Orateur
Description
Most of the known unstable nuclei undergo one of the main decay channels by emitting α/β particles, or γ rays. In some cases, however, more rare and exotic phenomena, like proton radioactivity, cluster radioactivity or β-delayed fission, emerge and characterise different regions of the nuclear chart.
Neutron-deficient nuclei approaching the proton drip-line start having negative proton separation energy and can open up to the possibility of proton radioactivity. While this decay channel has been studied in several nuclei with 50 < Z < 83 [1], there are still some gaps in different isotopic chains of this region that prevent mapping a precise outline of the proton drip-line. Additionally, a systematic characterisation of the phase transition between β decay and proton emission was not conducted so far.
While proton radioactivity involves the loss of a single nucleon, cluster radioactivity is characterised by the emission of a product heavier than an α particle but lighter than usual fission fragments. This process has been mostly observed in heavy nuclei in the actinides region with emitted clusters between $^{12}$C and $^{34}$Si [2, 3], but theoretical calculations predict the possibility of observing such decay mode in nuclei above the doubly-magic $^{100}$Sn, pointing to a new island of cluster radioactivity for lighter nuclei [4].
Beta-delayed fission (βDF), on the other hand, is a two-step process and has been so far studied in neutron-deficient and neutron-rich nuclei above thallium, with most of the experimental results in the neutron-deficient lead and trans-uranium regions of the nuclear chart [5, 6]. A recently developed theoretical framework can satisfactorily reproduce the experimental βDF probabilities with a global RMS deviation of two orders of magnitude, and was used to predict new cases to be studied experimentally both in the neutron-deficient and neutron-rich regions of the nuclear chart [6].
The nuclei undergoing the decays described above could be studied using the pure beams that will be achieved at S$^3$-LEB. Because of the rarity of these phenomena, it is important to build an experimental setup that would enable the detection of the decay products in the different exotic processes. The decay channels of interest are in competition with the other main decay modes, thus, the setup needs to have a good sensitivity and the capability of neglecting (if needed) all signals coming from the competing processes. Moreover, the system needs to be coupled to the S$^3$-LEB beamline where radioactive ion beams are delivered to the experimental setup with an energy of 3 keV. For this purpose, the possibility of using systems like a Time Projection Chamber (TPC), Si-Si or gas-Si telescope detectors is under investigation. This contribution will discuss the results from the first studies and tests, and future developments foreseen for the setup.
Acknowledgements
S3LEB has received funding from the French Research Ministry through the National Research Agency under contract number ANR-13-BS05-0013, from the Research Foundation - Flanders (FWO) under the International Research Infrastructure program number I002219N, from the Research Coordination Office – KU Leuven (C14/22/104), from the European Research Council under contract number ERC-2011-AdG-291561-HELIOS, from the FWO and F.R.S.-FNRS under the Excellence of Science (EOS) programme (40007501),from the European Union’s Horizon 2020 research and innovation program under grant agreement number 654002–ENSAR2–H2020-INFRAIA-2014-2015 and under grant agreement number 861198–LISA–H2020-MSCA-ITN-2019 and from IN2P3-DSM/CEA and GSI under the French-German collaboration agreement number PN1064.
References
[1] P. J. Woods, C. N. Davids, Annu. Rev. Nucl. Part. Sci. 47:541-90 (1997)
[2] D. N. Poenaru et al., J. Phys. G: Nucl. Phys. 10 L183 (1984)
[3] R. Bonetti, A. Guglielmetti, Rep. Phys. 59 (2), 301–310 (2007)
[4] C. Qi et al., Phys. Rev. C 80, 044326 (2009)
[5] S. Bara et al., Phys. Rev. C 111, 065803 (2025)
[6] A. N. Andreyev et al., Rev. Mod. Phys. 85, 1541 (2013)
[7] S. Bara, Experimental and theoretical studies of $\beta$-delayed fission. PhD thesis, KU Leuven (2025)