Near-yrast structure of odd-A, neutron-rich Pr isotopes

Abstract

The neutron-rich praseodymium isotopes 151 Pr and 153 Pr have been studied by prompt γ-ray spectroscopy using 248 Cm and 252 Cf spontaneous-fission sources placed inside the EUROGAM-II and Gammasphere germanium arrays, respectively. Rotational bands, based on 3/2 − [541] states, with similar structures, have been assigned to these nuclei. These bands decay by intraband E2 transitions. Interband E1 transitions, reported in other works, were not observed. Delayed conversionelectron and γ-ray spectroscopy of an A = 151 nucleus has been performed at the Lohengrin mass spectrometer. A previously reported 35.1-keV isomer of 151 Pr has been determined to decay by an E1 transition and its half-life of 50(8) µs measured for the first time. Calculations performed using a reflection-symmetric quasi-particle-rotor model successfully reproduce the energies of the excited states of these nuclei and their decay patterns. The spin of the isomer has been assigned to be (1/2 + , 3/2 + ) from a comparison with the calculations. The long half life of this isomer and the lack of intraband E1 transitions show an absence of strong octupole correlations in the observed states of 151,153 Pr. This is explained in terms of increasing quadrupole deformation reducing the number of Nilsson orbitals close to the Fermi surface available to form octupole collectivity.

Gamma-ray spectroscopy of fission fragments with state-of-the-art techniques

“…35a and b, the entire region around 144 Ba is characterized by sizable intrinsic electric dipole moment D 0 . In particular, 142 Xe, 144,146 Ba, 145,147 La and 148 Ce are found to display the strongest octupole correlations [12,254,[260][261][262][263][264], while weaker collectivity was found in the neighboring systems of 140,141 Xe, 141,143 Cs, 142,144 Cs, 149 Ce and 151,153 Pr [171,[265][266][267][268]. In Pm isotopes (Z = 61), octupole deformed shapes beyond N = 90 seem unlikely to be present, as follows from recent EXOGAM+VAMOS experiments with in-flight fission of 238 U [269].…”

“…2.1) [24,25,56,57,68,77,89,94,107,169,272], K isomerisms in the A=150 mass region (Sect. 2.3) [191,268], and on complex phenomena such as shape coexistence (Sect. 2.3) [149, 153, 154, 156-160, 233, 238].…”