Thick Target Bremsstrahlung Spectra Research Articles

Experimental thick target bremsstrahlung spectra produced by 5–25 keV electrons for 6 ≤ Z ≤ 82 and comparison with Monte Carlo PENELOPE simulations

Measurements of bremsstrahlung spectra of thick solid C(Z = 6), Ti(Z = 22), Zr(Z = 40), Nb(Z = 41), W(Z = 74) and Pb(Z = 82) targets by the impact of electrons with energies of 5–25 keV are presented. The experimental data exhibit an excellent agreement with the simulated results by means of the Monte Carlo code PENELOPE based only on ordinary bremsstrahlung. It demonstrates that the bremsstrahlung of thick solid targets in the energy range of interest has not shown any polarization bremsstrahlung contribution and this process can be described accurately by the PENELOPE code.

Effect of incident electron energy of beta emitter on the formation of bremsstrahlung spectra in the photon energy region of 1–5 keV

The effect of incident electron energy of beta emitter 204Tl (end-point energy=765keV) and 90Sr (end-point energy=546keV), on the formation of total bremsstrahlung spectra in thick targets, was investigated in the photon energy region of 1–5keV. Theoretical bremsstrahlung spectra were obtained from theory that describes ordinary bremsstrahlung (OB) and the theoretical model, which includes the contribution of polarization bremsstrahlung (PB) in OB in stripping approximation. The theoretical and experimental bremsstrahlung spectra were modified by applying corrections due to the range of beta particles, self-absorption of photons in target, absorption of photons in detector compounds, and backscattering of beta particle. It was observed that the experimental results were 10–15% higher than that of the theoretical model, which includes the contribution of PB in OB in stripping approximation, particularly for medium and high Z elements. The contribution of PB in OB was suppressed with the increase in the end-point energy of the beta emitters. The results reported here clearly indicate the inadequacy of stripping approximation and the need to include the term of interference of OB and PB while describing the total bremsstrahlung spectra.

Studies of total bremsstrahlung spectra from89Sr beta particles in Mo and Pt metallic targets in photon energy region of 1-100 keV

Total bremsstrahlung spectra in thick targets of Mo and Pt, produced by beta emitter 89 Sr (end point energy = 1464 keV) have been studied in the photon energy range of 1-100 keV. The experimentally measured spectra measured were compared with the theoretical spectral distributions calculated from Elwert corrected (non relativistic) Bethe-Heitler [EBH] theory, modified Elwert factor (relativistic) Bethe-Heitler (F mod BH) theory for ordinary bremsstrahlung (OB) and the modified Elwert factor (relativistic) Bethe-Heitler (F mod BH+PB) theory, which includes the polarization bremsstrahlung (PB) into total bremsstrahlung (BS). The present results indicate the correctness of F mod BH+PB theory in the low energy region, where the contributions of PB into BS are dominant. But at the middle and higher energy region of the bremsstrahlung spectrum, where the contribution of PB is negligible, the F mod BH theory is more close to the experimental results.

Studies of total bremsstrahlung in thick targets of Al, Ti, Sn and Pb for 90Sr beta particles in the photon energy region of 1–100keV

Abstract Total bremsstrahlung (BS) spectra in thick targets of Al, Ti, Sn and Pb produced by beta emitter 90Sr (End point energy=546 keV) are studied in the photon energy range of 1–100 keV. The experimentally measured BS spectra are compared with the theoretical spectral distributions calculated from Elwert corrected (non relativistic) Bethe–Heitler [EBH] theory, modified Elwert factor (relativistic) Bethe–Heitler [Fmod BH] theory for ordinary bremsstrahlung (OB) and the Avdonina and Pratt [Fmod BH+PB] theory, which include the contribution of polarization bremsstrahlung (PB) into OB. The present results are indicating the correctness of Fmod BH+PB theory in the low energy region, where PB dominates into the BS, but at the middle and higher photon energy region of the bremsstrahlung spectrum, the Fmod BH theory is more close to the experimental results. The description of the bremsstrahlung process in stripped atom (SA) approximation, which indicates the suppression of the bremsstrahlung at higher energy ends due to the production of PB in the low energy region, needs further considerations. Hence, the present measurements for BS for different target materials indicates that the considerations of the screening effects along with other secondary effects during the interaction of incident electrons with the target nuclei are important while describing the production of bremsstrahlung, particularly for the higher energy regions.

Role of polarization Bremsstrahlung in the formation of thick target Bremsstrahlung spectra in the energy range of 5–10 keV

Role of polarization Bremsstrahlung in the formation of total Bremsstrahlung (BS) spectra in thick targets of Al, Ti, Sn and Pb, produced by complete absorption of 90Sr beta particles having an energy range of 0–546 keV, are studied in the photon energy region of 5 to 10 keV. The theoretical BS spectral photon distributions, obtained from Elwert corrected (nonrelativistic) Bethe–Heitler theory, a modified Elwert factor (relativistic) Bethe–Heitler theory that describe ordinary Bremsstrahlung (OB) and a modified Elwert factor (relativistic) Bethe–Heitler theory for BS spectra that includes the polarization Bremsstrahlung (PB) into OB in stripped atom approximation, were compared with the experimentally measured BS spectral photon distributions. It has been observed that the experimental results are in agreement with the modified Elwert factor (relativistic) Bethe–Heitler theory at photon energy from 5 to 10 keV. It has been also observed that the contribution of PB into OB decreases with increase in end‐point energy of beta emitter and the energy of the emitted photon. Further, it has been found that the contribution of PB into OB increases with increase in atomic number of the target atom. This indicates the importance of PB in the formation of BS produced by continuous beta particle. Copyright © 2012 John Wiley & Sons, Ltd.

Total bremsstrahlung spectra in targets of Al, Ti, Sn and Pb produced by complete absorption of 90Sr β particles

AbstractTotal bremsstrahlung (BS) spectra in thick targets of Al, Ti, Sn and Pb produced by complete absorption of 90Sr β particles (0–546 keV) are reported in the photon energy region of 10–30 keV. The experimental BS spectral photon distributions were compared with the theoretical BS spectral photon distributions obtained from Elwert corrected (non‐relativistic) Bethe–Heitler theory, modified Elwert factor (relativistic) Bethe–Heitler theories for ordinary bremsstrahlung (OB) and the modified Elwert factor (relativistic) Bethe–Heitler theory, which include the polarization bremsstrahlung (PB) into OB in stripped atom approximation. It has been observed that the experimental results are showing better agreement with the modified Elwert factor (relativistic) Bethe–Heitler theory having the contribution of PB at photon energy from 10 to 30 keV. This indicates the importance of PB in BS spectra, while studying the spectral photon distributions produced by continuous β particles having energy range of 0–546 keV in thick metallic targets. Further, it is observed that the contribution of PB into OB increases with increase in atomic number of the target and decreases with increase in photon energy. Copyright © 2010 John Wiley & Sons, Ltd.

Measurement of the bremsstrahlung spectra generated from thick targets with Z=2–78 under the impact of 10 keV electrons

We present new experimental data on thick target bremsstrahlung spectra generated from the interaction of energetic electrons with bulk matter. The ‘photon yields’ in terms of double differential cross-sections (DDCS) are measured for pure elements of thick targets: Ti (Z = 22), Ag (Z = 47), W (Z = 74) and Pt (Z = 78) under the impact of 10 keV electrons. Comparison of DDCS obtained from the experimental data is made with those predicted by Monte-Carlo (MC) calculations using PENELOPE code. A close agreement between the experimental data and the MC calculations is found for all the four targets within the experimental error of 16%. Furthermore, the ratios of DDCS of bremsstrahlung photons emitted from Ag, W and Pt with those from Ti as a function of photon energy are examined with a relatively lower uncertainty of about 10% and they are compared with MC calculations. A satisfactory agreement is found between the experiment and the calculations within some normalizing factors. The variations of DDCS as a function of Z and of photon energy are also studied which show that the DDCS vary closely with Z; however, some deviations are observed for ‘tip’ photons emitted from high Z targets.

Thick target bremsstrahlung spectra produced by 204Tl beta particles in the photon energy region of 10–30 keV

Total bremsstrahlung (BS) spectra in thick targets of Al, Ti, Sn and Pb targets produced by complete absorption of 204Tl beta particles are studied at photon energy from 10 keV to 30 keV. The experimental BS spectra measured with X-PIPS Si(Li) detector are compared with the theoretical BS spectra obtained from Elwert corrected (non-relativistic) Bethe–Heitler theory and modified Elwert factor (relativistic) Bethe–Heitler theories, with and without the contributions of polarization bremsstrahlung in a stripped atom approximation, described by Avdonina and Pratt (1999 J. Phys. B: At. Mol. Opt. Phys. 321 4261). It is observed that the experimental results show better agreement with the modified Elwert factor (relativistic) Bethe–Heitler theory having the contribution of polarization bremsstrahlung at photon energy from 10 keV to 30 keV. This indicates that the polarization bremsstrahlung must be taken into account while studying the spectral photon distributions produced by continuous beta particles in thick target materials.

Experimental results on 2–30 keV bremsstrahlung from thick and thin targets

The recent experimental investigations on electron bremsstrahlung produced from impact of 2–30 keV electrons with thick solid and thin gaseous targets are reviewed. The theoretical models describing the energy and angular distributions of bremsstrahlung photons are discussed with their brief outlines and formulations to explain the experimental data. The results on thick target bremsstrahlung (TTB) spectra produced by keV electrons have suggested that there is a need to develop a comprehensive theory for accounting the solid state effects. It is further noted that the prediction of the modified KKD formula gives a reasonable agreement with the TTB data, whereas a semi-empirical formula gives a better fit to the data for thick targets. The available experimental data for dependence of double differential cross-sections of emitted photons on impact energy and their emission angles for gaseous atoms and molecules exhibit a good agreement with the theoretical calculations of Kissel et al., [1983. Shape functions for atomic-field bremsstrahlung from electrons of kinetic energy 1–500 keV on selected neutral atoms 1< Z<92. Atom. Data Nucl. Data Tables 28, 381–460].

A simple method for bremsstrahlung spectra reconstruction from transmission measurements.

A new method for evaluation of bremsstrahlung spectra from transmission measurements has been developed. In this method some very well known facts relating to thick target bremsstrahlung spectra are a priori included in the calculation procedure. Some characteristics of the method are preliminarily illustrated on a 6 MV therapy linear accelerator.

Determination of electron distribution functions from thick-target Bremsstrahlung

The energy distribution functions of electrons are obtained by analysing thick-target Bremsstrahlung spectra. The method consists of expanding the unknown function on an appropriate functions basis and of solving the resulting system of linear equations. The various atomic processes involved can be treated with the desired accuracy. Applications are given for a variety of cases such as hollow cathode discharge plasmas, hot magnetized plasmas, and electron beams of travelling wave tubes. The analysis includes cases when the thick target is covered by an impurity coat.

A model for low‐energy thick‐target bremsstrahlung produced in a scanning electron microscope

AbstractThick‐target bremsstrahlung measurements were obtained for various atomic numbers and for energies between 10 and 25 keV. A Jeol JSM 6100 scanning electron microscope was used for the electron beam and a Oxford Instruments Link Si(Li) detector for the bremsstrahlung spectrum. The experimental data were compared with a model that computes the thick‐target bremsstrahlung spectrum by integrating the tabulated relativistic partial‐wave doubly differential cross‐section for thin‐target bremsstrahlung over the target taking electron energy loss into account in the continuous slowing down approximation. The model corrects for electron backscattering, x‐ray attenuation in the target and the efficiency of the x‐ray detector. Very good agreement was found between the model and the experimental results. Extension of the model to consider multiple scattering in the target is also discussed. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Thick-target X-ray bremsstrahlung spectra produced in 6.5 keV and 7.5 keVe--Hf collisions

The absolute doubly differential cross-sections (DDCS) for production of the thick-target X-ray bremsstrahlung spectra in collisions of 6.5 keV and 7.5 keV electrons with thick Hf target are measured. The X-ray photons are counted by a Si(Li) detector placed at 90° to the electron beam direction. The bremsstrahlung spectra are corrected for various ‘solid-state effects’ namely, electron energy-loss, electron back-scattering, and photon-attenuation in the target, in addition to the correction for detector’s efficiency. The DDCS values after correction, are compared with the predictions of a most accurate thin-target bremsstrahlung theory [H K Tseng and R H Pratt,Phys. Rev. A3, 100 (1971); Kisselet al, Atomic Data Nucl. Data Tables 28, 381 (1983)]. Also, a dependence of the absolute DDCS on atomic numberZ of the targets (47Ag,79Au and72Hf) at 7.0 keV and 7.5 keV electron energies has been studied. The agreement between experiment and theory is found to be satisfactory within 27% systematic error of measurements. However, an apparent systematic difference between experiment and theory in the region of low-energy photons has been explained qualitatively by considering the fact that the hexagonal atomic structure of Hf offers possibly a greater magnitude of ‘solid-state effects’ in respect of blocking the low-energy bremsstrahlung photons from coming out of the target surface than does the cubic-face centered structure of Ag and Au target in similar conditions of the experiment.

Inversion of Thick Target Bremsstrahlung Spectra from Nonuniformly Ionised Plasmas

The effects of non-uniform plasma target ionisation on the spectrum of thick-target HXR bremsstrahlung from a non-thermal electron beam are analysed. In particular the effect of the target ionisation structure on beam collisional energy losses, and hence on inversion of an observed photon spectrum to yield the electron injection spectrum, is considered and results compared with those obtained under the usual assumption of a fully ionised target.

Efficiency calibration of a Si(Li) detector in the low-energy region using electron bremsstrahlung

In the low-energy region the determination of the detector efficiency is complicated by the fact of nonavailability of certificated calibration sources. To solve this problem the use of electron bremsstrahlung for determining the relative photon detection efficiency of a Si(Li) detector in the low-energy range 0.5–19 keV is proposed. The calibration is based on energy dispersive measurements of electron bremsstrahlung emitted by an X-ray tube. Model spectra are computed from thick-target bremsstrahlung spectra in a semiclassical approximation and from a physical model for the detector response. Model spectra are fitted to the measured spectra using a parametric adaptor term. Thereby, the error of the determined detector efficiency is approximately 5%.

Experimental thick-target bremsstrahlung spectra from collisions of 7.0-keV electrons with Ag and Au.

The x-ray spectra produced from 7.0-keV electrons in bombardment of thick targets of silver and gold have been measured using a Si(Li) detector at 90\ifmmode^\circ\else\textdegree\fi{} to the incident electron-beam direction. The spectra were corrected for electron backscattering, energy loss, photon attenuation in the target, and for inherent filtration, allowing a determination of absolute intensity for x-ray emission. The experimental spectra have been compared with two models, (i) a modified Kramers formula, and (ii) a semiempirical expression. There is an overall agreement between the experiment and the predictions of the models both for the shape and for the absolute magnitude of the thick-target bremsstrahlung intensity to within 21%. \textcopyright{} 1996 The American Physical Society.

Comparisons of thick-target bremsstrahlung calculations by EGS4/PRESTA and ITS version 2.1

Two Monte Carlo codes, EGS4/PRESTA and ITS version 2.1, have been used to calculate spectral distributions of bremsstrahlung and annihilation quanta in 10–30 MV beams from thick targets of Be, Al, and Pb. Spectra are absolute (photons per incident electron) and calculated in 44 annular regions of 1° widths, covering all angles. It was found necessary to do ITS calculations using shortened sub-step sizes for electrons near the target surface to remove a 30–40% error in the angular distribution of bremsstrahlung at small angles that occurs when using default sub-step sizes. The EGS calculations were done using the enhancement which randomly samples the bremsstrahlung angle from an appropriate distribution and giving due consideration to K-shell X-rays. A survey is done of the remaining discrepencies in the spectral distributions of fluence, the total fluence and the mean energies of each spectrum. In general, EGS and ITS agree to ±20% for fluence and ±5% for mean energy. Results are compared to a set of high-precision measurements of absolute thick-target bremsstrahlung spectra used previously to show that EGS is reliable to ±10% for fluence and ±2% for mean energy. The measurements did not clearly identify a strong preferance towards either EGS or ITS.

Calculation of bremsstrahlung spectra from a thick tungsten radiator as a function of photon energy and angle

A method for the calculation of bremsstrahlung spectra produced by 5–30 MeV electrons is described for the case of a thick tungsten radiator at observation angles from 0° to 20°. The computation is based on Shiff integrated-over-angle bremsstrahlung cross-section and includes energy losses, absorption and multiple scattering of the electrons in the radiator, the variation of the bremsstrahlung cross-section angular distribution with photon energy, and the absorption of radiation in the target material. The results obtained by the offered method were compared with known experimental data and Monte Carlo calculations of thick target bremsstrahlung spectra. A basic advantage of this method is that it needs only a small memory and short computing time.

Bremsstrahlung review: An analysis of the Schiff spectrum

A concise approximate formula computed by Schiff for the intensity spectrum of bremsstrahlung photons has been a valuable starting point for many medical physics applications, including the Task Group 21 protocols. This paper provides a brief review of the literature related to determination of the bremsstrahlung spectrum and to the Schiff formula in particular. It describes the approximations Schiff made to obtain this formula, including the Born approximation, and the exponential nuclear screening potential, the infinite-mass nucleus approximation, and the "extreme relativistic" approximation. A derivation of a more exact formula that avoids the last of these approximations is presented. This provides a check on the accuracy of the Schiff spectrum for linear accelerator energies used clinically. Comparisons with the Schiff thin-target result are presented. A thick-target bremsstrahlung spectrum is calculated and compared with the forward spectrum obtained from Monte Carlo simulations of the x-ray production in two linear accelerator treatment heads.

Measurements and simulations of low energy, thick target bremsstrahlung spectra

Abstract Nuclear resonance fluorescence (NRF) experiments on the isotopes 13 C, 23 Na, 27 Al, 31 P, 35 Cl, and 48 Ti with transitions of known strengths have been performed to determine the relative spectral shape of low energy, thick target bremsstrahlung spectra. The experimental results (endpoint energy E 0 = 4.1 MeV) are compared with Monte Carlo simulations. It is concluded that a linear function represents a rather precise approximation of the shape of this bremsstrahlung spectrum near the endpoint energy. Therefore, a linear interpolation of the photon flux between well known data points enables a fast and sufficiently precise analysis of NRF experiments using photon sources of this kind.