Monte Carlo method for determining the response of portable gamma detector for in situ measurement of terrestrial gamma ray field

A Monte Carlo method to study the response of portable detector to terrestrial gamma ray is proposed. This method is based on two-stage Monte Carlo simulation.First, the probability distributions of the phase space coordinates of the events that are most likely to be detected are reconstructed at the phase space shell level. The phase space shell is a closed surface enclosing the detector. The detector response to events originating from the phase space shell is then studied. The full absorption spectra as well as the partial absorption spectra are obtained for natural radionuclides uniformly distributed in the ground. For validation, this method is applied to a Hp Ge portable detector previously studied. The previous study is based on a semiempirical model. Good agreement is achieved when we compare the full-energy peak efficiencies and the total in situ spectra obtained by the two methods. As an application, the effective depth of the activity of the^(137) Cs artificial radionuclide in the soil is determined from the low-energy part of the total in situ spectrum.

Development of a Gamma Spectroscopy Detector Based on SiPMs and 1" Ce:GAGG Scintillator

In the field of nuclear radiation detection, sodium iodide (NaI(Tl)) and lanthanum bromide (LaBr3) are the primary scintillation crystals used for energy spectrum detectors. Furthermore, energy spectrum detectors based on gadolinium gallium aluminum garnet (Ce:GAGG) scintillation crystals are minor. In this work, a 1-inch Ce:GAGG and Silicon Photomultipliers (SiPMs) are employed to construct a detector, and the coupled medium was silicone oil. An optimal SiPMs quantity scheme for the energy resolution was determined by varying the number of SiPMs coupled to Ce:GAGG and studying the effect of the different number of SiPMs on the energy resolution of the detector. Energy-resolution contrast experiments between Ce:GAGG and NaI(Tl) were performed using this scheme. The experimental results demonstrate that increasing the number of SiPMs enhances the energy resolution of the detector significantly. Notably, the energy resolution of the Ce:GAGG detector is comparable to that of the NaI(Tl) detector. Additionally, both detectors exhibit an energy linearity exceeding 99.9%. .

Performance simulation and structure design of Binode CdZnTe gamma-ray detector

A new electrode structure CdZnTe(Cadmium Zinc Telluride) detector named Binode CdZnTe has been proposed in this paper.Together with the softwares of MAXWELL,GEANT4,and ROOT,the charge collection process and its gamma spectrum of the detector have been simulated and the detector structure has been optimized.In order to improve its performance further,Compton scattering effect correction has been used.The simulation results demonstrate that with refined design and Compton scattering effect correction,Binode CdZnTe detectors is capable of achieving 3.92%FWHM at 122 keV,and 1.27%FWHM at 662 keV.Compared with other single-polarity(electron-only) detector configurations,Binode CdZnTe detector offers a cost effective and simple structure alternative with comparable energy resolution.

Method for converting in-situ gamma ray spectra of a portable Ge detector to an incident photon flux energy distribution based on Monte Carlo simulation

A matrix stripping method for the conversion of in-situ gamma ray spectrum, obtained with portable Ge detector, to photon flux energy distribution is proposed. The detector response is fully described by its stripping matrix and full absorption efficiency curve. A charge collection efficiency function is introduced in the simulation to take into account the existence of a transition zone of increasing charge collection after the inactive Ge layer. Good agreement is obtained between simulated and experimental full absorption efficiencies. The characteristic stripping matrix is determined by Monte Carlo simulation for different incident photon energies using the Geant4 toolkit system. The photon flux energy distribution is deduced by stripping the measured spectrum of the partial absorption and cosmic ray events and then applying the full absorption efficiency curve. The stripping method is applied to a measured in-situ spectrum. The value of the absorbed dose rate in air deduced from the corresponding flux energy distribution agrees well with the value measured directly in-situ.

Geant4 analysis and optimization of a double crystal phoswich detector for beta–gamma coincidence detection

In this study, a novel phoswich detector for beta–gamma coincidence detection is designed. Unlike the triple crystal phoswich detector designed by researchers at the University of Missouri, Columbia, this phoswich detector is of the semi-well type, so it has a higher detection efficiency. The detector consists of BC-400 and NaI:Tl with decay time constants of 2.4 and 230 ns, respectively.The BC-400 scintillator detects beta particles, and the Na I:Tl cell is used for gamma detection. Geant4 simulations of this phoswich detector find that a 2-mm-thick BC-400 scintillator can absorb nearly all of the beta particles whose energies are below 700 keV. Further, for a 2.00-cmthick NaI:Tl crystal, the gamma source peak efficiency for photons ranges from a maximum of nearly 90% at 30 keV to 10% at 1 MeV. The self-absorption effect is also discussed in this paper in order to determine the carrier gas' s influence.

Microstructural Investigation of PM-355 Nuclear Track Detector Subjected to Low-Dose Gamma Irradiation: A Positron Annihilation Lifetime Study

Samples of the PM-355 polymeric solid state nuclear track detector were exposed to low gamma absorbed doses from 1 kGy (0.1 Mrad) up to 9 kGy (0.9 Mrad). Positron annihilation lifetime (PAL) in conjunction with transmission electron microscopy (TEM) and Thermo-gravimetric analysis (TGA) were performed on irradiated and pristine samples at room temperature. The observed lifetime spectra were resolved into three components where the ortho-positronium (o-Ps) lifetime component was associated with the pick-off annihilation of positronium trapped by the free volume. PAL studies of irradiated PM-355 samples showed that ortho-positronium (o-Ps) lifetime increases with an increase in dose up to 4 kGy and decreases at higher doses. In contrast, the intensity of the o-Ps component, I3, decreases with the dose up to about 2 kGy, followed by a much smooth decrease up to 7 kGy, and then it levels off. TGA analysis indicated that the PM-355 detector decomposed in one main breakdown stage. These results are discussed on the basis of chemical and physical changes occurring at the microscopic level in the PM-355 due to irradiation. Crosslinking dominates for doses between 1 and 4 kGy, while the degradation mechanism (Chain scission) prevails for doses up to 9 kGy.

Gamma-Index Passing Rates in Baseline Plans Measured with a Detector Array

Purpose: This study provides a simple protocol for validation of the gamma passing rates and to identify the optimum values of % dose and mm criteria for dose distributions measured with a detector array. Methods: We chose ArcCHECK detector array to illustrate the concepts. We used plans with uniform or quasi-uniform dose distributions along the detector array for testing in the presence of dose errors. For testing sensitivity to spatial shift we employed a plan with approximately constant dose gradient along the axis of the instrument. Results: We identified a representative set of parameters which describe performance of a detector array. We determined the minimum gamma-index acceptance criteria allowing the passing rates to reach 100% in the absence of errors, and identified the minimum fully detectable errors for such criteria. For our baseline plans delivered to ArcCHECK, 100% passing rates were obtained for 1.5% dose criterion together with ±3% minimum error detectable at 100% rate, and for 1.5 mm criterion together with the minimum fully detectable error of ±3 mm. We inspected the impact of selected program options on the passing rates. Conclusions: The protocol we developed provides a simple method of commissioning-style analysis of a detector array without a need for analysis of a large number of clinical plans.

Design and gamma sensitivity measurement of a novel dual-emitter vacuum Compton detector

A novel dual-emitter vacuum Compton detector （D-VCD） with higher gamma ray detecting efficiency is proposed. The emitters are made of Ta A1 clad metal. The gamma ray sensitivity is studied by Monte Carlo simulation using the MCNP code. A comparison between calculations and results measured by using the 1.25 MeV gamma ray of Co-60 is also performed. Experimental sensitivities for two sample D-VCDs with the same materials and structures are 1.92×10^-20 and 2.02×10^-20·cm^2/MeV separately, which are consistent with the simulation result of 1.98×10^-20·cm^2/MeV and are 4 times higher than that of VCD with a single Fe emitter. According to the simulation results, in a gamma energy range from 0.5 to 3 MeV, the maximum sensitivity variance for the D-VCD is less than 15%, and less than 5% in a range from 1 to 2 MeV in particular. The novel D-VCD is applicable to the detection of intense pulse gamma rays.

Determination the Effect of Gamma Radiation and Thermal Neutron on PM-355 Detector by Using FTIR Spectroscopy

The effect of gamma on nuclear track detector type PM-355 (at the dose range 200 to 1600 kGy) and thermal neutron (flux 105 n·cm-2·s-1) was calculated by using of two irradiation methods. First method (G + N) was an irradiation PM-355 detector by gamma radiation and then irradiation by thermal neutrons, and another method (N + G) was irradiated by thermal neutrons and then gamma radiation. FTIR-spectroscopy was used to measure the change in deferent of transmission percent ΔT% at the wavenumber 1260 cm-1 with wavenumber 2962 cm-1 [ΔT%]1260-2962 and wavenumber 1138 cm-1 [ΔT%]1260-1138. The values of [ΔT%]1260-2962 and [ΔT%]1260-1138 were increasing with the increase of gamma irradiation with maximum response at 820 kGy and then drop after this dose until to 1600 kGy. This study determined the linear equations relation between the effect of gamma radiation on PM-355 detector and the change of [ΔT%]1260-2962 and [ΔT%]1260-1138, and this change appeared in (N + G) irradiation method better than in (G + N) irradiation method. The appearance of wavenumber 2964 cm-1 in (G + N) irradiation method referred to alkyl asymmetry C-H bond stretched out of skelated plane after changes in chemical structure of PM-355 detector by gamma or neutrons radiation.

Design of a new vacuum Compton gamma-ray detector with clad metal electron-converter plate

A newly designed vacuum Compton gamma-ray detector with Ta-Al clad-metal electron converter plate is described. The detecting efficiency for 1.25 MeV gamma-ray is 7.85×10-3 electron/γ,which is 2.5 times higher than that with Fe converter plate. The designed detector has the merits of well processed and static vacuum keeping and can be used for intense pulsed gamma ray detecting.

Study of CdZnTeSe Gamma-Ray Detector under Various Bias Voltages

Cadmium zinc telluride selenide (CdZnTeSe) is a new semiconductor material for gamma-ray detection and spectroscopy applications at room temperature. It has very high crystal quality compared to similar materials such as cadmium telluride and cadmium zinc telluride. The consistency of peak position in radiation detection devices is important to practical applications. In this paper, we have characterized a CdZnTeSe planar detector for bias voltages in the range of -20 V to -200 V and amplifier shaping time of 2, 3 and 6 μs. The peak position of the 59.6-keV gamma line of 241Am becomes more stable as the absolute value of the applied voltage increases. The best energy resolution of 8.5% was obtained for the 59.6-keV gamma peak at -160 V bias voltage and 3-μs shaping time. The energy resolution was relatively stable in the -120 V to -200 V range for a 6-μs shaping time. Future work will be focused on the study of the peak position and energy resolution over time.

Uranium Series Disequilibrium and Precision Measurement of Radionuclides Activity in Sediment Sample Using Low Background Gamma Spectrometry

Low background gamma spectrometry was used to measure the radionuclides activity of 238U, 232Th, and 235U series as well as 40K and 137Cs in a sediment sample. The goal of the study was to measure the 238U (63.3 keV peak of 234Th;1001 keV peak of 234mPa) and 235U (143.76 keV, 163.33 keV, and 205.31 keV peaks) activity by low background gamma spectrometry in sediment sample. 235U activity in environmental samples is difficult to accurately measure by gamma spectrometry due to its low abundance in nature and low gamma line intensities at 143.76 keV, 163.33 keV, and 205.31 keV. We have shown that by using low background gamma spectrometry, it is possible to accurately measure the 235U activity in sediment samples. The 235U activity was measured without using the major peak of 185.7 keV (Iγ = 57.2%) which requires interference correction from 186.21 keV of 226Ra. 226Ra activity was determined by measuring 222Rn daughters (214Pb and 214Bi). The precision and accuracy of the gamma activity measurement in the sediment sample were verified by using the HPGe detectors with Certified Reference Material (CRM) Irish Sea Sediment (IAEA-385). The results obtained for the 63.33 keV energy line of 234Th are compared with the 1001 keV energy line of 234mPa. The values of 238U and 235U activities, as well as 40K, 137Cs, and 226Ra, agreed with the certificate values of CRM. The results show that the 238U is in equilibrium with its daughters (234Th, 234mPa, and 210Pb). 232Th is also in equilibrium with its daughters (228Ra, 212Pb, 212Bi and 208Tl). 235U/238U activity ratio of 0.046 ± 0.007 in the sediment is constant in nature but fluctuates due to geological processes. A value of 0.055 ± 0.008 was found in our sediment sample.

伴随粒子中子检测系统发展及应用

基于快中子技术的无损检测方法能够在不对检测物造成影响的情况下,发现其隐藏的危险品。利用D-T反应时伴随中子产生的反冲α粒子对有效中子进行标记,可大幅提高中子探测信噪比,同时通过空间分辨α粒子还可以获得被检测对象特征元素的空间信息,所以基于伴随α粒子的中子检测方法在安检领域具有重要的应用前景。本文简单介绍了基于伴随α粒子中子检测方法的原理和系统组成,并对系统的中子管、α粒子探测器和γ探测器等关键部件进行了介绍,接着介绍了目前世界上正在研究的伴随α粒子中子检测系统及其进展,最后对这种检测方法进行了展望。

SiC探测器的中子和γ性能测试

第三代SiC半导体探测器具有体积小、响应时间快、中子/伽马(n/γ)甄别容易等优点,广泛应用于反应堆堆芯剂量监测。本文针对自研的第三代SiC半导体探测器,采用电子束蒸发真空镀膜的技术将中子转换层材料^(6)LiF(^(6)Li丰度为95%)喷镀到SiC基底上,厚度为25μm,实现了中子转换层厚度优化。利用^(241)Amα放射源(活度9.37×10^(3)Bq)开展α粒子响应信号幅度的测量,并在^(137)Csγ放射源(活度6.23×10^(7)Bq)环境下开展γ射线的响应测试。另外,在标准辐射场系统中进行了SiC探测器的中子注量率响应线性度测量、γ剂量率响应线性度测量以及中子注量率响应线性标定。结果表明:该探测器在1×10^(3)~1×10^(6)cm^(−2)·s^(−1)中子注量率范围内线性响应拟合R^(2)=0.9969,具有良好的线性响应,n/γ剂量响应范围为0.005~20 Gy∙h^(−1),可用于核电现场反应堆中子和γ剂量的实时、精确监测。

面向行星表面元素测量的小型化伽马谱仪原理样机设计

对行星表面物质受宇宙射线激发或天然衰变而产生的伽马射线进行探测,是一种测量行星表面主要元素成分及其空间分布的可靠技术手段,已被多个行星探测任务采用。提出了将CZT探测器与SiPM读出闪烁晶体相结合的行星元素伽马谱仪方案,该方案兼具低能段的高能量分辨率和高能段的高探测效率,同时可以减小来自非探测方向伽马背景的影响,且具有较小的体积、重量和功耗。为进行初步的技术路线验证,设计了一个将CZT阵列(单个灵敏尺寸1 cm×1 cm×0.5 cm)与BGO探测器(晶体的主体尺寸8.4 cm×8.4 cm×4 cm)相结合的小型化伽马谱仪原理样机,并开展了物理模拟。完成了前端探测器模块、数据处理模块和FPGA控制逻辑的设计实现,以及原理样机的组装。使用放射源、上海光源激光伽马光束线和中子激发伽马对谱仪进行了测试,CZT探测器对^(137)Cs@662 keV伽马射线的能量分辨率(FWHM)为2.1%,可以较好地分辨低能伽马射线,BGO晶体能够较好地探测和分辨高能伽马射线。该方案为未来小型化行星伽马谱仪的工程设计提供了参考。

中波碲镉汞光伏探测器的实时gamma辐照效应（英文）

对中波碲镉汞光伏探测器进行了实时gamma辐照效应研究.通过在辐照过程中对器件的电流—电压特性曲线进行测试,得到了器件电学性能随着gamma辐照剂量的变化.研究发现器件在辐照过程中表现出两种典型的辐照效应:电离效应和位移效应.电离效应可以通过辐照过程中类似光电流的产生来表现出来,而位移效应则通过辐照过程中器件串联电阻的增加来体现.两种效应都表现为总剂量效应.分析认为,由于位移效应引入的辐照损伤随着辐照剂量的增加越来越多,辐照电离效应产生的自由载流子产额随之逐渐降低,说明随着辐照剂量增加,电离效应逐渐降低,而位移效应则逐渐增强,导致器件性能衰退.

Determination of Gamma point source efficiency based on a backpropagation neural network

Efficiency is an important factor in quantitative and qualitative analysis of radionuclides, and the gamma point source efficiency is related to the radial angle,detection distance, and gamma-ray energy. In this work, on the basis of a back-propagation(BP) neural network model,a method to determine the gamma point source efficiency is developed and validated. The efficiency of the point sources ^(137)Cs and ^(60)Co at discrete radial angles, detection distances, and gamma-ray energies is measured, and the BP neural network prediction model is constructed using MATLAB. The gamma point source efficiencies at different radial angles, detection distances, and gamma-ray energies are predicted quickly and accurately using this nonlinear prediction model. The results show that the maximum error between the predicted and experimental values is 3.732% at 661.661 keV, 11π/24, and 35 cm, and those under other conditions are less than 3%. The gamma point source efficiencies obtained using the BP neural network model are in good agreement with experimental data.

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.

Dosimetric Comparison of Amorphous Silicon EPID and 2D Array Detector for Pre-Treatment Verification of Intensity Modulated Radiation Therapy

Purpose: To study the dosimetric characteristics of amorphous silicon Electronic Portal Imaging Device EPID and 2D array detector for dose verification of radiotherapy treatment plans, and the quality assurance QA testing of IMRT was investigated. Materials and methods: All measurements were done with Varian IX linear accelerator, aSi-1000 EPID and 2D array detector. The dose linearity, reproducibility, output factors, dose rate, SDD and response with slap phantom thickness have been measured and compared against those measured by ion chamber. Results: The characteristics of EPID and 2D array: the response of EPID agreed with 2D array and ion chamber 0.6cc. EPID and 2D array showed short-term output reproducibility with SD = 0.1%. The dose rates of 2D array SD = ±0.7%, EPID = ±0.4% compared with a 0.6 cc SD = ±0.5%. Output factor measurements for the central chamber of the EPID and 2D array showed no considerable deviation from ion chamber measurements. Measurement of beam profiles with the EPID and 2D array matched very well with the ion chamber measurements in the water phantom. The EPID is more sensitive to lower energy photons by increasing solid water phantom thickness. The mean and standard deviation passing rates (γ%≤1) for film, 2D array and EPID for 30 IMRT fields of five patients were 95.93 ± 0.96%, 99.05 ± 0.24%, and 99.37 ± 0.12%, respectively. Conclusion: The study shows that EPID and 2D array are a reliable and accurate dosimeter and a useful tool for quality assurance. We found that the EPID was more accurate compared with both 2D array and ion chamber. The gamma criterion of 3%/3 mm is the most suitable criteria for IMRT plans of QA.

Collimated LaBr_3 detector response function in radioactivity analysis of nuclear waste drums

The properties of a Lanthanum bromide(LaBr3)detector and its response functions were investigated via experiments and simulations in this paper.The LaBr3detector had good relative energy resolution and higher efficiency than a high-purity germanium detector.Monte Carlo and other numerical methods were used to calculate the efficiencies of a LaBr3detector with a square collimation window.A model of the numerical method was established based on a pure geometric model that was consistent with the experimental situation.The results showed that the detector response functions calculated by these methods were in great agreement with experimental results.