We have generated a system concept for a non-destructive assay (NDA) system to certify identified isotopes and their activity concentrations for radioactive waste in a large container. Various optimization studies have evaluated the system performance in terms of the MDA (minimum detectable activity) results using the Monte Carlo simulation in conjunction with experimental studies. The proposed system consists of a total of eight HPGe (high-pressure germanium) detectors: four detectors on the top and the other four detectors on the bottom. The top and the bottom detector arrays are aligned and face each other. This detector arrangement has advantages in employing the attenuation correction as proposed by T. Chang [IEEE Trans. Nucl. Sci. NS-25, 638 (1978)]. We also found that the UFOV (useful field of view) of the detector highly influences the system efficiency, which leads to an improvement in the MDA performance. However, while the wider FOV of the detector improves the detection efficiency by allowing incoming radiation from other segmented volumes, it may suffer from non-uniform performance or increased errors in estimating an activity concentration for each segmented volume. To prevent such potential errors in employing the wider FOV, we have proposed an activity estimation algorithm, a so-called ‘fine volume reconstruction’, based on a back-projection method that estimates the activity concentration of each segmented volume. We demonstrate the feasibility of the conceptual system for use as a free release assay system for ISO containers up to a size of 2.4 × 6.0 × 1.3 m 3 (W x L x H). The detector efficiency was about four times higher than those of typical commercial systems. Future studies include fine-tuning of the activity reconstruction algorithm and a validation study on various materials and non-uniform activity concentrations.

中文翻译：

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用于认证大型容器中放射性废物的已识别同位素及其活度浓度的非破坏性分析系统的可行性研究

我们为非破坏性分析 (NDA) 系统生成了一个系统概念，以验证大型容器中放射性废物的已识别同位素及其活度浓度。各种优化研究使用蒙特卡罗模拟结合实验研究，根据 MDA（最小可检测活动）结果评估系统性能。所提议的系统由总共八个 HPGe（高压锗）探测器组成：顶部的四个探测器和底部的其他四个探测器。顶部和底部探测器阵列对齐并彼此面对。这种检测器布置在采用 T. Chang [IEEE Trans. 核。科学。NS-25, 638 (1978)]。我们还发现探测器的 UFOV（有用视场）对系统效率有很大影响，从而提高了 MDA 性能。然而，虽然探测器更宽的 FOV 通过允许来自其他分段体积的入射辐射提高了检测效率，但它可能会遭受不均匀的性能或在估计每个分段体积的活动浓度时增加的误差。为了防止在使用更宽 FOV 时出现这种潜在错误，我们提出了一种活动估计算法，即所谓的“精细体积重建”，它基于估计每个分段体积的活动浓度的反投影方法。我们证明了概念系统用作 ISO 容器的自由释放检测系统的可行性，该系统的尺寸最大为 2.4 × 6.0 × 1.3 m 3 (W x L x H)。检测器效率大约是典型商业系统的四倍。未来的研究包括对活性重建算法的微调以及对各种材料和非均匀活性浓度的验证研究。