Improvement of the performance of germanium detectors using pulse shape analysis for industrial and environmental applications

在安全、安保和环境应用中识别和量化放射性同位素的常用方法是使用高分辨率锗探测器测量伽马射线光谱。这允许精确地确定单个伽马射线能量，然后唯一地识别和量化同位素。锗探测器的局限性在于其对背景响应的峰值较差。由于感兴趣的伽马射线与探测器材料的最可能的相互作用是康普顿散射，因此在低于入射伽马射线能量的能量处的光谱中存在显著的康普顿连续谱。这可以导致来自高活性同位素的康普顿背景掩盖来自较低活性同位素的电子泄漏。降低康普顿背景是这项工作的目的之一。许多用户的需求是具有非常有效的检测器系统，以提高其灵敏度并减少其计数时间。一旦效率大于百分之几的重合，求和就成了一个问题。当同时探测到来自同一衰变事件的两条或更多伽马射线时，就会发生这种情况。这可能导致需要进行实质性的纠正。当同位素随许多γ射线衰变时，这些校正往往很难应用。用于工业应用的锗探测器必须是简单的，通常是单晶器件，以允许它们在广泛的机构中使用。目前市场上可获得的那些定时器通常具有较差的定时特性，并且用户不容易获得该定时信息。这项工作的第三个目的是开发一种算法，以准确地定义在检测器中的相互作用的时间，并测量如何立即收集电荷。这将通过观察从电子和空穴收集得到的信号来完成。这将导致改善的光谱响应，因为事件将被更好地表征。这项工作的最终目的是调查的可行性，使用一个相对简单的电极结构的锗单晶产生光谱γ射线图像。这项工作将使用电场模拟来调查的可能性。堪培拉是一个世界领先的供应商的仪器仪表的核工业。全球标准高纯锗探测器的年市场规模约为1300万英镑，其中堪培拉的份额约为50%（该领域的市场领导者）。该项目旨在优化堪培拉在数字时代的独特探测器组合，以实现英国已安装探测器基础的真实的世界改进。堪培拉预计该项目的结果将使这些探测器的销售额增长15%，堪培拉的市场份额增长7%。该项目产生的新探测器和仪器将直接影响堪培拉在英国的业务，他们是英国核电和退役部门，环境和公共卫生部门以及从事安全和英国反禁试条约工作的关键实验室的仪器和研发的主要供应商。

A commonly used method of identifying and quantifying radioactive isotopes in safety, security and environmental applications is to measure the gamma-ray spectrum using a high resolution germanium detector. This allows an individual gamma-ray energy to be determined exactly and then the isotope uniquely identified and quantified. A limitation of germanium detectors is their poor peak to background response. As the most probable interaction of the gamma rays of interest with the detector material is Compton scattering there is a significant Compton continuum in the spectra at energies below the incident gamma-ray energy. This can result in the Compton background from high activity isotopes masking the photopeaks from lower activity isotopes. Reduction of Compton background is one aim of this work. The demand from many users is to have very efficient detector systems to improve their sensitivity and reduce their counting times. Once the efficiency is greater than a few percent coincidence summing becomes a problem. This occurs when two or more gamma rays from the same decay event are detected simultaneously. This can lead to substantive corrections being necessary. These corrections are often very difficult to apply when the isotope decays with many gamma rays.The identification of coincidence summing events is a second aim of this work. Germanium detectors used for industry applications have to be simple, usually single crystal devices, to allow their use in a wide range of establishments. Those available on the market today, in general, have poor timing characteristics and this timing information is not easily available to the user. The third aim of this work is to develop an algorithm to define accurately the time of the interaction in the detector and to measure how the charge is collected immediately after this. This will be done by looking at signals derived from both electron and hole collection. This should lead to an improved spectral response as events will be better characterised. The final aim of this work is to investigate the feasibility of using a single germanium crystal with a relatively simple electrode structure to produce spectroscopic gamma-ray images. This work will used electric field simulations to investigate the possibilities.Canberra is a world-leading supplier of instrumentation for the nuclear industry. The annual market size for standard High Purity Germanium detectors worldwide is around £13M, with Canberra's share at approximately 50% (the market leader in this field). The project aims to optimise Canberra's unique detector portfolio for the digital era, in order to realise real world improvement in the UK's installed detector base. Canberra expects the results of this project to grow sales of these detectors by 15%, and Canberra's market share by 7%. The new detectors and instruments that arise from the project will directly influence Canberra's UK operation where they are a major supplier of instruments and R&D to key UK laboratories in the nuclear power and decommissioning sectors, the environmental and public health sectors and those working on security and the UK counter test ban treaty work.