Extended gamma sources modelling using multipole expansion: Application to the Tunisian gamma source load planning

In this work, we focus on the effect of the source geometry for radiation profile studies using the generalized Laplace's expansion. We develop a new method to express the bare gamma photon flux rate in terms of the standard Cartesian multipole moments. Using the properties of these moments we establish a close relationship between the radiation profile and the geometrical features of the source. As application a detailed study of the arrangement of the unit pencil sources of the Tunisian irradiation facility is performed. Using this method, millions of possible configurations for various load plans were investigated, in a reasonable time and even multisteps scenarios were considered. Furthermore, using this analytical method it was even possible to optimize the activity of each new unit source.