NUCLEAR RESONANT ABSORPTION IN LONG-LIVED ISOMERIC TRANSITIONS - COMMENT

In a recent paper [R. Coussement et al., Phys. Rev. B 45, 9755 (1992)] it was suggested that for a long-lived state that can undergo a Mossb auer transition, if the homogeneously broadened width, rather than the natural width, exceeds the solid-state-induced inhomogeneous width, i t should be possible to observe resonant emission and absorption. On t he other hand, it is expected that the probability of absorption from a spectral distribution of total width GAMMA should be proportional to GAMMA(gamma)/GAMMA, where GAMMA(gamma) is the radiation width of the absorbing nucleus. Generally GAMMA is expected to be larger than GAMMA (gamma) because of the possibilities of internal conversion, transitio ns between magnetic sublevels, etc., all of which contribute to homoge neous broadening and should reduce the Mossbauer effect. The present C omment addresses questions of principle, mathematical assumptions, and other aspects of the work of Coussement et al. and demonstrates that a correct statistical treatment recovers the conventional more stringe nt requirement on the broadening.