Comunicazione
Search for the shape coexistence phenomenon in selenium isotopes near the $N=50$ shell closure.
Ciconali G., Conca F., Sferrazza M., Bottoni S., Leoni S., Fornal B., Michelagnoli C., Corbari G., Luciani M., Colombi G., Porzio C., Crespi F., Cieplicka N., Iskra L., Jentschel M., Koester U., Borcea R., Boromiza M., Cualinescu S., Clisu-Stan C., Costache C., Filipescu D., Florea N., Gheorghe I., Ionescu A., Muarginean N., Muarginean R., Mihai C., Mihai R.E., Neaccsu C., Negrect A., Nictua C.R., Oluacel-Coman A., Pascu S., Petrone C., Stan L., Sotty C., Turturicua A., Turturicua G., Toma S., Ujeniuc S.
We discuss the investigation of the shape coexistence phenomenon near the $N=50$ shell closure in the neutron-rich selenium ($Z=34$) chain, by gamma-ray spectroscopy. The $^{84}Se$ ($N=50$) and $^{83}Se$ ($N=49$) nuclei have been populated by a sub-Coulomb barrier transfer reaction at IFIN-HH and by a neutron capture reaction at ILL, respectively. In the case of $^{84}Se$, two excited $0^+$ states, already known from the literature, have been confirmed at 2244 keV and 2654 keV, and their gamma decay to the first $2^+$ state was observed for the first time. Preliminary results from lifetime analyses indicate that the lifetime of the third $0^+$ is of the order of 1 ps, while a longer lifetime is expected for the second $0^+$ state. For the $^{83}Se$ nucleus, the current gamma-spectroscopy data allowed to significantly expand the decay scheme of the nucleus, through the observation of 28 new primary gammas, 89 new secondary transitions and 16 new populated energy levels. The data analysis is still ongoing and firm spin and parity assignments of newly found states will be obtained from angular correlation investigation.