能量色散X射线分析中对中厚靶的吸收校正

本文讨论了在能量色散X射线荧光分析中影响准确定量的厚靶基体吸收效应,着重研究了中厚靶的吸收校正方法。以头发样品为例,分别介绍了采用辐射体测得吸收校正系数和化学加入法测得经校正后的相对灵敏度等方法,建立了正确分析中厚靶样品的定量方法和计算程序。比较各种修正方法之间的一致性好于5％。     

Surface roughness correction in thick target pixe analysis

The influence of surface roughness upon the thick target correction function used in routine PIXE analysis is considered. New absorption parameters are deduced from data generated by the Monte Carlo method. The correction proposed due to surface roughness can be used for a surface roughness corresponding up to one half of the proton range.     

Neural network-based matrix effect correction in EDXRF analysis

In this paper we discuss neural network-based matrix effect correction in energy dispersive X-ray fluorescence (EDXRF) analysis, with detailed algorithm to classify the samples. The method can correct the matrix effect effectively through classifying the samples automatically, and influence of X-ray absorption and enhancement by major elements of the samples is reduced. Experiments for the complex matrix effect correction in EDXRF analysis of samples in Pangang showed improved accuracy of the elemental analysis result.     

核电厂气态流出物监测样品分析中的核素衰变校正应用探讨

在放射性样品分析工作中,样品测量阶段、闲置阶段、采样阶段都涉及到核素衰变校正。根据放射性核素的衰变规律,阐明了这三种类型的衰变校正方法原理及其系数的计算。针对核电厂气态流出物中短半衰期的放射性惰性气体和碘核素的监测分析工作,研究了对监测样品分析结果进行衰变校正的必要性。基于实验测量结果,探讨了衰变校正对γ能谱分析法中核素的活度浓度探测下限的影响。介绍并分析了核电厂气态流出物监测样品分析工作中的衰变校正方案,对于短半衰期放射性惰性气体和碘核素,采用合理保守的衰变校正方案,可减少监测分析中的偏差,同时又可保证统计排放量的偏保守性。     

地质样品中痕量铑的火试金预富集中子活化分析

简述了铅试金和镍锍试金富集地质样品中痕量铑的分离方法,并结合中子活化分析测量了5种地质标准物质中铑的含量。铅试金法的流程回收率（n=4）为81.5%±1.2%;镍锍试金法的流程回收率（n=6）为75.1%±3.9%,对简单化学标准和地质标准物质基体,铑的回收率相近。对5种地质标准物质中铑含量的分析结果与标准值在不确定度范围内一致。铅试金中子活化法可实现10^－9铑含量的准确测量,镍锍试金中子活化法可实现10^－10铑含量的准确测量。对两种富集方法中的干扰因素进行了讨论,并对铅的自吸收效应进行了修正。探测极限的计算结果表明：镍锍试金预富集并用平面锗探测器测量,可获得更好的分析灵敏度。     

Use of rutherford scattering on a secondary carbon target for correcting intermediate thickness sample PIXE measurements

A method is presented for correcting PIXE measurements on intermediate thickness targets. The correction deals with the X-ray attenuation and the incident proton energy loss. It is based on the simultaneous acquisition of the PIXE spectrum along with the energy distribution of protons elastically scattered by a thin secondary carbon foil located behind the PIXE target. These measurements allowed a linear correlation between the proton energy loss ΔE and the correcting factor for X-ray absorption XF to be demonstrated.The validity of these simplifying linear approximations is discussed. The method is applicable to inhomogeneous thickness samples like aerosol impactor stages.     

CORRECTION OF INFLUENCE OF SUBSTRATE ON MEASUREMENT OF INNER SHELL IONIZATION CROSS SECTIONS

The energy spectra of reflected electrons from the substrates of targets have been calculated by the bipartion model of electron transport,the contributions of the inner shell ionization events produced by the reflected electrons from the substrates in the targets to the x-ray counting in a Si(Li) detector have been estimated.It has been confirmed that,by such correction to the measured data.the experimental results of inner shell ionization cross sections by electron impact with fine precision may be obtained under the conditio of thick substrate.     

Proton-induced γ-ray analysis of lithium in thick samples

A method for proton-induced γ-ray analysis (PIGE) of Li (either elemental or isotopic composition) in thick samples is presented in this work, which is based on a code that integrates the nuclear reaction excitation function, measured at the same experimental conditions, along the depth of the sample. The energy steps needed to define accurately the excitation function are used as energy intervals for the integration procedure. The excitation function and cross-sections of the reaction ⁷Li(p,p^′γ)⁷Li, for protons in the energy range 0.60–2.5 MeV, were obtained and used as input to calculate lithium concentrations in thick and intermediate samples. The calculated thick target yields of samples with several amounts of lithium were compared with the respective measured yields, showing that this is a reliable and accurate method for PIGE analysis of Li in thick samples.     

体源的γ射线自吸收校正

测定了＾２４１Ａｍ圆柱状体源的自吸收校正因子，用此实验值对两种自吸收校正计算方法所给出的理论计算值作了比较，并对结果进行了探讨。     

γ射线自吸收修正因子精确计算方法研究

对具有一定几何尺寸的样品进行γ谱分析时,样品自身对γ射线的吸收影响对核素含量的精确测量。本文在对比国内外关于自吸收修正因子计算方法的基础上,分析了被广泛采用的简化计算模型存在的问题及对修正结果的影响。基于混合蒙特卡罗模拟的思想,提出了自吸收修正因子的精确计算模型,并使用FORTRAN程序进行了随机抽样和积分计算,得到精确的自吸收修正因子。通过加标样品及不同质量标准源的对比测量,将精确计算模型与简化计算模型和无源效率校准软件计算结果进行了对比分析。结果表明,简化计算模型过高评估了自吸收干扰,而精确计算模型计算结果与实验测量结果及无源效率校准软件计算结果具有较好的一致性,相对偏差不大于5%。最后针对核电厂周围环境中主要关注的γ核素,使用精确计算模型得到了不同γ核素在土壤中的自吸收修正因子。     

The analysis of thick target metal alloys

The application of proton induced X-ray emission (PIXE) for elemental analysis of metal alloys was studied. A simple correction function is introduced, which takes into account thick target effects. Calibration standards are thus avoided and the concentrations are obtained from X-ray production cross sections. The method was tested and good agreement was found between the reference and measured concentrations.     

Quantitative analysis of cascade impactor samples – revisited

Concentrations of aerosols collected in Singapore during the three months long haze period that affected the whole South-East Asian region in 1997 are reported. Aerosol samples were continuously collected by using a fine aerosol sampler (PM2.5) and occasionally with a single orifice cascade impactor (CI) sampler. Our results show that in the fine fraction (<2.5 μm) the concentrations of two well-known biomass burning products, i.e. K and S were generally increased by a factor 2–3 compared to the non-hazy periods. However, a discrepancy was noticed, at least for elements with lower atomic number (Ti and below) between the results obtained by the fine aerosol sampler and the cascade impactor. Careful analysis by means of Nuclear Microscopy, in particular by the Scanning Transmission Ion Microscopy (STIM) technique, revealed that thicknesses of the lower CI stages exceeded thick target limits for 2 MeV protons. Detailed depth profiles of all CI stages were therefore measured using the STIM technique and concentrations corrected for absorption and proton energy loss. After correcting results for the actual sample thickness, concentrations of all major elements (S, Cl, K, Ca) agreed much better with the PM2.5 results. The importance of implementing thick target corrections in analysis of CI samples, especially those collected in the urban environments, is emphasized. Broad beam PIXE analysis approach is certainly not adequate in these cases.     

BRISOL钾同位素放射性核束的产生

北京放射性核束装置在线同位素分离器（BRISOL）采用一台100 MeV回旋加速器提供的最大200 μA的质子束打靶在线产生放射性核束,其最高质量分辨率好于20 000。2015年,BRISOL装置建成并使用05 μA质子束轰击氧化钙靶产生了37K+、38K+放射性核束,其中38K+的产额为1×106 pps。为了提高氧化钙靶产生钾放射性核束的产额以满足物理用户需求,BRISOL于近期开展了氧化钙靶的在线实验。实验中使用氧化钙靶产生了36～38K+、43K+、45～47K+等多种放射性核束,同时将38K+的最大产额提高到了112×1010 pps。本文详细介绍氧化钙靶的研制及在线实验结果。     

A critique of inverse solutions to slab geometry transport problems

An inverse transport problem requires determination of the angular scattering and absorption coefficients of the medium using measurements of the intensity. Methods for solving such a problem for monoenergetic transport in a thick homogeneous (i.e. multiple-scattering) slab medium are critiqued. The methods include those that require local measurement of the intensity inside the slab plus remote measurement of the angular distributions entering and leaving (the local-&-remote methods) and those (remote methods) that require only the surface angular distributions. The possible use of these methods to determine the properties of a multi-layer slab medium is also examined.     

Analysis of sulphur with external beam proton induced gamma-ray emission analysis

Applicability of the ³²S(p, p′ γ)³²S reaction for sulphur analysis as a complementary method to PIXE has been investigated. The optimum energy region for the bombarding protons has been determined for both thick samples and for thin atmospheric aerosol samples. By optimizing the external beam method, sulphur concentrations at the 100 ppm level for thick organic samples and at the 100 ng/cm² level for aerosol samples are detectable.     

PESA as a complementary tool to PIXE at CTU Prague

Proton Elastic Scattering Analysis (PESA) is a simple convenient method for hydrogen analysis in thin samples. A Proton Induced X-ray Emission (PIXE) target chamber was equipped with a PIPS detector for detection of forward-scattered protons. One of the objectives was to perform PIXE and PESA analyses of air particulate targets simultaneously. Tests and calibrations were fulfilled mainly with Mylar foils 1.5–6.5 μm thick in the proton energy region between 1.35 and 2.3 MeV. The energy dependence of scattering cross section is different from the Rutherford formula. Comparison of PIXE/PESA analysis with the Guelph Scanning Proton Microprobe Laboratory at the University of Guelph, Canada on seven aerosol samples was carried out. The intercomparison results validated our PESA/PIXE quality assurance protocol. In addition, repeated measurements of Gelman Teflo^TM filters indicated a gradual increase of hydrogen content by 1 ng/cm² per 1 μC/cm² proton dose.     

Stopping power of 11B in Si and TiO2 measured with a bulk sample method and Bayesian inference data analysis

The popular stopping power interpolative schemes require experimental data to be developed. Where the data bases are sparse, with few experiments available, interpolations can be more inaccurate. This is the case for the stopping of heavy ions, where even for important targets such as Si there is a need for more measurements. For compounds, the situation is even worse with very few measurements available. In particular, the stopping in oxides and nitrides often deviates significantly from what would be expected using the Bragg’s rule. We apply a method that uses bulk or thick film samples to determine the stopping power of ¹¹B in Si and TiO₂. The method, which relies on Bayesian inference analysis of RBS spectra obtained at different energies, has been previously validated by verifying the results obtained in the well-known system ⁴He in Si.     

Application of linear-extended neutron diffusion equation in a semi-infinite homogeneous medium

The linear-extended neutron diffusion equation (LENDE) is the volume-averaged neutron diffusion equation (VANDE) which includes two correction terms: the first correction is related with the absorption process of the neutron and the second is a contribution to the neutron diffusion, both parameters are related to neutron effects on the interface of a heterogeneous configuration. In this work an analysis of a plane source in a semi-infinite homogeneous medium was considered to study the effects of the correction terms and the results obtained with the linear-extended neutron diffusion equation were compared against a semi-analytical benchmark for the same case. The comparison of the results demonstrate the excellent approach between the linear-extended diffusion theory and the selected benchmark, which means that the correction terms of the VANDE are physically acceptable.     

The measurement of pre-equilibrium heavy ion energy loss

A method is described for the measurement of pre-charge-state-equilibrium energy losses of heavy ions in solid targets. Preliminary results for 130 MeV ³⁵Cl incident on carbon targets between 3 and 130 μg/cm² thick are reported to demonstrate the techniques. The results are described in terms of the Bethe formula for energy loss.