WNM`25

12 mai 2025, 13:00 → 14 mai 2025, 17:20 Europe/Paris

bat. 100 (IJCLab, Orsay)

WNM25-2ndCircular.pdf

WNM25-3rdCircular.pdf

WNM25-Poster.pdf

lun. 12 mai

14:00 → 16:00 Session 1

14:00 Opening

Opening

14:05 Excited-state g-factor measurements: challenges and opportunities

Excited-state $g$ factors can be measured by a variety of techniques, depending on the lifetime of the state of interest. Examples include time-dependent perturbed angular correlations/distributions (TDPAC, TDPAD), integral perturbed angular correlations/distributions (IPAD, IPAC), implantation perturbed angular correlation/distribution methods (IMPAC, IMPAD), and recoil in vacuum methods (both time-dependent and integral).

Generally, the time-dependent methods require longer lifetimes (more than about 10 ns). Measurements on shorter-lived states in the picosecond regime usually require the use of hyperfine fields and integral precession methods, which present special experimental challenges.

This presentation will give an overview of methods considering both their challenges and the opportunities they give for nuclear structure research. There will be a focus on potential applications that take advantage of radioactive beams. While the focus will be largely on methods, opportunities for $g$-factor measurements will be discussed with respect to particular physics questions, some of which also require studies of ground-state moments.

Orateur: Prof. Andrew Stuchbery (The Australian National University)

14:35 The HISPEC-DESPEC experiment

The HISPEC/DESPEC experiments, which are part of the NUSTAR scientific collaboration, are intended to address questions in nuclear structure, reactions and nuclear astrophysics by means of high-resolution in-flight spectroscopy (HISPEC) and stopped-beam experiments (DESPEC) at the GSI FRagment Separator (FRS) in FAIR Phase-0 and the future FAIR Super-FRS facility. Those studies require a combination of different setups, to address the multiple aspects and complexity of the nuclear structure. In this talk I will cover the existing setups and present some recent results.

Orateur: Alejandro Algora (IFIC (CSIC-Univ. Valencia))

15:05 Nuclear structure studies via isomeric nuclear moments using spin-aligned RI beams

The magnetic dipole moment and the electric quadrupole moment are nuclear observables that provide key information on proton and neutron configurations, and on the shape of the nucleus, respectively. In precision nuclear spectroscopy of unstable nuclei, the anisotropy of radiation from spin-oriented nuclei allows monitoring of their spin motion. Therefore, techniques to produce spin-oriented RI beams have played an essential role. Recently, a two-step projectile fragmentation scheme was developed to achieve high spin alignment in RI beams, and has been applied to frontier studies of the nuclear structure of neutron-rich nuclei such as $^{75}$Cu and $^{99}$Zr. In this presentation, recent progress in isomeric nuclear moment measurements using highly spin-aligned beams at RIKEN RIBF will be reviewed, and future prospects for nuclear moment measurements will be discussed.

Orateur: Yuichi Ichikawa (Kyushu University)

15:30 Nuclear Moments with CLARION2-TRINITY and FDSi

A brief overview of CLARION2-TRINITY and the FRIB Decay Station initiator (FDSi) will be presented. For CLARION2-TRINITY, an emphasis will be placed on nuclear moment measurements by Coulomb excitation, including new opportunities for g factors by recoil-in-vacuum (RIV). For the FDSi, an emphasis will be placed on gamma-decaying isomers and opportunities for g factors far from stability.

*This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics.

Orateur: Mitch Allmond (ORNL)

16:00 → 16:20 Coffee break

16:20 → 18:20 Session 2

16:20 Nuclear moment measurements at the GANIL-LISE facility

An overview of the nuclear moment measurements performed in the past at the GANIL-LISE in-flight fragmentation facility will be given, highlighting strengths and weaknesses of the instrument.

Orateur: Jean-Charles THOMAS (Grand Accélérateur National d'Ions Lourds)

16:50 The Neutrons For Science Facility at GANIL/SPIRAL-2

The NFS (Neutrons For Science) facility at Ganil in Caen (France) offers neutron beams from 1 to 40 MeV with fluxes unique in the world. The neutrons are produced by p+Li or d+Be reactions thanks to the beams delivered by the SPIRAL-2 linear accelerator. The resulting collimated and pulsed neutron beam allows several experiments to be performed simultaneously. In addition to the neutron beam, an irradiation station and a pneumatic sample transfer system allow cross section measurements by activation technique for neutron or ion induced reactions. The facility has been in operation since 2021 and several experiments have been performed to study neutron induced reactions such as fission, production of light charged particles, (n,xng) cross section measurements or nuclear structure studies. Excitation function measurements of proton, deuteron or alpha induced reactions have also been performed. Finally, production tests of At211, an alpha emitter for medical applications, have been successfully performed. During this talk, the NFS installation will be presented and its technical characteristics will be developed. Some of the experiments already performed will then be shown.

Orateur: Xavier Ledoux

17:20 Collinear resonance ionization laser spectroscopy for nuclear structure studies at ISOLDE and DESIR

Understanding how nuclear structure emerges from the nucleon-nucleon interaction and how it evolves going far from the valley of stability has become one of the main quests of contemporary nuclear physic. High-resolution colinear laser spectroscopy has long been established as a very powerful tool to study ground-state nuclear properties, providing a nuclear model-independent access to the nuclear ground-state spin, changes in mean square charge radii, magnetic dipole, and electric quadrupole moments. It is used at several radioactive beam facilities all over the world and gives insight into many aspects of nuclear structure and provide crucial input for the development of nuclear theories.

At the ISOLDE facility of CERN, the Collinear Resonance Ionization Spectroscopy (CRIS) laser spectroscopy experiment has undertaken several experimental campaigns aiming at the study of nuclear structure evolution around 100Sn, 78Ni and the N=20 and 40 island of inversions. The neutron rich Cr isotopes, located between the magical Ca and Ni, display the highest level of deformation and collectivity of the region. 64Cr is understood to be at the center of the N=40 island of inversion and the study of Cr ground state property from the stability to the N=40 IoI allows to get a comprehensive picture of the evolution from spherical and single particle behavior to deformed and collective structures.

In the past decade, the GANIL facility has undergone a major upgrade with the development of a new radioactive ion beam facility SPIRAL2-S3 and a new low-energy experimental hall DESIR. The SPIRAL2 facility, coupled to the S3 recoil separator, will enhance the study of exotic nuclei by producing intense beams of rare radioactive isotopes. The DESIR facility, now under construction, will host several experimental setups, among which a new versatile high-resolution laser spectroscopy setup: LAser Spectroscopy At GaNil (LASAGN). Such setup combined to the many beam preparation and purification devices of DESIR will offer unique opportunities for nuclear structure studies.

In this talk, laser spectroscopy as a tool for nuclear structure studies will be introduced. Recent results on chromium moments from the CRIS experiment at ISOLDE/CERN will be shown. Finally ongoing laser spectroscopy projects and future plans at the DESIR facility will be presented.

Orateur: Louis-Alexandre LALANNE (IPHC)

17:40 Nuclear moments at TIFR (TBA)

Orateur: Rudrajyoti Palit

18:00 gSPEC

In this contrubution, physics motivations for the gSPEC project will be outlined. Current status and future plans will be discussed in view of the possible new ideas that may further enrich the project scope.

Orateur: Radomira Lozeva (CSNSM)

18:20 → 18:50 Discussion: Discussion (tbd)

19:00 → 20:30 Welcome cocktail

mar. 13 mai

09:00 → 10:50 Session 3

09:00 Lessons learned from the g-RISING campaign at GSI

In 2006 three g-factor experiments were carried out at the FRS in GSI. Two of them addressed a measurement of the g factor of the 19/2+ isomer in 127Sn. In the first one, it was populated in relativistic fission of 238U, and in the second one through relativistic fragmentation of 126Xe. The third experiment addressed the g factor of the 12+ isomer in 192Pb was studied in relativistic fragmentation. Lessons, which were learned in the experiments, will be discussed.

Orateur: Prof. Dimiter Balabanski (ELI-NP, IFIN-HH)

09:30 Laser spectroscopy studies, hot physics questions in nuclear moment measurements and perspectives

A fundamental open question in modern nuclear physics relates to the persistence of shell closures far from stability. Improvements in the capability of radioactive beam facilities, has allowed access to rare isotopes and enabled techniques with higher precision to be used. This has shown that in several regions of the nuclear chart there are surprising and dramatic changes in nuclear structure from previous theoretical predictions. These changes arise from the interplay between the central and tensor components of the nucleon-nucleon interaction. A key region of the nuclear chart to test the latest theoretical developments is around the $^{100}$Sn and $^{132}$Sn double magic nuclei. Measurement of the spins and nuclear moments in this region provides theory with robust observables to understand the underlying nuclear interactions. This has motivated a series of high-resolution laser spectroscopy experiments that have studied the isotope chains in the tin region. This talk will present the latest results and interpretation of this ongoing programme of work.

Orateur: Kieran Flanagan (University of Manchester)

10:00 Future paths for nuclear moments studies

Nuclear moments have, by now, been measured for many decades. When it comes to measurements of long-lived states (t1/2 > ms), laser spectrosocpy and magnetic resonance methods have delivered a wealth of accurate and reliable data. In this contribution, I will give a few examples of this state-of-the-art, sampling from measurements performed at ISOLDE/CERN and the accelerator laboratory in Jyvaskyla/Finland. This will provide context for the second part of the talk, which will discuss some (or all) of the following through the lens of up-and-coming high-precision techniques: hyperfine anomalies/higher-order nuclear moments/molecular probes. In doing so, I will give a short update on the current status of our offline development laboratory at IKS/KU Leuven, where we seek to improve the accuracy of laser spectroscopy techniques substantially.

Orateur: Ruben de Groote

10:30 Polynomial trends in nuclear electromagnetic observables

Nuclear species with large imbalances between protons and neutrons are tough to produce and live incredibly short. Ever fewer atomic nuclei become the subject of new scientific inquiries each year. In this emerging reality, contemporary nuclear data tend to be local, with the associated interpretations often limited in scope and applicability.

However, nuclear electromagnetic properties often follow simplistic mass-dependent trends that can be described with a simple polynomial. This subject has been reinvigorated by collinear laser spectroscopy, which tends to address an isotopic chain and as such is generally non-local.

Long sequences of electromagnetic moments and charge-radii changes in the vicinity of Tin fall into the above category. The observed straight and parabolic trends therein will be discussed.

Orateur: Deyan YORDANOV (IPN)

10:50 → 11:10 Coffee break

11:10 → 12:40 Session 4

11:10 N=40 : from IOI to IOI

The development of collectivity along the N = Z is one of the subjects that has recently attracted great experimental efforts. In particular, heavy N = Z nuclei in the mass region A = 80 are expected to be some of the most deformed ground states which have been found[1] in mid-mass nuclei, typically 8p−8h, 12p−12h for e.g. the cases of 76Sr, 80Zr. This strong enhancement of collectivity with respect to lighter N=Z nuclei has its origin in cross shell excitations across the N=40 shell gap to g9/2, d5/2 and s1/2 which are intruder quadrupole partners generating
deformations. These structures can be interpreted in terms of algebraic Nilsson-SU3 self-consistent model to describe the intruder relative evolution in the vicinity of 80Zr[2]. In this presentation, we will expose some of the latest developments in microscopic nuclear structure calculations for exotic nuclei far from stabilitity at the N=Z[3]. The new theoretical calculations for the very region of 80Zr will be presented for the first time within the interacting shell model framework using an enlarged model space outside a 56Ni core comprising the pseudo-SU3 p3/2 f5/2 p1/2 and quasi-SU3 g9/2 d5/2 s1/2 orbitals for both protons and neutrons. We will present and compare results from both exact Shell Model diagonalization [4] and our newly developed DNO Shell Model approach employing beyond mean field techniques [5]. These theoretical calculations allow a very good description of the rapid transition (A = 60 − 100) from spherical to deformed structures which can be interpreted in terms of “simple” many particles - many holes configurations. Emphasis will be put on the intimate relationship between shell evolution far from stability at the neutron-rich AND proton-rich edges.
[1] R. D. O. Llewellyn et al., Phys. Rev. Lett. 124, 152501 (2020).
[2] A. P. Zuker et al., Phys. Rev. C 92, 024320 (2015)
[3] D. D. Dao, F. Nowacki, A. Poves in preparation
[4] E. Caurier, G. Martı́nez-Pinedo, F. Nowacki, A. Poves, and A. P. Zuker, Rev. Mod. Phys. 77, 427 (2005).
[5] D. D. Dao and F. Nowacki, Phys. Rev. C 105, 054314 (2022).

Orateur: Dr Frederic NOWACKI (IPHC Strasbourg)

11:40 Can we measure g factors of short-lived excited states at GSI/FAIR?

A. Kuşoğlu
Extreme Light Infrastructure – Nuclear Physics, Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering (IFIN/HH), 30 Reactorului Street, 077125 Bucharest-Magurele, Romania

Nuclear g factors are highly sensitive to single-particle aspects of the wave function and serve as a particularly potent probe of nuclear structure in regions where the nuclear shell model holds. The sd shell has been studied for many years, giving rise to “universal” sd (USD) shell model Hamiltonians [1]. An M1 operator tailored for the sd shell has also been developed, strongly based on fits to the ground‐state magnetic moments of odd‐A nuclides [2]. For odd‐A ground states, the g factor is predominantly influenced by the odd nucleon and is less sensitive to configuration mixing of the core. However, there is a lack of precise experimental g‐factor data on excited states that could challenge this theory. Recently, a new level of accuracy in excited‐state g‐factor measurements in the sd shell was achieved using an innovative form of the Time Differential Recoil In Vacuum (TDRIV) method [3]. This experimental technique, conceived for applications involving radioactive beams [4], was demonstrated with the stable isotope $^{24}$Mg [3]. The resulting measurement, g(2$^{+}_{1}$) = 0.538(13), boasts exceptional accuracy for excited‐state g‐factor measurements on picosecond states. The present work prepared the way for a future measurement on the neutron-rich nucleus $^{32}$Mg in the “island of inversion”, where the $N = 20$ shell closure breaks down, and will also assess the M1 operator. In this talk, the possibility of measuring short-lived excited states at GSI/FAIR will be discussed.

Acknowledgements
This work was supported by the Romanian Ministry of Research and Innovation under research contract PN 23 21 01 06 and the ELI-RO-RDI-2024-002(CIPHERS) project sponsored by the Romanian Ministry of Research, Innovation and Digitization.

Orateur: Dr Asli Kusoglu (ELI-NP)

12:00 Prospects for IPAC measurements

The method of integral perturbed correlations (IPAC) will briefly be introduced and its potential for application at RIB facilities, in particular FAIR, will be considered. IPAC is a well-known method for the measurement of typically ns-lived excited states. It is based on the precession of nuclei in their excited states in a strong magnetic field, requiring a gamma-gamma coincidence measurement. Historically, the method has been used in conjunction with stable beams and decay spectroscopy. The feasibility for isotopes abundantly produced at RIB facilities will be discussed.

Orateur: Volker Werner (TU Darmstadt)

12:20 Possibilities for TF measurements (TBA)

Orateur: Samit Mandal

12:40 → 13:00 Discussion

13:00 → 14:10 Lunch break

14:10 → 16:00 Session 5

14:10 Isomers measured for a moment

Electromagnetic moments tell us about the distribution of charges and currents in atomic nuclei. Moments are therefore key nuclear observables for the understanding of both the collective and individual-particle properties. For experimental reasons, moment measurements typically benefit from half-lives of order nanoseconds or longer, in which case the existence of isomeric states becomes necessary for the determination of excited-state moments.

In this presentation, the occurrence of nuclear isomers will be outlined, with reference to spin, spin orientation, and shape [1]; examples of moment measurements will be considered, illustrating the nuclear structure issues that can be addressed; and future opportunities will be discussed.

[1] P.M. Walker and Zs. Podolyák, Nuclear isomers, Chapter 12 in "Handbook of Nuclear Physics", Eds. I. Tanihata, H. Toki and T. Kajino (Springer Nature Singapore 2023) p 487

Orateur: PHILIP WALKER (UNIVERSITY OF SURREY)

14:40 Selected cases of nuclear moments in the region of 100Sn

In the regions of doubly-magic nuclei certain states (e.g. isomers) have rather pure single-particle or two-particle(hole) configurations and provide unique opportunity to study different observables. On the other hand particle-hole excitations or configuration mixing can modify the values expected from simple models. Therefore, the study of nuclear electromagnetic moments is of particular interest since these provide most sensitive information on the nuclear configurations as well as deformations thus revealing the underlying nuclear structure. Experimentally more easily accessible are longer lived states like ground and isomeric states. Selected experimental and shell-model results related to quadrupole and magnetic moments of nuclear states in the region around 100Sn will be reminded and discussed.

Orateur: Andrey Blazhev (IKP, University of Cologne)

15:00 Search for ns to μs isomers in 73Zn

(for the collaboration around experiment e680)
The spectroscopy of the neutron rich N=41-49 Zn isotopes was performed using AGATA coupled to VAMOS++ at GANIL. The isotopes were produced using the 238U(@6.2 MeV/u) + 9Be fusion-fission reaction. The gamma rays were detected in AGATA and the light fission fragments were selected in VAMOS++. As Zn is the lower Z chemical element for which gamma-ray spectra could be constructed,the statistics is scarce. The isotopes from mass 73 to 79 could be identified and studied. A detailed analysis of the systematics in this region of the Segree map enables us to conclude that two isomeric states, not yet observed, exist in 73Zn and lie low above the known 5/2+ isomeric state (E*=196 keV, T1/2 = 13 ms). The experimental results will be presented as well as the related discussion about these two isomers. A discussion will be opened about their identification and the measurement of their nuclear moment.

Orateur: Gilbert DUCHENE (IPHC - CNRS - UNISTRA)

15:20 Using alpha-transfer reactions to populate new radioactive isotopes with radioactive beams

Alpha-transfer reactions have emerged as a powerful tool for studying excited states in radioactive nuclei, particularly for investigating nuclear species near the stability line that are challenging to produce with sufficient intensity at current radioactive beam facilities. This experimental approach has proven invaluable for characterizing nuclear electric and magnetic moments, validating theoretical models of nuclear-matter behavior near the drip lines, and exploring excited-spin states. The integration of $\alpha$-transfer reactions with next-generation high-intensity radioactive beam facilities promises to extend our reach to previously inaccessible nuclear species.

This presentation will examine the application of $\alpha$-transfer reactions in nuclear structure studies, featuring the specific case of the $^{224}$Ra($^{12}$C,$^8$Be)$^{228}$Th reaction at ~5.5 MeV/u for investigating low-energy states in $^{228}$Th. We will address current theoretical challenges, showcase experimental results from existing facilities, and discuss future opportunities and technical hurdles in extending this technique to regions further from the stability line. Special emphasis will be placed on the methodological advances required to fully exploit these reactions at upcoming radioactive beam facilities.

Orateur: Diego Torres (Universidad Nacional de Colombia)

15:40 Quadrupole moments from measurements in condensed matter: The “missing link” cases Cd, Sn, Pb

In order to determine reliable values for nuclear quadrupole moments (Q) from experiments accurate theoretical calculations of the electric-field gradients (EFG) acting at the nuclear site are needed. Though considerable progress in calculating the EFG in condensed matter has been made with density-functional methods (DFT), it has been become more and more evident over the years that this technique has some intrinsic deficiencies obtaining precision absolute EFG numbers. Many-electron theory, on the other hand, in principle does not suffer from such shortcomings. Calculations in atoms or simple molecules are therefore now considered to produce the most reliable EFG values.
Thus, experimental PAC measurements at ISOLDE for free molecules have recently solved this “missing link” gap for Cd isotopes. Similar experiments for Pb are planned. For the case of the119Sn Mössbauer state, however, such measurements would present extreme technical difficulties. Therefore, only data for simple molecules embedded in inert solids are available. Computing the EFG shift between free and embedded molecules with DFT techniques, of the order of 2-5%, has here also produced a reliable value for Q, much different from the presently accepted number.

Orateur: Prof. Heinz Haas (CERN)

16:00 → 16:20 Coffee break

16:20 → 18:00 Session 6

16:20 Simple models of nuclear moments

Nuclear magnetic dipole and electric quadrupole moments are sensitive probes of the single-particle as well as the collective properties of nuclei. In this talk I review the predictions of the shell model and the interacting boson model as regards nuclear moments. The emphasis is on elementary properties that can be understood from symmetry-based principles such as, for example, the consequences of (generalised) seniority in the shell model or the predictions in the dynamical symmetries of the interacting boson model. A number of applications of interest to current nuclear-structure studies are discussed. They include the notion of effective charges in the E2 operator of the shell model derived from quadrupole moments as opposed to B(E2) values and the description of dipole and quadrupole moments in terms of aligned neutron-proton pairs or high-angular-momentum bosons. The interplay between quadrupole and octupole collectivity will also be discussed in view of recent measurements of quadrupole moments in 208Pb.

Orateur: Piet Van Isacker (GANIL)

16:50 Nuclear moments in projectile fragmentation. Lessons from the past with a sight to the future.

The nuclear electromagnetic moments provide an essential insight into the structure of the nuclei. They are of special interest for exotic regions in the nuclear chart where new shell effects or rapid modifications of the nuclear structure could be expected. The magnetic dipole moments provide a fingerprint of the single-particle properties of the nuclear wave function while the electric quadrupole moment can offer the closest view towards the nuclear deformation.
The scarce production of the nuclei far from stability makes them especially challenging for nuclear moments studies. This is even more true for short-lived (microsecond) isomeric states. Methods for obtaining spin-oriented ensemble for nuclei produced in projectile fragmentation reactions have been developed over the last three decades and successfully applied in a number of laboratories. Some examples of TDPAD measurements will be presented and the lessons learned over the last 25+ years will be discussed. The preliminary results from a recent experiment at RIKEN will be mentioned and put in the context of future studies as for example at g-SPEC at FAIR.
Ideas for accessing even shorter-lived (nanosecond) excited states will be presented and the advantages of performing those measurements at fragmentation facilities will be discussed.

Orateur: Georgi Georgiev (CSNSM, Orsay, France)

17:20 g-factor measurements of the 171keV $(2^{-})$ and 375keV $(4^{-})$ isomeric states of $^{98}Y$

The shape transition from spherical nuclear states $(N<59)$ towards deformed states $(N>59)$ is of high interest as it provides fertile ground for the validation of nuclear models. The $N=59$ nuclide $^{98}$Y is located precisely at this transition point and is characterized by shape coexistence of several nuclear deformations.

g-factor measurements of the $(2^{-})$ 171keV and $(4^{-})$ 375keV excited states of $^{98}$Y have been performed in two separate experiments using the Lohengrin mass spectrometer at Institut Laue-Langevin (ILL). Decay gammas from the isotope were collected in LaBr$_{3}$ scintillator detectors coupled to Silicon Photomultipliers (SiPM), and analysis was performed via the Time-Differential Perturbed Angular Correlation (TDPAC) method.

This work presents the setup, analysis, and results of the experiment in addition to some comparisons with select nuclear models.

Orateur: David Friant (Institut Laue-Langevin / CEA Saclay)

17:40 Spin-alignment in abrasion-fission reaction – Nuclear moment measurements of isomeric states

J.M.Daugas1,2,3, F.Boulay2,3,4, G.S.Simpson5, Y.Ichikawa2, A.Takamine2, D.S.Ahn2, K.Asahi2,6, H.Baba2, D.L.Balabanski2,7, T.Egami8, T.Fujita2,9, N.Fukuda2, C.Funayama5, T.Furukawa10, G.Georgiev11, A.Gladkov2,12, M.Hass13, K.Imamura2,14, N.Inabe2, Y.Ishibashi2,15, T.Kawaguchi8, T.Kawamura9, W.Kim12, Y.Kobayashi16, S.Kojima6, A.Kusoglu7,17, R.Lozeva11, S.Momiyama18, I.Mukul13, M.Niikura18, H.Nishibata9, T.Nishizaka8, A.Odahara9, Y.Ohtomo2,6, D.Ralet11, T.Sato6, Y.Shimizu2, T.Shimoda9, T.Sumikama2, H.Suzuki2, H.Takeda2, L.C.Tao2,19, Y.Togano6, D.Tominaga8, H.Ueno2, H.Yamazaki2, X.F.Yang20

1) ILL, Grenoble, France; 2) RIKEN Nishina Center, Wako, Japan; 3) CEA, DAM, DIF, Arpajon, France; 4) GANIL, Caen, France; 5) LPSC, Grenoble, France; 6) Tokyo Institute of Technology, Japan; 7) ELI-NP, Magurele, Romania; 8) Hosei University, Japan; 9) Osaka University, Japan; 10) Tokyo Metropolitan University, Japan; 11) IJCLab, Orsay, France; 12) Kyungpook National University, Daegu, Korea; 13) Weizmann Institute, Rehovot, Israel; 14) Meiji University, Tokyo, Japan; 15) University of Tsukuba, Japan; 16) University of Electro Communications, Tokyo, Japan; 17) Istanbul University, Turkey; 18) University of Tokyo, Japan; 19) Peking University, China; 20) KU Leuven, Belgium

The measurement of the nuclear moments of isomeric states using the well-known TDPAD method requests a spin-aligned ensemble of nuclei. Spin-aligned isomeric nuclear states are produced in several types of nuclear reactions. Particularly, the amount of spin-alignment of fragments produced in spontaneous and neutron-induced fission was found to be up to 40%.

In order to produce neutron-rich isotopes the fragmentation reaction and the fission are of particular interest. Further, the abrasion-fission reaction allows the production of very exotic species. During the g-RISING campaign g-factors of 126,127Sn microsecond isomeric states produced in abrasion-fission reaction have been measured with an observed 18(8) % spin-alignment.

A measurement performed at the RIBF, RIKEN Nishina Center, using the abrasion-fission reaction, allows to observe the relationship between the momentum distribution of the produced isotopes and the amount of spin-alignment. The obtained results show the opportunity to perform nuclear moment measurements of neutron-rich microsecond isomers produced by the abrasion-fission reaction with respect to the momentum position of the fission fragment.

Orateur: Jean-Michel Daugas (ILL)

18:00 → 18:30 Discussion

20:00 → 22:30 Workshop Dinner

mer. 14 mai

09:00 → 10:50 Session 7

09:00 Nuclear DFT magnetic dipole moments in odd near doubly-magic nuclei

The study of nuclear electromagnetic moments plays a crucial role in understanding the structure of atomic nuclei [1]. While the electric quadrupole moments in atomic nuclei indicate nuclear deformation and collectivity, the magnetic dipole moments are sensitive to the single-particle properties of valence nucleons. In our nuclear DFT methodology, the intrinsic electric quadrupole and magnetic dipole moments in odd nuclei are generated by the self-consistent shape and spin core polarization effects induced by the unpaired nucleon. The spectroscopic moments of angular-momentum-projected wave function are determined and compared with available experimental data without introducing effective charges and g-factors. We have applied our methodology to calculate the spectroscopic moments in heavy deformed open-shell odd nuclei in several regions of the nuclear chart [2, 3, 4].

In contrast to the predicted quadrupole moments that generally reproduce the data very well, the calculated magnetic dipole moments may deviate from the data sometimes by a significant amount. To improve the agreement with the data, following Refs. [5, 6], we extended the one-body magnetic dipole moment operator used in the nuclear DFT by two-body terms derived from the meson-exchange currents. We have incorporated these terms into our recent calculations for the odd-nuclei around eight doubly magic nuclei ($^{16}$O, $^{40}$Ca, $^{48}$Ca, $^{56}$Ni, $^{78}$Ni, $^{100}$Sn, $^{132}$Sn, and $^{208}$Pb). This talk will focus on the spectroscopic magnetic dipole moments in the vicinity of doubly-magic $^{78}$Ni, $^{100}$Sn, and $^{132}$Sn nuclei, which are the main interests of the gSPEC collaboration [7].

[1] G. Neyens, Rep. Prog. Phys. 66, 633 (2023)
[2] P. L. Sassarini et al., J. Phys. G: Nucl. Part. Phys. 49, 11LT01 (2022)
[3] J. Bonnard et. al., Phys. Lett. B 843, 138014 (2023)
[4] H. Wibowo et al., to be published
[5] R. Seutin et al., Phys. Rev. C 108, 054005 (2023)
[6] T. Miyagi et al., Phys. Rev. Lett. 132, 232503 (2024)
[7] R. Lozeva, A. Stuchbery, J. Gerl et al., Hyperfine Interact 240, 55 (2019).

Orateur: Herlik Wibowo (Department of Physics, University of York)

09:30 Perspectives and Opportunities for Stopped Beam Experiments in the first years of FAIR

Synchrotron-driven exotic beam facilities provide unique advantages for experiments with stopped and thermalized beams. During the initial phase of FAIR, the Super-FRS will be operated with beams from the SIS18 synchrotron, already offering enhanced beam purity through an additional separation stage and improved transmission, particularly for fission and light fragments. The transition to the SIS100-driven First Science program will significantly increase beam intensities and energies, particularly for heavy-ion beams up to uranium. Together this will enable orders-of-magnitude higher secondary beam intensities. These advancements will open new possibilities for stopped beam experiments. This contribution will outline the timeline leading to First Science, the experimental opportunities and the technical boundaries conditions. Also the future beyond the first years will be discussed.

Orateur: Timo Dickel (GSI Helmholtzzentrum für Schwerionenforschung)

10:00 Perspectives for nuclear moment measurements using laser spectroscopy at S3

The SPIRAL2 facility of GANIL will extend the capability of studying short-lived nuclei by producing beams of rare radioactive isotopes with the highest intensities achieved so far. The SPIRAL2-LINAC coupled with the Super Separator Spectrometer (S3) recoil separator will facilitate the production of neutron-deficient nuclei close to the proton dripline and super heavy nuclei via fusion-evaporation reactions, and separate them from the intense background contamination [1]. At the focal plane of S3, the Low Energy Branch (S3-LEB) will enable low-energy nuclear physics experiments (laser spectroscopy, mass spectrometry and decay spectroscopy) by stopping the nuclei in a gas cell, then neutralising and extracting them in a supersonic jet. In the jet, resonant laser ionisation can take place, which will act as both a selective ion source and a method of spectroscopy.
Resonant laser ionisation spectroscopy in the low density and temperature of the supersonic jet will boost the spectral resolution by an order of magnitude, while maintaining the efficiency typical of in-source laser spectroscopy [2], allowing the investigation of isotope shifts and hyperfine structures at the extremes of the nuclear chart. This will give access to ground-state properties such as spins, charge radii and electromagnetic moments in a nuclear-model-independent manner. The S3-LEB setup has been commissioned offline and is currently being installed at the focal plane of S3, in preparation for online commissioning [3, 4].
This contribution will present the results of the offline commissioning of the setup and its current status. The focus will then be on the online commissioning plan, and the perspectives for nuclear moment measurements, based on the existing Letters of Intent which mainly deal with the N=Z 100Sn region and the (super)heavy region.
[1] F. Déchery et al., Nucl. Instrum. Meth. B 376, 125-130 (2016)
[2] R. Ferrer et al., Nat. Comm. 8, 14520 (2017)
[3] J. Romans, et al., Nucl. Instrum. Meth. B 536, 72 (2023)
[4] A. Ajayakumar, et al., Nucl. Instrum. Meth. B 539, 102 (2023)

Orateur: Sarina Geldhof (GANIL)

10:30 Production and application of oriented RI beam for future nuclear physics research

The production of oriented RI beams could be a key technique to extend nuclear moment measurements over the wide range of nuclei including ground and excited states. Our research group has been developing several experimental techniques to obtain the polarized/aligned states. In this presentation, we present our research activities such as the nuclear moment measurements based on the bNMR technique at RIPS, a future plan at RIBF based on fast/slow polarized RI beam. The nuclear spectroscopy based on a new technique will also be discussed.

Orateur: Shintaro Go (RIKEN)

10:50 → 11:10 Coffee break

11:10 → 13:00 Session 8

11:10 Shape coexistence effects in medium mass nuclei within a beyond-mean-field approach

Coexistence phenomena in proton-rich medium mass nuclei bring insights into fundamental symmetries and interactions. The exotic behavior of these nuclei manifested by drastic changes in structure with excitation energy, occurrence of isomeric states, and their complex decay are strongly influenced by shape coexistence and mixing.
Neutron-rich A≃100 nuclei display a large variety of shape coexistence phenomena dominating their structure and dynamics. Shape coexistence effects are revealed by the structural evolution with spin, excitation energy, and neutron number, as well as the appearance of isomeric states.
Aiming to a simultaneous description of the impact of shape coexistence and mixing on different exotic phenomena we investigated the structure and dynamics of proton-rich and neutron-rich medium mass nuclei in the frame of the beyond-mean-field complex Excited Vampir variational model using the effective interaction derived from a nuclear matter G matrix based on the charge-dependent Bonn CD potential in large model spaces. Results on the comprehensive treatment of different identified characteristics concerning the structure and dynamics of exotic nuclei will be presented.

Orateur: Alexandrina Petrovici (IFIN-HH)

11:40 Effect of the Coulomb interaction on nuclear moments

Solving the Hartree-Fock-Bogoliubov (HFB) equation self-consistently with a harmonic oscillator basis, we have systematically calculated even-even nuclei with proton numbers ranging from 2 to 118 using the SLy4 parameter set of the Skyrme functional and a mixed-type pairing interaction. To investigate the origin of nuclear deformation, which is crucial in various topics such as nuclear fission and cross-section calculations, we have focused on the effect of the Coulomb interaction on nuclear shape evolution. Our calculations compare cases where the Coulomb interaction, with the exchange term treated using the Slater approximation, is either included or omitted.

The results show that the Coulomb interaction interestingly enhances quadrupole and octupole deformations across a wide range of nuclei. Notably, in the hyper-deformation region, the absolute difference in quadrupole deformation between the two cases becomes particularly pronounced. Additionally, in some nuclei, the Coulomb interaction induces a shape transition from oblate to prolate or vice versa.

We will report on the mechanism behind the deformation enhancement and shape transitions by analyzing the impact of the Coulomb interaction on single-particle energies and energy landscapes.

Orateur: KENTA HAGIHARA (University of Tsukuba)

12:00 PolarEx, a facility for on-line nuclear orientation at ALTO-LEB: nuclear magnetic properties measurements

Low Temperature Nuclear Orientation (LTNO) experiments allow us to probe magnetic properties of polarized exotic nuclei. With this technique, we observe nuclei under extreme conditions, namely very low temperatures (~10mK) and very high magnetic field (10-100T). Under such conditions, radioactive emission becomes anisotropic, and its shape provides valuable information about the nucleus structure.
Nuclear orientation gives access to different observables. The nuclear magnetic moment can be directly measured, using NMR technique. The multipole mixing ratio, which is proportional to the ratio of two multipolarity matrix elements, can also be studied and provides access to structure information.
The PolarEx apparatus, composed of a 3He-4He dilution refrigerator, is located at ALTO in Orsay, France, and is designed for such studies. Its detection system supports up to 8 detectors, either gamma or particle detector, to study the spatial asymmetry of the gamma radiation.
At present, PolarEx operates off-line on long-lived nuclei, but it will soon be ready for on-line experiment. The coupling of PolarEx with ALTO will open a large range of studies of neutron-rich nuclei, thanks to its great versatility.
In this contribution will be presented the status of PolarEx and the results of multipole mixing ratio measurements. These results have reproduced known mixing ratios, improved the precision of some, and determined unknown mixing ratios.

Orateur: Carole GAULARD (IJCLab-Université Paris-Saclay)

12:20 Investigating the changes in nuclear structure below Z = 50 with Ag

Exploring ground-state nuclear properties is a powerful tool to investigate our understanding of the nuclear structure. Laser spectroscopy gives access to model-independent measurements of the ground-state properties (spin, nuclear electromagnetic moments, changes in the charge radius) of short-lived (≥10 ms) nuclei, providing an excellent benchmark for theoretical predictions close to magic shell closures far from stability [1]. Moreover, combining laser spectroscopy and state-of-the-art quantum chemistry can provide insight into the nuclear magnetization distribution parameter [2].

One region of high interest is the region between heavily deformed Zr(Z = 40) and near-spherical Sn(Z = 50), a region with many competing nuclear configurations, and thus the subject of recent investigations: tin [3], indium [1], cadmium [4], palladium [5], and silver [6-9] studies have been successfully performed before, and neutron-rich
silver has been studied recently at ISOLDE/CERN [10] and IGISOL in Jyväskylä [8, 9].

I will present the laser spectroscopy setup at IGISOL and the CRIS technique at ISOLDE. A new isomeric state was discovered, and the level ordering was unambiguously assigned. The nuclear spin and electromagnetic properties of the ground state and isomeric states are deduced. These data provide a benchmark for state-of-the-art nuclear
models, further broadening our knowledge in this region of the nuclear chart. Further, I will present an outlook on BW effect studies in silver as a probe to the nuclear magnetization distribution.

This work is supported by the FWO-Vlaanderen (Belgium).
References
[1] A. Vernon et al., Nature 607 (2022) 260-265.
[2] L. V. Skripnikov and A. E. Barzakh, PRC 109 (2024) 024315.
[3] D. Yordanov et al., Comm. Phys. 3 (2020) 2399-3650.
[4] D. Yordanov et al., PRL 110 (2013) 192501.
[5] S. Geldhof et al., PRL 128 (2022) 152501.
[6] M. Reponen et al., Nat. Comm. 12 (2021) 4596.
[7] R. Ferrer et al., PLB 728 (2014) 191-197.
[8] R.P. de Groote et al. PLB 848 (2024) 138352.
[9] B. van den Borne, et al. PRC 111 (2025) 014329.
[10] R.P. de Groote et al., CERN-INTC-2020-023 / INTC-P-551 (2020).

Orateur: Bram van den Borne (KU Leuven)

12:40 Developments in Collinear Laser Spectroscopy at COLLAPS

Collinear laser spectroscopy (CLS) is a well-established technique for observing nuclear moments of short-lived radioactive nuclei. However, sensitivity and isotope production bound the regions of the nuclear chart that can currently be explored with this method. A solution to this problem is to develop novel methods of spectroscopy with higher sensitivity. The COLLAPS experiment is pursuing techniques which use charge exchange as a quantum state selector to allow detection by particle counting, which can drastically increase the sensitivity of continuous beam laser spectroscopy. This presentation will cover; fundamentals and background on the CLS technique, recent/ongoing technical developments towards higher sensitivity spectroscopy at COLLAPS and discussion of our recent results, with particular focus on the nuclear moments of neutron deficient thallium and lead isotopes. By expanding the regions of the nuclear chart in which it is possible to observe nuclear moments it will help us develop a richer understanding of the underlying physics and provide a more robust benchmark to theory predictions.

Orateur: Edward Matthews

13:00 → 14:10 Lunch break

14:10 → 15:00 Session 9

14:10 Nuclear Moments Studied with High-Resolution Laser Spectroscopy and Recent Plans at BRIF

Over the past years, nuclear moments of unstable nuclei across different mass regions of the nuclear chart have been extensively investigated—particularly by high-resolution laser spectroscopy setups at ISOLDE—providing rich information that deepens our understanding of nuclear structure and nuclear forces. To study nuclear moments and other nuclear properties at the ISOL facility BRIF in China, a collinear resonance ionization laser spectroscopy system has been recently developed and successfully demonstrated.
In this talk, nuclear moments of selected nuclei studied with the COLLAPS and CRIS setups at ISOLDE will be presented. In addition, recent developments in high-resolution laser spectroscopy and upcoming plans to measure the moments of unstable nuclei at the BRIF facility will be introduced.

1)X.F. Yang, S.J. Wang, S.G. Wilkins, R.F.Garcia Ruiz, Prog. Part. Nucl. Phys. 129, 104005 (2023).
2)T. J. Zhang et al., Nucl. Instrum. Methods Phys. Res. Sect. B 463 (2020)123–127
3)H.R. Hu et al., arXiv:2503.20637 (2025)

Orateur: Xiaofei Yang

14:35 Summary discussion

14:55 Closing

15:00 → 16:00 Organising committee meeting

16:00 → 16:20 Coffee break