A Method of evaluating PuO particle diameters by an alpha particle imaging detector

イメージング検出器によるPuO粒子径評価法

森下 祐樹   ; 佐川 直貴; 高田 千恵 ; 百瀬 琢麿  ; 高崎 浩司  

Morishita, Yuki; Sagawa, Naoki; Takada, Chie; Momose, Takumaro; Takasaki, Koji

Alpha emitting radionuclides such as plutonium (Pu) isotopes require special consideration in terms of internal exposure. The evaluation of the diameters (activity median aerodynamic diameter (AMAD)) of PuO particles is very important for internal exposure dose evaluation. In this study, we propose a new method to determine the PuO particle diameter from the energy spectrum obtained by the developed alpha particle imaging detector. PuO particles with different diameters were modeled by Monte Carlo simulation. The change in the shape of the energy spectrum for each particle diameter was evaluated. Two different patterns were modeled: (1) the case of PuO, and (2) the case of PuO (including isotopic composition of Pu). The value of the energy resolution of the simulation was based on the measured value of the detector energy resolution. Multiple regression analysis was performed to determine the PuO particle diameter from the obtained parameters. The simulation results showed that the radioactivity (measured counts) was lower when the PuO particle size was smaller. In addition, the energy spectrum was sharper due to the smaller effect of self-absorption of the PuO particles themselves. On the other hand, when the PuO diameter was large, the radioactivity (measured counts) was high. In addition, the energy spectrum became broad and the position of the peak shifted to the lower side. Using the obtained parameters (measured radioactivity, peak counts, peak position, and peak width), multiple regression analysis was performed to evaluate the PuO diameter. The proposed method was compared with the conventional method and found to be in agreement.