Bremsstrahlung spectra produced by 10-25 keV electron impact on thick W, Au targets

Abstract

Bremsstrahlung emission produced by electron impact on thick or thin targets is one of the fundamental radiation processes, and the interest in its study continues to grow because of its importance for understanding the interaction of electrons with matter and also for many practical applications. Nowadays, there has been some disagreement concerning whether or not the polarization bremsstrahlung, which is emitted by the atomic electrons in a target polarized by the incident charged particles, contributes to the total bremsstrahlung when the incident electrons bombard a solid target. Some reports suggested that the polarization bremsstrahlung does not significantly contribute to the total bremsstralung in experiments involving solid targets. However, some recent experimental data indicated that a significant amount of polarization bremsstrahlung contributes to the total bremsstrahlung when electrons from -decays of radioactive nuclei bombard solid targets. In other papers, the comparison between the bremsstrahlung spectra produced by electron impact on different thick solid targets from low-Z to high-Z elements and the simulation spectra of Monte Carlo code PENELOPE showed that there are certain discrepancies between the experimental and simulation results, and on the whole the factors required for the experimental results and simulation spectra to match with each other seem to increase slightly with the target atomic number increasing and for high-Z elements experimental results are about 10% higher than simulation results. PENELOPE is a general-purpose Monte Carlo code that simulates coupled electron-photon transportation, in which simulation for bremsstrahlung is only based on ordinary bremsstrahlung and any contribution from polarization bremsstrahlung is not included Therefore, whether the discrepancies between the experimental and simulation spectra are caused by the polarization bremsstrahlung or by other reasons remains to be further studied. In this paper, we improve the Faraday cup to measure the incident electron charges more accurately Meanwhile, a highpurity Al film of 7.05 m thickness is placed in front of the ultra-thin window of the X-ray silicon drifted detector (SDD) to prevent the backscattered electrons that escape from the side hole of the Faraday cup entering into the SDD detector. The Al film thickness is measured by the method of Rutherford backscattering. In addition, we adopt a data processing method which is different from previous one, to take into account the interaction between backscattered electrons and the window of the SDD detector. New measurements of bremsstrahlung spectra generated by 10-25 keV electron impact, respectively, on thick targets of tungsten and gold are reported in this paper. The experimental data are compared with the simulation results of X-ray spectra obtained from the PENELOPE code, and they are in very good agreement except for the lower energy region ( 3 keV) where the experimental spectra are slightly lower than the simulation spectra. The reason for the small discrepancy for the lower energy region ( 3 keV) is also discussed. The results presented in this paper indicate that the X-ray spectra, which are produced by electron impact on solid targets, do not include obvious contribution of polarization bremsstrahlung, and the PENELOPE code can reliably describe the bremsstrahlung produced by electron impact on solid thick targets.