Studies of the beta decay of 71Kr have not been free of controversy. The first study by Oinonen et al. [1] showed a relatively too small ground state to ground state feeding for a mirror pair and prompted an immediate alternative explanation by Urkedal and Hamamoto [2] invoking possible shape effects and isospin breaking in the mirror system. Some years later, a careful in-beam study [3] restored the earlier interpretation of Oinonen, that since then has prevailed [4].
New insights have been recently obtained based on a high-statistics experiment performed at RIKEN Nishina Center. In this talk, I will present these new results from the perspective of deformation and isospin effects in the A= 70 region. Our results indicate that this is the very first identified case of isospin breaking in the ground state of a T=1/2 case [5]. We also find evidence of a long-sought 0+ state in 70Se populated in the beta delayed proton process.
[1] M. Oinonen et al., Physical Review C 56, 745 (1997).
[2] P. Urkedal and I. Hamamoto, Physical Review C 58, R1889 (1998)
[3] S. Fisher et al., Physical Review C 72, 024321 (2005).
[4] S. Waniganeththi et al., Physical Review C 106, 044317 (2022).
[5] A. Algora et al., Phys. Rev. Letts. 134, 162502 (2025)
