Isomer Depletion of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mmultiscripts> <mml:mrow> <mml:mi>Mo</mml:mi> </mml:mrow> <mml:mprescripts/> <mml:none/> <mml:mrow> <mml:mn>93</mml:mn> <mml:mi>m</mml:mi>

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 ^{93m}Mo 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 ^{93m}Mo 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 ^{93m}Mo arises from inelastic nuclear scattering rather than the previously proposed NEEC mechanism.