β-delayed fission of neutron-rich isotopes: the 230Ac case

Beta-delayed fission (βDF) is a decay mode by which a nucleus first undergoes β decay and then fissions from the excited state that was populated. Besides its relevance in understanding nuclear structure, this process may have a strong impact in the decay of the heavy elements at the end of the r-process of nucleosynthesis in contributing to fuel recycling and thus the different balance between the mid-heavy and heavy element abundances. βDF has been only partially studied experimentally, especially in the neutron-rich side of the nuclide chart of relevance to nucleosynthesis. Therefore, this project aims at expanding the knowledge of βDF towards the neutron-rich side. Moreover, βDF probes the study of low-energy fission in exotic nuclei, that are not accessible with other experimental techniques.

A first measurement was done at ISOLDE (CERN): radioactive ion beams of ^{230, 232, 234}Ra were implanted and decayed into ^{230, 232, 234}Ac to observe the βDF of the latter. For 230Ac a βDF probability of 1.19(40) x 10^-8 was already reported in literature [1]. However, during this measurement no fission fragment was observed from the implanted isotopes, and this allowed a preliminary estimation of an upper limit for the βDF probability of 230Ac of about 10^-10.

This contribution will introduce the setup for the investigation of βDF at ISOLDE, its validation with the known ²⁰²Fr, and finally present the results obtained on neutron-rich Ac.

(Poster presented at the LISA summer school (week 1) in August 2021)