Proposal for a Nuclear Gamma-Ray Laser of Optical Range

A possibility of the amplification of the 7.6 eV $\gamma$ radiation by the stimulated $\gamma$ emission of the ensemble of the ${}^{229m}\mathrm{Th}$ isomeric nuclei in a host dielectric crystal is proved theoretically. This amplification is a result of (1) the excitation of a large number of ${}^{229m}\mathrm{Th}$ isomers by laser radiation, (2) the creation of the inverse population of nuclear levels in a cooled sample owing to the interaction of thorium nuclei with the crystal electric field or with an external magnetic field, (3) the emission or absorption of the optical photons by thorium nuclei in the crystal without recoil, and (4) the nuclear spin relaxation through the conduction electrons of the metallic covering.

Figure 1

The transitions between the Zeeman sublevels of the ${}^{229}\mathrm{Th}$ nucleus in magnetic field. The gray ovals are proportional to partial level populations.

Figure 2

The transitions between sublevels of the ${}^{229}\mathrm{Th}$ nucleus in the case of quadrupole splitting: (a) the case $T_1\lesssim T_{1/2}^{\mathrm{is}}$; (b) the case $T_{1/2}^{\mathrm{is}}\ll T_1$ (see text for details).