A new treatment of radiation behaviour beyond one-body observables

ABSTRACT We propose a new treatment of radiation behaviour in transport calculations by introducing an event generator model in which we combine the nuclear data and the reaction models so as to trace all correlations of ejectiles keeping the energy and momentum conservation in a collision. By this new model, we can estimate the fluctuations around the mean values of one-body observables, for example, the deposit energy distribution in a cell, which cannot be obtained by the transport calculations based on the Boltzmann equation with the nuclear data.

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    ABSTRACT: The purpose of this study was to obtain the neutron energy spectrum on the surface of the moderator of the Tokyo University reactor YAYOI and to investigate the origins of peaks observed in the neutron energy spectrum by use of the Monte Carlo Code PHITS for evaluating biological studies. The moderator system was modeled with the use of details from an article that reported a calculation result and a measurement result for a neutron spectrum on the surface of the moderator of the reactor. Our calculation results with PHITS were compared to those obtained with the discrete ordinate code ANISN described in the article. In addition, the changes in the neutron spectrum at the boundaries of materials in the moderator system were examined with PHITS. Also, microdosimetric energy distributions of secondary charged particles from neutron recoil or reaction were calculated by use of PHITS and compared with a microdosimetric experiment. Our calculations of the neutron energy spectrum with PHITS showed good agreement with the results of ANISN in terms of the energy and structure of the peaks. However, the microdosimetric dose distribution spectrum with PHITS showed a remarkable discrepancy with the experimental one. The experimental spectrum could not be explained by PHITS when we used neutron beams of two mono-energies.
    Radiological Physics and Technology 07/2010; 3(2):144-50.
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    ABSTRACT: The "Event Generator Mode (E-mode)" has been introduced into the Particle and Heavy Ion Transport Code Sys-tems (PHITS) in the treatment of transport phenomena of low energy neutrons below 20 MeV. In E-mode, the evaluated nuclear data for neutron-induced reactions and a special statistical decay model are combined so as to trace all correlations of ejectiles and residuals in a collision under the energy and the momentum conservation. For the va-lidation of the E-mode below 20 MeV, we have calculated neutron-induced activation cross sections and double differential cross sections by the E-mode, and compared them with the experimental data and the evaluated nuclear data library such as ENDF/B-VII and JENDL-4. As results, calculated results for neutron emission reproduced the data well, but there was small discrepancy between calculated results for charged particle emission and the evaluated nuclear data. As an application of this mode, we indicated new calculations about the energy distributions of charged particles for the 10 B(n th , ) 7 Li and 24 keV 6 Li(n,)t reactions. In future, E-mode of PHITS will be modified and ap-plied to the analysis of the biological effects, the single setup error of semiconductor, and many other fields.
    Progress in NUCLEAR SCIENCE and TECHNOLOGY. 01/2011; 2:931-935.