Beta-decay of 27/2? isomers inN=83 nuclei

Abstract

In the N = 83 nucleus ~ 5 ~Er we observed the isomeric E 3 transition in conversion electron measurements following on-line mass separation and located its 0.6 s 27/2-isomer at 2.586 MeV. Gamma-ray data establish a 4.7(3)% Gamow-Teller/?-decay branch proceeding to high-spin states above 2 MeV excitation in '51Ho. A weak /?-decay branch of 0.7(3)% was also observed for the 0.5 s 27/2-isomer in the 149Dy isotone, and it was established that a similar 27/2-E3-isomer does not occur in 153yb. First results on the 1 s 1Tm and 151Er ground-state/?-decays are briefly discussed.

Isomeric and ground-state properties of78171Pt,76167<

“…Therefore we conclude that all three α decays are l = 0, hence all α-decaying states have the same spin and parity. The ground state of 159 Hf, the α decay daughter of 163 W, is reported to have a ground state spin and parity of I π = 7/2 − [30] as do the subsequent nuclei in the α-decay chain [31,32]. The I π = 7/2 − assignment of Ref.…”

“…As can be seen the energy differences between the 13/2 + and 9/2 − states remains almost constant across this decay chain down to N = 85. This is quite remarkable as at N = 83, the 13/2 + state in 151 Er is no longer a pure νi 31/2 state, but has been explained as a combination of an i 13/2 neutron with an admixture of νf 7/2 ⊗ 3 − , which is formed from an octupole excitation of the core [32]. This scenario is not expected in the heavier isotopes of this chain as the octupole states in the core nuclei are at excitation energies of 1.51 MeV for 166 Os [42] 13/2 + 9/2 − 7/2 − FIG.…”

“…A hindrance of ≈5 is observed for the M2 transitions as exhibited in the small B(M2) values for these transitions. Retarded M2 transitions have been observed across the nuclear chart, the reasons for which vary from its spin-flip character, core polarization, exchange currents reducing the spin magnetism, impure initial and/or final states, to a change in shape [32,[44][45][46][47][48]. It is possible that all these factors are at work.…”

Identification of153Lu ? decay

“…Ref. 7) indicates that the 13/2 + levels are not pure singleparticle states; they are possibly mixed with vf7/2 | 3-octupole collectivity. Direct proton emission from 153Lu was not seen.…”

“…Systematics of these single-neutron states in N=83 even-Z isotones, from 137Xe to 149Dy, were summarized in Ref. 6; more recently some of these levels have been identified in 151Er [7] and in 153yb [8]. …”