Search for Electron-Capture Delayed Fission in the New Isotope Md 244

Abstract

The electron-capture decay followed by a prompt fission process was searched for in the hitherto unknown most neutron-deficient Md isotope with mass number 244. Alpha decay with α-particle energies of 8.73-8.86 MeV and with a half-life of 0.30-0.09+0.19 s was assigned to Md244. No fission event with a similar half-life potentially originating from spontaneous fissioning of the short-lived electron-capture decay daughter Fm244 was observed, which results in an upper limit of 0.14 for the electron-capture branching of Md244. Two groups of fission events with half-lives of 0.9-0.3+0.6 ms and 5-2+3 ms were observed. The 0.9-0.3+0.6 ms activity was assigned to originate from the decay of Md245. The origin of eight fission events resulting in a half-life of 5-2+3 ms could not be unambiguously identified within the present data while the possible explanation has to invoke previously unseen physics cases.