高计数率放射性核束实验0度角阵列探测器一体化前端电子学研制

This project is aimed to develop, with technology innovation and application, a new kind of the integration of the front-end electronics of zero-degree detector array and the high speed signal processing and data acquisition system for high intensity radioactive nuclear beam (RNB) experiments. The new data acquisition system will play an important role in high level international cooperation of RNB studies. The current state-of-the-art heavy ion accelerators can easily produce RNBs (e.g. 8He, 19C, etc.) at the intensity of 10^6～10^7pps. Usually, detectors are arranged at a non-zero-degree angle to avoid direct RNB hits at high rate. To measure the nuclear reaction products at small angles around zero degree, the intensities of the RNB were greatly reduced to meet the performance of the traditional detector’s front-end electronics and the subsequent pulse shaper, amplifier and analog-to-digital (A/D) convertor. However, one trend of the RNB experiment has been focused on the zero-degree or small angle detection at high RNB intensity which gives the key physical information of the nuclear reaction associated with nuclear monopole transition and cluster structure. Usually, one channel of a commonly used experimental data acquisition system includes a charge sensitive pre-amplifier, a subsequent pulse shaper, a main amplifier and an A/D convertor, which gives the physical information of energy, momentum, spatial position and the kind of a detected particle. Analysis shows that one fundamental reason of signal accumulation, amplitude distortion and data error occurring in nuclear measurements is the long decay time of the output signal of the charge sensitive pre-amplifier. The key techniques that employed in the new data acquisition system include cutting the long tail of the pre-amplifier signal (pulse chop), using high speed A/D convertor, and tagging a real time value to the A/D data, which can effectively eliminate the long tail of the pulse, signal accumulation, amplitude distortion and data error in measurements. The new system can be extremely simplified with high energy resolution and efficiency of the measurement and highly accelerated in data acquisition because of the removal of the traditional pulse shaper and main amplifier circuits. The new data acquisition system can be used in time projection chamber (TPC) detector system and defense nuclear measurements.

通过技术创新，研制高计数率条件下放射性核束实验0度角探测器一体化前端电子学高速信号处理和直接数据获取系统，支撑国际高水平放射性核束实验研究。当今加速器产生的放射性次级束流如8He、19C强度已高达10^6～10^7pps。探测器通常被置于偏离0度角束流位置，但目前重要发展趋势是0度角测量以提取小角度反应产物携带的关键物理信息，用于原子核单极跃迁、集团结构等研究。过去将电荷灵敏前置放大器信号经过整形、放大、模数A/D转换得到粒子能量、动量和粒子种类信息。前放输出信号长下降沿时间会导致高束流计数率下信号过慢、堆积、幅度失真、数据出错。通过对前放输出信号直接高速模数转换，将长脉冲后沿斩断(斩波)缩短宽度、数据加时间标签，在高能量分辨率、单路10^5-10^6 pps下根本上解决测量信号堆积、幅度失真等问题。免去信号整形、放大，使测量系统得到极大简化和提速。可用于低能核物理中小型时间投影室信号读出

主要研究内容。目前世界水平的放射性次级束流强度大于106CPS。传统电荷灵敏前放输出信号下降沿时间长达几百微秒。因此0度角探测器前放输出会产生严重的信号堆积。采用斩波短脉冲、低噪声、防串扰设计，有效地解决了信号堆积、提高计数率。创新设计包括信号处理模式、高性能前置放大器单元电路、印刷电路板、机箱、散热、电磁屏蔽、“互联网+”测控计算机、指令交换机、软件等。增加了前放输出二级放大电路、新的主放（极零相消电路、有源滤波电路、整形和多级线性放大电路）和微分时间信号输出电路。研制了新的16路集成化前放+主放信号处理电路和印刷电路板, 以及新的高压输入、探测器接入、主放信号输出连接板、硅阵列探测器的安装连接板和信号连接板。完成16路高压独立输入硅探测器、气体电离室和3He管中子探测器能量、时间信号通用放大器整机系统。可识别完整脉冲宽度小于200纳秒，最高计数率大于5x106CPS。. 主要成果。(1)4套定制型Model-2019-16路集成式前放+主放一体化信号放大器；(2) 128路ATPC信号读出系统；(3)新型“互联网+”专用测量控制计算机。Model- 2019-16是为3He正比计数器（1英寸/2英寸直径）定制型信号放大电路，也是为适应新研制的“互联网+”测控计算机AD转换电路和数据获取、传输系统，具有16路模拟输入、16路能量、16路时间输出，高压隔离，输出脉冲幅度可调节等特点。128路前放+主放一体化实验信号读出系统的研制和使用，节省了ATPC (Active Time Projection Chamber)信号处理系统研制时间、确保了ATPC研制进度，提高了实验测量精度。新型“互联网+”测量控制计算机有丰富的板上资源，包括16路高速A/D模拟/数字转换电路。新型测控指令交换计算机具有5种标准通讯接口类型和16路高速A/D模拟/数字转换电路。. 主要应用。Model-2019-16路集成式放大器用于上海光源 SLEG项目激光-电子康普顿Gama中子源中子测量（信号输出脉冲宽度10微秒）。 128路ATPC信号读出系统用于北京大学核物理与核技术国家重点实验室李奇特研究组ATPC项目。另外，32路用于苏州大学文万信研究组硅探测器阵列信号读出系统。