Coincidence Studies in the Decay ofTb156andTb154

Abstract

${\mathrm{Tb}}^{156}$ (5.35 days) and ${\mathrm{Tb}}^{154}$ (7.5 hours and 21.5 hours) were produced by ($\gamma , 3n$) and ($\gamma , 5n$) reactions on stable ${\mathrm{Tb}}^{159}$. In addition, ${\mathrm{Tb}}^{156}$ was produced by a ($p, 2n$) reaction on stable ${\mathrm{Gd}}^{157}$. Gamma rays at 89±1, 200±2, 261±5, 300±10, 358±5, 420±5, 535±3, 1050±10, 1140±10, 1210±10, 1410±10, 1630±20, and 1830±20 kev were associated with the 5.35-day activity, and 88±1, 123±3, 180±5, 250±3, 340±10, 511±10, 640±15 and others greater than 1600 kev were associated with 21.5-hour and shorter activities. Levels of ${\mathrm{Gd}}^{156}$ are placed at 89(2+), 289(4+), 1140, 1500, and 2035 kev above the ground state. These follow electron capture in 5.35-day ${\mathrm{Tb}}^{156}$. The $K$-shell conversion coefficients of the 89- and 200-kev transitions are determined to be about 1.0 and 0.16, respectively.