30~160keV单能X射线装置的单色性实验研究

单能X射线光源是由X射线光机、双晶单色器、标准探测器以及准直系统组成。X射线光机产生的连续X射线,通过与双晶单色器发生布拉格衍射完成单色化,调节不同的特定布拉格角度得到能量范围30~160keV的单能X射线。为了研究标定装置的能量展宽,需要对该装置产生的单能X射线的能量分辨率进行研究。结果表明Si(220)晶体产生的单能X射线的能量分辨率为0.91%@30keV和2.3%@70.6keV,Si(551)晶体为1.97%@80.1keV和3.45%@142.6keV。使用这套装置对溴化镧晶体探测器的能量响应进行校准验证,实验发现该装置的能量分辨率良好,可以应用在多种类型探测器的标定实验、X射线质量衰减系数测量以及多层膜反射率测量等领域。     

同步辐射单能X射线空气质量衰减系数的测量

介绍了3种X射线空气质量衰减系数的测量方法:移动距离法、抽真空法、EGSnrc蒙特卡罗模拟计算法。给出了抽真空法中真空管内空气质量厚度改变量的计算公式,并模拟分析了真空管Be窗对实验的影响。移动距离法与抽真空法得到的结果较接近,验证了抽真空法实验的合理性。当X射线能量为6 keV、20 keV时,EGSnrc蒙特卡罗模拟计算结果与NIST标准数据库数值偏差分别为0.01%、0.26%。     

热释光剂量计刻度过程中有关电子平衡的Monte-Carlo模拟计算与实验验证

采用Monte-Carle模拟和实验测量的方法,开展在不同能量X射线辐照时LiF(Mg,Cu,P)热释光剂量计(TLD)达到电子平衡所需补偿材料厚度的研究.实验结果表明:模拟计算和实验测量的结果符合较好,在X射线有效能量为83 keV、118 key、208 keV时,均需在TLD照射面添加一定厚度的补偿材料,且厚度随能量不断增加.     

热释光剂量计测量X射线半值层法初步探讨

随着国内X光机数量的迅速增多,简易有效的X光机半值层(HVL)质量检测方法也越来越重要。使用Penelope软件模拟N80(65keV)、N100(83 keV)、N150(118keV)、N200(164keV)重过滤窄谱辐照场中氟化锂热释光(LiF(Mg,Cu,P))剂量计在不同铜过滤片厚度下的能量沉积,分析计算得到X光机HVL; 通过实验测量LiF在N100(83keV)3m处窄谱标准辐照场的X光机HVL,对模拟程序进行了验证。对模拟结果与标准实验室电离室测量结果进行比较表明:对于低能N80(65keV)、N100(83keV)辐照场,LiF剂量计测量X射线半值层的方法具有可行性;N150(118keV)、N200(164keV)辐照场中模拟结果与实验室给出电离法测量得到的半值层值相对误差较大,不建议直接使用LiF测量半值层。     

使用单能X射线辐射装置对CdTe探测效率的实验刻度

CdTe探测器对单能平行光子源的绝对测量之前,需要进行效率刻度。利用MCNP5蒙特卡罗模拟程序建立CdTe探测器物理模型,模拟计算了10~260keV能量段能点的本征探测效率,在10~60keV能量段探测效率高于75%。用单能X射线装置和HPGe探测器对CdTe探测器本征探测效率进行了实验刻度。结果表明,在10~100keV能量范围内CdTe探测器的模拟效率与实验效率趋势一致,最大误差不超过5.6%。因为Te元素在27keV和32keV处会产生逃逸峰,导致探测效率在这2个能量处有明显下降趋势。用241Am和133Ba放射源对CdTe探测器进行效率刻度验证,在能量为59.54keV和81keV放射源标定的探测效率与单能X射线辐射装置测量值相符。     

MC模拟高纯锗探测器准直器对X射线能谱测量的影响

为了研究不同限束光阑准直器对测量结果的影响,使用MCNP5蒙卡模拟软件建立带准直器的高纯锗探测器模型。通过模拟分析准直器各项参数对高纯锗探测器测量X射线能谱的影响,确立了准直器的最佳尺寸,为实验室使用高纯锗探测器测量X射线能谱提供一定的参考依据。计算了透射等效孔径(TEA)准直器指标,分析了高纯锗探测器测量X射线得到的探测效率。结果表明:对于能量小于80keV的低能量段X射线能谱测量,选择孔径小、屏蔽厚的准直器;对于80keV以上中高能量段的X射线应选择较大孔径的准直器,以避免由于从铅准直器中产生小角散射线和铅的特征线而影响X射线能谱的质量。     

带支撑结构的大高宽比硬X射线波带片制作

对利用X射线光刻制作大高宽比硬X射线波带片的设计和制作工艺进行了研究.采用电子束光刻制作X射线光刻掩模,并利用X射线光刻制作最终的硬X射线波带片.采用对光刻胶结构加入支撑点的方法,大大提高了X射线光刻制作硬X射线波带片的高宽比.对所加入支撑点的布置策略进行了优化,使得支撑点所占的面积比例减小.所制作的波带片最外环宽度为200 nm,厚度为2.8μm,具有优良的结构质量,预期可用于10 keV到25 keV波段,并具有优于250 nm的成像分辨率.     

6～70keV同步辐射X射线能量标定

为建立高注量率同步辐射X射线计量领域相关的国家标准,对同步辐射X射线能量标定方法进行研究。在北京同步辐射装置上选择6、10和20keV三个能量点进行实验,得到的传递探测器校准因子与辐射能量的关系曲线近似直线,变化趋势呈线性递减;在20keV能量点,不同直径光阑条件下进行的标定实验验证了传递探测器的校准因子与光源照射到基准电离室与传递探测器的光子通量有关。在上海光源上进行10～70keV能量标定实验,得到传递探测器的校准因子拟合曲线;10～20keV能量段的变化趋势与在北京同步辐射装置得到的校准因子变化趋势一致,30～70keV能量段的校准因子随着能量的增加而平稳缓慢增大。对各个能量点标定产生的A类不确定度进行评定,为后续建立国家计量标准同步辐射X射线空气比释动能量值传递体系提供了技术数据。     

γ射线线性衰减系数拟合计算方法研究

线性衰减系数是放射性体源测量中进行自吸收修正的重要参数。由于能量不同,无法用人工核素点源的透射实验获得对应于天然核素发射γ射线能量的线性衰减系数值。该文提出一种新的拟合公式和拟合方法,以便由人工核素点源透射实验获得的γ射线线性衰减系数求出被测样品在天然核素γ射线能量点的线性衰减系数。对选用的5种被测物质,分别用线性衰减系数的参考值和实测值进行拟合之后的计算结果显示,在γ射线能量为60～2 600 keV的范围内,该文提出的拟合方法计算出来的线性衰减系数的最大误差分别小于4%和10%。利用该文介绍的拟合方法,可以得到被测样品在指定能量范围内比较准确的线性衰减系数值。     

EAST水平硬X射线诊断单元研究

设计制作了用于EAST托卡马克装置水平窗口的基于CdTe探头的硬X射线诊断单元.经与EAST联机试验运行,结果表明,该诊断单元设计原理正确,空间分辨率精度及辐射屏蔽达到设计目标,能够满足测量20keV～200keY能量范围等离子体的硬X射线韧致辐射的要求.     

Calculation of radiation attenuation coefficients, effective atomic numbers and electron densities for some building materials

Some building materials, regularly used in Turkey, such as sand, cement, gas concrete (lightweight, aerated concrete), tile and brick, have been investigated in terms of mass attenuation coefficient (μ/ρ), effective atomic, numbers (Z(eff)), effective electron densities (N(e)) and photon interaction cross section (σ(a)) at 14 different energies from 81- to 1332-keV gamma-ray energies. The gamma rays were detected by using gamma-ray spectroscopy, a High Purity Germanium (HPGe) detector. The elemental compositions of samples were analysed using an energy dispersive X-ray fluorescence spectrometer. Mass attenuation coefficients of these samples have been compared with tabulations based upon the results of WinXcom. The theoretical mass attenuation coefficients were estimated using the mixture rule and the experimental values of investigated parameters were compared with the calculated values. The agreement of measured values of mass attenuation coefficient, effective atomic numbers, effective electron densities and photon interaction cross section with the theory has been found to be quite satisfactory.     

Measurements of the hard-x-ray reflectivity of iridium

In connection with the design of a hard-x-ray telescope for the Constellation X-Ray Observatory we measured the reflectivity of an iridium-coated zerodur substrate as a function of angle at 55, 60, 70, and 80 keV at the National Synchrotron Light Source of Brookhaven National Laboratory. The optical constants were derived from the reflectivity data. The real component of the index of refraction is in excellent agreement with theoretical values at all four energies. However, the imaginary component, which is related to the mass attenuation coefficient, is 50% to 70% larger at 55, 60, and 70 keV than theoretical values.     

High-Resolution Kaonic-Atom X-ray Spectroscopy with Transition-Edge-Sensor Microcalorimeters

We are preparing for an ultra-high resolution X-ray spectroscopy of kaonic atoms using an X-ray spectrometer based on an array of superconducting transition-edge-sensor microcalorimeters developed by NIST. The instrument has excellent energy resolutions of 2–3 eV (FWHM) at 6 keV and a large collecting area of about 20 mm \(^2\) . This will open new door to investigate kaon-nucleus strong interaction and provide new accurate charged-kaon mass value.     

Gamma-ray shielding properties of zinc oxide soda lime silica glasses

In the present work, the gamma ray shielding properties of zinc oxide soda lime silica, (ZnO)_x(SLS)_1?x glasses with 0 ≥ x ≥ 50 wt% have been investigated. By using WinXCom computer software, the mass attenuation coefficient (µ/ρ) and half value layer (HVL) for total photon interaction in the energy range of 1 keV–100 GeV were calculated. Furthermore and by Geometric Progression method exposure buildup factor values were calculated for incident photon energy 0.015–15 MeV up to penetration depths of 40 mfp (mean free path). The addition of zinc oxide (ZnO) into soda lime silica (SLS) glass resulted in an increase the mass attenuation coefficient and decreases both the half value layer and exposure buildup factor. The obtained results of the selected glass series have been compared, in terms of mass attenuation coefficient, half value layer and exposure buildup factor with some common shielding materials. The shielding effectiveness of the selected glasses is found comparable to that of common ones; which indicates that the SLS glasses with suitable ZnO content may be developed as gamma ray shielding materials.     

Thermophysical properties of rubidium and lithium halides by γ-ray attenuation technique

The temperature dependence of linear attenuation coefficient, density and thermal expansion of rubidium halides (RbCl, RbBr and RbI) and lithium halides (LiCl, LiBr and LiF) has been studied by γ-ray attenuation technique. The γ-ray attenuation studies have been carried out using a γ-ray densitometer. The mass attenuation coefficients (μ _m ) of rubidium and lithium halides have been determined using γ-beam of different energies viz. (0.0595, 0.662, 1.173 and 1.332 MeV) respectively. The variation of density and coefficients of temperature dependence of density have been measured using Cs (0.662 MeV) source. The values of density at different temperatures have been used to estimate the values of linear attenuation coefficients (μ _l ) of the alkali halides studied in the present work for other γ-energies. The variation of thermal expansion of alkali halides studied in the present work has been compared with the results obtained from other methods. The variation in these thermophysical properties have been represented by linear equations. Volume thermal expansion coefficients and mass attenuation coefficients (μ _m ) of these compounds for the different energies have been reported and compared with data calculated by empirical and experimental method.     

一种基于射线照相的X射线衰减系数获得方法

提出了一种通过射线照相法计算X射线在物质中衰减系数的方法,通过简单实验以及计算快速获取不同能量X射线在物质中的衰减系数。设计实验找出了底片黑度与工件厚度的关系曲线,推导出表达式,并得出表达式的可信区间。用射线照相法实测了管电压为140、130、120kV时钢质台阶试块的X射线衰减系数与理论值对比,其标准误差＜3%,证明了该方法的可靠性。射线照相法求物质衰减系数计算简单、操作便捷、误差小,有望推广应用于材料中X射线衰减系数的估算。     

A new mammography dosimetric phantom

Breast phantoms produced with tissue-equivalent materials are used in an attempt to simulate glandular and adipose tissues, in terms of X-ray attenuation and density. In this work, a set of breast tissue-equivalent phantoms (BTE phantoms) with semicircular shapes of different thicknesses and compositions were produced. Such phantoms may be used in the measurement of the incident air kerma (K(i)) and the mean glandular dose (D(G)) delivered to patients undergoing mammography. To characterise the materials used to produce the phantoms, a series of 17-keV X-ray attenuation coefficient measurements were performed. The carbon-nitrogen-hydrogen elemental composition and the densities of the tissue-equivalent materials were also determined and compared with values available in the literature. Linear attenuation coefficients of 0.724 and 0.923 cm(-1) were determined, respectively, for adipose and glandular tissues. Such values agree with data available in the literature. On the basis of the results obtained in this work, it is suggested that BTE phantoms are used instead of polymethyl methacrylate phantoms to select exposure parameters (kV, mAs and target/filter combination) specific for breast glandularities from 0 to 50 % in the optimisation of doses in mammography.