Speaker
Description
Intruder states that originate from the promotion of neutrons across the N=50 shell gap are observed along the N=49 isotones ($^{79}$Zn, $^{81}$Ge, $^{83}$Se, $^{85}$Kr), with the lowest energy in $^{83}$Se. The reduction of the N=50 shell gap towards $^{78}$Ni favors the lowering in the energy of these states. Moreover, since the $^{83}$Se nucleus (Z=34) is in the middle of the proton fp-shell (28$<$Z$<$40), it should have the maximum quadrupole correlations, lowering further the energy of these deformed configurations. This makes $^{83}$Se a good candidate for understanding the collectivity of the particle-hole intruder states in this region. Such information could also be used as a testing ground for theoretical models aiming to describe the region in the vicinity of $^{78}$Ni.
The nucleus of interest was populated using a (d,p) reaction in a recent experiment performed at the Laboratori Nazionali di Legnaro. The GALILEO $\gamma$-ray array at the phase II configuration was coupled to the SPIDER silicon array, allowing one to obtain the needed channel selectivity through coincidence measurements between $\gamma$ rays and the protons from the (d,p) reaction. This work reports on the lifetime of the 540-keV 1/2$^{+}$ and 1100-keV 3/2$^{+}$ intruder states of $^{83}$Se measured by using the Recoil Distance Doppler-Shift method (RDDS) and Doppler-Shift Attenuation Method (DSAM), respectively. The experimental outcome will be discussed in the framework of shell-model calculations and mean-field approaches. The present results challenge current theoretical models in this region.
| Email Address | julgen.pellumaj@lnl.infn.it |
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