X光管滤光片效应的蒙特卡罗仿真

在X射线荧光分析中,使用滤光片可有效降低原级光谱本底对待测元素的干扰,提高分析灵敏度。本文采用MCNP5方法仿真X光管滤光片对原级谱线的影响,比较了滤光片对不同能量电子束产生的X射线谱的差异,分析了不同滤光片材料及厚度与X射线原级谱衰减的关系,得到不同滤光片对X射线谱的衰减规律。     

X射线荧光分析中原级谱分布的计算

X射线荧光分析中,X射线管产生的原级谱的分布对荧光分析的影响很大。尤其是在元素间吸收增强效应的校正过程中,基本参数法要求准确获得X射线原级谱的强度分布。使用MCNP程序模拟不同加速电压、不同靶材料、不同铍窗厚度等条件下电子打靶后的X射线能谱分布,为X射线荧光分析仪研制过程优化X光管靶材、管压等提供依据,实现高精度的X射线荧光分析。     

准单能直流硬X射线装置的研制

以直流X射线光机为基础,利用元素具有特征X射线和吸收边的原理,通过设置荧光靶、滤光片,滤除不同元素K层特征线中的K_β线,研制了准单能直流硬X射线装置。该装置由直流X光机、荧光靶和滤光片组成,可产生十多种准单能X射线,X射线谱纯度大于80%,能峰宽小于3 ke V。各能点转换便利,强度可调,束流稳定性小于0.5%。该装置可部分代替放射源,用于测厚、探测器灵敏度标定、透过率标定等。     

正比计数管探测低能X射线时探测效率的MC计算

为研究各因子对正比计数管探测低能X射线时性能的影响,利用MCNP5软件计算了不同光子能量下管内气体种类、气体压强及壁效应、放置距离等因素对探测器探测效率的响应情况。结果表明正比计数管探测器对10~30 ke V X射线探测效率最佳;且在探测低能X射线时,正比计数管应尽可能靠近源项,同时管内最佳气体压强在1.515×105~2.02×105Pa之间。     

基于国产厚型气体电子倍增器的低能电子二维位置探测器

为探测0.1-50 Me V低能电子脉冲束流的位置分布,研制基于国产厚型气体电子倍增器(Thick Gaseous Electron Multiplier,THGEM)的二维位置探测器,位置分辨要求好于200μm,灵敏面积为50 mm×50 mm。THGEM的孔径为150μm、孔间距400μm、厚度100μm。用Geant4模拟了薄膜窗厚度、空气层厚度等对电子透过率和横向扩散的影响。根据模拟结果,优化了探测器的结构和设计。并用能量为5.9 ke V的X射线源55Fe测试不同工作气体的增益,单层最大增益好于1×10~4,双层最大增益好于6×10~4,能量分辨率好于23%。     

北京同步辐射装置4W1A光束线能谱测量

使用标准放射源对用于X射线测量的SDD探测器进行能量刻度。对北京同步辐射装置的4W1A实验站单色光模式下6~20 ke V的X射线能谱进行测量。测量结果表明,所测能量值与理论值偏差在3%之内,且除15 ke V外偏差随能量增加而增加。能量较低的单能X射线多次谐波现象较为严重,经过微调单色器角度,多次谐波受到抑制。并研究了本测量方法的测量精度,不同能量点精度偏差为3.1‰~1.75%。为高注量率同步辐射空气比释动能的绝对测量以及同步辐射光源的利用提供参考。     

450 kV X射线参考辐射场附加过滤初步研究

正利用蒙特卡罗程序对450kV X光机建立模型,首先计算各参考辐射质下的原级谱及平均光子能量;随后依据平均光子能量,并结合MCNP模拟结果对附加过滤进行初步研究。1光机模型建立与原级谱计算首先,依据YXLON 450kV X光机实际尺寸,经概化后利用蒙特卡罗方法建立光机模型,光机阳极靶材料为钨,靶角为30°,固有过滤为5mm Be。随后,通过电子运输得到250～450kV管电压下X射线原级谱,模拟结果如图1所示。     

X射线吸收光谱技术中的滤光片研制

在同步辐射X射线吸收光谱(XAS)实验中,X射线滤光片用于吸收样品的康普顿散射和弹性散射,改善荧光信号的质量。我们将ZnO颗粒分散在聚氨酯溶液里,通过恰当的喷涂工艺,获得ZnO滤片。X射线衍射(XRD),X射线荧光(XRF)及X射线吸收光谱(XAS)实验结果表明：在滤片制备过程中,ZnO结构保持不变。进一步地,ZnO滤片用于测量Ga2O3的GaK边XAS谱,显示出好的信噪比。采用同样的方法还制备了其它X射线滤光片,表明这种X射线滤光片制备技术的可行性和实用性。     

国产LiF(Mg,Cu,P)剂量片的X射线能量响应标定研究

针对国产Li F(Mg,Cu,P)热释光剂量片(TLD)开展了X射线能量响应的标定研究。利用标准剂量仪PTW-UNIDOS,以60Co源1.25 Me V的伽马射线为分析基础获得剂量-热释光输出之间的关系,在X射线机上通过荧光激发的方法解决单色X射线输出难题,建立了完整的标定方法。实验结果表明,对于100 ke V以下的X射线,本文封装的国产Li F(Mg,Cu,P)剂量片相对空气具有非常平坦的能量响应,能够用于脉冲X射线环境中的剂量测量要求,为器件的辐照损伤效应研究和抗辐射加固技术研究提供可靠保障。     

Si-PIN探测器灵敏体积最优厚度的MC模拟

Si-PIN探测器灵敏材料厚度影响探测时间、探测结果可靠性及设备价格。从能量响应谱的比对研究证实EGS4模拟适用于Si-PIN探测器能量色散X荧光仪的设计分析。通过不同入射X射线对不同厚度灵敏体积的Si-PIN探测器的能量响应模拟研究发现:探测器灵敏体积最优厚度随待测X射线的能量增加而变厚,厚度与特征峰计数或峰总比的饱和厚度相等。     

替代241Am低能光子源的准单色X射线机的研制

研究了用滤光片法产生50～60 keV的准单色X射线的条件,对输出的X射线进行了数种金属滤光片实验研究,选出合适的滤光片,通过实验对准直器的机械结构进行了确定。采用自行设计委托加工的X射线管、准直器和购买的高压电源,组装成符合实验要求的X射机。该装置输出了50～60 keV能量段的准单色光谱,在料位计上能替代²⁴¹Am低能光子源。     

Forward and Backward Photoemission Yields from Metals at Various X-Ray Angles of Incidence

X-ray generated photoemission from thin metal foils backed by graphite was measured with radiation incident from the front and back sides at several angles. Irradiation was provided by a 100-kV x-ray tube with three different filters to harden the spectrum. The total 2? photoelectron emission current from a surface was measured; a biased grid retarded the low-energy secondary electrons, which added only 10-30% to the current at zero grid bias. Investigated metals were: Mg, Al, Ti, Fe, Cu, Ag, Ta, Au, and Pb; also the total emission from just the graphite support was measured. The front-to-back ratio of emission currents at normal incidence ranged from about 1.9 for Al and Mg down to about 1.1 for Ta. The photoelectron yield was found to be Ge ?a Se electrons/photon, where ?a and Se are the energy-dependent photon absorption cross section and computed electron mean path length in the emitter, and Ge is a constant assumed independent of photon energy in the range studied (but does depend on radiation angle of incidence). For the photon energy range of 20-70 keV, the measured emission current densities corresponded to the following average values for ?e: 0.37 ± 0.06 for C, 0.30 ± 0.03 for Al, 0.21 ± 0.02 for Cu and Ag, and 0.18 ± 0.02 for Ta.     

高气压充氙多丝正比室

研制了一个高气压充氙多丝正比室。其灵敏面积近700cm~2,充以3个大气压的氙-甲烷混合气体(95％Xe+5％CH_4),可探测10—200keV的硬X射线。对~(241)Am的59.54keV X射线,单丝能量分辨率(FWHH)10％,全部阳极丝并联输出则为19％,对其29.8keV的逃逸峰则分别为17％和20％。在密封不流气状态下可工作数月而保持良好的能量分辨率。     

Radiation damage (blistering) in Al,Cu, Si by exposure to a plasma focus discharge

Plates of Al, Cu (polycrystalline) and Si (monocrystal) have been irradiated with beams of D⁺ ions (keV to MeV) and other radiation by exposure to a single discharge of a 5–10-kJ Plasma Focus in deuterium. Scanning electron microscope and elemental X-ray energy dispersive analysis are used for diagnostics. The nonuniformity of the ion beam causes a nonuniform damage with formation of clusters of blisters. A statistical analysis of blister parameters (diameter and skin thickness) is used to investigate the internal structure of a deuteron beam ejected from the plasma. The value K ～ 10–20 keV is obtained as the typical ion energy for the bulk of the deuterons and an ion energy E ～ 200–230 keV is typical for individual ion groups (ion strings) forming the high-energy deuteron beam.     

毛细管X光透镜聚焦的微束X射线荧光谱仪的研发及应用

针对不同样品的分析需求,本文设计了几种不同类型的微束X射线荧光谱仪。用高精度激光位移传感器实时校正样品表面被测量点与毛细管透镜出端之间的距离,以减少形状不规则的古陶瓷样品测量时带来的误差;利用毛细管X光透镜传输能量高于25 keV的X射线效率低的特点,将其应用于高铅釉瓷器彩料的无损分析中;采用大功率X射线源,扫描分析了大米中K、Ca等元素分布;以人民币5角硬币为例,研究了能量色散的微束X射线衍射方法。研究结果表明,本文研发的微束X射线荧光谱仪在生物样品和文物样品的分析研究中有广泛的应用前景。     

滤光片及X射线二极管响应面均匀性研究

介绍了用于软X光能谱测量的滤光片及X射线二极管能量应均匀性研究。实验利用北京同步辐射装置3WIB束线,流强40－80mA的运行条件,在100－1600eV能区对滤光片及X射线二极管（XRD）作能响曲线标定。重点对C滤片及Al阴极XRD的灵敏面作能响面均匀性研究,最后给出响应面均匀性测量结果及计算分析。     

Performance improvement of the filter-type ‘transXend’ energy-resolving detector by considering noise sensitivity

The filter-type ‘transXend’ detector is an energy-resolving X-ray detector consisting of an energy-integrating flat-panel detector and multiple filters. In our previous studies, we have shown the effectiveness of the transXend detector, but the filters used were not optimized. To obtain better performance, the filters, especially their thickness and material, should be considered. In this paper, we present a method that can preliminarily estimate filter performance by comparing their noise sensitivity before carrying out numerous experiments. Two kinds of filter sets, Cu–Sn and W–Ag, with various thicknesses were evaluated. The results suggest that to image a 20-cm-thick object with 120-kV X-rays, an unfiltered channel and a channel filtered with 0.5-mm-thick Sn or 0.4-mm-thick Ag may be the best combination. The optimal filter thickness will be smaller if the object is thinner and the tube voltage is lower. For applications that require a wide dynamic range of detector response, a channel with a W filter may be better than an unfiltered channel. To verify the calculation results, computed tomography imaging experiments with a 3-cm-diameter phantom were also performed, and the experimental results showed good agreement with the calculation results.     

四路并联二极管辐射X射线场参数计算

利用二极管的电压、电流计算了发射电子束能谱参数,建立了四路并联二极管阳极靶蒙特卡罗粒子输运计算模型,给出了辐射X射线场参数;将四路并联二极管的每个二极管划分为若干小单元,将其作为点源,采用数值积分的方法计算了辐射X射线剂量分布,并分析了空间不同位置处每路二极管对剂量的贡献。结果表明:真空中,距离四路并联二极管阳极靶5cm位置处,X射线注量为3.55mJ/cm2,光子平均能量为62.18keV,120keV以下的光子占辐射X射线谱总能量的81.84%,电子束转换效率为0.30%;在2 700cm2范围内,中轴线和对角线上的剂量均匀性分别为3.20和6.31;在2 000cm2范围内,中轴线和对角线上的剂量均匀性均小于2。     

Si(Li) Detector efficiency below 10 keV

The full-energy peak efficiency of a Si(Li) detector has been experimentally determined over the photon energy range 3–26 keV for use in accurate ion-induced X-ray cross-section measurements. The efficiency uncertainties are ± 2% to ± 4% for 4.5–9.9 keV photons — the energy region of primary interest in the present work. The techniques utilised are described in detail since it was found that the use of absolute theoretical efficiencies can lead to errors in excess of 30% over the whole efficiency curve with even greater errors appearing below about 3 keV. Recent electron-capture data are used to calculate the yield of 3.1 keV Ag L X-ray from the decay of a calibrated ¹⁰⁹Cd source in order to extend the efficiency curve down to 3 keV. The use of fluorescence sources as a novel way of accurately measuring efficiencies in the photon energy region 1–4 keV is outlined.