Neutron-induced backgound in proportional counters for x-ray astronomy

The influence of the secondary neutrons and photons, produced by cosmic ray interactions with the spacecraft, on the background of X-ray proportional counters used for astronomical observations from satellite, is investigated by means of two Monte Carlo codes. The GEANT3 code has been used to simulate the production and transport of particles and gamma rays in a structure that reproduces the masses and the materials of the satellite Spectrum-X-Gamma, to a relatively high degree of accuracy. Then, the MCNP code has been used to simulate the behavior of the multiwire proportional counters of SXRP, described in detail in a 3-D geometry, exposed to the neutron and gamma flux resulting from the interactions of the primary cosmic protons with the satellite. Preliminary results indicate that the photons produced as secondary particles in the structures of the satellite overwhelm by an order of magnitude those of the diffuse celestial background directly transmitted through the same structures, and that the estimated counting rate induced by the secondary neutrons and photons is comparable with that observed in similar space missions.