YRAST LEVEL STRUCTURE OF THE N=82 AND 83 NUCLEI HOLMIUM-149 AND HOLMIUM-150; NEGATIVE PARITY STATES IN OSMIUM-188 FROM THE TUNGSTEN-186(ALPHA, 2 NEUTRONS) REACTION
Abstract
The yrast level strucure of the N=82 and 83 nuclei ('149)Ho and ('150)Ho have been investigated by in-beam (gamma)-ray spectroscopy following reactions of 150-180 MeV ('32)S beams with ('121)Sb and ('122)Te targets. The holmium nuclei have 3 more protons than ('146)(,64)Gd(,82) which has recently been found to have many properties of a doubly closed shell nucleus. In the three valence proton nucleus ('149)(,67)Ho(,82), we have identified a ((pi)h(,11/2))('3) sequence of yrast levels and have found both the level spacings and the measured B(E2) value for the 27/2('-) (--->) 23/2('-) ((pi)h(,11/2))('3) recoupling transition to be in excellent agreement with shell model calculations in which the residual proton-proton interactions and the (pi)h(,11/2) effective E2 charge were taken from the experimental ((pi)h(,11/2))('2) spectrum of 148Dy. The expected 15/2('+), 19/2('+) and 23/2('+) yrast states arising from the coupling of the additional h(,11/2) proton to the 3('-), 5('-) and 7('-) ('148)Dy states have also been identified. In ('150)(,67)Ho(,83), the man yrast level sequence is found to agree closely with shell model predictions of level energies, isomeric half-life and deexcitation pathway for the ((pi)h(,11/2))('3) (nu)f(,7/2) configuration. The transition rate for the 17('+) (--->) 15('+) isomeric transition can be reproduced in shell model calculations only by using a very large neutron effective charge value of about 4e. Four negative parity yrast states below 2.5 MeV were also found in ('150)Ho and all four appear to be structurally related to known states in neighboring N=82 and 83 nuclei. High lying isomers in both ('149)Ho and ('150)Ho have been identified but not fully characterized. The yrast negative parity level structure of ('188)Os has been investigated following the ('186)W ((alpha),2n) reaction. Energies, spins and parities were established for many levels and I('(pi))=7('-) and 9('-) isomers with t(,1/2) = 16 (+OR-) 2 ns and 10 (+OR-) 1 ns were established. The properties of the negative parity states in ('188)Os are compared to those of (a) the semidecoupled bands built on 5('-) states in the oblate or triaxial even-even Hg and Pt nuclei, (b) negative parity two quasiparticle Nilsson states observed in prolate even-even W nuclei.
Degree
Ph.D.
Subject Area
Nuclear chemistry
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