Decay of aKπ=21/2−, 17-ms isomer inTa

Abstract

High-spin states in the neutron-rich nucleus 185 Ta, populated in the decay of a long-lived, three-quasiparticle state, have been studied using deep-inelastic reactions with 136 Xe ions and a 186 W target. The lifetime of the isomer has been measured as 17(2) ms and the spin and parity determined to be K π = 21/2 − , leading to a π 7/2 + [404]ν3/2 − [512]11/2 + [615] configuration assignment. The isomer decays into the rotational band built upon the π 9/2 − [514] intrinsic state via K-forbidden transitions with reduced hindrances of 52 and 71. The π 9/2 − [514] state is itself an isomer with a lifetime of 17(3) ns. It decays via K-allowed E1 transitions to states in the π 7/2 + [404] band with strengths that are similar to equivalent transitions in the lighter tantalum isotopes.

Review of metastable states in heavy nuclei

“…The measurements have led to extensive new information on isomers in a range of nuclei near stability and also somewhat neutron-rich, as depicted schematically in figure 24. Analysis of these data continues but details of completed results are published in a series of papers [33,67,74,94,126,128,129,130,443,444,445,446,447,448,449,450,451]. They cover a broad range in terms of physics, from the characterisation of comprehensive multi-quasiparticle isomers in 174 Yb [445], for example, to the identification of transitions to intermediate states that could connect the high-K and low-K isomeric and ground states in 176 Lu by photoexcitation, thus affecting elemental abundances in a stellar environment [33].…”

Identicity in high-K three quasiparticle rotational bands: a theoretical approach

“…Experimental data on Δ = I 1 transition energies ( γ E ) and B M B E ( 1) ( 2) ratios of these identical 3qp rotational bands are tabulated in table 1 after analyzing references [1][2][3][4][5][16][17][18][19][20][21][22][23][24][25][26].…”

“…At excitation energy ⩾1MeV, which is approximately the energy gap in the rare-earth region, a proton or a neutron pair break up and form a 3qp state in odd-A nuclei. The compilation of data [1][2][3][4][5] for 3qp intrinsic excitations in the mass region A = 153-187 (Z = 63-78, N = 88-112) indicates that the presence of Nilsson orbitals with relatively high angular momentum projections Ω i (i = 1-3) on the nuclear deformation axis near the Fermi surfaces of both protons and neutrons generate the low-lying high-K 3qp rotational states. These high-K rotational bands are known to display several puzzling features [1,[3][4][5], and many of them are still very poorly understood.…”

Structure of neutron-rich tungsten nuclei and evidence for a 10−isomer inW190

“…Indirect evidence that the two-neutron configuration is the correct assignment was presented in Ref. [28], although this has been questioned recently [29]. For 188 W, the multiquasiparticle calculations of Ref.…”