High-Z X-ray detectors for security imaging

该项目的主要目的是将高z半导体x射线探测器的开发和应用方面的专业知识和知识转移到DSTL Fort Halstead，该探测器是由萨里大学pparc资助的研究开发出来的。由Sellin博士领导的萨里小组是该国领先的高z半导体探测器开发中心之一，在宽带隙探测器材料的表征以及原型x射线和伽马射线探测器的开发方面具有特别的专业知识。这项工作主要集中在CdZnTe/CdTe器件上，用于室温硬x射线成像。PPARC对这项工作的支持有两个主要来源；(1) PPARC CASE奖学金（2006 / 2009）“用于硬x射线成像探测器的高z材料和像素化电子元件的表征”，与CCLRC卢瑟福阿普尔顿实验室（Paul Seller）合作；(2)获得PIPSS奖（2000-2003），与莱斯特大学航天中心合作，“基于罗克韦尔CMOS读出的CdZnTe像素探测器的表征”。该项目开发了用于未来空间科学应用的首批原型CdZnTe像素化成像探测器之一。在本提案中，我们解决了DSTL对能量范围超过100 keV / 1 MeV keV的x射线成像的特定要求。在各种可用的x射线探测器中，半导体设备在能量分辨率、空间分辨率和紧凑性方面比基于闪烁体的探测器有几个优势。然而，作为电荷粒子检测的首选材料，硅具有极低的x射线检测效率。因此，人们对用于高能x射线探测器的高z化合物半导体材料（如CdZnTe）产生了相当大的兴趣。对于DSTL要求的特殊安全成像应用，即使CdZnTe对~200 keV以上的光子能量也不够敏感。为此，我们提出了利用高z材料HgI2和TlBr制作辐射探测器，使其具有优异的光子探测效率和良好的光谱性能。基于我们在CdZnTe探测器方面的专业知识，萨里将开发和表征一套原型HgI2和TlBr探测器，这些探测器将转移到DSTL用于其特定应用。虽然HgI2和TlBr的光谱性能已经在实验室得到了验证，但这些相对较新的探测器材料尚未进入实际应用领域。由于这些材料的电荷输运差（特别是空穴迁移率低），可能会降低大有源体积探测器的光谱性能。因此，必须采用一系列仪器技术来最大限度地减少这些有害影响，包括使用弗里希网格电子结构和使用数字脉冲处理算法。这将需要探测器物理学的结合，以实现对设备性能的基本理解，数字数据采集和脉冲处理技术的发展，以及探测器在现实光子光束中的测试。通过两个中心之间的密切合作，从这一系列测试中获得的数据将用于优化探测器的性能，以满足DSTL特定的安全应用。该项目的最终目标是通过在国防部/DSTL内部直接开发或通过某种形式的合资公司或其他许可安排将这种新的探测器技术商业化。

The primary aim of this project is to transfer expertise and knowledge to DSTL Fort Halstead in the development and application of high-Z semiconductor X-ray detectors, which has been developed out of PPARC-funded research at the University of Surrey. The Surrey group, led by Dr Sellin, is one of the country's leading centres for high-Z semiconductor detector development, with particular expertise in the characterisation of wide bandgap detector materials, and the development of prototype X-ray and gamma ray detectors. This work has been focussed on CdZnTe/CdTe devices, for applications in ambient temperature hard X-ray imaging. The PPARC support for this work has come through two main sources; (1) PPARC CASE Studentship (2006 / 2009) 'Characterisation of High-Z materials and pixellated electronics for use as Hard X-ray imaging detectors', with CCLRC Rutherford Appleton Laboratory (Paul Seller) as the collaborating partner; (2) PIPSS award (2000-2003) 'Characterisation of CdZnTe pixel detectors based on Rockwell CMOS Readout', jointly with Leicester University Space Centre. This project developed one of the first prototype CdZnTe pixellated imaging detectors for future space science applications In this proposal we address a specific requirement from DSTL for X-ray imaging over the energy range 100 keV / 1 MeV keV. Of the various X-ray detectors available, semiconductor devices provide several advantages over scintillator-based detectors in terms of energy resolution, spatial resolution, and compactness. However silicon, which is the material of choice for charge particle detection, has an extremely low X-ray detection efficiency. As a result there has been considerable interest in high-Z compound semiconductor materials for use as high energy X-ray detectors, such as CdZnTe. For the particular security imaging application that DSTL require even CdZnTe is not sensitive enough for photon energies above ~200 keV. For this reason we propose to develop radiation detectors made from the very high-Z materials HgI2 and TlBr which combine an excellent photon detection efficiency with good spectroscopic performance. Based on our expertise with CdZnTe detectors, Surrey will develop and characterise a set of prototype HgI2 and TlBr detectors, which will be transferred to DSTL for use in their specific application. Although the spectroscopic performance of both HgI2 and TlBr has been proven in the laboratory these relatively new detector materials have not yet been transferred into the real application areas. There are potential problems due to poor charge transport (especially low hole mobility) in these materials which can degrade the spectroscopic performance in large active volume detectors. Consequently a range of instrumentation techniques must be adopted to minimise these deleterious effects, including the use of a Frisch grid electron structure and the use of digital pulse processing algorithms. This will require a combination of detector physics to achieve a fundamental understanding of the performance of the devices, the development of digital data acquisition and pulse processing techniques, and detector tests in realistic photon beams. By close co-operation between the two centres the data obtained from these series of tests will be used to optimise the performance of the detectors for DSTL's specific security-based applications. The final aim of the project is to commercialise this new detector technology through either direct exploitation within the MoD/DSTL or through some form of joint venture company or other licensing arrangement.