Introduction

A detailed simulation of the geometry and of the involved physics processes is required from the very early stages of a new instrument development. Indeed both the development and the optimization of new-instrument concepts, performed with detailed comparisons between different configurations, as well as the detailed characterization of instrument responses and the verification of the scientific objectives of a new instrument, require the same detailed simulation.

Geant4 is an object-oriented toolkit for the simulation of high-energy physics detectors that is now widely used in nuclear physics, medical physics, astrophysics, space applications, radiation background studies, etc. Geant4 is supported by a large international collaboration with the participation of various institutes around the world. It is also an experiment in the application of rigorous software engineering methodologies.

In particular the physics is open to the user, who has the possibility to select among different models of the same physics process or to extend existing models to cover new requirements.

Polarized photon interactions in Geant4

The Compton and Rayleigh processes are affected by the polarization of the incoming radiation, and even an unpolarized beam acquires a certain degree of polarization after a Compton or Rayleigh event. So a description of these processes in which the polarization is present is particularly relevant even though the incoming radiation is not polarized.