The possibility of observation of the hidden nuclear inversion below the lasing threshold from a change in the optical spectra of atoms containing the nuclei is considered.
We discuss a possibility for obtaining the self-amplified spontaneous emission of gamma radiation in an active medium with hidden population inversion of nuclear states. Hidden inversion appears in cooled nuclear ensembles due to assistance of the nuclear recoil in emission and absorption of gamma quanta. Establishing a hidden inversion allows an amplification of gamma radiation to occur in a particular frequency range without excess of the number of excited nuclei over the number of unexcited nuclei. We formulate a set of requirements to the pumping radiation and to the amplifying nuclear medium crucial to the development of gamma-ray lasing.
The resonance absorption and emission gamma-ray spectra are constructed for nuclear transitions in metals in large metal-carbon clusters. The possibilities of observing gamma lines with the natural linewidth in an isolated molecule and the suppression of the excess line broadening in an ensemble of molecules are estimated. The possibility of the appearance of the hidden population inversion of nuclear states and the quantum amplification of the type of coherent stimulated scattering is also analysed.