In-beam γ -ray spectroscopy of Cr62,64

An experimental view on shape coexistence in nuclei

“…The "normal" configuration, corresponding to the ground state in 68 Ni, the π(1h) ground state in 67 Co, and the π(2h) state in 66 Fe, may then appear as a lowlying 0 + state in the latter. Further away from Z = 28, low-lying 0 + states of a similar configuration were also predicted in 62,64 Cr (Z = 24), and a candidate in 62 Cr was observed experimentally [182]. It is stressed that while these states are labelled by their proton p−h content, all of them will involve neutron mp − mh contributions.…”

“…In general, the α decays of the 186,188,190 Pb isotopes to the 0 + 2 states in 182,184,186 Hg are strongly hindered compared to the decays proceeding directly to the ground state, and the observed hindrance factors are of similar magnitude (≈10-20) for all three isotopes. This was interpreted as resulting from the normal-order configuration of the ground states of Pb and Hg nuclei and an intruder nature of the 0 + 2 states in 182,184,186 Hg: the population of an intruder state in the α decay of a normal-configuration state involves the removal of a proton pair from an orbital below the Z = 82 gap and the promotion of a proton pair across this gap. Consequently, the ground states of all even Pb and Hg nuclei in the vicinity of N = 104 were assumed to have similar configurations corresponding to normal-order shell occupation, while the 0 + 2 states in the Hg isotopic chain were interpreted as predominantly π(2p − 2h) intruders.…”

“…The microscopic configurations of the two coexisting structures in light Hg nuclei were inferred via systematic α-decay studies [477,478]. In general, the α decays of the 186,188,190 Pb isotopes to the 0 + 2 states in 182,184,186 Hg are strongly hindered compared to the decays proceeding directly to the ground state, and the observed hindrance factors are of similar magnitude (≈10-20) for all three isotopes. This was interpreted as resulting from the normal-order configuration of the ground states of Pb and Hg nuclei and an intruder nature of the 0 + 2 states in 182,184,186 Hg: the population of an intruder state in the α decay of a normal-configuration state involves the removal of a proton pair from an orbital below the Z = 82 gap and the promotion of a proton pair across this gap.…”

“…The measured hindrance factors for the Hg → Pt α decay, combined with the information on mixing in the Pt daughter nuclei obtained from the perturbation of energies in the rotational bands [479], were used to estimate the mixing of normal-order and intruder 0 + states in 180,182,184 Hg. This analysis yielded a 3% admixture of the deformed configuration in the ground state of 180 Hg, while mixing of 16% and 18% was obtained for 182 Hg and 184 Hg, respectively [478].…”

In-beam γ -ray spectroscopy of Fe68 from charge exchange on Co68 projectiles

“…For the first half of the experiment, the magnetic rigidity of the spectrograph was optimized to center 64 Cr products from 65 Mn projectiles in the focal plane, while the second half proceeded with the magnetic rigidity slightly shifted to move 64,62 Cr ejectiles from 66 Fe and 68 Co beams more into the focal-plane acceptance-the spectroscopy of these two neutron-rich Cr isotopes was the original focus of the measurements, and results have been published recently [31]. Coincidentally, the first setting above also centered 68 Fe ions from reactions with the 68 Co secondary beam in the spectrograph.…”