Scattering in two targets with the vector code MCSHAPE

Using the Monte Carlo code MCSHAPE, some simulations have been made by varying the angle between the scattering plane with the incident beam (defined by the incident beam and the beam 1) and the scattering plane of the collision with the second target (defined by beam 1 and the outgoing beam). The code MCSHAPE, in fact, can simulate the behaviour of arbitrarily polarised photons and can follow the evolution of their polarisation state after the interaction with the atoms. The polarisation state of the photons is described using the Stokes parameters I, Q, U and V, having the dimension of an intensity and containing all the physical information about the polarisation state. Simulated experiments with a monochromatic unpolarised source of 59,54 keV (main gamma line of 241Am) and with an x-ray tube source have been considered. In the first case, the results of the simulations show that, after the 90° scattering in the first target, a part of the scattered beam (beam 1) is polarised (the degree of polarisation is a function of energy, and as it is shown, for some energies, 90% of the beam is polarised), but it is not fully polarised as for the single scattering (this is an effect of the multiple scattering in the target).The intensity collected by the detector, after the scattering with the second target, depends on the rotation between the first and the second pieces of the tube. The scattering is drastically reduced for a rotation angle around 90°, even if, due to multiple scattering, it is not zero. This behaviour was tested also with polychromatic excitation.