4. METHOD OF SOLUTION
There are three versions of the program in the code package.
SPACETRAN-I uses the surface angular fluxes calculated by the discrete ordinates SN code ANISN, as input.
SPACETRAN-II assumes that the surface angular flux for all energies can be represented as a function (COS(PHI))**N, where PHI is the angle between surface outward normal and radiation direction, and N is an integer specified by the user.
For both versions the energy group structure and the number and location of detectors is arbitrary. The flux (or response function) for a given energy group at some detection point is computed by summing the contributions from each surface area element over the entire surface. The surface area elements are defined by input data. SPACETRAN-III uses surface angular fluxes from DOT-3.
SPACETRAN-I handles contributions either from a cylinder 'end' or 'side', so the total contributions must be obtained by adding the results of separate end and side runs. ANISN angular fluxes are specified for discrete directions. In general, the direction between the detector and contributing area will not exactly coincide with one of these discrete directions. In this case, the ANISN angular flux for the 'closest' discrete direction is used to approximate the contribution to the detector.
SPACETRAN-II handles contributions from both the side and end of a cylinder in a single run. Since the assumed angular distribution is specified by a continuous function, it is not necessary to perform the angle selection described above.
For each detector specified, both versions compute the flux and a response proportional to flux in each energy group and also compute the sum of these quantities over all energy groups.