Speaker
Description
The isotopic mass region defined by the convergence of the Z = 20 and N = 28 magic numbers sits atop multiple areas of active study, offering a unique opportunity to constrain various distinct structural effects in a singular experiment. The evolution of $B(E2)$ values can be used to understand deformation and core breaking across the $N$ = 28 shell gap [1], approaching the 2$^{nd}$ island of inversion surrounding the collective $^{44}$Si [2]. Lifetime measurements of low-lying states in the yrast bands of $^{50,51,52}$Ca and $^{46,47,48}$Ar provides a mechanism of probing the largely unconstrained $B(E2)$ values for these states, providing a stringent test for the shell-model interactions in this region.
In 2024 at experiment at INFN LNL, a 305 MeV beam of $^{48}$Ca beam was delivered to the combined AGATA/PRISMA experimental station, populating $^{50,51,52}$Ca and $^{46,47,48}$Ar isotopes among other nearby nuclei in a multi-nucleon transfer reaction. This beam was delivered to a $^{238}$U target, surrounded by the Advanced GAmma Tracking Array (AGATA) [3,4], and the emitted recoils were collected in the PRISMA large acceptance magnetic spectrometer [5], providing event-by-event resolution of the mass and atomic number. Two target configurations were used to study two distinct lifetime ranges using the Doppler-shift attenuation method (DSAM) and recoil distance Doppler-shift (RDDS) technique, utilizing a $^{238}$U target with a thick $^{93}$Nb backing and a $^{238}$U target separated from a $^{93}$Nb degrader in the Cologne Compact Plunger [6], respectively.
In this contribution, we will discuss the ongoing lifetime analysis of states in the Ca and Ar isotopes beyond $N$ = 28, using shell-model calculations to provide further context to these observations.
[1] A. Gade et al. (2003) Phys. Rev. C, 68, 014302
[2] M. Mougeot et al. (2020) Phys. Rev. C, 102, 014301
[3] S. Akkoyun et al. (2012) NIM A, 668, 26
[4] J.J. Valiente-Dobón et al. (2023) NIM A, 1049, 168040
[5] S. Szilner et al. (2007), Phys. Rev. C, 76, 024604
[6] M. Beckers et al. (2022) NIM A, 1042, 167418