β -decay half-lives and β -delayed neutron emission probabilities for several isotopes of Au, Hg, Tl, Pb, and Bi, beyond N=126
Physical Review C
Previous measurements of β-delayed neutron emitters comprise around 230 nuclei, spanning from the ^8He up to ^150La. Apart from ^210Tl, with a minuscule branching ratio of 0.007%, no other neutron emitter is measured yet beyond A=150. Therefore new data are needed, particularly in the heavy mass region around N=126, in order to guide theoretical models and to understand the formation of the third r-process peak at A∼195. Purpose: To measure both, β-decay half-lives and neutron branching ratios
... f several neutron-rich Au, Hg, Tl, Pb and Bi isotopes beyond N=126. Method: Ions of interest are produced by fragmentation of a ^238U beam, selected and identified via the GSI-FRS fragment separator. A stack of segmented silicon detectors (SIMBA) is used to measure ion-implants and β-decays. An array of 30 ^3He tubes embedded in a polyethylene matrix (BELEN) is used to detect neutrons with high efficiency and selectivity. A self-triggered digital system is employed to acquire data and to enable time-correlations. The latter are analyzed with an analytical model and results for the half-lives and neutron-branching ratios are derived using the binned Maximum-Likelihood method. Results: Twenty new β-decay half-lives are reported for ^204-206Au, ^208-211Hg,^211-216Tl,^215-218Pb and ^218-220Bi, nine of them for the first time. Neutron emission probabilities are reported for ^210,211Hg and ^211-216Tl. Conclusions: The new β-decay half-lives are in good agreement with previous measurements in this region. The measured neutron emission probabilities are comparable or smaller than values predicted by global models like RHB+RQRPA.