DETECTION OF THE HYPERFINE STRUCTURE SPLITTING OF THE 8.42-kev $gamma$ RAY OF Tm$sup 169$ WITH THE MOSSBAUER EFFECT IN Tm$sub 2$O$sub 3$

The recoilless nuclear resonance absorption of the 8.42 kev gamma ray of Tm/sup 169/ in the oxide crystal was investigated. The source (Er/sub 2/O/sub 3/) and the absorber (Tm/sub 2/O /sub 3/ were kept at room temperature. The measured Mossbauer spectrum indicates pure quadrupole splitting of the 8.42-kev nuclear level of Tm/sup 169/ for the thulium ions with a C/sub 2/ symmetry as well as for those with C/sub 31/ symmetry. The energy of the electric interaction was found to be W/sub el/(C/sub 2/) = 8 x 10/sup -7/ ev and W/sub el/ (C/sub 3i/) = 1.9 x 10/sup -6/ ev. (auth)