Transformation of a system consisting of plane isotropic source and unit sphere detector into a system consisting of point isotropic source and plane detector in Monte Carlo radiation transport calculation

Abstract

In a nuclear power plant accident, radioactive nuclides may be released which are distributed uniformly on the ground. If estimation of dose rate from such a source by a Monte Carlo calculation is attempted, some difficulty is encountered because the calculation efficiency is very low. To solve this low efficiency problem, we show that a plane isotropic source can be transformed into a point isotropic source by changing the detector shape from a unit sphere to a plane. We verified the validity of this transformation by the numerical comparison of unscattered photon fluence. As an example of this transformation, the ambient dose rate D i was calculated from the uniform radioactive nuclide distribution on the ground using the EGS5 Monte Carlo code. We also measured the radioactivity and ambient dose rate (M) on the KEK campus within a month after the releases from the Fukushima No. 1 Nuclear Power Plant accident. Using radioactivity data and D i , we calculated the ambient dose rate (C). The calculated and measured ambient dose rates agreed reasonably well; their ratio (C/M) was 0.62 to 1.28.

Spectrum–dose conversion operator of NaI(Tl) and CsI(Tl) scintillation detectors for air dose rate measurement in contaminated environments

“…To improve the calculation efficiency, a few mathematical algorithms were proposed (Furuta & Takahashi, 2014;Namito et al, 2012;Saito & Moriuchi, 1985, Saito et al, 2012. Notably, such mathematical techniques were conceived for shielding calculations in other studies (Shultis & Faw, 1996).…”

Evaluation of ambient dose equivalent rates influenced by vertical and horizontal distribution of radioactive cesium in soil in Fukushima Prefecture

“…Note that the 137 Cs energy lines in NuDat2 [17] include the contribution from the short-lived daughter product 137m Ba. In each case the source region was scaled to a vertical line and the detectors transformed to planes to maximize the computational efficiency of the Monte Carlo simulations [18].…”

Ambient dose equivalent conversion coefficients for radionuclides exponentially distributed in the ground

“…Gamma-ray fields calculated under these conditions are equivalent to those at a point at 1 m height for exponential source in the ground with infinite extent in horizontal directions [17]. This method has been practically used for a long time [10,11,13], and recently the mathematical formulation of this equivalency was explicitly indicated [23,24]. The Monte Carlo code YURI [17] was developed to easily simulate environmental conditions in terms of transport media, source distribution and geometry, and has been verified by comparisons with calculated and measured data under various conditions [13,17,[25][26][27].…”