Speaker
Description
Isotopic chains close to the magic proton number \textit{Z}=50 have motivated extensive experimental and theoretical efforts in the last decades, since they provide an excellent ground to study shell-evolution and to investigate the interplay between single-particle and collective degrees of freedom. The systematic study of excited structure of nuclei in the region, and specifically the measurement of excited-state lifetimes, provide key observables to get a deeper insight on nuclear structure.\
The presentation will discuss results obtained during the experimental campaign performed at ISOLDE Decay Station (IDS) nuclei populated in the $\beta$ decay of Cd isotopes. High purity Cd (Z=48) beams were produced after the fission of a thick UC$_{x}$ target, selectively ionized by the ISOLDE Resonance Ionization Laser Ion Source (RILIS) and separated in mass using the General Purpose Separator (GPS) ISOLDE mass separator.
High resolution gamma spectroscopy using 6 highly efficient clover-type HPGe detectors was used to build level schemes, while the Advanced Time-Delayed $\beta\gamma\gamma$(t) [1,2] method was employed to access lifetimes down to the 10 ps range. The method relied on the use of a compact fast-timing setup with 2 $\gamma$-LaBr$_{3}$(Ce) detectors and 3 fast $\beta$-detectors around the IDS implantation point and it is deemed well suited to measure lifetimes in the sub-nanosecond range from low-lying isomers that are common in this region.
In this work we focus on the $\beta$-decay chain $^{128}$Cd$\rightarrow^{128}$In$\rightarrow^{128}$Sn [3-5]. The level scheme for both $^{128}$In and $^{128}$Sn has been expanded and completed. In the case of $^{128}$In we preliminarily propose 18 new transitions given rise to 6 new levels, while for $^{128}$Sn a completely new level scheme is proposed, with 28 new preliminary transitions and 10 new excited levels. The first lifetime measurements in the subnanosecond range are reported for $^{128}$In and $^{128}$Sn. The experimental $B(XL)$ results obtained derived from the analysis are discussed in the context of shell-model calculations and the seniority symmetry.
[1] H. Mach, R. Gill, and M. Moszy\' nski, Nucl. Instrum. Meth. A {\bf 280} , 49 (1989), ISSN 0168-9002.
[2] L.M. Fraile, Journal of Physics G: Nuclear and Particle Physics {\bf 44}, 094004 (2017).
[3] B. Fogelberg et al., Nuclear Physics A3Z3 (1979) 205-252.
[4] D.A. Nesterenko et al., Physics Letters B 808 (2020) 135642.
[5] B. Fogelberg et al., Proc. Int. Conf on Nuclear Data for Science and Technology, p.837 (1988)
