Investigation of neutron-rich rare-earth nuclei including the new isotopes 177Tm and 184Lu

Abstract

Decays of neutron-rich isotopes in the rare-earth region were studied by means of on-line mass separation and β− γ spectroscopy using multinucleon-transfer reactions between beams of 136Xe (9 and 11.7 MeV/u), 186W (11.7 and 15 MeV/u) and 238U (11.4 MeV/u) and targets of natW and Ta. The higher beam energies appear to be advantageous for the production of such isotopes. Two new isotopes were identified: 177Tm with a half-life T 1 2 = 85 −15 +10 s , and 185Lu with T 1 2 ≈ 18 s . A new 47 s activity found at A = 171 is tentatively assigned to the decay of the new isotope 171Ho. The properties of the ground and excited states of neutron-rich lanthanide isotopes are interpreted within the shell model using the deformed Woods-Saxon potential. A change of the ground-state configuration for odd-mass neutron-rich lutetium isotopes from π 7 2 +[404] to π 9 2 −[514] is suggested, this change being due to the influence of a large hexadecapole deformation. The role of the possible isomeric state in 180Lu for the nucleosynthesis of 180mTa is discussed.