A patch to the Los Alamos Monte Carlo code MCNP has been developed that automates the generation of source descriptions for photons from arbitrary mixtures and configurations of radioactive isotopes. Photon branching ratios for decay processes are obtained from national and international data bases and accessed directly from computer files. Code user input is generally confined to readily available information such as density, isotopic weight fractions, atomic numbers, etc. of isotopes and material compositions. The availability of this capability in conjunction with the "generalized source" capability of MCNP Version 3A makes possible the rapid and accurate description of photon sources from complex mixtures and configurations of radioactive materials, resulting in improved radiation transport predictive capabilities. This capability is combined with a first-principles calculation of photon spectrometer response-functions for Nal, BGO, and HPGe for £ 7 < 1 MeV,
Monte Carlo calculations of a bismuthgermanate scintillator's efficiency agree closely with experimental measurements. For this comparison, we studied the absolute gamma-ray photopeak efficiency of a scintillator (7.62 cm long by 7.62 cm in diameter) at several gamma-ray energies from 166 to 2615 keV at distances from 0.5 to 152.4 cm. Computer calculations were done in a two-dimensiona!.cylindrical geometry with the Monte Carlo coupled photon-electron code CYLTRAN.For the experiment we measured 11 sources with simple spectra and precisely known strengths. The average deviation between th~calculations and the measurements is 3u. Our calculated results also closely agree with recently published calculated results.
All three development programs (Pressurized Water Reactor. Light Water Breeder Reactor, and Advanced Water Breeder Applications) have been administered by the Division of Naval Reactors with the goal of developing practical improvements in the utilization of nuclear fuel resources for generation of electrical energy using water-cooled nuclear reactors. Technical information developed under the Shippingport, LWBR. and AWBA programs has been and will continue to be published in technical memoranda. one of which is this present report.
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