Production Of Characteristic X-rays Research Articles

Comparison of Bi2S3 and Ta2O5 as alternative materials to gold in nanoparticles used as agents to increase the dose in radiotherapy

Radiotherapy is an essential component in the treatment of all types of cancer. Radiotherapy uses ionizing radiation to destroy tumor tissue while reducing the damage to normal tissue as much as possible. In this work we study the effects of the spherical Bi2S3 and Ta2O5 nanoparticles (NPs) used as a radio-sensitization agent to increase local doses around the nanoparticle in a water medium. For low energy X-rays the dominant interaction is the photoelectric effect, which involves the absorption of a photon and the subsequent production of photoelectrons, characteristic X-rays and Auger electrons. Using a GEANT4 based simulation was determined the kinetic energy spectra of secondary electrons produced by the interaction of X-ray beam and Au, Bi2S3 and Ta2O5 NPs, after that was calculated the interaction processes, energy deposited, absorbed dose and the effective range distributions for the secondary electrons generated by the interaction of 100 million incident photons in the nanoparticles. The size of the nanoparticles was 20 nm and the energy distribution of the photons corresponds to the spectrum of a tube of x-rays with Tungsten anode and a peak voltage applied of 40 kV. This study demonstrates that Bi2S3 and Ta2O5 NPs are a viable alternative to Au NPs as a dose enhancing agent in radiotherapy.

High Speed Matrix Corrections for Quantitative X-ray Microanalysis Based on Monte Carlo Simulated K-Ratio Intensities.

Due to recent advances in modeling the production of characteristic X-rays, Monte Carlo simulation of electron-solid interactions can provide improved quantitative estimates of X-ray intensities for both homogeneous and heterogeneous interaction volumes. In the case of homogeneous materials, these modeled X-ray intensities can predict with excellent accuracy, matrix corrections for arbitrary compositions, arbitrary emission lines, and electron energies. By pre-calculating these Monte Carlo X-ray intensities for pure element standards and a range of compositions of binary systems, we can derive matrix corrections for complex compositions in real-time by parameterizing these k-ratios as the so-called alpha factors. This method allows one to perform Monte Carlo-based bulk matrix corrections in seconds for arbitrary and complex compositions (with two or more elements), by combining these binary alpha factors using the so-called beta expression. We are systematically calculating X-ray intensities for 11 compositions from 1 to 99 wt% for binary pairs of all emitters and absorbers in the periodic table, for the main emission lines (Kα, Kβ, Lα, Lβ, Mα, and Mβ) at beam energies from 5 to 50 keV, using Monte Carlo calculations based on a modified PENELOPE electron-photon transport code, although any other Monte Carlo software could also be utilized. Comparison of k-ratios calculated with the proposed method and experimental k-ratios from the Pouchou and Pichoir database suggest improvements over typical φ(ρz) methods. Additional comparisons with k-ratio measurements from more complex compositions would be ideal, but our testing of the additivity of the beta equation suggests that arbitrary compositions can be handled as well, except in cases of extreme fluorescence or absorption.

X-ray fluorescence analysis of low concentrations metals in geological samples and technological products

For the past several years many nuclear physics methods of quantitative elemental analysis have been designed. Many of these methods have applied in different devices which have become useful and effective instrument in many industrial laboratories. Methods of a matter structure analysis are based on the intensity detection of the X-ray radiation from the nuclei of elements which are excited by external X-ray source. The production of characteristic X-rays involves transitions of the orbital electrons of atoms in the target material between allowed orbits, or energy states, associated with ionization of the inner atomic shells. One of these methods is X-ray fluorescence analysis, which is widespread in metallurgical and processing industries and is used to identify and measure the concentration of the elements in ores and minerals on a conveyor belt. Samples of copper ore with known concentrations of elements, were taken from the Ural deposit. To excite the characteristic X-rays radionuclide sources 109Cd, with half-life 461.4 days were used. After finding the calibration coefficients, control measurements of samples and averaging of overall samples were made. The measurement error did not exceed 3%.

Design and performance of a laboratory based source of characteristic X-rays

A theoretical description for the production of characteristic X-rays (CX) is reviewed highlighting features that enhance the CX intensity. These are incorporated into the design of a secondary target system for excitation by white radiation produced by an industrial X-ray tube; Philips MCN-166, capable of continuous operation at up to 160 kVp and 1.6 kW. Results are presented for the measured spatial profile, CX intensity at 8–75 keV and spectral purity as a function of accelerating voltage. The beam is a narrow fan with half height (horizontal by vertical) 200 mm by 50 mm at 1 m from the source. The beam intensity is presented in units ph/s/mm 2 at 1 m per kW and is equivalent to an isotope source with activities 100–300 mCi per kW deposited in the anode. The source provides variable intensity and the ability to change energy by simply exchanging the target material.

Energy Deposition in Planetary Atmospheres by Charged Particles and Solar Photons

We discuss here the energy deposition of solar FUV, EUV and X-ray photons, energetic auroral particles, and pickup ions. Photons and the photoelectrons that they produce may interact with thermospheric neutral species producing dissociation, ionization, excitation, and heating. The interaction of X-rays or keV electrons with atmospheric neutrals may produce core-ionized species, which may decay by the production of characteristic X-rays or Auger electrons. Energetic particles may precipitate into the atmosphere, and their collisions with atmospheric particles also produce ionization, excitation, and heating, and auroral emissions. Auroral energetic particles, like photoelectrons, interact with the atmospheric species through discrete collisions that produce ionization, excitation, and heating of the ambient electron population. Auroral particles are, however, not restricted to the sunlit regions. They originate outside the atmosphere and are more energetic than photoelectrons, especially at magnetized planets. The spectroscopic analysis of auroral emissions is discussed here, along with its relevance to precipitating particle diagnostics. Atmospheres can also be modified by the energy deposited by the incident pickup ions with energies of eV’s to MeV’s; these particles may be of solar wind origin, or from a magnetospheric plasma. When the modeling of the energy deposition of the plasma is calculated, the subsequent modeling of the atmospheric processes, such as chemistry, emission, and the fate of hot recoil particles produced is roughly independent of the exciting radiation. However, calculating the spatial distribution of the energy deposition versus depth into the atmosphere produced by an incident plasma is much more complex than is the calculation of the solar excitation profile. Here, the nature of the energy deposition processes by the incident plasma are described as is the fate of the hot recoil particles produced by exothermic chemistry and by knock-on collisions by the incident ions.

Applications of pyroelectric particle accelerators

The discovery of pyroelectric X-ray generation in 1992 by Brownridge has led to a recent surge of interest in the use of the pyroelectric effect as a means of producing useful radiation. By heating or cooling a pyroelectric crystal such as lithium tantalate (LiTaO3) in a vacuum, a potential on the order of 100kV can be generated. This potential is great enough to eject electrons from the crystal for the production of characteristic or bremsstrahlung X-rays, or to cause field ionization near a tip mounted to the crystal. By using the combined fields of two polarized crystals, the acceleration potential can be doubled, with one crystal acting as a particle emitter and the other crystal serving as a target. Such a paired-crystal system was used to generate X-rays with energies of greater than 200keV, and can be used to fluoresce the K shell of thorium (Z=92). An alternative use of pyroelectric sources is the field ionization of a dilute gas. If the positively-charged crystal is used to ionize a deuterium gas, and the target crystal is coated with deuterated target, the deuterium ions can be accelerated into the target at high enough energy to cause D–D fusion. Results verifying the production of D–D fusion neutrons from a pyroelectric source will be presented. Future applications of pyroelectric accelerator technology, such as the use of the electron beam for materials testing, will also be discussed.

Cluster-laser interaction: fast production of hot electrons by short laser pulses

The surprisingly low laser intensity threshold of I≃1015Wcm−2 for production of characteristic X-rays in the interaction with large rare gas clusters (N>106 atoms) is investigated. We propose an efficient production mechanism of fast electrons involving the interplay of the acceleration in the laser field and backscattering at ionic cores resembling the Fermi shuttle. We show with the help of a Monte Carlo simulation that this mechanism provides an efficient heating mechanism for moderate laser intensities resulting in an X-ray production threshold in approximate agreement with the experiment.

The effect of the radial function on I-125 seeds used for permanent prostate implantation

The purpose of this study was to evaluate the integrity of eight commercially-available low-activity Iodine-125 ( 125I) seeds for their radial function g(r) and its effect on the dose delivered to the adjacent critical structures when used in permanent prostate implants (PPI). Ten previously treated patients were retrospectively used in this comparison. The Amersham Health Oncura seed was used to peripherally design an isodose distribution with urethral and anterior rectal wall sparing. Plan criteria included minimum coverage of 144 Gy to the planning target volume (PTV), ≤ 70% dose to 150% of the PTV volume (V150-PTV), and the quantity of needles ≤ 70% of the size of the PTV, in cc. Upon completion of the Oncura plan, the seed type was changed and the activity was adjusted until the V100-PTV for each of the other 7 seed types matched the V100-PTV defined by the Oncura seed. Computed tomography (CT)-based postimplant dosimetry was used to determine the dose to 40% (D40) of the bulb of the penis (in Gy). Dose-volume histograms (DVH) were used to evaluate the differences to V100 (in %) and D40 (in Gy) of the anterior rectal wall and bulb of the penis, and V100 (in %) of the urethra. The data was tabulated. Radioactive 125I sources included in this study were 125I Source 2301 (Best); I-Plant (MedTech), IoGold (Mentor), Oncura (Amersham Health), ProstaSeed (UroCor), SelectSeed (Nucletron), SourceTech (Bard), and Symmetra (UroMed). The sizes of the PTV for the 10 patients ranged from 18.82 cc to 48.99 cc. The Oncura seed was used as the reference seed and all other seed types were normalized to it for data comparison. It was determined that the dose rate constant (⋀) and anisotropy factor (φ) contribute to the activity needed to achieve comparable V100-PTV doses, but a strong dependence on the radial function g(r) was found to effect the doses to the critical structures studied. Values of g(r) at 4 cm were calculated and the IoGold and SourceTech seeds were determined to have the highest g(r) values, with ProstaSeed and SelectSeed having the lowest values. 125I Source 2301 and IoGold required less activity per seed to achieve the same dose to the V100-PTV due to the higher dose rate and anisotrophy constants (⋀.φ). The seed types with silver were less penetrating and resulted in the production of characteristic x-rays that modified the energy spectrum and influenced the radial function. The seeds requiring the lowest activity showed the highest dose to the anterior rectal wall, a posterior adjacent structure; the urethra, an interior structure; and the bulb, an inferior structure. This study was designed to investigate the integrity of eight different commercially-available seed types, and their dependence on the g(r) in seed choice. It was determined that the dose rate constant and anisotropy factor determine the activity needed for implantation but a strong dependence on the radial function was found to effect the doses to the adjacent structures.

Monte Carlo modelling of radiotherapy kV x-ray units

To obtain accurate information for absorbed dose calculations in water for kilovoltage x-rays, the photon spectrum, planar fluence and the angular distribution of the photons at the collimator exit of the x-ray unit have to be known. The only way to obtain this information is by Monte Carlo (MC) simulation. Compared with the situation for high-energy photons and electrons, where in recent years numerous papers have been devoted to MC modelling of complete clinical accelerator units, there is a lack of similar work for kV x-ray units. A reliable MC model for a kV x-ray unit would allow the output information to be used in a treatment planning system for regular and irregular treatment fields. Furthermore, with MC simulation, perturbation factors of dose-measuring devices, such as those specified in codes of practice, can be calculated. In this work, the MC code EGS4/BEAM was used to build realistic models of two complete x-ray units. The tungsten target, exit window, collimator, additional filtration and applicator were taken into account. For some aspects of the work, a comparison was made with the simulations from another MC code, MCNP4B. The contribution to the characteristic radiation from electron impact ionization and from the photoelectric effect of reabsorbed bremsstrahlung photons was studied. Calculated and measured photon fluence spectra in air and half-value layers for a Philips MCN410 tube were compared for several anode voltages and additional filtrations. Results from the two codes agreed well, and the agreement with measured spectra was found to be good for energies above 50 keV but rather less good below that energy. For a Siemens Stabilipan 2 Th300 x-ray tube, HVLs and dose distributions in water were compared with measurements for several clinical x-ray qualities. For most of the combinations of radiation qualities and applicators, good agreement was obtained, although there were also some cases where the agreement was not so good. Electron contamination and photon build-up at the water surface were studied using MC simulation. The influence of depth on the photon spectral distribution was investigated. Both EGS4/BEAM and MCNP4B, in their default versions, handle inadequately the production of characteristic x-rays. This was found to have only a minor influence on the calculated dosimetric quantities. Simulations with MCNP4B required the use of several variance reduction techniques in order to obtain results within reasonable calculation times.

Basic literacy in electron-excited x-ray microanalysis

Electron beam x-ray microanalysis with energy dispersive x-ray spectrometry (EDS), as performed in electron probe microanalyzers (EPMA)/scanning electron microscopes (SEM) for thick specimens and analytical electron microscopes (AEM) for thin sections, is a powerful technique with wide applicability in the physical and biological sciences and technology communities. The operation of an EDS x-ray microanalysis system has been automated to the point that many users now consider EDS to be a routine tool where the results reported by the automation system are always correct Unfortunately, there are numerous pitfalls awaiting the unwary analyst. All EDS users require a basic level of literacy in x-ray microanalysis to properly interpret spectra and develop a sensible analysis strategy for their problems. This “basic literacy” includes knowledge of the factors controlling the efficiency of production of characteristic and continuum x-rays, the characteristic energies and structure of x-ray families that provide the basis for qualitative analysis, the operational characteristics of energy dispersive x-ray spectrometers, including artifacts, and the systematic procedures for qualitative and quantitative analysis.

Kα x-ray emission induced by 1—100 MeV protons

In the course of a feasibility study of high-intensity sources of monochromatic x-rays to be used for XRF, extensive numerical calculations were conducted on the production of characteristic x-rays by proton bombardment of pure element targets. This paper presents the analytical model used for the computer simulations and compares the x-ray production by protons and alpha particles. The K x-ray production cross-section was calculated by the ECPSSR theoretical model and by Paul's analytical formula. The dependence of the x-ray yield on projectile energy, target atomic number, target thickness and irradiation geometry is discussed. The thick target Kα x-ray yields produced by 1—100 MeV proton bombardment were calculated for 66 elements from Na to Pb. From these results, a number of scaling laws and fitting procedures are given for proton-induced Kα x-rays.

Synchrotron Radiation Induced X-Ray Emission - SRIXE

The synchrotron radiation induced X-ray emission (SRIXE) technique was found very useful and sensitive for determination of trace elements content and distribution in different types of materials. Due to properties of synchrotron radiation the SRIXE technique became very unique and powerful for trace elements analysis. This paper describes the phenomena related to production of characteristic X-rays and principles of the method. The properties of SRIXE such as minimum detectable limit, spatial resolution, radiation damage, and depth sensitivity are also discussed. Selected applications are given to emphasize the usefulness of the technique. PACS numbers: 78.70.En, '87.15.Mi

Characteristic X-ray flux from sealed Cr, Cu, Mo, Ag and W tubes

The flux of characteristic Kα radiation from sealed X-ray tubes with Cr, Cu, Mo, Ag and W targets is determined on an absolute scale by measuring integrated intensities of Bragg reflections from well characterized powder samples. The values of the flux are corrected for absorption in the tube target. The tube voltage is varied, and the flux is observed to vary as (U 0−1) p , where U 0 is the ratio of tube voltage to the excitation voltage of characteristic Kα radiation (over-voltage). The exponent p is very close to the theoretical value of 1.67 in the cases of Cr, Cu, Mo and Ag, while in the case of W the value of p is 1.45. The absolute values of the flux are close to the theoretical estimates of Green & Cosslett [Proc. Phys. Soc. (London) (1961), 78, 1206–1214] for Cr and Cu, 10 to 20% higher for Mo and Ag, but only about 1/3 of the calculated flux of W Kα radiation. This is due to an inadequate calculation of the indirect production of characteristic X-rays. A simple formula for the flux per unit solid angle is given in terms of the atomic number of the target, the tube voltage and the K excitation voltage.

An empirical calculation of the depth distribution of primary X-ray production

The depth distribution of the primary X-ray production at normal electron incidence is calculated by using a simple empirical consideration of the multiple reflection of electrons at imaginary planes parallel to the specimen surface to describe the electron scattering in the target. The ionisation cross-section for the production of characteristic X-rays is described by the non-relativistic expression of Bethe (1930). The calculated distributions are compared with experimental results and also with some theoretical results of Monte Carlo calculations. The calculated depth distributions show a strong dependence on the excitation potential in accordance with the strong tracer effect found in experimental distributions. The present distributions are also applied to the calculation of the absorption correction, and the results are compared with those from other models.

Proton induced X-ray emission as a tool for trace element analysis

For protons and heavier ions with energies in the MeV range we have studied the production of characteristic X-rays from elements with Z≳13 using a semiconductor X-ray spectrometer. Various competing background processes have been identified. Theoretical estimates of the background radiation due to bremsstrahlung from secondary electrons and due to proton bremsstrahlung have been evaluated, and on this basis we have calculated lower limits for the sensitivity obtainable for the concentration of the trace element, ranging down to values of 10 −6−10 −7. Different projectiles and incident energies have been compared, and it is shown that this method of X-ray production is about 3 orders of magnitude cleaner than can be obtained by electron bombardment.

The production of characteristic X-rays by proton bombardment, and the ratio of characteristic to continuous radiation

Absolute measurements of K and L characteristic X-rays produced in thick targets of Ni, Cu, Mo, Ag, and W are reported. The data for K X-rays are compared with a theoretical result obtained by integration of the expression for the cross section given by Merzbacher and Lewis (1958). The expression for yield as a function of energy can be put into a very simple form without the need for an empirical function, and this is verified experimentally. A new absolute comparison can be made between thick-target theory and the present data for nickel and gives good agreement. Tungsten L-radiation is investigated, and spectra are obtained using a Si(Li) detector. The number of L-ionizations per proton in tungsten is found to be greater than the number of K-ionizations expected in an element with a K-shell binding energy equal to the LIII binding energy of tungsten, by a factor of 2.9. The proton bremsstrahlung is measured and the ratio of characteristic to continuous radiation found to be 1.63*103 for 420 kV protons on nickel. This is shown to be about 3 orders of magnitude greater than for electron bombardment under optimum conditions.

Characteristic X-ray production by heavy ion bombardment as a technique for the examination of solid surfaces

Over the past few years, intense effort has been expended on studying the physical processes responsible for the production of characteristic X-rays during heavy ion/atom collisions. It is considered timely at this stage to assess one of the applications of this work, viz., the use of heavy ions to detect elements at or near to surfaces. It emerges that one of the advantages of the technique is its ability to detect light elements with high sensitivity and to examine the depth distribution of implanted elements. As an example of its application, evidence is presented for the detection of sulphur on the surfaces of copper, nickel and stainless steel.

X-Ray Production Efficiencies for K-, L-, M-, and N-Shell Excitation by Ion Impact

AbstractA systematic study of the production of characteristic X-rays by both light and heavy charged particles has been made. Using protons in the energy range 70-200 keV, data have been obtained for twenty-one X-ray lines encompassing a wavelength region from 1.44 to 44.00 Å from K-, L-, M-, and N-shells of elements with 6 ≤ Z ≤ 92. Additional X-ray production efficiencies have been measured in the K-, L-, M-, and N-shells using incident H2+, He++, N++, O++, and Ar++ ions in the energy range 90-400 keV. The ion beams were obtained from a 300 kV electrostatic accelerator, and beam analysis was obtained using a 7 kilogauss analysing magnet.The data for proton excitation show that, for X-rays of a given wavelength, the X-ray production efficiency increases with the principal quantum number of the atomic shell being excited. These results contradict results reported by Sterk et al, but agree with results obtained earlier by Khan et al.The results also show that the use of heavy ions (z > 5; obtains X-ray yields which are orders of magnitude higher than a repredicted by the direct scattering theory as used for protons and alpha particles.Ion excitation of X-rays has been applied to the study of the oxidation kinetics of iron as part of a surface physics program. The wide range of target penetration depth as a function of both mass and energy of the ion has allowed us to study oxide film thickness as a function of oxidation temperature and impurity depth and concentration. Data are presented for protons and argon ions incident on high- purity ion with surface oxide films varying in thickness from 35 Å to 750 Å. Oxygen and carbon sensitivities to equivalents of fractional monolayers are routinely obtained using nondispersive analysis of the X-rays.

On the production of characteristic X-rays in thin metal crystals

According to the two beam approximation of the dynamical theory of electron diffraction an electron propagating through a crystal is represented by a combination of two Bloch waves, one of which (the type 1 wave) tends to channel the electron between the planes of atoms while the other (the type 2 wave) locates the electron on average closer to the centres of the atoms. It has been suggested that as X-ray production might be expected to occur in regions close to the nuclei of the atoms, the type 2 wave should be more efficient at producing X-rays than the type 1 wave, and that this should result in a variation of X-ray production with orientation (Hirsch, Howie & Whelan 1962). This paper describes an experimental investigation of this effect. A more complete theoretical treatment of the process is given followed by a description of the apparatus used in the experiments. It is shown that the results are in qualitative agreement with the simple theory, and can be explained quantitatively by extending the theory to take into consideration the effect of the other scattering processes which act upon the electrons which produce the X-rays.

Production of Characteristic X-Rays by Protons of 1.7- to 3-Mev Energy

Characteristic x-rays produced when protons of 1.7- to 3-Mev energy are stopped in thick targets of Mo, Ag, Ta, Au, and Pb have been studied using a NaI scintillator. $K$ and $L$ radiation for the three heavy elements produced well-separated differential pulse-height peaks, while only the $K$ radiation was detectable for Mo and Ag. Cross sections for $K$ ionization have been calculated, with corrections for the Auger effect, and compared with the theory. Ratios of experimental to theoretical cross sections vary from one to four, with good agreement for the light elements and low proton energies. The measured cross sections at 2.4-Mev proton energy are 11, 3.0, 0.036, 0.016, and 0.010 barns for Mo, Ag, Ta, Au, and Pb, respectively.