Configuration dependence ofK-forbidden transition rates from three-quasiparticle isomers

Abstract

Reduced hindrance factors for K-forbidden E2 transitions from two-and three-quasiparticle isomers in the A ≈ 180 deformed region are compared. Evidence is presented that when all three quasiparticles are of the same nucleon type (proton or neutron) there is a strong dependence of the E2 reduced hindrance factor on the isomer excitation energy.

Three-quasiparticle isomer in Ta173 and the excitation energy dependence of K -forbidden transition rates

“…It is seen that the new data point for 173 Ta (filled square in Fig. 4) is consistent with the earlier analysis [6], thus lending support to the significance of this correlation. A similar correlation had been demonstrated previously for four-and five-quasiparticle isomers [24], later extended to higher quasiparticle numbers [4,5,25].…”

“…It is assumed that g = 1 and g = 5.59 for protons (and 0 and −3.83 for neutrons, respectively) and that there is an additional g quenching factor of 0.6 to account for the nuclear medium. Hence, the Nilsson model predicts g K = 1.26 for the 9/2 − [514] configuration, which is in satisfactory accord with the experimental value of 1.17 (6). [The alternative sign of (g K − g R ) gives g K = −0.37(6) which is unphysical, in the sense that no one-proton configuration could generate such a small value.…”

“…The systematic variation of decay rates from threequasiparticle isomers in the A ≈ 180 region has been discussed recently by Walker et al [6]. They showed that, when all three quasiparticles are of the same nucleon type, reduced hindrance factors for E2 decays display a strong inverse dependence on excitation energy relative to a rigid rotor of appropriate mass.…”

“…For the K π = 9/2 − band, Carlsson et al [9] use g R = 0.40 and Q 0 = 7.0 eb. With those values we find, using their branching ratios and (g K − g R ) > 0, that g K = 1.17 (6), assuming an uncertainty of ±0.05 in the g R value [15,16]. This "experimental" value of g K = 1.17(6) can be compared with the "theoretical" estimate for the Nilsson 9/2 − [514] configuration in the strong-coupling approximation (Kg K = g + g , where and are the Nilsson orbital and intrinsic asymptotic quantum numbers, respectively).…”

“…Despite the large body of data on these "K-forbidden" transitions [3], the understanding of the corresponding transition rates remains poor. Nevertheless, the systematic variation of hindrance factors has the potential to provide critical predictive power [2,5,6], which may be helpful in the study of exotic nuclei.…”