Nuclear isomers as a tool for studying the influence of zero-point fluctuations of an electromagnetic field on the probability of spontaneous electromagnetic transitions

A review of works on the influence of zero-point fluctuations of the electromagnetic (EM) field (ZPFs) on EM transitions in atomic nuclei inside metals is presented. In a metal, as well as in a resonator of extremely small dimensions, ZPFs are suppressed in the region of low frequencies ω, for which the reflection of EM waves from the metal surface is still significant (ħω is less than ~ 1 keV). Based on the concept of the stimulation of spontaneous EM transitions of energy ħω₀ by resonant ZPFs of frequency ω₀, one could expect suppression of transitions of energy up to ~ 1 keV for excited nuclei in a metal matrix. In experiments with nuclear isomers, such an effect was indeed found for conversion transitions of 76, 910, and 2173 eV energy, which cannot be explained only by the deformation of the electron shells of isomeric atoms or by the scattering of conversion electrons by matrix atoms. Qualitatively, the effect corresponds to the suppression of conversion transitions with a decrease in the ZPFs energy density in metals at the transition frequencies.