共面栅碲锌镉探测器读出电路设计及性能研究

为有效读出共面栅碲锌镉(CPG-CZT)探测器的核脉冲信号,本文结合CPG-CZT探测器工作原理及国内外研究,设计了可用于CPG-CZT探测器的读出电路,主要包括高压偏置电路、前置放大电路、增益调节及减法电路。为研究读出电路性能,本文测试了各单元电路的性能及探测系统能量分辨率随偏置电压、增益调节电路中两路信号的相对增益G的变化规律。结果表明：高压偏置电路两路输出偏压与输入偏置电压的相关系数R²均为0.998;前置放大电路输出噪声为5 mV;增益调节及减法电路输出信号噪声为10 mV;输入偏置电压、相对增益G的变化均会影响探测系统能量分辨率,当偏置电压为-1650 V、相对增益G为0.7时对¹³⁷Cs源产生的γ射线能量分辨率最佳,可达3.65%,且无明显拖尾现象。     

基于SiPM的硫化锌闪烁探测器设计与研制

基于SiPM的优良性能和特征,以SiPM和硫化锌闪烁瓶组合探测方式设计探测器。该探测器包括前端信号探测与采集电路和温度控制系统。信号探测与采集电路以交流耦合方式设计前置放大电路,经单道脉冲幅值甄别电路输出计数脉冲用于放射性含量计算。温度控制系统依据分布式测温模块反馈结果,配合模糊PID算法调节半导体制冷器输出功率,实现探测器实时温度调控。实验结果表明,在温度控制系统作用下,当环境温度为40℃时探测器的探测效率由80%提升至94%,其稳定工作的动态温度范围由(-15～30)℃扩展到(-15～40)℃,基本满足野外实际环境的应用需求。     

硅光电倍增器件(SiPM)的自动增益校正

硅光电倍增器件(SiPM)是近年来逐渐兴起的一种用于PET(Positron Emission Tomography)的光电探测器件。与传统的光电倍增管(PMT)相比,它有着尺寸小、工作电压低、对磁场不敏感等优点,但其缺点是增益对环境温度敏感。在PET探测器的研发中,为了改善温度变化引起的增益漂移,设计了一个SiPM的增益校正系统。该系统通过测量环境温度对SiPM的偏置电压实时调节,从而保证其增益的相对稳定。最后对该系统对温度变化引起的SiPM增益漂移的抑制能力做了定量评估。采用增益校正系统后,在相似的温度变化范围内,SiPM的最大增益漂移由校正前的79.67%减小到11.03%。该结果显示此系统对温度变化引起的SiPM增益漂移具有良好的抑制能力。该系统能够补偿因温度变化引起的SiPM增益漂移,从而提高基于SiPM阵列探测器模块的PET系统的稳定性。     

半导体探测器输出电流检测系统前置放大器设计

为满足半导体探测器输出电流检测系统的需求,设计了与之相适应的前置放大器。该前置放大器基于超低偏置电流运放ADA4530,采用单个反馈电阻和T型反馈网络的I/V变换前置放大电路组成。测试结果表明:该前置放大器的放大倍数可达10 mV/pA,直流偏移为8μV;对于pA级分辨率,其输出噪声电压频谱密度仅为17.75 nV/(Hz)~(1/2),输出总噪声为409μV;可用于μA~pA范围内的核辐射探测器电流信号测量。     

576×6长波红外探测器多通道高速数据采集系统设计

设计了一个应用于线阵扫描型长波红外焦平面阵列的,高速,高精度,多通道数据采集系统。系统中的适配电路为探测器提供工作环境,并对图像信号进行缓冲和电平变换。采集电路完成模数转换和图像数据排序后,通过PCI接口板将数据上传至主机。对图像信号处理电路和精密偏置电压信号发生电路的动态性能及噪声性能给出了详细设计。使用两片异步静态存储器构建了图像数据排序电路。     

基于碳化硅探测器的前端信号调理电路设计

碳化硅探测器能够在高温、高辐射强度下稳定工作,适用于核辐射探测。碳化硅探测器输出端连接前端信号调理电路,能够放大碳化硅探测器输出的微弱信号,从而使后端设备采集到准确的数据。设计了前端信号调理电路,包括电荷灵敏前置放大电路和脉冲成形主放大电路,重点分析了影响电荷灵敏前置放大电路变换增益、上升时间、噪声等性能指标的影响因素,采用阻容反馈、极零相消、有源滤波成形等设计提升电路的整体性能。实验室仿核脉冲测试及²⁴¹ Am中子源辐照测试表明,该电路可用于碳化硅探测器的核辐射测量。     

基于GAGG:Ce晶体耦合SiPM的位置灵敏探测器的设计与评估

为满足当前γ相机对高分辨率、低成本、小型化探测器的需求,提出了采用硅光电倍增管（SiPM）耦合GAGG:Ce晶体阵列的方式代替传统的位置灵敏型光电倍增管（PSPMT）耦合晶体阵列的方式以构成新型γ相机探测器,并设计了均匀电荷分配电路（SCDC）和阻抗电桥电路作为探测器的读出电路,同时设计了前沿定时电路作为数据采集触发电路。实验结果表明：当温度为25 ℃、探测器供电电压为28.5 V时,该探测器在511 keV射线的激发下,散点图的峰谷比高达3.84,对511 keV和662 keV射线的平均能量分辨率分别为10.63%和9.71%,具有较好的分辨性能。     

576×6长波红外探测器多通道高速数据采集系统设计

设计了-个应用于线阵扫描型长波红外焦平面阵列的,高速,高精度,多通道数据采集系统.系统中的适配电路为探测器提供工作环境,并对图像信号进行缓冲和电平变换.采集电路完成模数转换和图像数据排序后,通过PCI接口板将数据上传至主机.对图像信号处理电路和精密偏置电压信号发生电路的动态性能及噪声性能给出了详细设计.使用两片异步静态存储器构建了图像数据排序电路.     

基于硅光电倍增管的Cs2LiYCl6(CLYC)探测器快中子辐照效应研究

实验通过将硅光电倍增管(silicon photomultiplier, SiPM)器件和Cs₂LiYCl₆(CLYC)闪烁体探测器暴露于14 MeV的快中子场中,最高累积注量达到1.53×10¹¹ cm^-2,分析了中子辐照对SiPM器件参数和CLYC探测器性能的影响。重点研究了不同注量辐照前后,SiPM的增益、暗计数率、暗电流、击穿电压和淬灭电阻等参数,以及CLYC探测器探测性能的变化情况和原因,其中暗计数率最高上升了3个数量级,暗电流最高上升了2个数量级,CLYC探测器的能量分辨率去除本底后下降了1.4%。辐照实验后,在室温条件下对SiPM和CLYC探测器进行退火,研究SiPM器件参数和探测器性能恢复情况。SiPM和CLYC探测器的性能会随着中子注量的增加而逐渐变差。对于SiPM,主要表现为暗计数率和暗电流的提高。对于CLYC探测器,主要表现为能量分辨率的降低。退火过程有助于减轻中子辐照的影响,恢复SiPM和CLYC探测器的部分性能。     

一种用于高计数率周期采样的主放及峰值保持电路

对用于望远镜探测器阵列的主放电路进行了研究,该主放电路主要由集成运放芯片ADA4851-4构成,用于电压信号的放大和整形。同时设计了基于复位芯片OPA615的峰值保持电路,用于电压信号的周期性采样和幅度保持。16路独立的主放及峰值保持电路构成一套高密度的电压信号处理电子学系统,该系统的信号处理能力可满足进行带电粒子阵列探测所需的误差及计数率要求。     

Preparation of Zn/TiO2 powder and its photocatalytic performance for oxidation of P-nitrophenol

Zn-doped TiO2 catalysts were prepared using a sol-gel method and characterized by XPS,UV-Vis, BET, XRD in this study. Under the irradiation of simulant sunlight, the photocatalytic activity for the degradation of p-nitrophenol was studied too. After irradiation for 2.5 h, the degradation percentage of p-nitrophenol could rise to more than 80 %. The results showed that the spectrum absorption band edge of Zn/TiO2 powder does not broaden obviously comparing with pure TiO2 powder. Zinc exists as Zn （11）. When calcined at 973 K, there is a new phase as ZnTiO3 in Zn/TiO2 catalyst. The order of photocatalytic activity of Zn/TiO2 catalysts calcined at different temperatures for p-nitrophenol is 773 K 〉 673 K 〉 873 K 〉 573 K 〉 973 K and the photocatalytic activity of Zn/TiO2 catalyst calcined at 773 K is better than TiO2 catalysts heated at the same temperature, and outclasses that of commercial TiO2 catalyst. It also showed that the photocatalytic degradation of p-nitrophenol follows first-order kinetics under the irradiation of simulant sunlight.     

Current status of radiation therapy for prostate cancer

Radiotherapy for the treatment of prostate cancer has been extensively explored in the past. Along with the comprehensive understanding of the biology of prostate cancer and rapid advances in terms of technology, the out- come of treatment for the patients with prostate cancer has improved. The authors review radiotherapy as the primary treatment for the disease, with particular emphasis on the technological advances from both the radiobiological and radiophysics aspects. Nonconventional fractionated irradiation like hyper- or hypo-fractionation has been imple- mented in the clinic, the final results still need to be confirmed in the future. Technological advances like IMRT, IGRT, in the last two decades have significantly improved the delivery of external radiotherapy to the prostate. This has re- sulted in an overall increase in the total dose that can be safely delivered to the prostate, which has led to modest im- provements in the biochemical outcome. However, establishing the standard therapy for prostate cancer remains con- troversial. It is hoped that the next decades will bring continued advances in the development of biologicals that will further improve current clinical outcomes.     

The control system for SSRF injection and extraction

This paper introduces the injection and extraction control system design for SSRF,which is a distributed control system aimed at stability and reliability of the pulse power supplies,PPS(Personnel Protection System)and MPS(Machine Protection System).The hardware environment is mainly based on PLC(Programmable Logic Con- troller),and ARM(Advanced RISC Machine)is also applied for studying stability of the power supplies.WinCC and EPICS(Experimental Physics and Industrial Control System)have been selected as the platforms of SCADA(Super- visory Control and Data Acquisition).For unifying the interfacing to the control computer,all front-end equipments are connected via Industrial Ethemet.     

水平管内含空气蒸汽强制对流冷凝换热模型研究

为研究含空气蒸汽在水平管内强制对流冷凝换热特性,基于对传热传质过程的分析,建立了管内为环状流与波状流条件下的流动冷凝换热模型。从潜热、显热和液膜3个环节对整个换热过程进行建模,最终得到计算局部冷凝换热系数的理论关系式。模型预测结果与实验数据的对比表明,二者相对偏差在±20%以内,验证了该换热模型的准确性与适用性。通过进一步的研究发现：从换热管入口至出口,随着冷凝的进行,管内换热主要热阻由液膜热阻向气液界面的凝结热阻转变;主流气体对流换热过程基本可忽略。     

Investigations on landmine detection by BF3 detector

Experiments were carried out to investigate the possible use of neutron backscattering for the detection of polyethylene (PE) sample buried in the soil. In detection of landmine by neutrons, the neutron detector and its shield play an important role. In this paper, the effects of graphite, heavy water, polyethylene and boric acid moderators on the flux of back scattered neutrons were investigated. We have also experimentally verified the effect of BF3 detector shield and obtained good agreement with theory.     

Web Services interface of SSRF archive data analysis system

Accelerator database stores various static parameters and real-time data of accelerator. SSRF (Shanghai Synchrotron Radiation Facility) adopts relational database to save the data. We developed a data retrieval system based on XML Web Services for accessing the archive data. It includes a bottom layer interface and an interface applicable for accelerator physics. Client samples exemplifying how to consume the interface are given. The users can browse, retrieve and plot data by the client samples. Also, we give a method to test its stability. The test result and performance are described.     

有效探测面积大于1000 cm2的正比计数器测量系统性能测试

为对自制的活性面积高达1 000 cm²的大面积源进行表面发射率定值,同时作为现有2πα、2πβ表面发射率标准装置能力的扩充,研制了一套内置式大面积2π多丝正比计数器测量系统,并利用活性区直径为8 mm的²⁴¹Am点源及活性区面积为10 cm×15 cm的大面积²⁴¹Am和⁹⁰Sr-⁹⁰Y源对其进行计量学性能测试。结果表明：计数器内计数响应均匀性优于±0.4%,有效探测面积达1 400 cm²;所得²⁴¹Am源高压坪曲线的坪长为1 400 V,坪斜为0.27%/100 V,坪区内计数变化为0.87%;⁹⁰Sr-⁹⁰Y源高压坪曲线的坪长为300 V,坪斜为0.75%/100 V,坪区内计数变化为0.80%;10次测量重复性好于0.4%,8 h内短期稳定性好于0.3%,1 a内长期稳定性好于0.8%。     

Assessment of radioactivity levels in some oil samples from the western desert, Egypt

Distributions of natural gamma-emitting radionuclides were determined in 93 oil samples collected from some petroleum fields in the western desert of Egypt. The radioisotope activities in the area under investigation lay in the range of (21 ± 4) to (38 ± 13) Bq?L-1 for 226Ra, (9 ± 2) to (15 ± 5) Bq?L-1 for 232Th, and (154 ± 28) to (303 ± 54) Bq?L-1 for 40K. The mean values were 27, 12, and 201 Bq?L-1, respectively. Among oils, variations in radionuclide ac- tivities could be on account of differences in TDS, HCO3, and Ba, with high or low pH. In this environment, oil prop- erties differently affected the mobilization of natural radionuclides. The range of 226Ra variation had been compared with available data from other countries. The calculated absorbed dose rate ranged from 22.33 to 32.66 nGy?h-1 in lo- cation (B) and (E) respectively, which was less than the accepted value.     

Preparation and properties of 117m Sn(IV)-TTHMP in in-vitro and in small animals

In this work,TTHMP was synthesized and labelled with 117m Sn.The preparation conditions,stability and lipophilicity of 117m Sn(IV)-TTHMP were investigated.Biodistribution of the complex in rabbits and mice was studied.It was found that the quantity of TTHMP and pH value of the prepararion solution had vital effects on the labeling yield of 117m Sn(IV)-TTHMP.It was also found that 117m Sn(IV)-TTHMP was hydrophilic and stable at room temperature and 37℃ in open air 117m Sn(IV)-TTHMP showed unexpectedly high bone uptake and bone-to-blood ratio in the animals.This made it potentially useful as an reagent for skeletal scintigraphy and radiotherapy of bone tumors.     

The role of AGFA high-energy CR in the calibration and quality control of multileaf collimators （MLC）

Linear accelerators equipped with multileaf collimators （MLC） are becoming more common and are widely used in the intensity-modulated radiotherapy （IMRT）. There is an imperative need to ensure the commissioning specification of the linear accelerators for the sake of quality assurance （QA） and quality control （QC）. This paper is aimed to investigate the role of AGFA high-energy CR （Computed Radiography） in calibrating dynamic multileaf collimators and evaluating the accuracy of the leaf position. The result shows that AGFA high-energy CR can easily and conveniently be used to calibrate MLC and verify its position. Hence, the application of AGFA high-energy CR is proved to be an accurate and time-saving method for routine MLC QC, especially when MLC calibration adjustments are required.