BESⅢ飞行时间探测器电子学中的光电倍增管测试

讨论了北京谱仪(BESIII)飞行时间探测器(TOF)前端电子学的物理需求.因光电倍增管信号为前端电子学实际使用,而以光电倍增管信号作为信号源测试电子学性能是一种方便易行的方法,所以本文采用光电倍增管信号作为信号源测试电子学的性能.测试结果表明现行设计的电子学性能已达到BESⅢ飞行时间探测器对电子学的预期目标.     

大面积位置灵敏中低能中子谱仪的时间刻度系统的研究

在利用飞行时间法测量中子位置和能量的大面积位置灵敏中子谱仪的研制过程中,提出了利用“绝对时间差”刻度的方法来测量各个电子学的相对时间,系统研究了对光电倍增管时间分辨影响的因素,其中包括光源的种类、光源的发光时间等,并得到使光电倍增管的时间分辨达到最佳60ps的实验条件。     

基于FPGA的单光子脉冲信号发生器设计

针对光电倍增管(Photomultiplier Tube,PMT)批量测试实际需求和单光电子谱精确测试光源的要求,通过对光电倍增管性能测试系统进行分析,设计制造了一种多通道输出可调的脉冲信号发生器的控制板,可用于光电倍增管单光电子谱的性能测试。该脉冲信号发生器在上升时间、下降时间等参数性能方面优于目前测试系统采用的商用信号源RIGOO-DG5352 350 MHz。用此脉冲信号发生器对光电倍增管进行单光电子测试,其输出信号能满足单光子测试的基本要求,利用其多路信号输出的特点,通过性能扩展即可用于光电倍增管的批量测试。     

光电倍增管倍增极信号定时性能的研究

介绍一种从光电倍增管倍增极引出快信号的电路。分析了信号的产生机理,研究了它的定时性能。使用两支Philips XP2020Q光电倍增管,与BaF2闪烁体组成时问谱仪探头,从D9倍增极引出快信号,在使用Ortec935恒比定时和Ortec567时幅转换的条件下,测量^60Co的瞬发时间谱,在2：1能窗下得到FWHM=138ps的时间分辨。表明,此方法明显改善了谱仪的时间分辨性能。     

用单光电子法测试快光电倍增管的时间分辨特性

本文叙述用单光电子法测试快光电倍增管时间分辨的装置和结果。本装置的电子学系统时间分辨小于25ps/道,系统标定值为13.645ps/道。RCA8575的T_(FWHM)为37—56ps,GDB50的T_(FWHM)为35—70ps。     

PMT电源纹波滤除电路设计

针对基于光电倍增管的计数型探测器易受高压电源纹波干扰的问题,探讨了一种抑制纹波的方法.该方法主要是在电源端增设电阻—电容滤波电路,对高压电源纹波进行事先滤波处理.通过光电倍增管的单光电子谱测试、计数率测试及渡越时间分布验证滤波效果,结果表明:利用该方法,电源的纹波得到有效抑制,减少了电源对光电倍增管单光电子测试信号的干...     

基于SiPM的乳腺专用PET探测模块研制与评价

基于单点型硅光电倍增管(Si PM)与LYSO闪烁晶体,研制了一种新型乳腺专用PET探测模块,并对其性能进行研究。该探测模块采用28×28根1.9 mm×1.9 mm×15 mm的LYSO晶体组成阵列,与8×8个单点型Si PM组成的阵列通过光导耦合,所产生的脉冲信号分别经过模拟、定时电路处理后送入高速采样电路完成信号处理。该探测模块能够实现1.9 mm位置分辨,12.73%平均能量分辨以及2.66 ns双探头符合时间分辨,具有较好的分辨性能,能够满足乳腺专用PET成像的设计需求。     

光电探测器件的单光电子谱数据获取

在常规光电器件性能研究中,测试光电倍增管(Photomultiplier Tube,PMT)的单光电子谱(Single Photoelectron Spectra,SPE)系统一般是采用基于VME和NIM机箱的电荷数字转换器(Charge-to-DigitalConverter,QDC)和时间数字转换器(Time-to-Digital-Converter,TDC)电子学插件等,而测试硅光电倍增管(Silicon Photomultiplier,SiPMT)的系统则倾向于使用基于快速模数转换器(Flash-Analog-to-Digital-Converter,FADC)的便携式桌面机电子学。本文基于相同型号的20吋PMT和SiPMT对比测试,通过比较PMT的性能参数(增益、峰谷比、相对探测效率和能量分辨率等)测试结果,从硬件配置和软件分析等方面深入比较两套数据获取系统的异同,明确使用FADC的一些必要操作过程和数据分析方法。实验结果表明:便携式的FADC系统,可以和基于VME机箱的QDC系统一样,可实现对PMT工作于脉冲模式的阳极信号精确测试,但性能各有优劣。     

平板型光电倍增管64路信号的简化处理

HAMAMATSU的H8500型64路多阳极平板型光电倍增管以其非常优越的位置分辨被广泛地应用于各种小型探测装置和大型阵列探测装置,多信号的有效、快速和最为经济的简化电子学线路读出成为多阳极光电倍增管非常重要的研究内容.基于DPC电桥简化处理多阳极光电倍增管信号,在未采用铅准直的情况下测量137Csγ源最好位置分辨(FWHM)达到了2mm左右.     

Chooz 中微子探测器电子学系统的设计

介绍了Ｃｈｏｏｚ中微子探测器中的电子学系系统,简述ＥＭＩ９３５６ＫＢＡ Ｂ５３型光电倍增管的性能和组成该电子学系统的信号扇入／扇出、信号多级触发、时间数字转换、波形数字化以及数据获取等各系统的设计原理。     

Investigation of a Multi-Anode Microchannel Plate PMT for Time-of-Flight PET

We report on an investigation of a mulit-anode microchannel plate PMT for time-of-flight PET detector modules. The primary advantages of an MCP lie in its excellent timing properties (fast rise time and low transit time spread), compact size, and reasonably large active area, thus making it a good candidate for TOF applications. In addition, the anode can be segmented into an array of collection electrodes with fine pitch to attain good position sensitivity. In this paper, we investigate using the Photonis Planacon MCP-PMT with a pore size of 10 μm to construct a PET detector module, specifically for time-of-flight applications. We measure the single electron response by exciting the Planacon with pulsed laser diode. We also measure the performance of the Planacon as a PET detector by coupling a 4 mm × 4 mm × 10 mm LSO crystal to individual pixel to study its gain uniformity, energy resolution, and timing resolution. The rise time of the Planacon is 440 ps with pulse duration of about 1 ns. A transit time spread of 120 ps FWHM is achieved. The gain is fairly uniform across the central region of the Planacon, but drops off by as much as a factor of 2.5 around the edges. The energy resolution is fairly uniform across the Planacon with an average value of 18.6±0.7% FWHM. While the average timing resolution of 252±7 ps FWHM is achieved in the central region of the Planacon, it degrades to 280±9 ps FWHM for edge pixels and 316±15 ps FWHM for corner pixels. We compare the results with measurements performed with a fast timing conventional PMT (Hamamatsu R-9800). We find that the R9800, which has significantly higher PDE, has a better timing resolution than the Planacon. Furthermore, we perform detector simulations to calculate the improvement that can be achieved with a higher PDE Planacon. The calculation shows that the Planacon can achieve significantly better timing resolution if it can attain the same PDE as the R-9800, while only a 30% improvement is needed to yield a similar timing resolution as the R-9800.     

Optimization of a LSO-Based Detector Module for Time-of-Flight PET

We have explored methods for optimizing the timing resolution of an LSO-based detector module for a single-ring, "demonstration" time-of-flight PET camera. By maximizing the area that couples the scintillator to the PMT and minimizing the average path length that the scintillation photons travel, a single detector timing resolution of 218 ps fwhm is measured, which is considerably better than the ~385 ps fwhm obtained by commercial LSO or LYSO TOF detector modules. We explored different surface treatments (saw-cut, mechanically polished, and chemically etched) and reflector materials (Teflon tape, ESR, Lumirror, Melinex, white epoxy, and white paint), and found that for our geometry, a chemically etched surface had 5% better timing resolution than the saw-cut or mechanically polished surfaces, and while there was little dependence on the timing resolution between the various reflectors, white paint and white epoxy were a few percent better. Adding co-dopants to LSO shortened the decay time from 40 ns to ~30 ns but maintained the same or higher total light output. This increased the initial photoelectron rate and so improved the timing resolution by 15%. Using photomultiplier tubes with higher quantum efficiency (blue sensitivity index of 13.5 rather than 12) improved the timing resolution by an additional 5%. By choosing the optimum surface treatment (chemically etched), reflector (white paint), LSO composition (co-doped), and PMT (13.5 blue sensitivity index), the coincidence timing resolution of our detector module was reduced from 309 ps to 220 ps fwhm.     

PET Performance Evaluation of an MR-Compatible PET Insert

A magnetic resonance (MR) compatible positron emission tomography (PET) insert has been developed in our laboratory for simultaneous small animal PET/MR imaging. This system is based on lutetium oxyorthosilicate (LSO) scintillator arrays with position-sensitive avalanche photodiode (PSAPD) photodetectors. The PET performance of this insert has been measured. The average reconstructed image spatial resolution was 1.51 mm. The sensitivity at the center of the field of view (CFOV) was 0.35%, which is comparable to the simulation predictions of 0.40%. The average photopeak energy resolution was 25%. The scatter fraction inside the MRI scanner with a line source was 12% (with a mouse-sized phantom and standard 35 mm Bruker 1H RF coil), 7% (with RF coil only) and 5% (without phantom or RF coil) for an energy window of 350-650 keV. The front-end electronics had a dead time of 390 ns, and a trigger extension dead time of 7.32 μs that degraded counting rate performance for injected doses above ~0.75 mCi (28 MBq). The peak noise-equivalent count rate (NECR) of 1.27 kcps was achieved at 290 μCi (10.7 MBq). The system showed good imaging performance inside a 7-T animal MRI system; however improvements in data acquisition electronics and reduction of the coincidence timing window are needed to realize improved NECR performance.     

双面硅条探测器的研制与测试

研制了双面硅条探测器。探测器灵敏面积为48mm×48mm,厚约300μm,结面和欧姆面的硅条互相垂直,均由相互平行、宽度相等的48条组成,每条宽0.9mm、间距0.1mm。对其电气特性(耗尽偏压、反向漏电流、条间电阻)和探测特性(上升时间、能量分辨、条间串扰)进行了测试。在偏压为-15V时,各条平均反向漏电流小于10nA。对于从结面入射的5.157 MeV的α粒子,前放信号上升时间约45ns,结面各条的能量分辨率约0.6%~0.7%,基本无条间串扰;欧姆面各条能量分辨率较差,存在条间串扰。     

High Speed HPD for Photon Counting

We have succeeded in the development of a high-speed Hybrid Photodetector (HPD), by using a reduced electron lens and a newly developed avalanche diode (AD) with very low capacitance. The HPD shows fast time response of less than 500 ps in both rise and fall times, and good timing resolution of 26 ps (one sigma) for single photons at full illumination on a photocathode 8 mm in diameter. Limiting factors of the timing resolution were further investigated, and were found to be the transit time difference of electrons in vacuum along the photocathode and the jitter of the electronics. The timing resolution is 15 ps for illumination of less than 5 mm on the central part of the photocathode, which includes the jitter of 13 ps from the electronics. This resolution is the world's highest for HPDs, and matches the resolution of MCP-PMTs. Both a GaAsP photocathode having close to 50% quantum efficiency in the visible and a bialkali photocathode having 34% QE in the UV were fabricated in view of making this device available for various applications. In this paper, we report the results of our evaluation, including discussion about the limiting factors of the timing resolution for the new HPD.     

关联α粒子探测器设计和性能研究

关联粒子成像技术（API）是进行爆炸物检测和有源核查的重要手段,而关联α粒子探测器的空间分辨和时间分辨直接决定成像系统的空间分辨能力。本文依托中国原子能科学研究院核数据重点实验室移动中子发生器,结合具有快时间响应的ZnO：Ga与最新的位置灵敏光电倍增管(PSPMT)H13700,设计可用于API的关联α粒子探测器系统。通过SCDC-TCOG将256路信号简化为4路信号,利用数字化仪对信号进行采集分析。通过离线实验对关联粒子探测器的时间性能和空间分辨性能进行了测试。利用刀口法测得空间分辨好于1 mm,并通过狭缝法和栅条法进行了验证。通过测量²⁵²Cf裂变碎片和瞬发伽马符合测量获得系统时间分辨好于1 ns,达到了应用需求。     

利用二维平台扫描系统研究光电倍增管阴极位置响应

大型高海拔空气簇射观测站(LHAASO)计划中的各种探测器将使用几万只光电倍增管测量探测器收集到的光子数,光电倍增管阴极位置响应的均匀性是影响探测器能量分辨的重要因素之一.为此搭建了由步进电机驱动的二维扫描平台控制LED光源,逐毫米扫描光电倍增管光阴极,测量光源照射光阴极不同位置时的阳极输出信号.实验中对多种候选光电倍...     

Imaging Properties of a Positron Tomograph with 280 Bgo Crystals

The basic imaging properties of the Donner 280-BGO-Crystal positron tomograph were measured and compared with the same system when it was equipped with 280 NaI(T1) crystals. The NaI(T1) crystals were 8 mm × 30 mm × 50 mm deep, sealed in 10 mm wide stainless steel cans. The BGO crystals are 9.5 mm wide × 32 mm × 32 mm deep and as they are not hygroscopic do not require sealed cans. With a shielding gap of 3 cm (section thickness 1.7 cm FWHM) the sensitivity of the BGO system is 55,000 events per sec for 1 ?Ci per cm3 in a 20 cm cylinder of water, which is 2.3 times higher than the NaI(T1) system. For a 200 ?Ci/cm line source on the ring axis in a 20 cm diameter water cylinder, the BGO system records 86% of the scatter fraction and 66% of the accidental fraction of the NaI(T1) system. The lower light yield and poorer time resolution of BGO requires a wider coincidence timing window than NaI(T1); however, the ability to use full-energy pulse height selection with a 2.3-fold improvement in sensitivity results in an overall reduction in the fraction of accidental events recorded. The in-plane resolution of the BGO system is 9-10 mm FWHM within the central 30 cm diameter field, and the radial elongation at the edge of the field in the NaI(T1) system has been nearly eliminated.     

TOF-PET探测器定时性能初步研究

本工作采用LYSO晶体阵列和平板型位置灵敏光电倍增管H8500对TOF-PET探测器进行了初步设计,能分辨3.2mm×3.2mm的晶体阵列。与BaF₂探测器组成时间谱仪,测量正电子湮没射线的瞬发时间谱,得到379ps的符合时间分辨率。根据已测量的BaF₂探测器时间分辨率（159ps）,可计算得到所设计的TOF-PET探测器时间分辨率为344ps。预计与此相同的两个TOF-PET探测器对正电子湮没射线的符合时间分辨率可达486ps左右,为新型PET的研究提供了有利条件。     

Optimum beam duty cycle for coincidence experiments

It is argued that continuous beam is commonly thought to be ideal for a coincidence experiment because it minimizes the false coincidence rate. A false coincidence rate up to a factor of two lower can be obtained (for fixed average current) by a pulsed beam with relatively short pulses separated by the resolution time of the detector. The micropulse structure of the beam is discussed. Most RF accelerators produce a train of micropulses within a macropulse during which the RF is on. Macropulse timing is generally very long compared to resolution times, hence a macropulse structure that is continuous is desirable. An analysis is given of the errors associated with different duty cycle lengths