On the application of Monte Carlo methods to problems in neutron and gamma-ray transport theory

The theoretical treatment of the transport of particles and radiationgives rise to problems of great mathematical complexity. Thestandard methods which are presently used to solve the transportproblems that appear in reactor, accelerator, space, and weaponsshielding as well as in medical radiology are often questionable.Extensive, and not always realistic idealizations have to be made toachieve numerical solutions even when using the most up-to-dateelectronic computing equipment. The first aim of the present thesisis to indicate the possibility of using Monte Carlo techniques as ageneral tool for routine calculations in photon and neutron transporttheory. This has not generally been possible before as Monte Carlowork required too much of intuition and numerical experimentationto make the method practically applicable on a broader scale. Thesecond aim of this thesis is to show, in a number of cases, the possibilitiesof constructing simplified mathematical models which give asatisfactory picture of the physical problem to be solved to permitapproximate results to be obtained by essentially analytic means.The Monte Carlo methods were used to test the applicability of thesemodels. The third aim of the present thesis is to give some resultsof problems which have not hitherto been satisfactorily solved.Papers I, II, and III deal with the reflection of gamma radiation,and Monte Carlo results are compared with results obtained by simplifiedcomputational models. Paper IV gives an account of the MonteCarlo procedures used in the previous papers and some additionalresults of practical interest are shown. In papers V and VI a generalmethod for deep penetration calculations is outlined and applicationsto photon problems are demonstrated. In paper VII the method isgeneralized with regard to geometry and applied to neutron penetrationproblems. In paper VIII, finally, the approach used for analyzingdeep-penetration problems is shown to be efficient also for reflectionproblems. Results are displayed of some neutron back-scatteringproblems involving a variety of materials and source energies