极低辐射本底多电极高纯锗探测技术研究

It is very important to develop a multi-polar high pure germanium detector with sub micro Becquerel per kilogram detection capability to meet the advance requirements of radioactivity screen for some ultra-low radiation background experiments that would run in China Jinping underground laboratory, such as dark matter direct measurement, neutrino detection experiments, and neutrinoless double beta decay experiments. To achieve this object, the internal radioactivity background contributed from the radioactivity contained in the components of high pure germanium detector should be very little. And on the other hand, if the incident gamma-ray track in the detector can be reconstructed, the irrelevant background event maybe identified. With the help of both sides above, the measurement capability of multi-polar high pure germanium detector could be more sensitive. To accomplish these considerasion, the design of the multip-polar layout should be optimized with good energy resolution and position resolution, and the heterojunction technology should be developed. After that, the geometry layout of whole detector, include the front electronics, and supported structure and so on, should be study carefully to reduce the internal backgroud as possible. The tracking algorithm and event discrimination method should be also developed to reduce irrelevant background event. The multi-polar high germanium is also useful for atomic nuclides fine structure research and nuclear astrophysics to improve their sensitivity.

本项目针对中国锦屏地下实验室暗物质直接探测、无中微子双贝塔衰变等极低辐射本底前沿物理实验要求，提出了研制极低辐射本底多电极高纯锗探测器，以实现亚微贝克每公斤量级探测水平。为满足极低辐射本底实验要求，极低辐射本底伽马高纯锗谱仪既需要自身本底尽可能低，又需要具备径迹重建能力，能通过事件甄别，进一步减少无关本底，从而提高极低辐射本底伽马谱仪的灵敏度。通过优化单晶体多电极设计，突破异质结工艺，能同时实现高能量分辨率和径迹重建；优化设计多电极高纯锗探测器结构，尽量减少结构件与前端电子学本底贡献，能实现更低自身本底。开展基于径迹重建的本底抑制方法研究，进一步减少无关本底，能提高探测灵敏度。通过极低辐射本底多电极高纯锗探测器研究，也能为我国原子核精细结构研究、核天体物理关键反应截面测量等提供更灵敏的测量手段。

本项目针对中国锦屏地下实验室未来开展更大质量更高灵敏度的极低辐射本底前沿物理实验过程中，实现极低本底、高效率、高峰总比伽马射线测量的需求，突破国内多电极高纯锗探测器相关的关键技术难题，从而发展新型低本底探测技术。在多电极高纯锗探测器关键技术研究方面获得重大突破，突破了我国高纯锗异质结工艺的技术空白，在一个直径3 cm厚度1 cm的高纯锗晶体上，实现9电极读出，在获得良好的能量分辨率同时，具备亚毫米的位置分辨能力；研制形成16通道同时读出的16-Bit、125 MSPS高精度采样通道，为实现多电极高纯锗高时间分辨率、高精度的波形甄别提供关键支持；研究多电极高纯锗探测器波形甄别方法，实现了将不同电极上均有信号的本底事例的有效去除，实现物理事例的有效甄别，为进一步减少伽马射线探测本底提供新的解决方案。此外，针对单电极高纯锗无法甄别的单/双电子事例，基于所突破的多电极高纯锗探测器，开发了基于多电极专用波形甄别方法，实现了单/双电子事例71%的有效甄别率，提出了在锦屏地下实验室开展多电极高纯锗探测器76Ge无中微子双贝塔衰变的新技术路线。