Improved Timing with NaI(Tl)

By timing on the earliest component of the anode current pulse of the photomultiplier, the time resolution obtained with NaI(TI) at 300°K can be made somewhat superior to that reported for pure NaI at 77°K. For example, the time distribution for x rays (31. 6 keV) relative to the conversion electrons from a Cs137 source, shows a full width at half maximum of 1.6 nsec and a slope corresponding to a half life T? = 0.63 nsec. This implies that ? /R is much smaller than commonly believed, where ? is the mean life of the scintillation and R is the average number of photoelectrons per event. This small value is not due to a small ? because only the usual slow component is observed when the shape of the scintillation is measured by a probability technique. Therefore R must be larger than expected; the observed time resolution requires at least 8.7 photoelectrons/ keV. This is consistent with the value 9.3 p.e./ keV inferred from the pulse-height resolution obtained with artificial light pulses which are equivalent in amplitude to a 662-keV event in NaI(Tl). It is also consistent with the value (9. 1 p.e./keV) obtained by combining the absolute efficiency of NaI(Tl) measured by Van Sciver and Bogart with the quantum efficiency that RCA lists for the bi-alkali photocathode.     

大体积NaI(Tl)探测器性能研究

利用蒙特卡洛方法,对不同体积NaI(Tl)探测器的探测效率进行了计算.对圣戈班(Saint-Gobain)5"×8"NaI(Tl)探测器的能量分辨及时间响应进行了测试.在14 MeV氘-氚中子源照射条件下,测量模拟样(化学式:HCNO)的特征瞬发伽马谱,与国产φ"×4"NaI(Tl)探测器进行了比较.结果表明,圣戈班的...     

车载式NaI(Tl)大晶体组的多道谱仪

文章介绍车载式NaI(Tl)大晶体组的γ多道谱仪,该谱仪选用2个10 cm×10 cm× 40 cm NaI(Tl)方晶体探头,采用高速ADC集成芯片、USB微控制器等先进技术,具有实时、灵敏度高、识别核素的特点,可用于搜寻失控放射性源、核与辐射突发事件中的快速探察和应急监测、环境辐射调查等工作.     

涂硼CsI(Tl)探测器n-γ信号仿真及数字甄别方法研究

根据在涂硼CsI(Tl)探测器中产生的γ射线、中子脉冲信号的特征,利用电荷比较法、上升时间法、频率梯度法、向量投影法、聚类分析法、神经网络法完成了n/γ射线甄别。结果表明了这些方法均可以实现对涂硼CsI(Tl)探测器的中子甄别,这为今后搭建涂硼CsI(Tl)探测器的中子实时甄别系统打下基础。     

减小模板状NaI(Tl)探测器的边缘死区

用在环状ＳＰＥＣＴ系统中的ＮａＩ（Ｔｌ）探测器模板存在着严重的边缘死区。介绍了一些减少该死区的办法,包括：一个ＰＭＴ管跨接两个探测器模板,在边缘刻槽等等。实验结果证明通过这些处理,这个死区可以减小到５ｍｍ。     

Scintillation Characteristics of Thin NaI(Tl) and CsI (Tl) Layers Fabricated by Vacuum Deposition

The scintillation characteristics of thin vacuum-deposited layers of NaI (Tl) and CsI (Tl) were investigated. Scintillation layers with thicknesses ranging from 0.2 to 20 mg/cm2 were evaluated as detectors with 6- and 22-keV x rays. In this energy region they were found to be comparable in performance to the thicker, commercially available NaI (Tl) and CsI (Tl) scintillation crystals. Fabrication methods, scintillator evaluation techniques, and applications in selective low-energy x-ray detection will be reported.     

NaI(Tl)γ谱的计算机稳峰技术

介绍了一种改进型NaI(Tl)γ谱仪的稳谱技术。该稳谱技术基于241Am源的等效γ峰作为系统的参考峰,根据参考峰位偏差运用数字PID调整可编程增益放大器来稳谱,是一种“硬件 参考源 软件”的稳谱技术。这种计算机稳谱技术具有稳定度高,稳谱速度快等优点。     

基于傅里叶变换的NaI(Tl)仪器谱散射本底估计方法

有效地估计NaI(Tl)仪器谱的散射本底可提高仪器的分析精度。本文提出了一种基于傅里叶变换的散射本底估计方法。通过在模拟谱线和实测NaI(Tl)仪器谱上的应用,表明该方法适用于NaI(Tl)仪器谱数据处理,能自主、有效估计散射本底。     

Resolution in large rectangular NaI(Tl) detectors: a study

Experiments were carried out for studying the resolution of 4-in (10-cm)×4-in (10-cm)×16-in (40-cm) NaI(Tl) detectors used in high-sensitivity airborne gamma-ray spectrometric surveys. Change of resolution with source-detector geometry emphasized the inadequacy of existing specifications for resolution in explaining the detector response. An additional specification for resolution measurement, namely, overall resolution, is proposed. Measurement and applications of overall resolution of the detector are discussed     

基于数字多道NaI(Tl)探测器的死时间研究

在放射性测量中,有时候需要对计数率进行精确的测量,因此需要对探测器死时间效应进行修正处理。本文基于DMCA-iCore数字化多道模块,从理论出发分析了数字多道NaI(Tl)探测器产生死时间效应的原因,得出数字多道死时间也服从扩展型分布的结论;同时根据牛顿迭代法推导了死时间修正函数,在计数率较高、探测器死时间较大时该修正函数依然有较好的修正效果。基于双源法测试了系统的死时间,死时间t=20.6 μs,最后在¹³⁷Cs标准剂量场中对NaI(Tl)探测器进行了测试,进一步证明了修正方法的有效性。     

Maximum scintillation yields in NaI(Tl) and CsI(Tl) crystals estimated from the scintillation model for liquid rare gases

The maximum scintillation yields in NaI(Tl) and CsI(Tl) crystals were estimated theoretically by applying the scintillation model for liquid rare gases to crystal scintillators. Average energies required to produce one scintillation photon in the maximum scintillation yield, W_so, were estimated to be 10.6 ± 0.3 or 11.6 ± 0.3 eV for NaI(Tl) and 11.6 ± 0.3 or 12.5 ± 0.3 eV for CsI(Tl). The new experiment on scintillation yields gives W_so of 10.8 ± 2.0 eV for NaI(Tl) and 11.3 ± 2.1 or 9.3 ± 1.7 eV for CsI(Tl). The values show good agreement with the theoretical estimations. These results demonstrate that the scintillation model in liquid rare gases is applicable to inorganic scintillators such as NaI(Tl) and CsI(Tl) crystals.     

NaI(Tl) 闪烁谱仪峰总比的蒙特卡罗计算

简单分析NaI(Tl）闪烁谱仪探测原理的基础上，运用蒙特卡罗程序MCNP计算了该谱仪对不同能量点源的峰总比（或光分数），并同实验结果做了对比，解释了计算结果比实验值偏高的原因。     

大体积阱式NaI(Tl)探测器的效率计算与测量

使用蒙特卡罗方法模拟计算了一个用于4πγ计数的大体积阱式NaI(Tl)探测器的效率和能谱。采用一系列单能γ源标定探测器,对计算结果进行检验,其结果基本一致,两者间的最大偏差不超过±8%,证明计算结果是可靠的。     

NaI(Tl)晶体对面源全能峰效率刻度的点源模拟法

介绍了用点源模拟法来刻度面源全能峰效率的方法,并将刻度结果与数值分析法的理论计算值进行了比较,两者在８％内一致。     

Validation of a NaI(Tl) detector's model developed with MCNP-X code

The Monte Carlo method was used to calculate the photon detection efficiency and energy resolution curves for a 1.5″ × 1″ NaI(Tl) scintillator detector (crystal + housing + photomultiplier tube material equivalent) exposed to gamma rays in the energy range from 20 keV to 662 keV. This work aims to design a precise computational model, based in Monte Carlo simulation, which can be used in practical application. The energy resolution curve was used to improve the response of the mathematical simulation of the detector. The detector was modeled with the MCNP-X code and the results were compared to experimental photopeak efficiency measurements of radiation sources. The results showed good agreement with the experimental data.     

NaI(Tl)、Ge(Li)探测器对大圆柱体源的效率

本文介绍用蒙特卡洛方法,采用加权技巧计算 NaI(Tl)、Ge(Li)探测器对大体积圆柱形体源的效率。文中首先对计算方法作了简要叙述。然后介绍在 PDP11/34A 小型计算机上用蒙特卡洛方法计算了76×76mm NaI(Tl)晶体对76mm 直径的水圆柱体源的效率,在80—3000keV 能区,计算值与文献值在±1%内一致。对本实验室的一台 Ge(Li)探测器,分别计算了它对 NBS参考物质和水圆柱体源(源半径大于 Ge(Li)晶体半径)的效率,计算中对探测器 N 层和包装外壳等项因素作了修正。实验测定了点源的峰总比,得到 Ge(Li)探测器的峰效率。将 Ge(Li)探测器峰效率的计算值与用~(152)Eu、~(60)Co、~(137)Cs、U、U-Ra 和 Th 标准源测得的实验值进行了比较,在93—2614keV 能区,估计两者在±4%内一致。最后讨论了样品体积与探测下限的关系。     

Energy Transfer and the Role of Thallium Dimers in the Nal(Tl) Scintillation Process

The thallium dimer center, which is a pair of thallous ions occupying nearest neighbor cation sites in NaI, is found to have a decay time of less than 7 nanoseconds. Analysis of the emission spectrum of a typical NaI(Tl) scintillation crystal indicates that the dimer centers are responsible for approximately 25% of the scintillation light although only a small part of this is rapid. It is proposed that energy of excitation migrates among the monomers and between monomers and dimers as a result of thermal excitation.