Modelling of X-ray tube spot size and heel effect in Arion

X-rays produced in X-ray tubes originate from a focal spot on the target material. This spot is not infinitely small, but has a finite size. This finite size of the spot will affect the radiographic projections taken during X-ray Compted tomography. In order to simulate correct radiographic projections, this finite spot size needs to be taken into account during the simulations. This can be done by modelling a two dimensional profile of the spot and use this model to convolve the simulated radiographic projections simulated with an infinitely small spot size. A second effect, the heel effect that originates in directional X-ray tubes will also have an influence on the final projections. This effect can also be modelled and this model can be used to correct the simulated projections for this effect