EXCITATION OF ISOMERIC NUCLEAR-STATES IN A CRYSTAL BY SYNCHROTRON RADIATION

The time dependence of delayed radiation is investigated when a pulse of synchrotron radiation undergoes resonance Bragg scattering by the nuclei in a crystal that have an isomeric level with a Mossbauer transition. Instead of the usual exponential law exp(-t/ tau 0) characteristic of an isolated nucleus, a time dependence in the form ( tau 0/t)2 exp(-t/ tau 0) was discovered at small deviations alpha from the Bragg angle. The acceleration of the decay is connected with the collective nature of the excitation of the nuclei in the crystal-the nuclear exciton formation. The exponential law remains at large alpha but the intensity decreases as 1/ alpha 2. In the case of large divergence of the incident beam the law ( tau 0/t) exp(-t/ tau 0) is obeyed. The frequency distribution of the reflected pulse and the possibility of formation of a resonance structure with sufficient resolution are analysed in detail.