Lifetimes in the Ground-State Band ofHg184

Evidence for nuclear shape coexistence in180Hg

“…For a quantitative estimate we have investigated cascades of statistical E1 and collective E2 transitions starting from a fully aligned entry state. The hyperfine interaction after recoil into vacuum has been characterized by a damping constant of 0d/ps [13], while typical lifetimes in the yrast sequence of lS~ have been estimated to be ~ 2ps above the 6 + level and 10, 40 and 700 ps for the 6 +, 4 + and 2 + states, respectively, using the B(E2) values from laeHg [2]. Under the assumption of initial spins around 12 and 5 statistical ), rays the model calculations give sufficient attenuation to explain the nearly isotropic overall angular distribution observed.…”

“…The delicate balance realized in these nuclei is illustrated by the wellknown behaviour of the even mercury isotopes between 188Hg and la4Hg [1][2][3]. Here the 0 § band head of the deformed configuration drops from 824 keV to 375 keV above the nearly spherical ground state.…”

Observation of the weakly deformedvi 13 2/2 band in188Hg

“…In the heavier isotopes 19~ the strongly deformed band head is expected to have an excitation energy of > 1 MeV, and the band therefore can not easily be identified. On the other hand in the lighter isotopes 18~'as6'188Hg the levels of the strongly deformed band become yrast above the 4 + state, and only these yrast levels have been observed in previous (HI, xn) studies [3][4][5]. The continuation of the weakly deformed ground band above U=4 + is known from radioactive decay studies only up to the 8 + level [2].…”

The interacting Boson Model applied to the mercury isotopes

“…Morrison [14] has done IBM calculations in the 0(6) limit on 196'198Hg and 2~ Models used to describe 19~ include cluster vibration [15], and rotation alignment [16]. The light isotopes, 184-~SSHg, have been of considerable recent interest because of the apparent coexistence of two sets of bands based on different shapes, one nearly spheri- cal and the other deformed [17][18][19][20]. Several twoband mixing calculations have been done on these isotopes [21][22][23][24], including a preliminary study by Duval and Barrett [25], who have developed a method of treating configuration mixing within the IBM.…”