Direct Observation of the Optical Anisotropy of the Holmium Nucleus

Abstract

The optical anisotropy of the holmium nucleus in the giant-resonance energy region has been shown to exist by measuring the yield of photoneutrons as a function of the orientation of the nucleus with respect to a bremsstrahlung beam direction. The nuclei were aligned by the Bleaney method using a continuously operating ${\mathrm{He}}^{3}$ refrigerator to cool a single crystal of holmium ethyl sulfate to 0.29\ifmmode^\circ\else\textdegree\fi{}K. The orientation effects observed could be explained if the absorption cross section for holmium was made up primarily of a component given by the dynamic collective theory, but also included a small scalar component (about 15% of the total) which had no orientation effects associated with it. In fitting the data, a reanalysis of previous data on the holmium absorption cross section was made.