Analysis on influence of beam emittance on spatial distribution of exposure using Monte Carlo simulation

The exposure at 1 m just in front of the target is an important parameter for evaluating the radiation ability of the accelerator light source. The X-ray photons produced by the electron beam striking a high-Z target show a distinct forward angular distribution, so the spatial distribution of the exposure is closely related to the beam emittance. The Gauss model is applied to simulate the positional distribution and the directional distribution of the incident electrons interacting with the convertor target for various beam emittances. The bremsstrahlung radiation process that the electron beam impinges on the target is simulated utilizing the Monte Carlo method, by which the influence of the beam emittance on the exposure is analyzed. The exposure of the bremsstrahlung light source using the multi-foil target is also calculated and compared with the one using the standard slab target. The results indicate that the divergence angle of the electron beam is the main factor that affects the exposure of the bremsstrahlung radiation. Compared with using the slab target, the spatial distribution of the exposure obtained by using the multi-foil target is basically the same except that the exposure decreases by 2%-3% within a small angular range of 0-4.