ANGLE CALCULATIONS FOR 3- AND 4-CIRCLE X-RAY AND NEUTRON DIFFRACTOMETERS.

Methods are derived for calculations useful in the operation of 3and 4-circle X-ray or neutron singlecrystal diffractometers. These include: (1) establishing the sample orientation from the cell parameters and the observed angles for two reflections, or from the observed angles for three reflections only, (2) calculating the angles for observing a given reflection either in a special setting or at a specified azimuthal angle, (3) obtaining the vectors needed for calculating absorption corrections, and (4) u sing observations of several reflections to refine cell and orientation parameters by the method of le ast squares.