Characteristic X-ray Production Research Articles

MEASUREMENT OF THE CROSS SECTIONS FOR THE YIELD OF CHARACTERISTIC X-RAY RADIATION FROM 1-MeV PROTONS

This article presents the results obtained by measuring the characteristic x-ray production cross sections arising from the interaction of accelerated protons with the target atoms (PIXE). The PIXE production data were measured at the excitation of the K-, L-, and M-shells of target atoms in the mass range from Mg to Bi by 1 MeV protons. We use the approach based on the calculation of the PIXE production cross sections through the Rutherford backscattering cross section, which can be calculated from the Rutherford formula with high accuracy. This approach makes it possible to reduce the errors in measuring of the PIXE production cross sections and, thus, to improve the accuracy of the data obtained. Further, it is planned to expand the research area including protons of other energies and heavy charged particles in the energy range of 0.5–1.7 MeV/nucleon.

Computed corrections for recollision effects on ionization and x-ray production cross sections obtained in positron-impact studies

The accurate experimental measurement of inner-shell ionization cross sections induced by positrons near the threshold energy is of great significance both for theory and practical application. So far, there are few published experimental data in this field, most of which involve a slow positron beam device and acceleration fields to achieve the desired collision energies. Most previous experimental studies, in which a negative acceleration potential was applied to the target, neglected to consider how backscattered positrons might be accelerated back to the target, generating surplus characteristic x-rays and inflating the cross-section estimates derived therefrom. Using Geant4 and Ansys Maxwell to simulate charged-particle transport, the experimental collision process in the negative high-voltage electromagnetic field of the target chamber is simulated realistically in this paper. Through the simulation process, the effect of the negative high-voltage electromagnetic field on backscattered positrons, hence on ionization and characteristic x-ray production cross sections, is obtained. We then estimate corrections for previously published experimental Ti K-shell ionization cross sections and Ag-Lαβγ, Bi-Mαβ, Pb-Mαβ x-ray production cross sections obtained by positron impact. In addition, we use simulation to demonstrate that such undesired effects can be suppressed by adjusting the size of the target and the tilt angle between the target normal and the positron beam axis.

Research the Effect of the Negative High-Voltage Electromagnetic Field in the Target Chamber on the Characteristic X-Ray Production Cross Sections by Positrons Impacting on the Thick-Target

Research the Effect of the Negative High-Voltage Electromagnetic Field in the Target Chamber on the Characteristic X-Ray Production Cross Sections by Positrons Impacting on the Thick-Target

Measurements of K-shell ionization cross sections and L-shell X-ray production cross sections of Al, Ti, Cu, Ag, and Au thin films by low-energy electron impact

The K-shell ionization cross sections of Al, Ti, Cu and L-shell characteristic X-ray production cross sections of Cu, Ag and Au (Lα, Lβ and Lγ subshells for Au) by electron impact at incident energy of 5–27 keV are determined experimentally. Thin films of the studied elements, deposited on thin carbon substrates, are employed as targets in the experiments. The thickness of the thin carbon substrate is 7 μg/cm<sup>2</sup>, the targets are Al, Ti, Cu, Ag and Au and their thickness values are 5.5 μg/cm<sup>2</sup>, 28 μg/cm<sup>2</sup>, Cu 35.5 μg/cm<sup>2</sup>, 44 μg/cm<sup>2</sup> and 44 μg/cm<sup>2</sup>, respectively. The target thickness values are checked by using Rutherford Backscattering Spectrometry (RBS). The electron beam is provided by a scanning electron microscope (KYKY-2800B). The characteristic X-rays produced are recorded by a silicon drifted detector (XR-100SDD, Amptek), which has a C2 ultrathin window and can detect the low-energy X-rays down to boron Kα line (0.183 keV). The detector efficiency is calibrated by using the standard sources (<sup>55</sup>Fe, <sup>57</sup>Co, <sup>137</sup>Cs and <sup>241</sup>Am) for X-ray energy larger than 3.3 keV while using the characteristic peak method (i.e. by measuring characteristic X-ray spectra produced by 20 keV electron impacting various thick solid targets) for X-ray energy less than 3.3 keV. The experimental results are corrected by the Monte Carlo code PENELOPE for the effects of target structure and Faraday cup. Meanwhile, the electron escape rates obtained from the Faraday cup and the signal pile-up effect are also considered. The results show that when the incident electron energy is low, the influences of electron energy loss and target thickness are significant. The thinner the target , the smaller the correction is. Experimental uncertainties for K-shell ionization cross sections of Al, Ti and Cu are about 5.0%, 5.6% and 5.1%, respectively; experimental uncertainties for L-shell X-ray production cross sections for Cu and Ag are about 5.3% and 4.0%, and for Lα,Lβ,and Lγ of Au are about 6.1%, 8.9% and 11.0%, respectively. The experimental L-shell characteristic X-ray production cross sections of Cu are given for the first time. Compared with the theoretical values of the semi-relativistic distorted-wave Born approximation (DWBA), most of the experimental values in this work are in good agreement within 7% deviation. The best agreement between the experimental results and the theoretical values is obtained for the K shell ionization cross section of Al, and the deviation is less than 1.7% for the data where the incident energy is above 10 keV. The least consistency with the theoretical values is the experimental L shell characteristic X-ray production cross sections of Cu, with a deviation being about 5–22%. The comparison of the experimental L shell characteristic X-ray production cross sections of Cu (including Ga and As elements) with those from the DWBA theory indicates that the theoretical calculations of L shell ionization cross sections of medium heavy elements and the corresponding atomic parameters (such as fluorescence yields and Coster-Kronig transition probabilities) need to be more accurately determined. According to the present results, the ionization cross sections or characteristic X-ray production cross sections measured by the thin target thin substrate, the thin target thick substrate and the thick target methods are equivalent to each other within the uncertainties.

PIXE and Its Applications to Elemental Analysis

When charged particles collide with atoms, atomic inner shell electrons become ionized, producing characteristic X-rays. This phenomenon is called particle-induced X-ray emission (PIXE). The characteristic X-ray production cross-sections from PIXE are very large, and the characteristic X-rays of elements contained in a sample are easily measured by a Silicon detector with a high energy resolution. Hence, sodium to uranium can be detected with a sensitivity of ppb~ppm, and PIXE has been applied to trace element analysis. Scanning ion beams can be used to obtain the spatial distributions of elements in a sample. Furthermore, the distributions of elements inside a cell can be investigated using micro ion beams. PIXE analysis is a very useful technique for multi-elemental analysis and is now widely used in many fields and applications, including chemistry, medicine, biology, archaeology, agriculture, materials science, fisheries science, geology, petrology, environmental study, contamination monitoring, resource search, semiconductors, metal, astrophysics, earth science, criminal investigations, and food.

Measurements of Lα, Lβ, Lγ and M X-ray production cross sections of Os, Ir and Pt by low-energy electron impact: Comparisons of experiment with theory

Experimental determinations of Lα, Lβ, Lγ and M X-ray production cross sections and their ratios for Os (Z=76), Ir (Z=77) and Pt (Z=78) by electron impact at incident energies of 6–30keV are presented. Thin films of the studied elements deposited on thick carbon substrates were employed as targets in the experiments. Enhancements in L- and M-shell characteristic X-ray production due to electron-scattering effects in the double-layer structure target were corrected by means of Monte Carlo simulations. Comparisons were made between the measured Lα, Lβ, Lγ and M X-ray production cross sections and their ratios with the DWBA and PWBA-C-Ex theories and with other experimental data in the literature. In the case of L-subshells, the measured data of Os and Pt agree well with the theoretical values within the experimental uncertainties, but appreciable discrepancies between the experiment and theory exist for Ir; in the case of the M-shell, measured data for Ir show good agreement with theoretical values within the experimental uncertainties, but the measured results are somewhat lower than the theoretical values for Os and Pt. Finally, possible factors that could affect the comparisons between experiment and theory on cross-section ratios are discussed.

K-, L- and M-shell x-ray production cross sections by 1–1.3 MeV protons

In 2012, our institute had initiated a series of research activities aimed to measure the characteristic x-ray production cross-section, arising from interaction of accelerated particles with target atoms. This paper presents the data of x-ray production cross-sections under excitation of K-, L- and M-shells of target atoms in the range of mass from Mg to Bi by protons of the energies in the range of 1–1.3MeV. We used the approach based on calculation of x-ray production cross sections through the cross-section of Rutherford backscattering, which can be calculated with high accuracy from the Rutherford formula. Such approach reduces the measurement errors of x-ray cross-sections and thus improves the accuracy of the obtained data. It is further planned to expand the area of research to protons of other energies and heavy charged particles in the energy range of 0.5–1.7MeV/nucleon.

Monte Carlo simulation of X-ray spectra and evaluation of filter effect using MCNP4C and FLUKA code

The general-purpose MCNP4C and FLUKA codes were used for simulating X-ray spectra. The electrons were transported until they slow down and stop in the target. Both bremsstrahlung and characteristic X-ray production were considered in this work. Tungsten/aluminum combination was used as target/filter in the simulation. The results of two codes were generated in 80, 100, 120 and 140 kV and compared with each other. In order to survey filter effect on X-ray spectra, the attenuation coefficient of filter was calculated in 120 kV. More details of filter effect have been investigated. The results of MCNP4C and FLUKA are comparable in the range of bremsstrahlung spectra, but there are some differences between them especially in specific X-ray peaks. Since the specific peaks have not significant role on image quality, both FLUKA and MCNP4C codes are fairly appropriate for production of X-ray spectra and evaluating image quality, absorbed dose and improvement in filter design.

Characteristic X-ray production in the RCE process

Density matrix approach [V.V. Balashov, I.V. Bodrenko, Moscow State Univ. Bull. Phys. Astron. 1 (2001) 27] to describe characteristic X-ray production under resonant coherent excitation of channeled ions (the RCE process) is applied to the case of helium-like N 5+ ions in gold crystal.

Measurement of internal electric field in coated grounded quartz irradiated by an electron beam

Physical mechanisms involved in insulators submitted to electron irradiation inside a scanning electron microscope (SEM) are investigated by combining some simple considerations of electron trapping mechanisms with basic equation of electrostatics. To understand such mechanisms, only widely irradiated samples having a uniform trapping sites distribution are considered. This hypothesis leads to develop simple models for the trapped charge distributions and subsequently for the distribution of the electric field build-up in ground coated specimens as investigated in electron probe microanalysis (EPMA). This enables us to study the distortion of the Φ(ρz) function (the depth distribution of characteristic X-ray production) as well as the modification of the specimen’s local composition. In this paper, an experimental method, using a series of quartz samples, is described for evaluating the magnitude of the electric field build-up within specimens; thus allowing to establish clearly the electric field influence on the measured Φ(ρz) function.

EPMA analysis of insulating materials: Monte Carlo simulations and experiments

Using a realistic model for the electric field build-up that takes into account detrapping processes in insulating materials irradiated by electrons, a Monte Carlo approach has been applied to ground-coated binary oxides such as Al2O3 and Nb2O5. Changes entailed by the internal electric field build-up on the generation of the characteristic x-ray quanta and also on backscattered electron emission are investigated. The results clearly show that the depth distribution of characteristic x-ray production is modified and the Φ(ρz) function for both metal and oxygen Kα lines is compressed towards the surface while the backscattering electron emission is roughly unchanged. The change of the x-ray intensities as a function of the electric field is clearly established. The outcome is checked experimentally by measuring simultaneously the trapped charge and the emitted x-ray spectra during electron irradiation.

Monte Carlo simulation of x-ray spectra in diagnostic radiology and mammography using MCNP4C

The general purpose Monte Carlo N-particle radiation transport computer code (MCNP4C) was used for the simulation of x-ray spectra in diagnostic radiology and mammography. The electrons were transported until they slow down and stop in the target. Both bremsstrahlung and characteristic x-ray production were considered in this work. We focus on the simulation of various target/filter combinations to investigate the effect of tube voltage, target material and filter thickness on x-ray spectra in the diagnostic radiology and mammography energy ranges. The simulated x-ray spectra were compared with experimental measurements and spectra calculated by IPEM report number 78. In addition, the anode heel effect and off-axis x-ray spectra were assessed for different anode angles and target materials and the results were compared with EGS4-based Monte Carlo simulations and measured data. Quantitative evaluation of the differences between our Monte Carlo simulated and comparison spectra was performed using student's t-test statistical analysis. Generally, there is a good agreement between the simulated x-ray and comparison spectra, although there are systematic differences between the simulated and reference spectra especially in the K-characteristic x-rays intensity. Nevertheless, no statistically significant differences have been observed between IPEM spectra and the simulated spectra. It has been shown that the difference between MCNP simulated spectra and IPEM spectra in the low energy range is the result of the overestimation of characteristic photons following the normalization procedure. The transmission curves produced by MCNP4C have good agreement with the IPEM report especially for tube voltages of 50 kV and 80 kV. The systematic discrepancy for higher tube voltages is the result of systematic differences between the corresponding spectra.

Monte Carlo dose parameters of the BrachySeed model LS-1 125I brachytherapy source

Using a modified EGS4 code and associated user code DOSCGC, the two-dimensional dose rate distribution in water and air-kerma strength are calculated for a BrachySeed (model LS-1) 125I brachytherapy source, based on geometry and material data provided by the manufacturer. The AAPM TG-43 dose parameters derived from these results include the dose rate constant, the radial dose function, the anisotropy function, and the anisotropy factor and constant. The value of the dose rate constant so obtained is 0.932±0.003 cGy h −1 U −1. The source strength calculation excludes the contribution from titanium characteristic X-rays (4.5 and 4.9 keV) in the source in order to comply with a new primary calibration standard implemented by the National Institute of Standards and Technology in 1999. A sampling procedure for simulating silver characteristic X-ray production in the mixture material of the source core is developed in the EGS4 code. The calculated results reveal the good dose isotropy of the LS-1 source. The Monte Carlo dose parameters obtained are compared with measurements and calculations of other investigators.

Measures for spectral quality in low-voltage X-ray microanalysis.

Characteristic x-ray production with energetic electrons depends strongly on the overvoltage, the ratio of the incident beam energy to the critical excitation energy for the atomic species of interest. Low-voltage x-ray microanalysis (beam energy < or = 5 keV) is especially susceptible to artifacts due to sample charging because the overvoltage is low and even slight charging can strongly affect peak intensities. The Duane-Hunt bremsstrahlung limit is a good diagnostic to detect sample charging. Dynamic charging effects, however, can influence spectra despite an apparently satisfactory Duane-Hunt limit. Dynamic charging effects must be examined by time series experiments, or through use of dynamic energy windows continuously measuring count rates placed across the spectrum. When charging is a problem, conductive surface coatings can eliminate the effects. When pristine surfaces must be examined without coating, the use of a conductive grid can control charging so that useful x-ray spectra can be obtained.

Characteristic X-ray production in heavy ion collisions

The characteristic K X-ray production from projectile and solid target atoms in heavy ion collisions have been measured using a high-resolution Ge-detector. Ni projectiles in the energy range 15–25 MeV have been used to irradiate various thick targets made of materials in the Z range 22–32. In this energy region, the transition from predominantly quasi-molecular excitation to predominantly Coulomb excitation occurs. These measurements have been done in connection with our programme with a fairly new analytical technique, a combination of accelerator mass spectrometry (AMS) and the detection of characteristic X-rays. From the measurements, experimental K X-ray cross-sections have been extracted. Comparisons with other experimental data as well as with theoretical values are presented.

Monte Carlo simulation of x-ray spectra in mammography

A model for generating x-ray spectra in mammography is presented. This modelused the ITS version 3 Monte Carlo code for simulating the radiationtransport. Various target/filter combinations such as tungsten/aluminium,molybdenum/molybdenum, molybdenum/rhodium and rhodium/rhodium were used in thesimulation. Both bremsstrahlung and characteristic x-ray production wereincluded in the model. The simulated x-ray emission spectra were compared withtwo sets of spectra, those of Boone et al (1997 Med. Phys. 241863-74) and IPEM report 78. The χ2 test was used for the overallgoodness of fit of the spectral data. There is good agreement between thesimulated x-ray spectra and the comparison spectra as the test yielded aprobability value of nearly 1. When the transmitted x-ray spectra for specifictarget/filter combinations were generated and compared with a measuredmolybdenum/rhodium spectrum and spectra generated in IPEM report 78, closeagreement is also observed. This was demonstrated by the probability value forthe χ2 test being almost 1 for all the cases. However, minordifferences between the simulated spectra and the `standard' ones are observed.

Electron Probe Microanalysis of Insulating Oxides: Monte Carlo Simulations

Using a model for the electric field built up in insulating materials irradiated by electrons, a Monte Carlo simulation method has been applied to the binary oxides Al 2 O 3 , MgO, SiO 2 , Y 2 O 3 and Nb 2 O 5 . The results show the alteration of the shape of the depth distribution of characteristic x-ray production, the Φ(ρz) function, for both metal and oxygen Kα lines. The influence of the electric field built up on the measured x-ray intensities was clearly established. The changes in other physical quantities, such as the energy and angular distribution of backscattering electrons and energy deposition were also investigated.

EGS4 dosimetry calculations for cylindrically symmetric brachytherapy sources.

Computer algorithms for electron binding correction to Compton scattering and for detailed simulation of K-edge characteristic x-ray production were incorporated into EGS4 unix version 2.0. Based on detailed modelling of the internal structures of sources, the modified version was used to calculate dose rate constants, radial dose functions, and anisotropy functions on the long axis for an 125I model 6711 source, 169Yb Type 5 and Type 8 sources, and a stainless steel clad (SS) 192Ir source. The geometry of these sources is cylindrically symmetric. Calculated results are generally in good agreement with corresponding values recommended by TG-43 and Monte Carlo results published by other authors. The influence of electron binding in Compton scattering on the calculated dose distribution for an 125I model 6711 source in water, and of different characteristic x-ray production models for 125I model 6711 and 192Ir SS sources, were also studied.

Standardless quantitation of thin film specimens

This paper reviews the procedures available for the X-ray microanalysis of specimens in the form of thin self-supporting films without the use of standards. Standardless analysis refers to the procedure in which there is no requirement to prepare standards and then measure them during the course of the current analysis. The factors by which the measured X-ray intensities are converted to compositions are calculated for the elements of interest after the experimental measurements have been completed. These calculations are based on published tabulated data for the physical constants required, or evaluated from theoretical or empirical models. The physical parameters which are required to evaluate the characteristic X-ray production in the specimen are the fluorescence yield, the partition function and the X-ray production cross-section. Most analytical procedures ensure that other variables such as the specimen thickness and electron beam current are not required. Of the parameters mentioned, the first two have been examined and extensively tabulated in the literature. This paper focuses primarily on methods of evaluating the X-ray cross-sections for both the characteristic and bremsstrahlung production.

K-shell ionization cross section of Si atoms by relativistic electrons

Characteristic X-ray production cross sections are measured, and the cross sections for K-shell ionization of Si atoms by 15.7 and 25.7 MeV electrons are deduced. Experimental K ionization cross sections for Si are compared to some theoretical and semi-empirical calculations.