Thick Target PIXE Analysis Research Articles

APPLICATION OF PIXE ANALYSIS TO THE STUDY OF ELECTROKINETIC REMOVAL OF CESIUM FROM SOIL

Thick-target PIXE analysis was applied to the study of electrokinetic soil remediation technique. In order to simulate radioactive soil contamination by 137 Cs , salt of stable cesium was mixed with soil samples. These soil samples were subjected to electrolysis for up to 36 hours with a field gradient of ≈ 1-3 V/cm. After the electrolysis, we measured the distribution of Cs concentration in the soil along the electrolysis cell by PIXE analysis. LX-rays of cesium were used for the analysis. The Cs concentrations in the drain water sampled from the cathode well were also evaluated. After the electrolysis the migration of cesium from the anode to the cathode was clearly observed. Water supply into the anode well enhanced the removal rate. We found that the main driving force of the migration of Cs + observed in this work was not electrophoretic migration, but electroosmotic flow in the soil samples. Owing to the spectral interference by major metallic elements in the soil, the minimum detectable concentration of cesium by the present method was limited to ≈ 800 ppm.

PIXE ANALYSIS OF URBAN ROADSIDE SOIL

In order to study the influence of motor vehicles on a local soil environment, depth profiles of elemental concentration of urban roadside soil were investigated by means of thick-target PIXE analysis. For comparison, we analyzed the soil sampled in a university campus with very low traffic intensity. From the measured depth profiles, it was found that the roadside surface layers up to the depth of approximately 5 cm from the ground level are highly polluted by S and Zn. According to cluster analysis this pollution can be attributed to the deposition of tire dust due to the heavy vehicular traffic volumes on the highways.

Study of seasonal variations of trace-element concentrations within tree rings by thick-target PIXE analyses

Thick-target PIXE has been used for the quantitative determination of trace elements in annual growth rings of different tree species. A scanning device was developed for the remote control of the sample and a video-camera system for the exact monitoring of the spot to be analyzed. The samples were analyzed in steps of 1 mm. The widths of the tree rings studied were in the range 2.5–8.0 mm. Samples of Norway spruce and Scots pine were collected from Harjavalta, a polluted area in southwestern Finland. The elements studied were S, Cl, Br, K, Ca, Mn, Fe, Zn, Cu, Ni, Pb, Rb and Sr. Large variations were observed in elemental concentrations within individual tree rings. The highest concentrations for most elements were obtained for earlywood in the beginning of the growth season and the lowest values for latewood thus reflecting the biological activity. The method was calibrated using international standard reference materials. For most elements the matrix effects were found to be negligible. The detection limits for most metals studied were in the range 1–5 ppm.

Foil thickness measurement via the [formula omitted] intensity ratio of proton-induced X-Rays

A differential method for measuring the thickness of aluminum foils used as X-ray absorbers in thick-target PIXE analysis is described. It involves the change in K β K α X-ray intensity resulting from transmission through the foil and provides better acc than direct X-ray attenuation measurements.

Limits of detection and quantitation in PIXE analysis of thick targets

X-ray spectra induced by the impact of 1–5 MeV protons on pure single-element matrices of carbon, aluminum, silicon, titanium, iron, germanium, molybdenum, silver, tin, ytterbium and lead have been used to investigate analytical detection limits in thick-target PIXE. Particular attention is paid to the choice of appropriate aluminum X-ray filters for suppression of the matrix characteristic X-ray lines and their pile-up peaks, and to the choice of optimum proton energy.

Minimum detection limits in PIXE analysis of thick targets

Various factors which influence MDLs in proton-induced X-ray emission analysis of thick specimens are surveyed. Their roles are illustrated by measurements using 2 MeV protons on a set of six pure single-element matrices ranging from carbon to tin. Particular attention is paid to the role of X-ray absorbers in suppressing peak pileup, and to errors incurred by use of these.

Thick target X‐ray yields from proton bombardment

AbstractThe production yields for characteristic x‐rays from the bombardment of thick targets by protons are calculated by integrating the x‐ray production cross‐section for each element for the whole range of the protons, taking into account the self‐absorption of x‐rays. A simple approximation which can be applied with a pocket calculator is also presented, using simplified relationships for the energy dependence of the proton stopping power and the x‐ray production cross‐sections. The approximation allows very fast calculations, has an accuracy of better than 5% for low‐energy protons and is also very useful for the first steps in a computer program for PIXE analysis of thick targets, using the method of iterations. The calculated yields are compared with experimental results obtained on thick specimens of pure elements, compounds and standards.

Multilayer pixe analysis

Thick target PIXE analysis has been extended to cases where there is a superposition of layers of different compositions. A computer program was developed for calculating the K α X-ray yield of up to three layers containing up to five different elements each, when bombarded by protons of arbitrary energy. The enhancement of peaks due to secondary fluorescence is included, with the possibility of the primary and secondary emitters being in any of the three layers. The thickness of titanium films deposited on steel backings was measured using the Ti Fe ratio method, and proton energies of 400 to 700 keV.

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.

The analysis of the power approximation in thick target PIXE analysis

The analytical approximation for the calculation of the thick target X-ray yields based on the power approximation for the X-ray production cross-section and for the proton stopping power is studied for K lines of the elements 11 ⩽ Z ⩽ 51 and for proton energies 1 MeV ⩽ E 0 ⩽ 4 MeV. A procedure for the determination of best fit parameters is proposed. The systematic mean error and the maximum error for Z ⩾ 6 targets were found to be 0.6% and 2%, respectively.

Effects of random surface roughness in pixe analysis of thick targets

The ratio of proton-induced X-ray yields from thick targets with perfectly smooth and randomly rough surfaces is computed as a function of proton energy, target-detector geometry and X-ray attenuation coefficient. The rough surfaces are obtained by a Monte Carlo technique. Attenuation coefficient is shown to be the dominant parameter governing the effect of roughness.

PIXE analysis of thick targets

A review of thick-target PIXE is presented. Particular attention is paid to the relative efficacies of various methods of calibration, to achievable detection limits and to various experimental factors which affect analytical accuracy.

Dependence of X-ray yields on different parameters for light element matrices in thick target PIXE and use of standards for calibration in such analysis

Matrix, beam energy and geometry dependent effects in PIXE analysis of thick samples have been investigated in light element matrix in the proton energy range 2.61–4.22 MeV. The experimental results have been compared with the results of numerical calculations using different prescriptions for cross sections. It is shown that experimental sensitivities as a function of atomic number of elements and beam energy can be accurately reproduced by some prescriptions. It is also shown that modification of intensity ratios of K X-ray lines obtained experimentally can be explained as due to absorption in matrix and absorbers. It is further shown that calibration using multielement standards and numerical calculations can be fruitfully utilized to reduce the uncertainties in thick target PIXE analysis. The sources of these uncertainties and limitations of the use of standards are discussed in the light of experimental results and calculations.

Specimen surface effects in thick-target PIXE analysis

Calculations are performed to illustrate the effect of surface defects upon proton-induced X-ray yields for various representative combinations of trace X-ray emitters homogeneously dispersed in thick targets.

Uncertainties in thick-target PIXE analysis

Thick-target PIXE analysis involves uncertainties arising from the calculation of thick-target X-ray production in addition to the usual PIXE uncertainties. The calculation demands knowledge of ionization cross-sections, stopping powers and photon attenuation coefficients. Information on these is reviewed critically and a computational method is used to estimate the uncertainties transmitted from this data base into results of thick-target PIXE analyses with reference to particular specimen types using beams of 2–3 MeV protons. A detailed assessment of the accuracy of thick-target PIXE is presented.

PIXE calibration and correction of matrix effects in the case of thick samples

Differences in the experimental results of thin target calibration, using different types of reference standards, are discussed and compared to published data of X-ray production cross sections. To correct for matrix effects in PIXE analysis of thick targets, a computer code is being developed considering the decrease of ionization cross section due to the slowing down of protons, the X-ray attenuation by the target material, and the enhancement of X-ray fluorescence. The approximations involved are discussed, and the code is checked by comparison with PIXE analyses of thick samples of known composition.

Applications of PIXE to studies in dental and mental healths

The elemental composition of healthy and diseased teeth from 25 South Australian children have been determined using thick-target PIXE analysis. Different dental hard tissues, namely enamel, dentine, cementum and the amelodentinal junction, were analysed independently. A number of elements, Na, Mg, Al, P, S, Cl, Ca, V, Cr, Mn, Fe, Ni, Cu, Zn, Sr and Pb have been detected, and their concentrations measured. The concentrations of some of the elements were found to vary considerably between: (a) healthy and diseased teeth, (b) teeth of the same type, and (c) different parts of the same tooth. Attempts have been made to correlate the concentrations of the various elements with the health of the teeth. In a pilot study, PIXE has also been applied for Pb analysis in the teeth of a few mentally retarded children. The teeth of all the children, with the exception of one who was suffering from Downe's syndrome, were found to contain appreciable amounts of lead. It is suggested that PIXE would provide a more convenient and accurate form of analysis than destructive chemical methods, for correlating Pb in children's teeth with their mental abilities.