On the scintillation response of NaI(TI)-crystals

Several articles have been reviewed on the scintillation response of NaI(Tl). Those publications which report results obtained with radioactive sources either dispersed throughout the NaI(Tl)-lattice or located inside the wells of NaI(Tl)-crystals match within a ±0.9% standard deviation of a linear scintillation response between 3 MeV and 3 keV. Several authors who plated their sources outside the crystals measured nonlinear responses of NaT(TI) with up to ±7% of standard deviations between 700 and 4.5 keV. The presented analysis suggests that the observed nonlinearity is not an intrinsic effect of NaI(TI) but could be caused, at least partly, by effects occurring at the radiation entrance surfaces of the crystals     

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.     

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.     

蒙特卡罗方法模拟放射源位置对井型NaI(Tl)晶体探测效率的影响

利用Geant4数值计算程序,对放射源137Cs和60Co发射的单能γ射线(0.662 MeV和1.331MeV)经过井型NaI(Tl)晶体探测器后的能谱进行了蒙特卡罗模拟,并通过改变放射源在井型NaI(Tl)晶体中的位置对探测效率的影响做了进一步的研究。计算结果表明:对比常用的圆柱形NaI(Tl)闪烁探测器,由于井型NaI(Tl)晶体对放射源所张立体角很大,所以其对γ射线的源峰探测效率更高,并随着放射源在井内高度的增加而逐渐减小;在固定了放射源在晶体井下深度的情况下,放射源位置在水平面内的变化对源峰探测效率的影响并不大。     

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.     

闪烁体耦合SiPM测量γ能谱的模拟研究

硅光电倍增管(Silicon photomultiplier,SiPM)是一种新型的光电探测器件,由工作在盖革模式下的雪崩二极管阵列组成。利用GEANT4蒙特卡罗软件包对LaBr_3:10%Ce~(3+)、Na I(TI)闪烁晶体耦合SiPM测量γ射线能谱进行了细致的模拟,通过单色光LED光源照射SiPM,得到SiPM自身暗电流噪声经电子学放大后,与集成的盖革雪崩二极管之间的间隙引起吸收光子涨落对能谱的展宽。对模拟得到的662 keVγ射线能量分辨率进行修正,最后与实验结果对比能够很好地符合,还得到了一组对应闪烁晶体本征能量分辨率的程序参数Pr,s。结果验证了模拟程序设置的闪烁晶体与封装材料光学参数的合理性与可靠性,为闪烁体探测器设计提供了一套开发工具。     

G(E)法与Gravel法处理能谱-剂量转换效果研究

为准确地得到γ射线的辐射剂量,对G(E)函数法和Gravel算法处理能谱-剂量的转换效果进行了研究。根据实际应用需求,采取蒙特卡罗方法模拟获取了?50 mm×50 mm NaI(Tl)探测器的Gravel法响应矩阵,并使用Matlab得到探测器的G(E)函数。使用NaI(Tl)探测器和多道谱仪系统测量标准源的能谱,分别使用G(E)法和Gravel法计算剂量值并与理论值进行比较,同时在计算过程中总结对比了两种方法的特点。     

闪烁上升时间机理及其对读出波形和时间分辨的影响

本文讨论了闪烁上升时间的凝聚和气态激子系衰变机制。分析了上升、衰减和光子的光电倍增迁移,回路渡越等时间对闪烁波形的贡献。用计算机解出NE102A、NE110,PILOT-U,NE111,ST401,ST411,NaI(Tl),BGO 等闪烁体的波形,研究了其上升前沿对快前沿甄别的时刻游动和晃动的影响。     

硅光电管-闪烁体探测器γ谱仪研制

实验研制了硅光电管-闪烁体探测器γ谱仪。该γ谱仪用硅光电倍增管代替普通光电倍增管作为闪烁体探测器的光学读出端,配置闪烁体探测器,构成新型γ谱仪。测试结果表明:新型γ谱仪随温度漂移变化程度大;能量线性较好,线性相关度R为0.9987;配置LaBr_3:10%Ce~(3+)晶体,其能量分辨率为4.3%~4.9%;配置NaI(TI)晶体,其能量分辨率为8.4%。     

NaI(Tl)晶体探测器对面源的γ绝对探测效率

用数值积分方法计算了ＮａＩ（Ｔｌ）晶体探测器对Ｍａｒｉｎｅｌｌｉ Ｂｒｅａｋｅｒ型容器内表面源的γ绝对探测效率。     

NaI(Tl)探测器的源几何特性对峰总比影响模拟研究

利用蒙特卡罗工具Geant4模拟了~(137)Cs和~(60)Co这两种放射源的几何形状以及探测距离这两个因素对γ射线在NaI(Tl)闪烁体探测器内能量沉积的影响。研究结果表明,当放射源的几何形状不一样时,不同的核素在峰总比达到最大时的探测距离不一样,模拟结果为放射性测量提供了参考。     

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。     

NaI(Tl)闪烁探测器对铯源响应的蒙特卡罗模拟

对NaI(Tl)探测器的γ能谱进行了MC模拟,模拟研究了不同源-探距、不同能量分辨率、不同模拟时间和平面源分布等条件下的137Cs γ能谱.137Cs点源的模拟谱与实测谱的对比表明两者基本相符.     

Cerium-doped lutetium oxyorthosilicate: a fast, efficient newscintillator

The authors discuss a single-crystal inorganic scintillator, cerium-doped lutetium oxyorthosilicate (Lu_2(1-x)Ce_2x (SiO₄) or LSO). It has a scintillation emission intensity which is ~75% of NaI(Tl) with a decay time of ~40 ns. The peak emission wavelength is 420 nm. It has a very high gamma-ray detection efficiency due to its density of 7.4 g/cm³ and its effective atomic number of 66. Its radiation length of 1.14 cm is only slightly longer than bismuth germanate (BGO). The scintillation properties of Ce-doped LSO are compared to NaI(Tl), BGO, and cerium-doped gadolinium oxyorthosilicate (GSO). In addition to desirable physical properties such as high density and high atomic number, LSO also processes a combination of high emission intensity and fast decay which together are superior to any other known single crystal scintillator     

Recent Advances in X-Ray Detection Technology

A review is presented of recent developments in x-ray photon detectors and in the associated detector electronics. The first portion of the paper is devoted to a survey of the presently available physical inforrnation on the "intrinsic" resolution of silicon and germanium radiation detectors, proportional counters and NaI(Tl) scintillation crystals. Semiconductor detectors suitable for x-ray applications and low noise electronics are then analyzed in some detail. Discussions follow on scintillation detectors, proportional counters, and "external" photoelectric detectors. Recent spectral achievements and interesting applications are illustrated.     

NaI(TI)探测器晶体体积对主要性能影响研究

使用~(137)Cs、~(60)Co和~(22)Na三种点射线源,分别探讨了由不同体积闪烁晶体组成的探测器对不同能量γ射线的峰效率、能谱响应及有效中心的影响。实验结果表明:随着闪烁晶体体积的不同,不同能量γ能谱光电峰的峰位及其能量分辨率都发生了变化。还发现探测器有效中心点的位置依赖于闪烁晶体的体积,其峰效率的倒数与探测器有效距离平方成反比。此实验结果可为改善不同体积NaI(Tl)闪烁探测器的能谱响应和高精度测量提供参考。     

An inversion decomposition method for better energy resolution of NaI(Tl) scintillation detectors based on a Gaussian response matrix

NaI(T1) scintillation detectors have been widely applied for gamma-ray spectrum measurements owing to advantages such as high detection efficiency and low price.However,the mitigation of the limited energy resolution of these detectors,which detracts from an accurate analysis of the instrument spectra obtained,remains a crucial need.Based on the physical properties and spectrum formation processes of NaI(T1) scintillation detectors,the detector response to gamma photons with different energies is represented by photopeaks that are approximately Gaussian in shape with unique full-width-at-half-maximum(FWHM) values.The FWHM is established as a detector parameter based on resolution calibrations and is used in the construction of a general Gaussian response matrix,which is employed for the inverse decomposition of gamma spectra obtained from the detector.The Gold and Boosted Gold iterative algorithms are employed to accelerate the decomposition of the measured spectrum.Tests of the inverse decomposition method on multiple simulated overlapping peaks and on experimentally obtained U and Th radionuclide series spectra verify the practicability of the method,particularly in the low-energy region of the spectrum,providing for the accurate qualitative and quantitative analysis of radionuclides.     

Bismuth Germanate: A High-Z Gamma-Ray and Charged Particle Detector

The room-temperature scintillation characteristics of single crystals of Bi4Ge3O2 under gamma-ray and alpha-particle excitation have been determined. The wavelength of maximum intensity in the scintillation spectrum is 480 nm. A decay constant of 0.30 microseconds was measured. Scintillation efficiency (pulse height) varied linearly with gamma-ray energy, E, and the resolution varied as E-1/2. 8% pulse height relative to NaI(Tl) with 15% resolution was measured for a 2.2 cm × 1.7 cm crystal under excitation by Cs137 0.662 Mev gamma-rays.     

便携式γ能谱仪闪烁探头改进设计及性能研究

为满足当前便携式γ能谱仪对高性能闪烁探头的需要,本文提出了采用CsI(Tl)晶体耦合雪崩光电二极管的方式代替NaI(Tl)晶体耦合光电倍增管以构成新的闪烁探测器,并设计了低噪声电荷灵敏放大器作为探测器读出电路。根据唯一变量原则分别测试了能量分辨率随温度与偏压的变化规律,并对多种放射源的γ射线进行能谱响应实验。实验结果表明：当温度为23 ℃且偏压为370 V时,该闪烁探头对¹³⁷Cs、²²⁶Ra、⁶⁰Co和¹⁵²Eu源的γ射线具备优异的能谱响应特性,其中,对¹³⁷Cs源的γ射线能量分辨率可达4.98%,输出信号信噪比可达21∶1,上升时间为80 ns。可见,改进后的闪烁探头的性能有大幅提升,具备能量分辨率更佳、体积更小、抗机械性能与适用性更强等优点。