Crystals as a Source of Gamma Quanta. (arXiv:1802.01962v1 [cond-mat.other])

Conditions for the appearance of a nuclear exciton in a crystal consisting of
excited and unexcited nuclei of a given type are determined. The total
probabilities for spontaneous -emission by a single excited nucleus or by an
arbitrary number of excited nuclei in the crystal are derived. It is shown that
the formation of a nuclear exciton is connected with an increase of the width
of the emitting level and with the concentration of the radiation in a narrow
solid angle.

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