NUCLEAR ORIENTATION EXPERIMENTS WITH Pr142 AND Yb175 NUCLEI

Abstract

Pr142 has been oriented as an impurity in cerium magnesium nitrate, and the anisotropy of the 1.57 Mev γ-ray was measured as a function of temperature in the range 0.003° K to 1.0° K, both in zero external field and in a field of 320 gauss parallel to the trigonal crystal axis. The results are not consistent with what has been published about the spin Hamiltonian of Pr+++ in this lattice. The magnetic moment of Pr142 is very small, and it was not possible to see any saturation of the anisotropy at low temperatures. Values for the magnetic moment of Pr142 were found for two different assumed decay schemes, these are 0.11 nuclear magnetons for the spin assignments [Formula: see text], and 0.15 nuclear magnetons for the spin assignments [Formula: see text]. Similar experiments were carried out on Yb175. Measurements were made in a variety of external magnetic fields up to 700 oersted, and at temperatures as low as 0.003° K. No anisotropy was observed for the 396 kev γ-ray, nor for the 282 kev γ-ray. The most likely explanation for this result is that the lifetime of the γ-emitting state is about 10−10 seconds. The relation between the results of this experiment and others on the same isotope (Phil. Mag. 2, 1079 (1952)) is discussed.