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HAN Miaomiao1, GUO Zhirong1, 2, PENG Minjun1, LIU Haifeng2, LI Qinghua2, and CHEN Xianglei2 1. Fundamental Science on Nuclear Safety and Simulation Technology Laboratory, Harbin Engineering University, Harbin 150001, China (miaomiaohan321@163.com; heupmj@163.com)
2. Wuhan Second Ship Design and Research Institute, Wuhan 430205, China (guoeg112@sina.com; liuhf2634@163.com; liqinghua@whhwtech.com; chenxianglei@whhwtech.com)
Abstract: Detection
As the precondition of Tomographic Gamma Scanning (TGS) technique to assay nuclear waste drums, detection efficiency calibration is an essential task and needs high accuracy for the emission reconstruction stage. As a key issue, how to conduct detection efficiency calibration for the TGS technique still needs to be solved, without by means of the existing commercial detection efficiency calibration software such as the In Situ Object Counting System/Software (ISOCS). In this paper, TGS measurement geometries are analyzed using the point source model in detail from three aspects, i.e., limited fields of view (FOVs) of the collimated High Purity Germanium (HPGe) detector, the spatial position overlap and the symmetry of point sources relative to the collimated HPGe detector, intending to obtain independent matrix elements in the calibrated detection efficiency matrix to avoid redundant workload. Then, the Monte Carlo N-Particle (MCNP) code as a Monte Carlo simulation method is used to compute values of these independent detection efficiency matrix elements. To verify detection efficiency calibration results, two different 200 liters drums are simulated with the same 3 gamma point sources distribution of different inner-heights and radio-activities. Algebraic Reconstruction Technique (ART) with the non-negativity constraint and Maximum Likelihood Expectation Maximization (MLEM) are respectively applied to the emission reconstruction stage. Results reveal that all 3 point sources can be easily recognized and precisely located, and their own corresponding radio-activities fit standard setting values very well with relative errors ~ 3%, indicating the feasibility of the simplified method to calibrate detection efficiency using point source model in TGS technique.
Keyword: Tomographic Gamma Scanning (TGS); radioactive waste drums; detection efficiency calibration; point source model |
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