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The isomer depletion of ^{93m}Mo was recently reported [Chiara et al., Nature (London) 554, 216 (2018)NATUAS0028-083610.1038/nature25483] as the first direct observation of nuclear excitation by electron capture (NEEC). However, the measured excitation probability of 1.0(3)% is far beyond the theoretical expectation. In order to understand the inconsistency between theory and experiment, we produce the ^{93m}Mo nuclei using the ^{12}C(^{86}Kr,5n) reaction at a beam energy of 559 MeV and transport the reaction residues to a detection station far away from the target area employing a secondary beam line. The isomer depletion is expected to occur during the slowdown process of the ions in the stopping material. In such a low γ-ray background environment, the signature of isomer depletion is not observed, and an upper limit of 2×10^{-5} is estimated for the excitation probability. This is consistent with the theoretical expectation. Our findings shed doubt on the previously reported NEEC phenomenon and highlight the necessity and feasibility of further experimental investigations for reexamining the isomer depletion under low γ-ray background.

In this paper, the electromagnetic deformation combined with heat treatment (ET) process was studied, which was meaningful for the forming of high performance Al-Li alloy sheet metal parts. In the ET process, the annealed sheet was firstly subjected to solution treatment, electromagnetic deformation. and artificial age until it reaches the peak aging state. Compared with the traditional T6 heat treatment, the time efficiency of the ET process is significantly improved, and the mechanical properties of the specimen are enhanced. The ET process only takes 6 hours to reach the peak aging, and the time efficiency of precipitate strengthening is reached up to 4 times compared with the T6 process. At the same time, the mechanical properties of the ET specimen are higher than the T6 one, an increase of 17.6% in Vickers hardness. Moreover, the mechanism of higher time efficiency and mechanical properties of the ET process is revealed. It is found that a high density of cellular dislocations and sub-grain were introduced during the electromagnetic deformation process, which is conducive to the nucleation and growth of the T1 precipitate during artificial aging. The T1 precipitates of the ET specimen are more dispersed and finer.