High-spin negative-parity states in 200Hg from 200mAu decay and 198Pt(α, 2nγ) reaction spectroscopy

Abstract

Levels in 200Hg populated in the β − decay of the 19 h isomer of 200Au and in the reaction 198Pt(α, 2nγ) 200Hg have been investigated. The β-decay populates an 11 − level in 200Hg at 2642 keV, which de-excites through levels at the following energies (spin-parities): 2144(9 −), 1963(7 −), 1852(5 −), 1707(6 +), 947(4 +) and 368(2 +) keV. The relative γ-ray intensities measured in the in-beam experiment were invaluable in the construction of an unambiguous 200Hg level spectrum. The 9 − → 7 − and 7 − → 5 − E2 transitions are considerably enhanced suggesting that the negative-parity levels constitute a collective “band”. It is proposed that the β − decay involves a one-particle transition between the ( h 11 2 π, i 13 2 ν)12 − isomer of 200Au and a ( h 9 2 ν, i 13 2 ν) two-neutron admixture in the 200Hg 11 − state. Indications of the systematic occurrence of similar sequences of negative-parity levels in other A = 190–200 transitional nuclei are discussed.