Angular distributions of absorbed dose of Bremsstrahlung and secondary electrons induced by18-, 28- and 38-MeV electron beams in thick targets

Abstract

Angular distributions of absorbed dose of Bremsstrahlung photons and secondary electrons at a wide range of emission angles from 0 to 135 degrees, were experimentally obtained using an ion chamber with a 0.6 cm 3 air volume covered with or without a build-up cap. The Bremsstrahlung photons and electrons were produced by 18-, 28-, and 38-MeV electron beams bombarding tungsten, copper, aluminum, and carbon targets. The absorbed doses were also calculated by multiplying simulated photon and electron energy spectra with simulated response functions of the ion chambers, using the MCNPX code. Our simulation results agree with the experimental results, within a factor of 2, over wide ranges of emission angles, incident electron energies, and atomic numbers of targets. The angular distributions of absorbed doses at forward angles for incident energies are similar to those for targets. On the other hand, the absorbed doses at backward angles depend on target species. The dependences of absorbed doses on electron energy and target thickness were compared between the measured and simulated results, and showed good agreement. We also measured the attenuation profiles of absorbed doses of Bremsstrahlung beams at 0, 30, and 135 degrees to the electron beam axis. Simulated attenuation profiles agree, in relative values, with the experimental results at incident electron energies and angles. To achieve further accuracy of calculation, angular absorbed-dose measurements are necessary for bremsstrahlung radiation dosimetry.