Development of radiation hard Silicon Carbide (SiC) neutron detectors - CASE award with AWE

该项目的目的是开发使用碳化硅的新一代辐射硬快中子探测器，并评估其在高通量光核反应中作为伽马盲快中子探测器的性能。这项工作是与AWE的减少威胁部门合作进行的，目的是从该大学转让一种新的探测器技术，该技术经过优化，可用于其光核材料审讯方案。该项目受益于STFC资助的萨里郡现有的辐射硬重离子探测器研发(例如，钻石)，用于GSI的核物理实验。光核材料审问是未来减少威胁方案的一种很有前途的方法。在这里，我们提出了一种新的基于化合物半导体碳化硅的快中子探测器。碳化硅的独特性能结合了室温操作、极高的辐射硬度、高的中子灵敏度和伽马盲性能。因此，它是在高通量混合n/伽马场进行中子探测的理想选择。2008年，Cree Inc.在碳化硅材料质量方面取得了突破，现在已经可以获得电子级碳化硅的独立晶片，这是辐射探测器所需的质量。我们建议在萨里的探测器实验室制造碳化硅探测器的原型，然后在AWE和NRL测试设施中测试它们的性能。目前正在开发各种用于减少威胁和SNM探测的主动询问方法，包括核共振荧光和主动中子询问。在这种情况下，准确测量试验对象发射的中子注量的能力至关重要，通常是在存在强烈的混合中子-伽马场的情况下。特别是，使用脉冲中子束产生瞬时中子激活(PNA)是一种很有前途的屏蔽SNM询问技术。在这项技术中，持续时间为100-200微秒的短中子爆发被用来从被询问的材料中产生快裂变中子。由于热化和俘获，SNM周围的铅、镉或含氢屏蔽材料的存在会使发射的中子产生较短的衰变时间。因此，PNA技术的成功需要使用在每次入射中子爆炸后立即具有快速反应和灵敏的中子探测器。原型碳化硅探测器最近被证明是一种紧凑型半导体快中子探测器。一般来说，基于半导体的中子探测器应满足以下标准：-对快中子具有高灵敏度，具有伽马盲选择性以拒绝光子事件。-能够在室温下工作的紧凑型探测器，有可能扩大到大范围的活动区域。-能够承受显著的中子/伽马剂量的辐射硬探测器。与硅探测器相比，碳化硅具有独特的优势，主要是因为它具有优异的辐射耐受性，并且能够在极端环境中在极低的温度下工作。来自AWE(Value~GB 30k)的直接资金已获批准，用于支持该项目内的案例合作伙伴活动。这笔钱将用于支付额外的学生津贴以及项目所需的消耗品(主要是购买碳化硅晶片)。学生每月将在AWE学习大约一周，并将在AWE的威胁减少小组和萨里的探测器物理小组之间建立合作伙伴关系。

The aim of the project is to develop a new generation of radiation hard fast neutron detectors using SiC, and to assess their performance as a gamma-blind fast neutron detector in high flux photonuclear reactions. This work is collaboration with the Threat Reduction Department at AWE, and aims to transfer a new detector technology from the University which is optimsed for use in their photonuclear material interrogation programmes. The projecrt benefits from the existing STFC funded detector R&D at Surrey for radiation hard heavy ion detectors (eg. diamond) for nuclear physics experiments at GSI. Photonuclear material interrogation is a promising method for future threat reduction programmes. Here we propose to develop a new fast neutron detector based on the compound semiconductor SiC. The unique properties of SiC combine room temperature operation, extreme radiation hardness, high neutron sensitivity, and gamma-blind performance. It is therefore ideal for neutron detection in high-flux mixed n/gamma fields. In 2008 a break through in SiC material quality from Cree Inc has now made available free-standing wafers of electronic grade SiC, of the quality required for radiation detectors. We propose to fabricate prototype SiC detectors at Surrey's detector laboratories, and then test their performance at AWE and NRL test facilities. Various active interrogation methods for threat reduction and SNM detection are currently being developed, including nuclear resonance fluorescence and active neutron interrogation. In such cases, the ability to accurately measure the neutron fluence emitted from a test object is crucial, often in the presence of a strong mixed neutron-gamma field. In particular, the use of a pulsed neutron beam to create prompt neutron activation (PNA) is a promising technique for the interrogation of shielded SNM. In this technique, short neutron bursts of duration 100-200 us are used to generate fast fission neutrons from the interrogated material. The presence of lead, cadmium or hydrogenous shielding materials around the SNM produced short decay times for the emitted neutrons, due to their thermalisation and capture. Therefore the success of the PNA technique requires use of neutron detectors that have a rapid response and are sensitive during the period immediately after each incident neutron burst. Prototype SiC detectors have recently been demonstrated as a compact semiconductor-based fast neutron detector. In general, semiconductor-based neutron detectors should fullfill the following criteria: - High sensitivity to fast neutrons, with gamma-blind selectivity to reject photon events. - Compact detectors capable of operating at room temperature, with the potential to scale-up to large active areas. - Radiation hard detectors which are capable of withstanding significant neutron/gamma dose. SiC offer particular advantages over silicon detectors, principally in its superior radiation hardness, and its ability to operate in extreme environments at eleavated temperatures. Direct funding from AWE's (value ~£30k) has been approved to support the CASE partner activities within this project. This money will cover the additional CASE student stipend plus plus the provision of consumables for the project (mainly purchase of SiC wafers). The student will spend approximately 1 week per month at AWE, and will establish a collaborative partnership between the Threat Reduction group at AWE and the Detector Physics group at Surrey.