Isomer depletion of Mo 93m triggered by inelastic nuclear scattering rather than nuclear excitation by electron capture

Abstract

Isomer depletion serves as a prerequisite for a variety of important applications. Several mechanisms are proposed to trigger the isomer depletion. In the previous work [Chiara et al., Nature (London) 554, 216 (2018).NATUAS0028-083610.1038/nature25483], isomer depletion with an exceptionally high probability in Mo93m was reported and attributed to nuclear excitation by electron capture (NEEC). However, contradictory probability values were subsequently reported from both experimental and theoretical aspects. This Letter reports a new and more precise measurement of the isomer depletion of high-energy Mo93m ions during the slowing-down processes in lead and carbon foils via a low-background beam-based experimental approach. By employing a purified isomer beam, the depletion probabilities are determined to be 2.0(2)×10-5 in lead and 4.7(13)×10-6 in carbon, agreeing well with the inelastic nuclear scattering calculations. We conclude that the observed isomer depletion in Mo93m arises from inelastic nuclear scattering rather than the previously proposed NEEC mechanism.