Ultra-low-temperature neutron diffraction. Final report, July 1, 1983-June 30, 1985. Final report

An ultra-low-temperature neutron diffraction facility has been constructed at Argonne National Laboratory. The initial and primary purpose of this facility is to study nuclear magnetic ordering phenomenon. Magnetic structure information is commonly recognized as being fundamental to the progress in theoretical and experimental efforts in the field of magnetism. We have initiated study of the nuclear spin in solid /sup 3/He and in metals. In /sup 3/He the nuclear spins order at 1.1 mK. Structure information for neutron diffraction would contribute significantly to this problem of nuclear magnetism. Despite substantial experimental difficulties, careful evaluation suggests that examination of the nuclear structure in this unique quantum crystal is indeed feasible by neutron diffraction. Substantial progress has been made in growing single crystals of /sup 3/He and establishing its temperature in the presence of a neutron flux. We have also initiated investigation of nuclear ordering in copper and PrCu/sub 6/.