A He³ Cryostat for Performing Experiments with Oriented Nuclei

Abstract

The use of liquid He³ is proving to have many advantages over magnetic cooling for the convenient production of temperatures in the limited but useful range from about 1^o to 0.3°K. This is especially so in the field of nuclear orientation, for in favorable cases (e.g., Ho, Tb, U, Np) considerable nuclear polarization—up to 85% in one case—can be obtained. It should be noted also that these nuclei are of special interest for study in such experiments, since they all possess very large permanent deformations. The apparatus described was designed for carrying out such experiments, in particular, for performing nuclear reactions with oriented nuclei. The first experiment that has been performed was to measure the (γ, n) cross section for aligned Ho¹⁶⁵ nuclei in conjunction with a betatron [¹]. Although certain features of the construction of the apparatus, especially the lower parts, are peculiar to this experiment and to nuclear orientation in general, the design is such as to make a wide variety of experiments possible by means of simple modifications. This is accomplished by making much of the lower part of the apparatus, i.e., the experimental space, demountable and therefore interchangeable, without altering at all the main cryogenic features of the apparatus.