Deformed band structures in neutron-rich Pm152–158 isotopes

Abstract

High spin band structures of neutron-rich 152−158 Pm isotopes have been obtained from the measurement of prompt γ-rays of isotopically identified fragments produced in fission of 238 U+ 9 Be and detected using the VAMOS++ magnetic spectrometer and EXOGAM segmented Clover array at GANIL and also from the high statistics γ-γ-γ and γ-γ-γ-γ data from the spontaneous fission of 252 Cf using Gammasphere. The excited states in 157 Pm and those above the isomers in even-A Pm isotopes 152,154,156,158 Pm have been identified for the first time. The spectroscopic information on the rotational band structures in odd-A Pm isotopes has been extended considerably to higher spins and the possibility of the presence of reflection asymmetric shapes is explored. The configuration assignments are based on the results of Cranked Relativistic Hartree-Bogoliubov calculations. From the systematics of bands in odd-A Pm isotopes and weak population of opposite parity bands, octupole deformed shapes in neutron rich Pm isotopes beyond N = 90 seem unlikely to be present.

Configuration and bandhead spin assignments for the two-quasiparticle rotational bands in the neutron-rich nuclei Pm154,156

“…The single-particle level structures for all Pm isotopes considered in the present work are very close to each other, so we only show 155 Pm as an example. The present calculation shows that the ground states for 153,155,157 Pm are all π5/2 − [532], which is consistent with the experimental data [13,18,20]. In addition, for the neighboring nuclei Nd and Sm, the experimental data show that the ground states for N = 93 isotones ( 153 Nd and 155 Sm) are ν3/2 − [521] [42,43], which is also reproduced by the present calculation.…”

“…Therefore, the cranked Nilsson levels adopted here are quite reasonable. Figure 2 shows the comparison between experimental [13,43,44] Thus, the present calculation in turn supports the configuration assignments for these 1-qp bands in Ref. [13].…”

“…The data are taken from Ref. [13]. For 154 Pm, two isomers with half-lives of 2.68 minutes and 1.73 minutes were observed several years ago [45].…”

“…Up to now, parity doublet bands in Pm isotopes have been observed in 147 Pm [9], 149 Pm [10], and 151 Pm [11,12]. Recently, high-spin structures in the neutron-rich 152−158 Pm isotopes, including both odd-A and odd-odd nuclei, have been observed experimentally by the spontaneous fission of the actinide nuclei [13]. Compared with pervious experiments [14][15][16][17][18][19][20], these rotational bands either have been obtained for the first time, or have been extended considerably to higher spins.…”

“…However, due to the lack of firm spin and parity assignments, reasonable configurations have not been assigned for these 2-qp rotational bands in odd-odd Pm isotopes in Ref. [13]. In the present work, the cranked shell model (CSM) with pairing correlations treated by a particle-number conserving (PNC) method [24,25] will be used for investigating the rotational bands in these Pm isotopes, and the configuration and bandhead spin assignments will be made for the three 2-qp bands observed in 154,156 Pm.…”