LAPHAN0, P0 Gamma Production Matrices from ENDF/B

1 - Nature of physical problem solved: LAPHAN0 retrieves photon production cross sections or multiplicities and corresponding neutron interaction cross sections from the ENDF data file, applies suitable weighting functions over G specified photon groups and N specified neutron broad groups, and constructs A G X N photon production matrix (microscopic and/or macroscopic). As an option, it operates on this matrix with flux vectors from a neutronics code, as well as with scalar multipliers such as atom number densities and effective photon group energies, to directly provide spatially dependent photon source vectors (number or energy) for transport calculations. Multiple zones can be accommodated, with separate cross-section weighting functions for each zone. Input is in the DTF-IV format and source vector output is also in this format, allowing direct coupling to DTF-IV. Complete freedom is allowed to pick those materials and reaction types for which photon production matrices are desired. 2 - Method of solution: LAPHAN0 first constructs photon production cross sections, pointwise in neutron and photon energy, from the ENDF data. These cross sections are then integrated over photon energy groups with either constant or direct energy weighting. After integrating over neutron energy in all neutron fine groups, weighting in neutron broad groups is by input fine-group weighting functions, usually the scalar fluxes from a fine-group neutronics calculation. Macroscopic photon production matrices and photon energy production matrices are then computed by scalar multiplication. Photon source vectors are computed by operating on these matrices with spatially dependent neutron flux vectors. 3 - Restrictions on the complexity of the problem: The microscopic pointwise data must be in ENDF format. The code is presently restricted to 99 fine or broad groups, 49 photon groups, and 50 mixture specifications