Abstract
The levels in Sn-129 populated from the beta(-) decay of In-129 isomers were investigated at the ISOLDE facility of CERN using the newly commissioned ISOLDE Decay Station (IDS). The lowest 1/2(+) state and the 3/2(+) ground state in 129Sn are expected to have configurations dominated by the neutron s(1/2) (l = 0) and d(3/2) (l = 2) single-particle states, respectively. Consequently, these states should be connected by a somewhat slow l-forbidden M1 transition. Using fast-timing spectroscopy we havemeasured the half-life of the 1/2(+) 315.3-keV state, T-1/2 = 19(10) ps, which corresponds to a moderately fast M1 transition. Shell-model calculations using the CD-Bonn effective interaction, with standard effective charges and g factors, predict a 4-ns half-life for this level. We can reconcile the shell-model calculations to the measured T-1/2 value by the renormalization of the M1 effective operator for neutron holes.
Highlights
The curves representing the centroid positions of time spectrum vs γ -ray energy deposited in the LaBr3(Ce) crystals [15,16] were determined both for Compton events and full-energy peak (FEP), by using the timing information of transitions in 138Ba which de-excite short-lived levels that are directly fed in the β decay of 138Cs [13,14]
The half-life of the lowest 1/2+ state in 129Sn populated in the β− decay of 129In is reported for the first time
It is expected that they are connected by a retarded l-forbidden M1 transition
Summary
As the N/Z ratio increases, several aspects of the effective interaction between protons and neutrons are revealed, providing unique views into the nuclear structure In this context, the predictive power of nuclear models is subject to a stringent scrutiny, especially when the measurement of the electromagnetic transition probabilities connecting nuclear states can be achieved. In the case of the 135Sb system (132Sn+2n+1p), for example, the B(M1; 5/2+ → 7/2+) transition rate from the first-excited 281.7-keV level to the ground state calculated with free g factors is two orders of magnitude larger than the experimental value This discrepancy cannot be removed by using effective g factors, but only by considering an effective.
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