Speaker
Description
The beta-delayed fission of very heavy and extremely neutron-rich nuclides is believed to play an important role in the so-called 'fission termination' of the astrophysical $r$-process, together with spontaneous and neutron-induced fission. However, its properties are very difficult for investigations, because of the experimental problems to reach relevant regions of nuclei. Due to this, only about 25 cases of the Electron Capture Delayed Fission (ECDF), being a sub-type of beta-delayed fission, are known so far, in the neutron-deficient nuclides [1].
The talk will introduce the general concepts of beta-delayed fission, and will present an overview of results from recent ECDF experiments at several facilities. A special emphasis will be given to the two representative experiments. First, an ISODLDE study of ECDF of $^{180}$Tl (Z=81), in which a new island of asymmetric fission was discovered [2]. The second experiment will concern the ECDF of the very neutron-deficient isotope $^{234}$Bk (Z=95), performed at the gas-filled recoil separator SHANS2 at the Institute for Modern Physics, IMP-Lanzhou, China. The isotope $^{234}$Bk was produced in the fusion-evaporation reaction $^{40}$Ar+$^{197}$Au $\rightarrow$ $^{237}$Bk$^{*}$ $\rightarrow$ $^{234}$Bk+3n. The highest ECDF probabilities, PECDF($^{234}$Bk)=0.57(11) and PECDF($^{230}$Am)=0.34(9), among all beta- or EC-delayed fission cases known so far are reported, showing the tendency of approaching the expected saturation towards PECDF=1 [4]. The comparison of the PECDF systematics with two theoretical fission models shows significant discrepancies in respect of corresponding fission barrier values. The important role of beta-decay strength function and the comparison of ECDF systematics in the lead and heavy actinides will be presented. The need for a theoretical framework that can provide realistic beta-delayed fission probabilities for astrophysical predictions will be strongly underlined.
[1] A.N. Andreyev, M. Huyse, Piet Van Duppen, Reviews of Modern Physics 85 (4), 1541 (2013)
[2] A.N. Andreyev et al., Phys. Rev. Lett., 105, 252502 (2010)
[3] Z. Zhang et al., submitted, May 2026