Study of an electron linac driven x-ray radio-tomographic system response as a function of the electron beam current

At the Dipartimento di Fisica, Universita di Messina, a high energy X-ray radio-tomographc system driven by a 5 MeV electron linac, has been recently assembled. It has been tested and has already provided good results in inspecting heavy materials. In order to achieve good radiographic results, especially when inspecting heavy or thick materials, an enhancement of the X-ray dose at the sample position can be required and most of times this is associated to an enhancement of the grey level in the acquired image, according to a linear function. Nevertheless, in the hypothesis to work at the maximum magnetron power, a variation of the X-ray dose, obtained changing the electron beam current, is associated to a variation of the electron beam energy. As a consequence, the X- ray energy spectrum varies thus influencing the response of the radio-tomographic system. This does not allow a linear correspondence between the X-ray fluence (or the electron beam current) and the image grey level. By means of MCNP-4C2 simulations, the influence of electron beam energy variations on the produced bremsstrahlung spectrum has been studied and the theoretical results seems to be confirmed by the preliminary experimental ones.