Induced decay of 178Hfm2: Theoretical analysis of experimental results

This article reviews experimental results obtained recently on the x-ray-induced acceleration of the decay of the long-lived isomer ¹⁷⁸Hf^m2. Two basic mechanisms for the induced decay are considered: (1) direct interaction of the incident x rays with the nucleus and (2) the nucleus-ray interaction proceeding via atomic shells. We establish that the absence of K forbiddenness for all transitions to a hypothetical “mixedK“ level cannot explain the measured cross sections even if collective nuclear matrix elements, resonant conditions, and so on, are assumed. We also tested, and rejected, the hypothesis that the enhancement is due to normal nuclear transitions in the inverse nuclear excitation by electron transition process. The possibility to make measurements with intense laser radiation is considered too. Thus, there appears to be no explanation of these experimental results within quantum electrodynamics and the contemporary concepts of atomic nuclei.