MONTE CARLO STUDIES OF GAMMA-RAY AND NEUTRON TRANSPORT IN INFINITE HOMOGENEOUS MEDIA
Two Monte Carlo codes were written for the IBM 704 computer. One simulates gamma transport from a monoenergetic point source in an infinite medium; the second is a similar code for neutron transport. Statistical variance reduction techniques designed for use in the codes allowed the calculation of more accurate values of gamma and neutron deep-penetration number and energy spectra than would be possible in a straightforward Monte Carlo calculation. A form of exponential importance sampling was used to emphasize long particle transit distances and small polar scattering angles, thus favoring deeply penetrating particles. Studies were made of gamma energy spectra and buildup factors for l-Mev-source gamma rays in water and 6-Mev-source gamma rays in tin at various penetration depths. These calculations were done both with and without inclusion of the importance sampling. Comparisons were made with moments- method solutions for the same problems; the agreement was good at shallow penetrations in both cases. In addition, deep penetration results, at 7 and l0 source energy relaxation lengths, obtained by importance sampling also agreed well with moments-method solutions. A low-energy spectral peak was observed in the Monte Carho calculation for the case of 6-Mev gamma rays in tin; this is due to gamma rays from pair-production positron annihilation and is not present in the momentsmethod results, which do not include the effects of pair production. Calculations of neutron number spectra for 6-Mevsource neutrons at various penetration depths in water showed good agreement with nioments-method results. Importance sampling became necessary to produce reasonable agreement at penetration distances greater than 30 centimeters. Monte Carlo results were rehiabhe to as deep a penetration as 90 centimeters, or 12 source energy mean free paths. (auth)
- Research Organization:
- National Aeronautics and Space Administration. Lewis Research Center, Cleveland
- NSA Number:
- NSA-16-002620
- OSTI ID:
- 4832648
- Report Number(s):
- NASA-TN-D-850
- Resource Relation:
- Other Information: Orig. Receipt Date: 31-DEC-62
- Country of Publication:
- United States
- Language:
- English
Similar Records
SPACE, ENERGY, AND TIME DISTRIBUTION OF NEUTRONS AT THE GROUND-AIR INTERFACE--CALCULATED BY MONTE CARLO CODE NHM
NDA technology for uranium resource evaluation. Progress report, July 1--September 30, 1977. [Gamma ray spectra calculations; disequilibrium probe; photoneutron probe]