to nuclear physics, astrophysics, and fundamental interaction studies using exotic nuclei provided by the SPIRAL1 and S3 production sites of GANIL-SPIRAL2. The commissioning of beam preparation devices is ongoing at LP2iB, where a high-resolution mass-separator (HRS-1P) and a double Penning trap (PIPERADE) coupled to a RFQ cooler and buncher (GPIB) are being tested offline. The refurbishment of a high-acceptance RFQ cooler (RFP-1P) will start soon at LPC Caen. Experimental setups are being tested online (MORA@Jyväskylä) or will be soon commissioned offline (MLLTrap@IJCLab). On the infrastructure side, the safety authorization for the construction of the facility has been granted in spring 2023, and the ongoing Public Enquiry (April-May 2023) should allow the Construction Permit to be obtained before the summer. The final delivery of the DESIR buildings is expected by 2025, as well as the installation of the transport beam lines and associated utilities, that should allow to start the operation of the facility by 2026-2027.
The DESIR facility at GANIL will receive neutron-deficient ion beams produced by fusion evaporation at S3 (Super Separator Spectrometer) and exotic light nuclei produced by fragmentation at SPIRAL1. DESIR is an experimental hall dedicated to the study of nuclear structure, astrophysics and weak interaction using beta decay spectroscopy, laser spectroscopy and trap-based experiments at low energy (30-60 keV). Those experiments require highly pure samples of nuclei at odds with the non-selectivity of all the production methods. Therefore, in order to deliver large and very pure samples of exotic nuclei to the different experiments, the LP2iB is currently developing three new devices; a High resolution mass separator (HRS), a radiofrequency quadrupole cooler buncher [1] and a double Penning trap mass spectrometer PIPERADE**[2] that will be placed at the entrance of the DESIR facility. We aim at extracting ion bunches from the GPIB with the best compromise between energy and time dispersion to fit the needs of the downstream experiment using the beam. For now, these bunches are directly sent to PIPERADE. With this device we will be able to perform mass measurements and/or purification at the isomerical level. Indeed Penning traps are designed to reach resolving power of the order of $10^5$ to $10^7$ depending on the separation techniques. Whether PIPERADE is used to purify or to measure masses, we will have to deal with short-lived nuclei. And since theses techniques are time consuming, one of the challenges is to develop short operating cycles while keeping a high mass resolving power to extract the nuclides of interest from the large amount of isobaric and/or isomeric contaminants. The HRS, the GPIB and PIPERADE are now fully assembled at LP2iB and currently under commissioning before being moved to GANIL when the DESIR hall will be accessible. The latest achievements and the first mass measurements will be presented.
[1] M. Gerbaux, P. Ascher, A. Husson, A. de Roubin, P. Alfaurt, M. Aouadi, B. Blank, L. Daudin, S. E. Abbeir and M. Flayol, et al.
``The General Purpose Ion Buncher: A radiofrequency quadrupole cooler-buncher for DESIR at SPIRAL2'',
Nucl. Instrum. Meth. A 1046 (2023), 167631
doi:10.1016/j.nima.2022.167631
[2] P. Ascher, L. Daudin, M. Flayol, M. Gerbaux, S. Grévy, et al.. PIPERADE: A double Penning trap for mass separation and mass spectrometry at DESIR/SPIRAL2. Nucl.Instrum.Meth.A, 2021, 1019, pp.165857. ⟨10.1016/j.nima.2021.165857⟩.
Désintégration, Excitation et Stockage d'Ions Radioactifs i.e. Decay, Excitation and Storage of Radioactive Ions
GPIB – General Purpose Ion Buncher
**PIeges de PEnning pour les RAdionucléides à DEsir i.e. Penning traps for radionuclides at DESIR
The use of exotic states of matter allows us to probe the underlying symmetries of the universe to ever greater precision and expose shortcomings of the Standard Model of particle physics (SM), arguably the most successful physical theory created to date. Radioactive ion beams (RIB), in particular, significantly expand the number of available experimental systems to address the SM's lack of sufficient CP-symmetry violation to explain the matter-antimatter asymmetry, the unknown mass mechanism of neutrino's, the nature of dark matter and a host of equally puzzling questions in the weak interaction. In this talk, we will provide an overview of the current landscape and how RIBs intersect with it, and focus on a selection of experiments using novel techniques and systems taking advantage of upgraded facilities worldwide.
Precision measurements in beta decay play an essential role in the search for new physics beyond the standard model (SM), by probing “exotic” phenomena such as scalar and tensor interactions. The existence of such interactions induces deviations on certain observables away from their SM predictions. The study of the full beta energy spectrum offers a sensitive property to probe these interactions.
The goal of this work is to perform the most precise measurement of the $\beta$-energy spectrum in $^6$He decay, in order to extract the Fierz interference term $b$ with a precision in the order of $4\cdot10^{-3}$. This term depends linearly on exotic coupling constants, allowing to search for or to constrain the presence of tensor interactions in nuclear beta decay.
The main instrumental effect observed in previous measurements of the beta energy spectrum resides in the energy loss due to electrons backscattering outside the detector volume. A new technique is used to overcome this effect. It consists of using a very low energy beam of $^6$He$^+$ ions (25 keV) deposited between two scintillation detectors forming a 4$\pi$ calorimeter. The use of this technique ensures the deposition of the entire energy of the detected beta particles. An experiment with this setup was performed at the Grand Accélérateur National d’Ions Lourds (GANIL) in 2021.
This contribution will introduce the general context of the project, describe the experimental setup, report the status of the data analysis and present the preliminary results
Around us we see an universe filled with galaxies, stars and planets like ours. But when we look back to the Big Bang and the processes that created the matter in it, at first we observe that there should have been created the same amount of matter and antimatter, thus the universe would be empty or different than it is. Sakharov proposed several mechanisms to explain the matter-antimatter asymmetry, one of them being the violation of the CP symmetry.
In the MORA experiment, we aim to measure the D correlation, which is non zero for violation of T symmetry in polarized nuclei, thus it can be related to CPV. For this we use a detector setup made of MCP’s, Phoswiches and Si detectors, to measure coincidences between beta emissions and recoil ions, product of the beta decay of trapped Mg23 ions.
Here I will present an introduction to D correlation, how we acquired the previous data in Jyvaskyla in November 2022, how we analyzed it and the results we got concerning the calibration of detectors and polarization measurement.
The neutron lifetime discrepancy between beam and bottle experiments of 4σ could be interpreted as a possible sign of the neutron decaying into dark particles [1]. If such a decay exists, it could also occur in unstable nuclei with sufficiently low neutron binding energy, a quasi-free neutron decay into a dark matter particle χ; as is the case of 6He with S2n = 975.45keV < mn −mχ [2]. This quasi-free neutron dark decay would be as followed: 6He →4He+n+χ which is the only way to have the emission of a free neutron in the decay of 6He. The SPIRAL1 facility at GANIL was used in June 2021 in order to produce a pure 6He1+ radioactive beam at 25keV to observe an excess of neutrons in the decay of 6He which would be a unique signature for dark matter creation. In this presentation, we report the results of this experiment to set an upper limit for this dark decay mode in 6He.
References
[1] Bartosz Fornal and Benjamin Grinstein. “Dark Matter Interpretation of the Neutron Decay Anomaly” in: Phys. Rev. Lett. 120 (19 May 2018), p. 191801. doi: 10.1103/PhysRevLett.120.191801. url: https://link.aps.org/doi/10.1103/PhysRevLett.120.191801.
[2] M. Pfützner and K. Riisager. “Examining the possibility to observe neutron dark decay in nuclei” in: Phys. Rev. C 97 (4 Apr. 2018), p. 042501. doi: 10.1103/PhysRevC.97.042501. url: https:
//link.aps.org/doi/10.1103/PhysRevC.97.042501.
For several years, many radionuclides (RN) are routinely used in nuclear medicine either for imaging ($\gamma$ and $\beta^+$ or positron) or for therapy ($\alpha$, $\beta^–$, Auger electron emitters). They are most-often administered in the form of a radiopharmaceutical, composed of the selected RN and a targeting unit (nanoparticles or biological vectors, like peptides or antibodies) responsible for the specific accumulation of the drug in the diseased tissues. Numerous efforts are still needed to create a “tool box” and expand the catalogue of clinically relevant RN.
In that context, Terbium is an emerging "theranostic" element, which offers four clinically interesting radioisotopes with complementary physical decay characteristics: $^{149}$Tb (T$_{1/2}$ = 4.12 h, $\alpha$ therapy), $^{152}$Tb (T$_{1/2}$ = 17.5 h, PET imaging), $^{155}$Tb (T$_{1/2}$ = 5.32 d, SPECT imaging and Auger therapy), and $^{161}$Tb (T$_{1/2}$ = 6.9 d, $\beta^–$ and possibly Auger therapy). It is a so-called “theranostic” element (contraction of THERApy and diagNOSTIC), since it enables the development of a unique bioconjugate for radiolabelling prior to administration at both the diagnosis and curative stages. Both radiopharmaceuticals have then strictly identical biodistribution and pharmacokinetic properties,enabling a better adaptation of the targeted treatments, paving the way for more personalized medicine.
The major limitation today for the further use of these RNs is their economically sustainable production in sufficiently large quantities with high chemical and isotopic purities. The ongoing TTRIP project (Tools for Tb RadioIsotope Production for nuclear medicine) * aims to face two challenges related to the $^{155}$Tb: to develop an alternative method for producing isotopes that are difficult to obtain using conventional methods, and to develop specific chelators for terbium that are compatible with the use of monoclonal antibodies as biological vectors.
These two aspects of our programme will be detailed, with a more specific focus on the $^{155}$Tb production part. First results will be presented.
* This project is financed by the contract ANR-21-CE19-0037
The REPARE ANR project aims at developping a high power targetry to optimize the production of the promising alpha emitter $^{211}$At in the $^{4}$He($^{209}$Bi,2n)$^{211}$At fusion-evaporation reaction. For this, a first task is the precise measurements of several cross-sections to control the production of potential contaminants and to optimize the synthesis of $^{211}$At. Several measurements have been performed and will be presented separately at this colloque. A second task is the design of high power target systems. Two options have been investigated : a solid state $^{209}$Bi target and a liquid target.
For the first option, the goal is to design, build and use a target station able to sustain 10 kW of beam power. In July 2023, the functionalities of the target station (cooling, current measurements, beam synchronization,…) will tested using a $^{20}$Ne beam and a dummy target. If the tests are satisfactory, the REPARE irradiation station will be installed in the NFS converter room in September 2023 for a first $^{211}$At synthesis run.
For the second option, a milestone is a design study to evaluate the feasibility of a liquid target. Several designs have been evaluated using either pure Bi of a Lead Bismuth Eutectic mixture.
Finally an indirect production route is also under investigation. It consists in the production of $^{211}$Rn which beta decays to $^{211}$At. This so-called generator technique has several advantages compared to the direct production one.
In this talk the status of these developments will be discussed and presented in a more general perspective.
Targeted Alpha Therapy (TAT) offers a promising approach to treat cancer, particularly micrometastases, by utilizing the short range of alpha particles and their high linear energy transfer. Astatine-211, which belongs to the halogen family also shares chemical properties with Iodine, a radioisotope commonly used for imaging and also widely used to treat thyroid cancer. This similarity enables the use of Iodine as an analogue for biodistribution and dosimetry studies while using $^{211}$At for treatment. For these reasons, the production of $^{211}$At and the characterization of the contaminants must be studied and optimized.
In this study, we used an alpha beam at SPIRAL2, NFS to produce $^{211}$At via the reaction $^{209}$Bi(α,2n)$^{211}$At. The production cross-section of $^{211}$At increases with increasing alpha energy up to 31 MeV. However, caution must be exercised as $^{210}$At production also occurs via the $^{209}$Bi(α,3n)$^{210}$At reaction above 28.6 MeV. $^{210}$At decays to $^{210}$Po, an alpha-emitting radionuclide with a half-life of 138.3 days and is highly toxic, if released in tissues.
We irradiated $^{209}$Bi target at various alpha beam energies between 28 to 31 MeV to measure $^{210,211}$At cross-sections and to determine the $^{210}$At/$^{211}$At ratio. We employed gamma-ray spectroscopy using germanium detectors to evaluate the respective contribution of $^{210,211}$At. The incident particle flux was monitored using an instrumented Faraday cup. This flux measurement combined with the number of detected γ-rays allowed to determine the production cross-sections of $^{210,211}$At as a function of energy and the results are in good agreement with the literature values. We have also used well-known cross-sections of alpha on Cu from literature to cross-check and improve the accuracy of our flux measurements.
Astatine-211 is a promising radionuclide for TAT and needs careful monitoring of unwanted radionuclides. This study represents the first step in evaluating the cross-section to optimize the alpha beam energy and maximize $^{211}$At production while maintaining an acceptable level of $^{210}$At contamination. The next step will be $^{211}$At production with a high power target for interdisciplinary studies.
This study was financially supported by the REPARE ANR project (Projet-ANR-19-CE31-0013).
Multi-Nucleon Transfer (MNT) reactions is a useful mechanism, to perform nuclear structure studies in nuclei moderately far from stability line. Moreover, MNT allows to directly populate the low lying states in the reaction products.
The development of set-ups involving high acceptance tracking magnetic Spectrometers as VAMOS++ [1], coupled with the Advanced GAmma Tracking Array (AGATA) [2] opened new possibilities, especially if they are used in conjunction with the high-intensity stable beams provided by the GANIL laboratory [3]. With such set-ups it is nowadays possible to have sufficient sensitivity to perform precise lifetime measurements using Doppler-shift-based techniques such as the RDDS method [5], employing the plunger, for lifetimes in the range from few tenths to hundreds of picosecond. This technique rely on a precise Doppler correction that can be provided by the position resolution of the AGATA array coupled to VAMOS++ the latter providing an accurate kinematic reconstruction of the detected ejectile. VAMOS++ do not only allows to identify and select the reaction product of interest but also to perform an event-by-event Doppler correction. Additionally, taking advantage of the Total Kinetic Energy Loss (TKEL) measurement, the contribution from the feeding transitions, a major source of systematic errors, can be controlled.
In a recently published work [6] we have use the set-up and techniques described above to perform accurate lifetime measurements in the $N=50$ isotones with $Z\ge40$, i.e. with protons occupying the g9/2 orbital. It is well known that seniority is conserved in orbitals with $j\le7/2$ while for orbitals with $j\ge9/2$, seniority breaking effects may be observed being the eigenstates admixtures of states with different seniorities [7,8].
An extensive study of reduced transition probabilities in $^{90}Zr$, $^{92}Mo$ and $^{94}Ru$, together with other known B(E2)’s in the $N=50$ isotones, has allowed us to conclude that seniority is a good quantum number, i.e. is largely conserved, along the $(g_{9/2})^n$ yrast states at $N = 50$. The experimental evidence of the seniority conservation is a direct evidence of the validity of the short-range pairing interaction, with far-reaching implications for nuclear structure.
The capabilities of the mentioned set-up and the experimental findings will be discussed in this contribution
[1]H. Savajols, and Vamos Collaboration. Nucl. Phys. A 654, 1027c (1999)
M. Rejmund et al., Nucl. Instr. Methods Phys. Res. Sect. A, 646, 184–191 (2011)
[2]S. Akkoyun et al., Nucl. Instr. Methods Phys. Res. Sect. A 668, 26 (2012)
[3]E. Clément et al., Nucl. Instr. Methods Phys. Res. Sect. A, 855, 1 (2017)
[5]A. Dewald, O. Möller, P. Petkov, Prog. Part. Nucl. Phys. 67, 786 (2012)
[6]R.M. Pérez-Vidal et al., Phys. Rev. Lett. 129, 112501 (2022)
[7]P. Van Isacker, Inter. Jour. Mod. Phys. E 20, 191 (2011).
[8]C. Qi, Phys. Lett. B 773, 616 (2017).
Nuclear radii and densities are key quantities that naturally bridge nuclear structure and reactions and open a window towards a detailed understanding of the nuclear interaction within a given theoretical framework. Long restricted to light systems due to model-space convergence limitations as well as interactions deficiencies, recent progress on both accounts now allow for accurate ab initio description of those quantities up to and above the tin isotopic chain.
I will present ab initio radii and density distributions for Sn and Xe isotopes and show how they can be compared with past experimental results such as SCRIT in RIKEN, as well as inform current experimental endeavours, e.g. aimed at constraining the nuclear symmetry energy slope parameter at GSI/R3B. This paves the way for fruitful collaboration between experiment and theory in the context of upcoming programs at SPIRAL2 and beyond.
In the last decade, a considerable progress in the understanding of the structure of nuclei in the vicinity of 132Sn, the heaviest doubly-magic nucleus far-off stability accessible for experimental studies, was achieved. The vast amount of results obtained in several experimental campaigns performed at the Radioactive Isotope Beam Facility (RIBF) in Japan, in combination with state-of-the-art theoretical investigations, contributed in a significant way to this progress. In the present contribution, we will discuss unpublished results from several different experiments. We will start with new (and maybe last?) results from an experiment which was dedicated to decay spectroscopy in the 132Sn region and performed during the EURICA campaign in 2014. This experiment already delivered a lot of very valuable information giving rise to the publication of numerous articles over the last years. Some examples are the first observation of the decay of the isomeric 6+ states in 136,138Sn or the identification of the p3/2 proton single-hole state in131In. Regarding in-beam g-ray spectroscopy, exciting new results from various experiments performed with the DALI2+ spectrometer consisting of NaI scintillator detectors as well as with the HiCARI array, which is based on both segmented and unsegmented Ge detectors, will be discussed. The talk will close with a glance at the exciting future perspectives in the region around 132Sn.
The study of the structure of neutron-deficient actinides is of particular interest since several theoretical calculations predict strong octupole deformations in this region of the nuclear chart [1, 2, 3]. However experimental data are scarce due to very low production rates.
There is an ongoing program at the IGISOL (Ion Guide Isotope Separation On-Line) facility, University of Jyväskylä, to study actinide isotopes, including the decay spectroscopy of neutron-deficient actinides produced through proton-induced fusion-evaporation reactions on a $^{232}$Th target. A successful experiment was performed in July 2020 where short-lived actinide isotopes were produced, mass separated and guided to a decay spectroscopy station. Using an experimental setup composed of Ge, Si and Si(Li) detectors, $\alpha$, $\gamma$ and electron decay spectroscopy of the selected nuclei was performed to reconstruct the decay schemes that are missing or incomplete in this region of the nuclear chart. In this presentation, I will show results focusing on $^{225}$Pa, for which very little decay information was available before this experiment, as well as its daughter nucleus $^{221}$Ac. Reconstruction of the decay scheme and measurement of $\alpha$ hindrance factors indicates a static quadrupole-octupole deformation in $^{221}$Ac. In particular the level scheme of $^{221}$Ac is interpreted in terms of parity-doublet bands arising from this octupole deformation.
The second goal of this experiment was to measure production yields in order to consider a laser spectroscopy program in the future. Indeed laser ionisation spectroscopy is well established as a powerful tool in nuclear structure studies [4]. It allows the measurement of spins, magnetic dipole moments, electric quadrupole moments and changes in the mean-square charge radii independently of nuclear models.
\newline
In the near future, the possibility to perform laser ionisation spectroscopy of neutron-deficient actinides at S$^3$-LEB will allow to continue this program towards nuclei further from stability. In particular the SEASON (Spectroscopy Electron Alpha in Silicon bOx couNter) detector will enable the coupling of two approaches : laser ionisation spectroscopy and decay spectroscopy.
I will conclude my talk discussing perspectives for the study of octupole deformations in the neutron-deficient actinides, in particular those offered by SEASON at S$^3$-LEB.
[1] S.E. Agbemava, A.V. Afanasjev, Phys. Rev. C 96, 024301 (2017).
[2] S.E. Agbemava, A.V. Afanasjev and P. Ring, Phys. Rev. C 93, 044304 (2016).
[3] L.M. Robledo and R.R. Rodr ́ıguez-Guzm ́an, J. Phys. G: Nucl. Part. Phys. 39, 105103 (2012).
[4] P. Campbell, I.D. Moore and M.R. Pearson, Prog. Part. Nucl. Phys. 86, 127-180 (2016).
The superconducting LINAC (LINear ACcelerator) of SPIRAL2-GANIL will deliver very intense heavy-ion beams up to uranium by virtue of the additional NEWGAIN (NEW GAnil Injector) with mass to charge ratio (A/Q = 7)[1]. The S$^3$ (Super Separator Spectrometer) of SPIRAL2 was designed to have high transmission, high beam rejection and high mass resolving power capabilities to study rare isotopes like superheavy and exotic nuclei far from the stability with very low production cross-sections[2]. At the focal plane of S$^3$, a state-of-art detector array called SIRIUS (Spectroscopy and Identification of Rare Isotopes Using S$^3$)[3] will be installed to perform decay spectroscopic studies in the region of the very heavy and superheavy nuclei where very little spectroscopic data[4] is available. SIRIUS will be capable of detecting heavy ions and their subsequent decay products: alpha particles, beta particles, internal-conversion electrons, gamma rays, X rays and fission fragments. It is composed of an ion tracker to track the ERs (Evaporation Residues) passing through it and also to measure their time of flights, a DSSD (Double-Sided-Silicon-Strip Detector) for implanting the ERs and to establish their spatial and temporal correlations with their successive decays, four stripy pad silicon detectors in a tunnel configuration placed upstream to the DSSD to detect the escaping charged particles from the DSSD thus allowing performance of internal-conversion-electron spectroscopy, five clover detectors placed in a close geometry around the silicon detectors to carry out detailed gamma spectroscopy. Currently, we are commissioning the setup using sources and beam. In this conference, I will present the current status of the SIRIUS project.
References
[1] D. Ackermann et al., NEWGAN White Book (2021) 1-39.
[2] F. Déchery et al., Eur. Phys. J. A 51 (2015) 66.
[3] N. Karkour et al., IEEE Nuclear Science Symposium 51 (2016) 1-6.
[4] Ch. Theisen et al., Nucl. Phys. A 944 (2015) 333-375.
*S$^3$ has been funded by the French Research Ministry, National Research Agency (ANR), through the EQUIPEX (EQUIPment of EXcellence) reference ANR-10EQPX- 46, the FEDER (Fonds Européen de Développement Economique et Régional), the CPER (Contrat Plan Etat Région), and supported by the U.S. Department of Energy, Office of Nuclear Physics, under contract No. DE-AC02-06CH11357 and by the E.C.FP7-INFRASTRUCTURES 2007, SPIRAL2 Preparatory Phase, Grant agreement No.: 212692.
SIRIUS has been funded by the CPIER (Contrat Plan Etat Inter Régional) and the Région Normandie \& the European Union through the RIN-Tremplin Grant SoSIRIUS.