INTERMEDIATE-STATE REORIENTATION OF ORIENTED NUCLEI

Abstract

When radioactive nuclei in a paramagnetic ion at low temperatures become oriented (the magnetic h.f.s. method of nuclear orientation) and decay by β emission followed by a delayed γ ray, frequently, these nuclei become reoriented between the emission of the β ray and the γ ray, and this reorientation affects the observed angular distribution of the γ ray. The theory of this reorientation process is presented, assuming a time-independent Hamiltonian during the reorientation period. Numerical calculations of the effects to be expected on this static reorientation model have been made for 175Yb, 147Nd, and 141Ce in cerium magnesium nitrate, 57Co in cerium zinc nitrate, and 147Nd in neodymium ethyl sulphate. These calculations are compared with the reported experimental results. The experimental values for 147Nd in neodymium ethyl sulphate, 141Ce in cerium magnesium nitrate, and 57Co in cerium zinc nitrate could be explained by the static reorientation model; the others could not. The need is stressed for more reliable experimental results, in order to develop the theory of reorientation further.