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The interaction of polarized and unpolarized 350-keV neutrons with oriented and unoriented 165 Ho nuclei was investigated in order to study the effect of nuclear deformation and to search for a possible spinspin interaction. The ORNL 3-MV pulsed and bunched Van de Graaff proton beam was used in conjunction with a time-of-flight spectrometer. The 7 Li(p,n) reaction at a laboratory angle of 51° provided a source of 55% polarized, 350-keV neutrons. Using the NBS transportable 3 He refrigerator, a single crystal of 165 Ho metal was cooled to 0.34°K and a nuclear polarization of approximately 15% was obtained with a superconducting split solenoid. The differential cross section for unpolarized 350-keV neutrons, elastically scattered from unoriented 166 Ho nuclei, was measured in a cylindrical geometry and is in good agreement with the results of a coupled-channel calculation. The total cross section of unoriented 165 Ho was measured between 300 and 400 keV. A coupled-channel calculation of the total cross section using the same optical-model parameters as those which fitted the angular distribution is found to agree very well with these data. To investigate the spin-spin interaction, measurements were made of the transmitted intensities with the target nuclei polarized alternately parallel and antiparallel to the direction of neutron polarization. The observed change in intensity, (-0.11 ±0.32)%, and the observed total cross section of 7.94 b imply a change in cross section of (+30=1=85) mb, where the plus sign corresponds to a larger cross section for the parallel orientation. Comparison of this result with that of the coupled-channel calculation indicates that if the spin-spin interaction in the optical-model potential is written as -F ss (or • I) times a Saxon form factor, then V 83 lies between -130 and +280 keV. Since the 165 Ho nucleus is highly deformed, a transmission measurement was made to determine the change in cross section between a highly oriented and a nearly unoriented target. The transmission of the target decreased by (1.3=1=0.4)% for the higher orientation value, which corresponds to a cross-section increase of 350=fcl00 mb. This deformation effect on the total cross section is also in good agreement with that derived from the coupled-channel calculation. The deformation parameter 0 used in the optical-model potential was +0.3, in agreement with other measurements.

The subject of temperature measurement below 0.3 K is reviewed, with particular attention paid to developments reported in the period [1970][1971][1972][1973][1974]. Sensors, measurement techniques, primary and secondary thermometers, and fixed points are discussed and attempts are made to assess the accuracy and relative merits of the various devices and methods.

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