Novel methods for estimating 3D distributions of radioactive isotopes in materials
Novel methods for estimating 3D distributions of radioactive isotopes in materials
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DOI：
10.1016/j.nima.2016.03.098
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发表时间：
2016-09-21
影响因子：
1.4
通讯作者：
Yamamoto, S.
中科院分区：
文献类型：
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作者：
Iwamoto, Y.;Kataoka, J.;Yamamoto, S.
近年来，各种伽马射线可视化技术，或伽马相机，已被提出。这些技术对于识别“热点”或放射性同位素积聚的区域非常有效。这方面的例子是受核灾难影响的地区，如福岛或核反应堆附近。然而，伽玛照相机获得的图像不包括放射性同位素与照相机之间的距离信息，因此在同位素的方向上是“简并”的。此外，当同位素被嵌入水、沙子和混凝土等材料中时，图像中的深度信息就会丢失。本文提出了两种获取材料中放射性同位素深度信息的方法，通过比较(1)材料的光谱和(2)材料散射的入射伽马射线图像和直接伽马射线。在第一种方法中，获得了放射性同位素的光谱和散射与直接伽马射线的比值。我们通过实验验证了该比率随着深度的增加而增加，正如模拟预测的那样。虽然利用能谱的方法已经研究了很长时间，但我们的方法的一个优点是使用低能（50-150 keV）光子作为散射伽马射线。在第二种方法中，比较了直接和散射伽马射线获得的图像的空间范围。通过使用Geant4进行详细的蒙特卡罗模拟，我们验证了伽马射线散射位置的空间范围随着深度的增加而增加。为了证明这一点，我们正在开发各种伽马相机来比较低能量（散射）伽马射线图像与完全吸收的伽马射线图像。我们还证明了同位素/热点的三维重建是可能的，我们提出的方法。这些方法在医疗领域和福岛核灾害影响地区等恶劣环境中具有潜在的应用前景。(C) 2016 Elsevier B.V.版权所有
In recent years, various gamma-ray visualization techniques, or gamma cameras, have been proposed. These techniques are extremely effective for identifying "hot spots" or regions where radioactive isotopes are accumulated. Examples of such would be nuclear-disaster-affected areas such as Fukushima or the vicinity of nuclear reactors. However, the images acquired with a gamma camera do not include distance information between radioactive isotopes and the camera, and hence are "degenerated" in the direction of the isotopes. Moreover, depth information in the images is lost when the isotopes are embedded in materials, such as water, sand, and concrete. Here, we propose two methods of obtaining depth information of radioactive isotopes embedded in materials by comparing (1) their spectra and (2) images of incident gamma rays scattered by the materials and direct gamma rays. In the first method, the spectra of radioactive isotopes and the ratios of scattered to direct gamma rays are obtained. We verify experimentally that the ratio increases with increasing depth, as predicted by simulations. Although the method using energy spectra has been studied for a long time, an advantage of our method is the use of low-energy (50-150 keV) photons as scattered gamma rays. In the second method, the spatial extent of images obtained for direct and scattered gamma rays is compared. By performing detailed Monte Carlo simulations using Geant4, we verify that the spatial extent of the position where gamma rays are scattered increases with increasing depth. To demonstrate this, we are developing various gamma cameras to compare low-energy (scattered) gamma -ray images with fully photo -absorbed gamma -ray images. We also demonstrate that the 3D reconstruction of isotopes/hotspots is possible with our proposed methods. These methods have potential applications in the medical fields, and in severe environments such as the nuclear-disaster-affected areas in Fukushima. (C) 2016 Elsevier B.V. All rights reserved.