Ratio of the Quadrupole Moment of the First Excited State ofXe129to That of the Ground State ofXe131

Abstract

The Mossbauer effect in Xe 129 and Xe 131 contained in XeF4 has been used to measure the ratio of electric quadrupole moments of the lowest f + states in the two isotopes. This is the ground state in Xe 131 and the first excited state in Xe 129 . The value Q(Xe 129 *)/Q(Xe 131 )=3.45±0.09 is obtained. The sign of the moment in Xe 129 is obtained by use of a source containing oriented crystals of KI 129 CU which produces XeCU in its beta decay. The quadrupole moment is found to be negative. The known quadrupole moment of the ground state of Xe 131 , -0.12b, then gives Q(Xe 129 *) = -0.41b. The large ratio of the moments is interpreted as due to the abrupt onset of a region of permanent deformation by analogy with a similar situation in the europium isotopes. Discussions of such a region appear in the literature. The linewidth observed in Xe 131 yields a value for the first-excited-state lifetime, rj=0.504±0.0l7 nsec, in good agreement with delayed-coincidence measurements. The measured value for the ratio of the moments removes a difficulty in understanding the structure of xenon fluorides generated by an earlier assumption that the ratio was unity.