[en] 1 - Description of program or function: G33-GP estimates gamma-ray scattering from a point source to a series of point detectors. The output includes detector response due to each source energy, as well as a grouping by scattered energy in addition to a simple, un-collide result. Although G33 is basically a single-scatter calculation, it also includes a correction for multiple scattering by applying a buildup factor for the path segment between the point of scatter and the detector point. Results are recorded with and without buildup. Surfaces, defined by quadratic equations are used to provide a three-dimensional description of the physical geometry. It evaluates scattering effects in those situations where more exact techniques are not economical. 2 - Method of solution: An orthogonal scattering geometry is superimposed on the original QAD geometry; the midpoint of the orthogonal cube is ascertained; the QAD region in which this point is located is determined; and the entire scatter volume is assumed to be of the ascertained QAD material and concentrated at the midpoint. G33 traces a ray from the source point to each scatter point, calculates un-collided photon flux at that point, and determines the contribution from each scatter to the detector. The library of photon cross sections and buildup factor coefficients are read from data files. The buildup factor is computed from the coefficients using the Geometric Progression (GP) fitting function. 3 - Restrictions on the complexity of the problem: - The following limits apply: 20 x 20 x 20 scatter grid, 50 QAD boundaries, and 30 energy groups