Orateur
Description
A little more than ten years ago, the very first electron beam was produced with the ALTO electron LINAC. 50 MeV and 10 µA later, the induced photofission process allow the production of exotic neutron rich isotopes. Based on the ISOL technique, ALTO has shown its capability to produce radioactive ion beams in the $^{78}$Ni mass region. Since then, the Orsay team working with the facility developed a set of instruments dedicated to the study of neutron rich nuclei β -decay such as BEDO or the neutron counter named TETRA [1]. The availability of these setups allowed the investigation of possible existence of low-lying structures in the β -strength function above the neutron separation energy (Sn). This endeavor was further encouraged by two remarkable serendipities. The first one concerns the unexpected observation of “ultra”-high-energy γ-rays (8-9 MeV) [2] in the β-delayed emission products of $^{83}$Ga (Z=31 ; N=52 ; T1/2=312 ms ; Qb=11.7 MeV) sources collected at the BEDO station [3]. The second one concerns β-delayed neutron-emission probability (Pn) measurements of the $^{82,83,84}$Ga (N=51,52,53) precursors [4] using the neutron counter TETRA: quite unexpectedly, after a steep increase of the Pn values from N=51 to 52, the Pn falls down again at N=53 by a factor ~2. More recently, manifestation of Pygmy Dipole Resonances (PDR) was observed in $^{80}$Ge [5]. These results will be presented and discussed. It will be shown that they clearly point towards the existence of structures in the threshold region of the daughter-nucleus excitation spectrum, governing the decay properties in the $^{78}$Ni region. Perspectives for further investigation of these questions at ALTO using the PARIS, TETRA and MONSTER (γ and neutron) spectrometers will be presented.
Others β-decay activities of the Orsay research group will also be presented.
[1] D. Testov, D. Verney, B. Roussière et al., NIM A815, 96 (2016)
[2] A. Gottardo, D. Verney, I. Deloncle et al. PLB 772, 359 (2017)
[3] A. Etilé, D. Verney, N. N. Arsenyev et al. PRC 91, 064317 (2015)
[4] D. Verney, D. Testov, F. Ibrahim et al., PRC 95, 054320 (2017)
[5] R. Li, Ph. D. Thesis, Université Paris-Saclay (2022)
