DOT-III MULTIGROUP TWO-DIMENSIONAL DISCRETE ORDINATES CODE WITH ANISOTROPIC SCATTERING.

The DOT-III computer program solves the energy and angular dependent Boltzmann equation with general anisotropic scattering for rectangular, polar, or cylindrical geometries.Principal applications are to neutron and/or gamma-ray transport problems in either forward or adjoint mode.Both homogeneous and external source problems can be solved and searches on multiplication factor, time absorption, nuclide concentration, and zone thickness are available.However, the code is particularly designed and suited to the solution of deep penetration radiation transport problems.The discrete ordinates, or Carlson's S , method is utilized to solve the Boltzmann equation.A good account of the historical de\'elopment and application of this method is included by Mynatt e£ al. in a description of the development and verification of two-dimensional transport theory for radiation shielding applications.l Briefly, the discrete ordinates method involves the solution of difference equations derived in a term-wise manner by integrating the analytic form of the Boltzmann equation over a fivedimensional finite cell defined in terms of location, direction, and energy phase space variables.Supplementary difference equations are required to obtain a solution to the flux.These equations relate the average flux for a cell with each pair of associated cell face fluxes.The equations should provide a good approximation to the true variation and at the same time be easily and quickly solved on the computer.Two forms of the supplementary equations which have been utilized in earlier versions of DOT are "diamond difference" and "step function" equations.The cross sections required by DOT-III are of the multigroup, P n , expansion type generated by codes such as AMPX, which is described in Mrs. Maskewitz's paper.The utilization of this type of multigroup cross-section data allows the solution of coupled neutron and secondary gamma-ray transport problems with anisotropic scattering.Various versions of DOT and related computer programs have been developed over the years and several have been placed at RSIC.Some examples of fResearch sponsored by Union Carbide Corporation under contract with the U. S. Atomic Energy Commission.