The limit of stability of proton-rich thallium isotopes: a search for the decay of¹⁷⁷Tl

Abstract

The fusion reaction⁷⁴Se+¹⁰⁶Cd→¹⁸⁰Pb^* at a compound nucleus excitation energy E_x ≃ 40 MeV, has been used in a search for the decay of the unknown nucleus¹⁷⁷Tl. Evaporation residues were velocity and mass analysed prior to implantation into a position sensitive silicon surface barrier detector. No evidence was discovered for the proton or alpha-decay of¹⁷⁷Tl for a cross-section > 10 ⁵⁺¹⁰₋ nb. This indicates either that¹⁷⁷Tl decays too rapidly (t_1/2 < 1 μs) by proton emission for the decay to be detected, or that¹⁷⁷Tl is produced with a cross-section less than the limit established in the present experiment. The following nuclear decay half-lives were measured with improved accuracy;¹⁷⁷Hg (t_1/2 = 130±5 ms),¹⁷⁸Hg (t_1/2=250±25 ms) and¹⁷⁷Au (t_1/2=1180±70 ms). The experiment also provided the first direct confirmation of the correct mass assignment of the alpha-decay, E_α=6.26 MeV, to the decay of¹⁷⁶Au. Two additional halflife measurements of proton-rich Osmium isotopes are also presented from a previous similar experiment;¹⁶⁵Os (t_1/2=73±8 ms) and¹⁶⁶Os (t_1/2 = 194±17 ms).