Selection and Optimization of Radiation Detector Materials

减少威胁和防扩散活动迫切需要改进辐射探测器。因此，至关重要的是，我们超越了探测器材料发现和优化的主要经验方法。我们建议将原子尺度的计算机模拟和实验材料科学相结合，以发现和优化候选闪烁体探测器的材料组成。当适当地结合时，这些技术将创建一个基于物理的反馈回路，这将导致一种方法，通过这种方法，有可能优化候选闪烁体的能量分辨率。此外，这种方法与材料类型(系统)无关。虽然这里使用单晶来确定闪烁体的性质，但对缺陷的理解和控制方面的改进可以融入其他材料形式(例如纳米荧光粉或多晶闪烁体)。虽然防扩散和安全活动是拟议工作的受益者，但其他活动也将直接受益，例如用于被动评估核电设施的高分辨率射线照相。此外，对于石油测井和医学成像等应用，存在着对探测器开发感兴趣的活跃的工业市场。对探测器材料的一般要求是致密(阻止功率)、明亮(将入射辐射能量转化为光输出)和快速(快速将入射能量转化为光输出)。虽然许多目前的探测器材料具有其中的一些性质(例如，Tl掺杂的NaI是明亮和快速的，但不是密集的)，但也有一系列化合物提供了改进，特别是稀土氧化物(密度更高)和卤化物(更明亮)。大多数用于辐射探测的固态系统要求入射能量激发电子，该电子最初与嵌入在主体晶格中的激活剂离子相关联。随后，电子返回基态，发出光(这可以通过电子检测来产生信号)。这一闪烁过程主要取决于电子(和空穴)的行为，因此取决于晶体中激活剂离子的局部环境，以及电子或空穴被捕获到晶格中其他缺陷位置的倾向。在这里，我们将利用原子尺度的计算机模拟和实验技术以及与观察到的探测器效率相关的结果来研究三个系列的主体材料和活化剂，作为它们的组成化学物种的函数。通过预测缺陷行为，原子尺度模拟将识别潜在重要的成分区域。随后的实验工作，单晶生长，发光，位置选择激发和拉曼光谱，将集中在特定的组成和确定它们的性质。这除了验证材料作为基于发光的辐射探测器的有效性之外，还提供了对模拟方法的测试。这种结合的方法将允许关键的、基于缺陷的属性优化，而在历史上，改进一直是经验的。

Threat reduction and nonproliferation activities urgently require improved radiation detectors. As such, it is vital that we move beyond the largely empirical approach of detector material discovery and optimization. We propose to integrate atomic scale computer simulation and experimental material science, to discover and optimize candidate scintillator detector material compositions. When appropriately coupled, these techniques will create a physics-based feedback loop, which will lead to an approach through which it is possible to optimize the energy resolution of candidate scintillators. Furthermore, this approach is independent of material type (system). Although single crystals are used here to determine scintillator properties, improvements in the understanding and control of defects can be incorporated into other material forms (e.g. nanophosphors or polycrystalline scintillators).While nonproliferation and security activities are beneficiaries of the proposed work, other activities will also directly benefit, such as high resolution radiography for passive evaluation of nuclear power installations. Furthermore, an active industrial market interested in detector development exists for applications such as oil well logging and medical imaging.The general requirements for detector materials are that they are dense (stopping power), bright (conversion of incident radiation energy to light output) and fast (quickly convert the incident energy to light output). While many current detector materials offer some of these properties (e.g. Tl doped NaI is bright and fast but not dense) there are families of compositions that offer improvements, in particular, rare earth oxides (which are much more dense) and halides (which are brighter).The majority of solid state systems for radiation detection require that the incident energy excites an electron that is initially associated with an activator ion embedded in a host lattice. Subsequently, the electron returns to the ground state and light is emitted (that can be detected electronically to produce a signal). This scintillation process depends crucially on the behaviour of the electron (and hole) and hence on the local environment of the activator ion in the crystal as well as the propensity for electrons or holes to become trapped at other defect sites in the lattice. Here three series of host materials and activators will be investigated, as a function of their constituent chemical species, using atomic scale computer simulation and experimental techniques and the results correlated with observed detector efficiency. By predicting defect behaviour, the atomic scale simulations will identify compositional regions of potential significance. Subsequently the experimental work, single crystal growth, luminescence, site selective excitation and Raman spectroscopy, will focus on the specific compositions and determine their properties. This provides a test of the simulation approach in addition to a verification of the efficacy of the materials as luminescence based radiation detectors. The combined approach will allow for a vital, defect property-based optimization, where historically improvements have been empirical.