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An improved data set of gamma-ray buildup factors for point isotropic sources in infinite homogeneous media has been generated by the method of invariant embedding. The points of improvement compared with the standard data set ANSI/ANS-6.4.3 include (1) extension of the buildup factors up to depths of 100 mean free paths, (2) improved treatment of bremsstrahlung, (3) addition of the effective dose buildup factors, (4) consistent use of the cross-section PHOTX to all materials and (5) a quantitative evaluation about the accuracy in transport calculation. The data set obtained are compared precisely with the standard data set ANSI/ANS-6.4.3.

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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