Garrett et al. systematically investigated band-crossing frequencies resulting from the rotational alignment of the first pair of i 13/2 neutrons (AB) in rare-earth nuclei. In that study, evidence was found for an odd-even neutron number dependence attributed to changes in the strength of neutron pairing correlations. The present paper carries out a similar investigation at higher rotational frequencies for the second pair of aligning i 13/2 neutrons (BC). Again, a systematic difference in band-crossing frequencies is observed between odd-N and even-N Er, Yb, Hf, and W nuclei, but in the BC case, it is opposite to the AB neutron-number dependence. These results are discussed in terms of a reduction of neutron pairing correlations at high rotational frequencies and of the effects of Pauli blocking on the pairing field by higher-seniority configurations. Also playing a significant role are the changes in deformation with proton and neutron numbers, the changes in location of single-particle orbitals as a function of quadrupole deformation, and the position of the Fermi surface with regard to the various components of the neutron i 13/2 shell.
We report the results of a study of rotational bands in 219 Ra via the 208 Pb( 14 C,3n) reaction to look for evidence that this nucleus is statically octupole deformed. We add 19 γ rays not previously observed to the level scheme and extend the two most strongly populated alternating parity bands to J=51/2 and 45/2. The magnitude of the energy splitting between the spin-parity doublets in the two bands appears to exclude the possibility that 219 Ra has a static octupole deformation.PACS numbers: May be entered using the \pacs{#1} command.
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We report the results of a γ ray spectroscopic study of 211 Po via the 208 Pb(α,n) reaction at 24 MeV incident energy using a thick target. We observe 26 new γ rays, allowing us to identify 18 states that were not observed in previous γ ray studies. In total, we observe 45 states below 2.0 MeV. A shell model calculation using the modified Kuo-Herling interaction developed by Warburton and Brown predicts 46 states below 2.0 MeV having spins of 21/2 and below, demonstrating the power of this calculation to provide detailed nuclear structure information on nuclei in the vicinity of 208 Pb.PACS numbers: May be entered using the \pacs{#1} command.
Maximal ground-state deformation should occur when both proton and neutron Fermi surfaces are located at midshell. However, subshell gaps that stabilize large deformation can exist at proton or neutron values other than midshell. One such gap may occur at Z = 60 in the rare-earth region, as the energy of the first 2 + states in even-even nuclei are often lowest in an isotonic chain for neodymium (Z = 60) rather than the midshell isotopes of dysprosium (Z = 66). Further evidence of this deformed gap has now been observed by investigating the signature splitting systematics of the νi 13/2 bands found in the odd-N, rare-earth nuclei. These were aided by the present observation of the νi 13/2 band in 159 Gd and the confirmation of the same structure in 155 Sm via the transfer of a neutron from a 160 Gd beam to a 154 Sm target.
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