Recoilless Nuclear Resonant Absorption inI129

Recoilless resonant absorption has been observed with the 26.8-keV gamma ray of ${\mathrm{I}}^{129}$ using the parent, ${\mathrm{Te}}^{129m}$, as a source. With a ZnTe source and NaI·2${\mathrm{H}}_2$O absorber the absorption spectrum has a structure which is interpreted in terms of quadrupole splitting in the absorber. The field gradient $q(1-\gamma )$ at the iodine nucleus is experimentally found to be $-2.3\mathrm{}{a_0}^{-3\mathrm{}}$. The broader spectrum which is obtained with a Te metal source appears to contain many unresolved lines. It is interpreted as resulting from simultaneous quadrupole splitting in source and absorber. From the observed linewidth, the first-excited state of ${\mathrm{I}}^{129}$ is estimated to have a mean life of 1.5×${10}^{-8\mathrm{}}$ sec. The small observed percentage effects result, at least in part, from dilution by x rays emitted by the source and the absorber.