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) 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。     

Applied Moving-Temperature-Gradient Technique for CsI(Tl) Crystal Growth

A simple high-temperature furnace with two independent heating zones was developed based on the moving-temperature-gradient concept with an operating range of 400 to 1,200°C. Programmable temperature reduction rates of the two heating zones are independently controlled in a closed chamber for better thermal stability throughout the growth zone. In order to eliminate the driving mechanism and reduce subtle vibration, which could adversely affect crystal quality, the charge crucible and furnace are made stationary during the growth process. Measurement results of temperature distributions of gradient drifting rates at various positions along the growth zone are presented. The growth of CsI(Tl) scintillation crystals prepared from a mixture of 99.9% pure CsI powder and Tl powder, using the growth rate of 1 mm/h, temperature gradient of 25.5°C/cm, and temperature gradient drift rate of 2.5°C/h, was achieved with crystal sizes of 10 and 22mm diameter, both 70mm in length. Test results of gamma energy resolution at 662 keV of Cs-137 spectrum measurement revealed a resolution of 7–9%.     

Experimental response function of NaI(Tl) scintillation detector for gamma photons and tomographic measurements for defect detection

The response function of gamma detector is an important factor for spectrum analysis because some photons and secondary electrons may escape the detector volume before fully depositing their energy, of course destroys the ideal delta function response. An inverse matrix approach, for unfolding of observed pulse-height distribution to a true photon spectrum, is used for construction of experimental response function by formulating a 40 × 40 matrix with bin mesh (E^1/2) of 0.025 (MeV)^1/2 for the present measurements. A tomographic scanner system, operating in a non-destructive and non-invasive way, is also presented for inspection of density variation in any object. The incoherent scattered intensity of 662 keV gamma photons, obtained by unfolding (deconvolution) the experimental pulse-height distribution of NaI(Tl) scintillation detector, provides the desired information. The method is quite sensitive, for showing inclusion of medium Z (atomic number) material (iron) in low Z material (aluminium) and detecting a void of ∼2 mm in size for iron block, to investigate the inhomogeneities in the object. Also, the grey scale images (using “MATLAB”) are shown to visualise the presence of defects/inclusion in metal samples.     

CsI(Tl)探测器对带电粒子能量响应的入射位置依赖关系

在放射性核束物理的实验研究中,通常采用CsI(Tl)探测器对反应产物中的带电粒子进行总能量测量.使用GEANT4软件对CsI(Tl)闪烁体探测器能量响应通进行了蒙特卡罗模拟,在考虑了晶体外表面包覆材料反射率、耦合光敏二极管面积、射程等影响因素后,重点研究了CsI(Tl)闪烁体探测器对带电粒子能量响应的入射位置依赖关系....     

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     

CDEX实验中CsI(Tl)晶体反符合探测器实验测试

CDEX(China Dark matter EXperiment)合作组将在中国锦屏极深地下实验室(CJPL China Jin-Ping deep underground Laboratory)利用极低能阈高纯锗(ULE-HPGe)探测器进行暗物质的直接探测。在地下实验之前,对CsI(Tl)晶体反符合探测器进行了地面的实验研究。主要包括光导的选择,光反射层的选择,CsI(Tl)晶体的高度一致性测试,不同侧面非均匀性的测试,以及所有晶体的测试结果。通过地面实验的前期工作,我们对反符合探测器有了一定认识,为地下实验做了准备。     

Radiation damage in undoped CsI and CsI (Tl)

Radiation damage in undoped CsI and CsI(Tl) crystals using ⁶⁰ Co gamma radiation for doses up to ~4.2×10⁶ has been studied. Samples from various manufacturers were measured, ranging in size from 2.54-cm-long cylinders to a 30-cm-long block. Measurements were made on the change in optical transmission and scintillation light output as a function of dose. Although some samples showed a small change in transmission, a significant change in light output was observed for all samples. Recovery from damage was also studied as a function of time and exposure to UV light. A short-lived phosphorescence was observed in undoped CsI, similar to the phosphorescence seen in CsI(Tl)     

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。     

Particle identification using CsI(Tl) crystal with three different methods

Three pulse-shape-discrimination (PSD) methods are applied to study the particle identification (PID) by using CsI(Tl) crystal, especially for identifying light charged particles. The zero-cross time method, fast and total component method and signal rise time method are used. The experiment, data analysis and results are compared. Good PID for p, α and γ can be achieved with a CsI(Tl)-photomultiplier assembly.     

半导体探测器的厚度确定及CsI(Tl)的刻度

根据核反应过程中发射带电粒子在硅半导体中的最大能量沉积,利用带电粒子在硅半导体中的阻止本领曲线,同时实现半导体探测器的厚度确定及与之组合的CsI(Tl）的刻度。     

New Technical Approach to Monitoring of Low-Level Environmental Gamma Radiation Using NaX(Tl) Scintillation Instrument

The environmental dose evaluation around a nuclear facility is usually performed by means of calculational methods on the basis of effluent monitoring at a release point. It has been desired to develop practical techniques of direct monitoring in the environment, because the Japan Atomic Energy Commission set up 5 mrem/yr as an objective dose value for the whole-body exposure due to normal operation of LWRs on a single site.

In evaluating gaseous plume doses less than 5 mrem/yr in routine monitoring, there are many difficult problems to be solved. We have developed two techniques for separation of the plume exposures less than 1 mrem/yr from the background radiation, using a NaI(Tl) scintillation counter having flat energy response.

One technique is based on the difference in energy spectrum distribution between plume gamma and natural gamma radiation. And, separation of the respective exposures is made by analysis of the two informations obtained by a two-channel monitoring system. Another technique is to reduce the natural gamma radiation components by using a special concave lead shield for the NaI(Tl) scintillation probe. A combination of the techniques can much improve the efficiency of separation of ⁴¹Ar plume radiation from fluctuating background radiation.     

A new value for the half-life of Be by Heavy-Ion Elastic Recoil Detection and liquid scintillation counting

The importance of ¹⁰Be in different applications of accelerator mass spectrometry (AMS) is well-known. In this context the half-life of ¹⁰Be has a crucial impact, and an accurate and precise determination of the half-life is a prerequisite for many of the applications of ¹⁰Be in cosmic-ray and earth science research. Recently, the value of the ¹⁰Be half-life has been the centre of much debate. In order to overcome uncertainties inherent in previous determinations, we introduced a new method of high accuracy and precision. An aliquot of our highly enriched ¹⁰Be master solution was serially diluted with increasing well-known masses of ⁹Be. We then determined the initial ¹⁰Be concentration by least square fit to the series of measurements of the resultant ¹⁰Be/⁹Be ratio. In order to minimize uncertainties because of mass bias which plague other low-energy mass spectrometric methods, we used for the first time Heavy-Ion Elastic Recoil Detection (HI-ERD) for the determination of the ¹⁰Be/⁹Be isotopic ratios, a technique which does not suffer from difficult to control mass fractionation. The specific activity of the master solution was measured by means of accurate liquid scintillation counting (LSC). The resultant combination of the ¹⁰Be concentration and activity yields a ¹⁰Be half-life of T_1/2 = 1.388 ± 0.018 (1 s, 1.30%) Ma. In a parallel but independent study (Chmeleff et al. [11]), found a value of 1.386 ± 0.016 (1.15%) Ma. Our recommended weighted mean and mean standard error for the new value for ¹⁰Be half-life based on these two independent measurements is 1.387 ± 0.012 (0.87%) Ma.     

Effect of Ag and Li ion irradiation on superconducting Tl2Ca2Ba2Cu3O10 single crystals

The effect of irradiation by 50 MeV Li³⁺ and 200 MeV Ag¹⁵⁺ ions on single crystals of Tl₂Ca₂Ba₂Cu₃O₁₀ (Tl2223) superconductor has been investigated at different fluences. Isothermal magnetization hysteresis loops have been recorded at different temperatures using a SQUID magnetometer and the effect of irradiation on the critical current density, irreversible field, second magnetization peak and pinning force has been studied. Irradiation by 200 MeV Ag¹⁵⁺ ions resulted in increased hysteresis and irreversibility field while no change in second magnetization peak position and critical temperature was observed. A broadening in the hysteresis loop before the second magnetization peak was also observed for the crystals irradiated by Li³⁺ ions. Annealing of irradiated crystals at 500 °C resulted in reduction of point defects created by Li³⁺ ions.     

PIXE characterization of CsI(Tl) scintillators used for particle detection in nuclear reactions

Particle-Induced X-ray Emission has been used to measure Thallium concentration in several CsI(Tl) scintillators from different manufacturers, in order to check their nominal declared values and correlate their behaviour with actual Tl concentration. Indeed, both Tl doping level and its uniformity affect light emission of these detectors, which are largely employed in nuclear physics experiments.In some of the examined crystals Tl concentration values from PIXE measurements came out to be quite different from those declared. This allowed us to explain apparent anomalies in the trend of their α/γ-induced light yield ratio versus Tl content. In some cases, the presence of unexpected contaminants was also pointed out.     

CSR外靶实验终端中CsI（Tl）晶体的测试

为测量重离子加速器冷却储存环（HIRFL-CSR）的外靶实验终端上不同能量的γ射线,一种用于探测γ射线的高能量分辨的探测装置正在中国科学院近代物理研究所建设,该探测器由中国科学院近代物理研究所自行生长的铊激活的碘化铯CsI（Tl）晶体组成。与日本Hamamatsu公司生产的S8664-1010型雪崩光二极管（APD）耦合,测试其光输出的非均匀性和能量分辨,从测试结果给出了所需CsI（Tl）晶体合格的标准。目前已完成该γ探测球计划的六分之一,所提供的晶体合格率达94%以上。     

Measurement of thermal neutron cross section and resonance integral for (n,γ) reaction in Sm

This study implies that ⁵⁵Mn(n,γ)⁵⁵Mn monitor reaction may be a convenient alternative comparator for the activation method and thus, it was used for the determination of thermal neutron cross section (TNX) and the resonance integral (RI) of the reaction ¹⁵²Sm(n,γ)¹⁵³Sm. The samples of MnO₂ and Sm₂O₃ diluted with Al₂O₃ powder were irradiated within and without a cylindrical 1 mm-Cd shield case in an isotropic neutron field obtained from the ²⁴¹Am–Be neutron sources. The γ-ray spectra from the irradiated samples were measured by high resolution γ-ray spectrometry with a calibrated n-type Ge detector. The correction factors for γ-ray attenuation, thermal neutron and resonance neutron self-shielding effects and epithermal neutron spectrum shape factor (α) were taken into account in the determinations. The thermal neutron cross section for ¹⁵²Sm(n,γ)¹⁵³Sm reaction has been determined to be 204.8 ± 7.9 b at 0.025 eV. This result has been obtained relative to the reference thermal neutron cross section value of 13.3 ± 0.1 b for the ⁵⁵Mn(n,γ)⁵⁶Mn reaction. For the TNX, most of the experimental data and evaluated one in JEFF-3.1, ENDF/B-VI, JENDL 3.3 and BROND 2.0, in general, agree well with the present result. The RI value for ¹⁵²Sm(n,γ)¹⁵³Sm reaction has also been determined to be 3038 ± 214 b, relative to the reference value of 14.0 ± 0.3 b for the ⁵⁵Mn(n,γ)⁵⁶Mn monitor reaction, using a 1/E^1+α epithermal neutron spectrum and assuming Cd cut-off energy of 0.55 eV. In surveying literature, the existing experimental and evaluated data for the RI values are distributed from 1715 to 3462 b. However, when the Cd cut-off energy is defined as 0.55 eV, the present RI value agrees with some previously reported RI values, 3020 ± 163 b by Simonits et al., 3141 ± 157 by Van Der Linden et al., and 2962 ± 54 b by Kafala et al., within the limits of error.     

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。     

CsI(Tl)晶体的APD前端读出特性研究

雪崩光电二极管(Avalanche photodiode,APD)体积小、探测效率高、内置增益、对磁场不敏感,但其内置增益、输出脉冲信号的信噪比受偏置电压与温度影响明显。将APD作为Cs I(Tl)闪烁晶体的光电读出器件,并配以低噪声的电荷灵敏前置放大器,组成闪烁探测器的探头。在不同的偏置电压与温度下,测试了该探头组成的闪烁探测器的能量分辨率。实测表明,偏置电压、温度将影响探测系统的能量分辨率,在室温且APD两端的偏置电压为370 V时,对能量为662 ke V的γ射线能量分辨率为4.98%;在-20-40oC内,能量分辨率随温度的降低而提高。     

Measurement of keV-neutron capture cross-sections and capture γ-ray spectra of Fe and Fe

The neutron capture cross-sections and the capture γ-ray spectra of ⁵⁶Fe and ⁵⁷Fe have been measured in the neutron energy range from 10 to 90 keV. Pulsed keV-neutrons were produced from the ⁷Li(p,n)⁷Be reaction by bombarding a lithium target with a 1.5-ns bunched proton beam from a 3 MV Pelletron accelerator. The incident neutron spectrum on the capture sample was measured using a time-of-flight method with a ⁶Li-glass detector. The capture γ-rays emitted from an iron or standard gold sample were detected with a large anti-Compton NaI(Tl) spectrometer. The capture yield of the iron or gold sample was obtained by applying a pulse-height weighting technique to the corresponding capture γ-ray pulse-height spectrum. The capture cross-sections of ^56,57Fe were derived with errors less than 5% using the standard capture cross-sections of ¹⁹⁷Au. The capture γ-ray spectra were obtained by unfolding the observed capture γ-ray pulse-height spectra. The present results for the capture cross-sections were compared with the previous measurements and the evaluated values of ENDF/B-VII.0 and JENDL-3.3. The Maxwellian-averaged capture cross-sections of ⁵⁶Fe and ⁵⁷Fe at 30 keV are derived as 12.22 ± 2.06 mb and 44.48 ± 7.56 mb, respectively.