High energy resolution PIXE with high efficiency using the heavy ion microbeam

An X-ray crystal spectrometer using a position sensitive proportional counter combined with tandem microbeam line at Osaka National Research Institute have been developed. This system realizes high energy resolution PIXE analysis using a heavy ion microbeam (E < 6 MeV) with reasonable detection efficiency. The design of the spectrometer, such as detection geometry, detectable energy range and energy resolution, are described. This system was applied to high energy resolution PIXE analysis of Ti, SUS and Si with 2 MeV proton and 5 MeV Si³⁺ focused or collimated beams. The best energy resolution was 2 eV for the Si K line.     

A comparison between pixe and rbs thin film thickness measurements in binary targets

A method for measuring the thickness of a light element thin film deposited on a heavy substrate, using particle induced X-ray emission (PIXE) at low energies (below 0.7 MeV) is described. The lines detected are the L X-rays of the substrate. The procedure is explained by means of the aluminum-tungsten system. A comparison with Rutherford backscattering spectrometry (RBS) of protons is made, showing that, in the same incident energy range, the latter gives unreliable results, while PIXE is fairly accurate.     

Stoichiometric characterization of YBaCuO superconductors with nuclear probes

Nuclear probes using energetic (MeV range) charged particle irradiation and prompt detection of atomic and nuclear signals are powerful tools to determine quickly and accurately the chemical constituants of YBaCuO superconductors. PIXE in milliprobe geometry is used to determine the actual concentration ratios of Y/Ba and Cu/Ba, with an accuracy of 3% or better. Calculated matrix effects in the detection of characteristic K X-rays allow accurate determinations even when the composition of samples are very different from reference materials. RBS of 2 MeV α-particles is used to certify the homogeneity of the Y-Ba-Cu composition without reference material to a thickness of 250 μg/cm² under the surface. Deuteron microbeam irradiation leads to simultaneous composition maps of all the elements (YBaCuO) in volume of 5 × 5 × 5 μm using X-rays and protons as identification signals.     

External scanning micro-PIXE for the characterization of a polycapillary lens: Measurement of the collected X-ray intensity distribution

We developed a PIXE detection system for the analysis of medium-light elements which exploits a weakly focusing polycapillary lens for the transmission of the X-rays emitted from the target material to a Silicon Drift Detector. The polycapillary lens efficiently collects X-rays, while prevents back-scattered protons from impinging on the detector chip, thus avoiding electronics perturbation and consequent quality loss of PIXE spectra. The system is optimized for the detection of X-rays in the energy range 1–10 keV, when the emission from the target is induced by MeV proton beams with size of the order of a few hundreds of micrometers.This work reports the results of the lens characterization in terms of X-ray collection spot, i.e. the area of the sample actually “seen” by the lens, and its dependence on the X-ray energy. The lens properties have been measured using the external scanning microbeam facility of the Tandetron accelerator at LABEC-INFN in Florence. The detection system was used to detect X-rays from a set of pure elemental standards with an incident 3 MeV proton beam focused to a size of about 30 μm scanning an area of 1.9 × 1.6 mm². By measuring the spatial distribution of characteristic X-rays from each given material, the collection profile of the lens at the corresponding X-ray energy was obtained. Using several standards, the behaviour throughout the range 1–10 keV was examined. The sensitivity of the lens collection profile on the lens-sample out-of-focus distance was also investigated.     

MV级EPID成像系统中滤过板的应用

与kV级X射线成像相比,MV级电子射野影像系统(EPID)成像质量较差,图像模糊,影响患者图像定位和摆位验证的精确性。本文结合Monte Carlo模拟计算的方法,在不改变治疗靶的现有MV级EPID系统中,提出增加滤过板进行康普顿散射线的滤过,通过Monte Carlo模拟、Matlab作图、临床实验,得出在6 MV级EPID系统中,增加1层2 mm厚铜材料的滤过板,有助于成像质量的改善。     

The Columbia University proton-induced soft x-ray microbeam

A soft X-ray microbeam using proton-induced X-ray emission (PIXE) of characteristic titanium (K_α 4.5 keV) as the X-ray source has been developed at the Radiological Research Accelerator Facility (RARAF) at Columbia University. The proton beam is focused to a 120 μm × 50 μm spot on the titanium target using an electrostatic quadrupole quadruplet previously used for the charged particle microbeam studies at RARAF. The proton induced X-rays from this spot project a 50 μm round X-ray generation spot into the vertical direction. The X-rays are focused to a spot size of 5 μm in diameter using a Fresnel zone plate. The X-rays have an attenuation length of (1/e length of ∼145 μm) allowing more consistent dose delivery across the depth of a single cell layer and penetration into tissue samples than previous ultrasoft X-ray systems. The irradiation end station is based on our previous design to allow quick comparison to charged particle experiments and for mixed irradiation experiments.     

Dual detector system for PIXE measurement covering a wide element range

Two different type of X-ray detectors were used for simultaneous PIXE measurement over a wide element range. One is a pure-Si detector with a thin Be-window, which is to keep high sensitivity for the detection of low Z element. The other is a CZT detector with a thick Be window of 250 μm. It has almost 100% detection efficiency for the X-rays with high energy of up to about 80 keV. By using the CZT detector that was arranged to have a large solid angle, the detection sensitivity of the high energy X-rays of around 30 keV was enhanced by about two orders of magnitude than that by the pure-Si detector. A pair of small permanent magnet was used to sweep away the back-scattered protons from the detector. With this magnet system, the background level in the spectrum of the pure-Si detector was significantly reduced.     

A new mapping acquisition and processing system for simultaneous PIXE-RBS analysis with external beam

The combination of ion beam analysis techniques is particularly fruitful for the study of cultural heritage objects. For several years, the AGLAE facility of the Louvre laboratory has been implementing these techniques with an external beam. The recent set-up permits to carry out PIXE, PIGE and RBS simultaneously on the same analyzed spot with a particle beam of approximately 20 μm diameter.A new mapping system has been developed in order to provide elemental concentration maps from the PIXE and RBS spectra. This system combines the Genie2000 spectroscopy software with a homemade software that creates maps by handling acquisition with the object position. Each pixel of each PIXE and RBS maps contains the spectrum normalised by the dose. After analysing each pixel of the PIXE maps (low and high energy X-ray spectra) with the Gupixwin peak-fitting software, quantitative elemental concentrations are obtained for the major and trace elements. This paper presents the quantitative elemental maps extracted from the PIXE spectra and the development of RBS data processing for light element distribution and thin layer characterization. Examples on rock painting and lustrous ceramics will be presented.     

Observation of the evanescent wave excited by proton beam

An exit angle dependence of the intensity of carbon K line during proton bombardment was measured to observe the evanescent wave. A Soller type spectrometer was used to measure the intensity of X-ray lines. A mirror polished Si (1 1 1) wafer was used as a substrate and carbon was deposited onto this surface. As a result a curious exit angle dependence which is similar to the evanescent wave of X-rays was found . The calculated transmission coefficient of X-ray evanescent wave is compared with measured exit angle dependence of X-ray emission. The experimental and theoretical values are in good agreement. Utilization of this phenomenon permits to enhance the surface sensitivity of the PIXE analysis method.     

Quick change of ion species of heavy-ion microbeam by cocktail beam acceleration technique with the JAEA AVF cyclotron

A heavy-ion microbeam with hundreds of MeV energy is utilized for research in biotechnology and materials science at the JAEA AVF cyclotron facility. Beam users need microbeams providing a wide range of the LET. We have to change ion species and/or energy in order to vary the LET widely. However, it takes much time to develop a new microbeam of different ion species step by step using a flat-top acceleration system. A cocktail beam acceleration technique is frequently used to change the ion species and energy quickly. The cocktail beam acceleration has been first applied to the microbeam formation for quick change of the ion species. As a result, we have succeeded to reduce considerably microbeam changing time to within 30 min between a 520 MeV ⁴⁰Ar¹⁴⁺ and a 260 MeV ²⁰Ne⁷⁺. No deterioration of the microbeam spot size has been confirmed using a SE image of a copper grid.     

复旦大学单粒子微束研制进展

建设了一基于复旦大学2×3 MV串列加速器的单粒子微束装置。离子束经分析磁铁30°水平偏转传输后再经90°偏转磁铁竖直上行至辐照终端,以内径1.5 μm的毛细玻璃管微准直器获取离子微束。采用薄膜闪烁体结合光电倍增管的探测结构对微束离子进行精确探测和计数,并以高压静电偏转开关快速关断束流以实现对离子数目的精确控制。目前实验已获得在质子能量为3 MeV时,能散（能量分布曲线中半高宽FWHM）<60 keV、束分辨<2.2 μm、定量照射精度>95%的质子微束。本文对复旦大学单粒子微束的束流管道设计、微束获取、束开关及单粒子探测等核心环节的研制进展进行介绍。     

The Characteristics of an Ultra-High Resolution Ge(Li) Spectrometer for Singles and Coincidence X-Ray and Gamma-Ray Studies

The use of an ultra-high resolution Ge(Li) photon spectrometer in low and high energy X-ray and gamma-ray measurements has been evaluated. Studies were made of the resolution, low energy cutoff, the full energy and K X-ray escape efficiencies, tha effective detector dead layer and the detector linearity. The detector was used simultaneously with a high resolution Si(Li) detector to measure fast coincidences between Ka1 , Ka2 and L X-rays, as well as coincidences between K, L conversion electrons and L X-rays. A detailed discussion is presented of the electronic problems associated with making these kind of measurements. Measurements were also made of X-ray beams produced by clinical X-ray machines at 40, 78 and 220 kV.     

Application of PIXE to study ancient Iranian silver coins

A number of ancient Iranian silver coins belonging to Khosrau II (592-626 A.D.) minted during Sasanians dynasty were analyzed using proton induced X-ray emission (PIXE) technique. The 2 MeV proton beam with a current of 2-3 nA from AEOI, Van de Graaff accelerator was used to bombard the coins. The characteristic X-rays emitted from the samples, were detected by a Si(Li) detector from ORTEC with an energy resolution of 170 eV at 5.9 keV. The detector was placed in the beam direction at 135°. The elements Cl, Ca, Ti, Mn, Fe, Cu, Au and Pb were observed in the coins along with the major component silver. The percentage of silver varied between 85.87 and 93.39%. The possible correlation between the composition of coins and the minting time or the minting location of coins was the prime goal. There was a negative correlation between copper and silver. The weight of coins varied between 4.02 and 4.30 g. Going through the results, it seems that the local mines were used to die-strike the coins. The obtained results are in good agreement with archaeological records.     

超薄窗Si（Li）探测器在实验中的应用

用超薄窗Ｓｉ（Ｌｉ）探测器测量低能Ｘ射线，将传统的ＰＩＸＥ谱测量范围推广到如Ｓｉ、Ａｌ、Ｎａ等低原子序数元素。还对超薄窗Ｓｉ（Ｌｉ）探测器的具体应用作了描述。     

Quantitative analysis of phosphorus in amorphous silicon using PIXE with a crystal spectrometer and PIPC

A PIXE (particle induced X-ray emission) method for analyzing impurities in solid materials was developed using a crystal spectrometer combined with a position sensitive proportional counter (PSPC). Numerical expressions for quantitative analysis of impurities by this method are established. This technique was applied to the nondestructive measurement of P in a-Si matrix. The concentration of P obtained in this method is 0.717%, which is consistent with the value of 0.68% deduced from the Auger electron spectroscopy.     

External PIGE–PIXE measurements at the São Paulo 8UD tandem accelerator

An external PIGE–PIXE setup was installed on a beam line of the 8 MV tandem Pelletron accelerator of the Open Nuclear Physics Laboratory (LAFN). Proton beam energy was chosen in the 8–12 MeV range, sufficient to get an acceptable gamma ray yield but not so high as to prevent us from measuring X-rays. This also allowed the use of a thick aluminum exit window (0.5 mm) instead of the usual thin and sometimes fragile plastic windows. This external PIXE–PIGE system was used to analyze trace element concentrations in the enamel of human and animal teeth. The main interest was to find compatible human teeth substitutes for dentistry laboratory practice and chemical tests. In spite of their morpho-histological similarity, trace element concentrations in human and animal teeth have not yet been compared. Teeth from humans, cattle and swine collected primary at São Paulo region were analyzed. The elements Cu, K, Zn, Fe, Ti, Sr, V, Mn and Zr were detected by high energy external beam PIXE technique. Though preliminary, the results showed that the trace element concentrations observed in the enamel of human and swine are more similar to each other than to cattle teeth.     

Trace elements of soil samples from mining area

The affect of mining activity on the environment has been long of public concern. The present paper deals with the elemental analysis of soil samples from a mine and the area around it, located in E 48°59′ and N 34°11′ in Hamadan province of Iran. Elemental analysis was done using Proton Induced X-ray Emission (PIXE) technique. Spectra analysis and quantification was done using GUPIX software. Besides the major elements Si, P, K, Ca, Mn and Fe the other elements, namely Cl, Ti, V, Cr, Co, Ni, Cu, Zn, Rb, Sr and Pb were also present. Arsenic could be detected in some samples only. The presence of Ba and Ce needs more investigations by other techniques due to overlap of the L X-rays of these elements with the K X-rays of the major elements Mn and Fe, etc. Many elements V, Cr, As and Pb are known to be toxic and needs further understanding and proper handling in the mining process.     

STIM evaluation in GeoPIXE to complement the quantitative dynamic analysis

The GeoPIXE software for quantitative PIXE trace element imaging and analysis is a well established package for evaluation of characteristic X-ray data for both PIXE and SXRF. For the case of microbeam applications on semi-thick samples knowledge of the local areal density distribution is important for precise quantification. A technique is reported to achieve this using the measurement of beam particle energy loss as it traverses the sample, as in scanning transmission ion microscopy (STIM). New functionality is added to the GeoPIXE code through integration of routines for STIM sorting of event-by-event data to create elemental maps of the mean energy after traversing the sample. Integration of stopping powers for a given sample matrix then permits the measured energy loss to be related to the local areal density. In a further step, this information is used for X-ray absorption corrections made directly to the PIXE analysis results.As a complement, user-written plugins operating on single STIM spectra have been used to compare the estimated areal density from chosen spots with the corresponding values calculated with the new GeoPIXE routines. The additions made to the code allow a more precise quantification to be done on inhomogeneous, semi-thick samples.     

适用于微分析质控的标准物质的探索

本工作选择一种水系沉积物的天然基体进行研究,经研磨、筛选、粒径分布测定后,进行了样品分装和灭菌。结合NAA-PIXE-SRXRF3种核分析技术,在跨越9个量级,即亚g到亚ng的取样量范围内,对这种基体进行了多元素取样行为研究。对准确可称的取样量（几百mg至1mg）,利用INAA测定了30余种元素,其中,16种元素的取样不确定度小于1%;利用常规PIXE和微束SRXRF结合的方法,对不可准确称量的更小取样量（<1mg）下的多元素取样行为进行研究。根据入射粒子和待测元素特征X射线在基体中的吸收系数,对实验条件下不同元素的有效取样量进行了估算。初步结果表明：在有效取样量几百μg的条件下,取样不确定度好于1%的有7种元素,在亚ng到几十ng的取样量下,Fe、Cu、Rb的取样不确定度均小于10%,其中,Rb的取样不确定度小于5%。本工作将为研制适用于固体取样的微分析质控天然基体的标准物质提供一个可能的途径。     

Homogeneity study of an Fe impurity in unalloyed Zn using PIXE

We have studied the distribution of an Fe impurity in unalloyed Zn material along line scans in spots of 1 mm diameter each using PIXE. In order to achieve the necessary precision (1%) in the determination of this low Fe content (about 100 mg/kg), a sufficient counting rate of Fe X-rays is needed without overloading the counting electronics with Zn X-rays at the same time. Therefore, the development of our PIXE analysis system had to take into account: (a) optimising the thickness of a Ni absorber foil in order to selectively reduce the counting rate of Zn without adding an unproportionally high Ni counting rate, (b) implementing a triggered ion beam deflection system capable of handling very high counting rates (up to 8 kcps), (c) developing the spectrum evaluation code to take account of the selective absorption by the Ni foil. The results of our PIXE measurements showed an inhomogeneity in Fe of up to 10%, considered too high to accept this zinc material as a new reference material.