Modification and benchmarking of MCNP for low-energy tungsten spectra

The MCNP Monte Carlo radiation transport code was modified for diagnostic m edical physics applications. In particular, the modified code was thoroughl y benchmarked for the production of polychromatic tungsten x-ray spectra in the 30-150 kV range. Validating the modified code for coupled electron-pho ton transport with benchmark spectra was supplemented with independent elec tron-only and photon-only transport benchmarks. Major revisions to the code included the proper treatment of characteristic K x-ray production and sco ring, new impact ionization cross sections, and new bremsstrahlung cross se ctions. Minor revisions included updated photon cross sections, electron-el ectron bremsstrahlung production, and K x-ray yield. The modified MCNP code is benchmarked to electron backscatter factors, x-ray spectra production, and primary and scatter photon transport. (C) 2000 American Association of Physicists in Medicine. [S0094-2405 (00)00809-9].