The natural isotope Rh-103 has two low-lying levels with energies of 357.4
keV and 295.0 keV, the lifetimes of which are 107 and 9.7 ps, respectively,
Thus the lower level has a considerably shorter lifetime than the upper on
e, a situation favorable for generating population inversion. Nuclear Reson
ance Fluorescence (NRF) experiments have been performed in which 26 high-ly
ing levels have been identified, from which either the upper or the lower l
evel or both can be populated by radiative decay. An evaluation of the data
shows that this "feeding" mechanism indeed resulted in inversion on the 62
.4 keV transition.