$\beta$-delayed fission of ${}^{186,188}$Bi isotopes

By using the technique of correlating implanted evaporation residues and their subsequent fission decay, $\beta$-delayed fission ($\beta$DF) of ${}^{186}$Bi has been identified for the first time and $\beta$DF of ${}^{188}$Bi has been unambiguously confirmed. The experiments were performed at the velocity filter SHIP (GSI, Darmstadt). The $\beta$DF probabilities for both nuclides were qualitatively estimated, and, in particular indications for a large value in the case of ${}^{186}$Bi are regarded.

Figure 1

Calculated fission barriers, $B_f$(Pb) (open symbols), of daughter Pb isotopes and the $Q_{\mathrm{EC}}$(Bi) values (closed symbols) of the $\beta$ decay of the parent Bi isotopes according to the FRDM/FRLDM [14] and the Thomas-Fermi models [24].

Figure 2

(a) Energy spectrum measured during the 5-ms “beam on” and 15-ms “beam off” periods in the PSSD for the ${}^{142}$Nb(${}^{50}\text{Cr},p3n$)${}^{188}$Bi reaction at a beam energy of 252 MeV. (b) The same as (a), but within the 15-ms “beam off” period only.

Figure 3

(a) Energy spectrum measured during the 5-ms “beam on” and 15-ms “beam off” periods in the PSSD for the ${}^{144}$Sm(${}^{46}\text{Ti},p3n$)${}^{186}$Bi reaction at 239 MeV. (b) The same as (a), but within the 15-ms “beam off” period only.