摘要:

AbstractMonte Carlo transport calculations have been carried out to estimate the dose travelers in supersonic aircraft will receive from a typical spectrum of solar-flare protons. The dose, from both primary protons and secondary particles, as a function of depth in a tissue slab placed at various depths in the atmosphere, has been obtained. The incident spectrum is broken into eight energy regions and the dose from the incident protons in each of these regions is presented.

ISSN:0029-5639    

DOI:10.13182/NSE67-A18259

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

AbstractRecent work on the transport of high-energy massive particles (protons, neutrons, alpha particles, etc.) through dense matter as it applies to the shielding of manned space vehicles is reviewed. The transport of heavy particles through tissue and the resultant physical dose (rad) is considered, but the important question of the biological effects of radiation is not discussed. Throughout the discussion an attempt is made to indicate the areas of uncertainty where further research is required and particularly to indicate the areas where experimental confirmation of theoretical results is needed.

ISSN:0029-5639    

DOI:10.13182/NSE67-A18260

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

AbstractA review of the state-of-the-art of electron transport theory and calculations for electrons in the energy range below 10 MeV is presented. The basic interactions that influence the behavior of electrons are reviewed and theory and experimental results are compared wherever possible. The continuous slowing down model, the straggling model, and multiple scattering models are discussed and their use in thick-target moments method and Monte Carlo calculations is described. Results of the thick-target calculations are also compared with experimental results. Included in the review is a detailed description of the various complex-geometry electron transport programs presently being used.

ISSN:0029-5639    

DOI:10.13182/NSE67-A18261

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

AbstractThe use of the Monte Carlo method for the study of deep penetration of radiation into and through shields entails the use of sophisticated methods of variance reduction to make such calculations economical or even feasible. This paper presents an exposition of the most useful methods of variance reduction. The exposition is unified by consistent exploitation of adjoint formulations to estimate expected values, as in previous work, and further to evaluate the variance of the resulting estimates., The connection between adjoint formulations and the choice of biasing schemes is also investigated. In particular, it is shown that the value function (the solution of the integral equation of the adjoint formulation) is always a good choice for importance function biasing; a sharp upper bound, independent of the particular problem, is found for the resulting variance. Predicted (analytic) and experimental (Monte Carlo) results are also given for a simple one-dimensional problem.

ISSN:0029-5639    

DOI:10.13182/NSE67-A18262

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

AbstractCalculations were set up to determine the effect of the grazing flux on the surface-crossing flux estimator and the pillbox track-length estimator used in Monte Carlo calculations. It was found that grazing particles make only higher order contributions to current or flux but significantly increase the variance. These effects are more pronounced at internal surfaces than at external boundaries. The use of nonstochastic methods to estimate contributions of grazing particles is justified.

ISSN:0029-5639    

DOI:10.13182/NSE67-1

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

AbstractThe theoretical expression for the singly scattered angular and energy flux of radiation from a point source is studied in the limit of very small source-detector separation distances (πOr<<1). It is shown that both the angular and energy distributions are related in a simple way to the scattering kernel. Examples are given for gamma and neutron point sources in air. The applicability of the distributions at separation distances of the order of a mean free path (π0r≍1) is discussed.

ISSN:0029-5639    

DOI:10.13182/NSE67-A18264

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

AbstractCalculations were performed by the Monte Carlo method to determine the dose at various detector locations behind a vertical barrier and below an adjacent horizontal barrier. Results were obtained, using two different Monte Carlo approaches, for a 1.25-MeV simulated ground source incident on 60, 40, and 20 psf of concrete. The results of the Monte Carlo calculations were used to calculate reduction factors. The above-ground reduction factors compared with those of Spencer to within 10%. The below-ground reduction factors were compared with those calculated from the OCD Engineering Manual, and the agreement in this case was found to be unsatisfactory. In some instances, discrepancies were found to be as high as a factor of 3. For the case of the open basement, agreement among the three methods was found to lie within 10 to 20%. The results obtained by the two Monte Carlo methods used were found to be in excellent agreement. These results also compared to within 10 to 15% with results of experiments performed at Technical Operations Research. The results indicate that further investigation is necessary to determine the amount of scattered radiation within a basement.

ISSN:0029-5639    

DOI:10.13182/NSE67-A18265

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

AbstractThe method of invariant imbedding has been applied to neutron shielding problems in plane geometry with realistic energy and angle-dependent cross sections. The method seems to offer advantages over competing methods when the shield is heterogeneous and very thick or when the shield is composed of a very large number of different regions. Reflection and transmission equations are derived by the method of invariant imbedding and their numerical solution discussed. A simple exponential approximation is shown to work well for the solution of these equations. Results for several problems including a thick homogenous water shield and a thinner heterogeneous iron/polyethylene/iron shield are compared with results obtained by other methods.

ISSN:0029-5639    

DOI:10.13182/NSE67-A18266

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

AbstractThe transfer matrix for the neutron flux in slab geometry is expressed analytically, along with a number of auxiliary quantities, for energy-independent interactions with isotropic scattering. The eigenvalues and eigenfunctions of the transfer matrix are readily expressed in terms of those introduced by Case, working directly with the Boltzmann equation. The results are applied to the albedo problem, the Milne problem, and the critical slab problem. Since the transfer matrix approach works in principle for any cross sections, the ease of application implies that numerical calculations for more complicated cross sections will be reasonably straightforward.

ISSN:0029-5639    

DOI:10.13182/NSE67-A18267

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor

摘要:

AbstractThe spectral intensity of the fast-neutron flux penetrating a water medium was measured for two configurations: a large-source, poor-geometry arrangement; and a small-source, almost-good-geometry configuration., In the large-source experiment, the spectral intensity of the angular flux was obtained at six positions in the water shield of a pool-type reactor and for as many as three angles at each position. In addition to the measurements, the spectral shape and the absolute intensity of angular flux in the shield were calculated. In conjunction with this, the absolute neutron source density was mapped throughout the reactor volume and the distribution along the reactor center line was used as input to two neutron-transport calculations that were carried out for a onedimensional, spherical geometry., In the small-source experiment, a 2-cm-thick lead target irradiated with short bursts of 33-MeV electrons provided a source of photoneutrons with approximately a fission spectrum at a distance of 40 cm from water slabs of various thicknesses. This distance, together with the large separation of slab and detector and a small-aperture collimator, approximated a good-geometry arrangement for measurements of neutrons leaking normally from the slab. Consequently, these leakage spectra were very sensitive to total neutron cross sections and a distinct peak was observed at 5 to 7.5 MeV. This peak was not at first reproduced by transport calculations that used the measured source spectrum as input; however, when the neutron total cross sections of oxygen were updated with relatively recent high-resolution data, the agreement both in spectral shape and in attenuation (the latter determined from sulfur-activation ratios) was noticeably improved.

ISSN:0029-5639    

DOI:10.13182/NSE67-A18268

出版商:Taylor&Francis    

年代:1967

数据来源: Taylor