Reproducible neutron diffraction patterns were obtained from samples of powdered deuterium with paralpar;Jthinsp;equals;thinsp;1rpar;concentrations equal to 3percnt;, 33percnt;, 63percnt;, and 80percnt;. The diffraction patterns were obtained at various temperatures in the range 1.9deg;ndash;13deg;K and for the 80percnt; sample at temperatures both above and below thelgr;anomaly in the heat capacity. The deuterium powdered samples were randomly oriented except for an estimated preferred orientation of 8percnt; or less. All of the samples froze from the liquid to a hexagonal structure with the molecules at the closehyphen;packed sites. In the case of the 80percnt; paradeuterium sample a transformation from the hcp structure to a cubic structure occurred at a lower temperature than has been observed for thelgr;anomaly in the heat capacity. Observations of the transformation between the hexagonal and cubic phases, on warming or cooling, have shown a large hysteresis effect. The cubichyphen;phase diffraction patterns corresponded to space groupPa3with four molecules per unit cell andathinsp;equals;thinsp;5.074 Aring;. Absolute integrated intensities of the five observed lines were calculated and are in excellent agreement with observed values. The hexagonalhyphen;phase lattice parameters for the above samples are presented. An analysis of the integrated intensities of the six observed hexagonal lines indicated a disordered structure. Four of the five structural models under consideration gave an average site symmetry which is equivalent to that produced by a molecule precessing about thezdirection with a mean precession angledgr;. In general,dgr;was found to increase with increasing para concentration except for 63percnt; paradeuterium, at 2deg;K, where a spherical average site symmetry (i.e., complete disorder) was indicated.
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