Calculation of thick target electron bremsstrahlung spectra with collimation at high energies

Abstract

Calculations have been performed of the spectral distribution of bremsstrahlung photons produced by high energy electrons in targets of thickness up to several tenths of a radiation length. Consideration is given to the influence of a collimator on the energy distribution of the photons. It is shown that collimation can lead to considerable relative enhancement of the high energy content of thick target spectra, particularly for collimators subtending angles of the order of m/ E 0 at the bremstrahlung target. In the calculation of the un-collimated thick target spectrum shape, allowance is made for the emission of more than one photon by the same electron and for the loss of photons by pair production and Compton scattering. The thin target Bethe-Heitler cross section is used in the computation. Consideration of multiple Coulomb scattering of the incident electrons in the target and their subsequent emission of bremsstrahlung with an angular distribution derived from the Schiff cross section leads to an estimate of the effect of collimation on the thick target spectral distribution. The relative importance of the various processes is discussed and some examples are given of the results of the computations.