Detection of high-energy photons and fast neutrons with BaF2 scintillators

Extensive Monte-Carlo calculations using the code GEANT3 have been performed for the design of a spectrometer for photons (π0,η) at GSI Darmstadt. Simulations of the photon-induced electromagnetic shower in BaF2 showed, that for photon energies below 100 MeV a detector of 20 cm length is sufficient, while at higher energies the detector length has to increase to 25 cm to provide the necessary efficiency and energy resolution. Calculated lineshapes compare very well with experimental data obtained at a photon energy of 50 MeV. Properties of BaF2 as a detector of neutrons with kinetic energies below 22 MeV were studied. The detection efficiency strongly depends on the light-output threshold, since the detector response is of exponential shape. The pulse shape analysis used to distinguish photons from charged particles does not allow to separate photons from neutrons at energies below 22 MeV. However, at neutron energies above 11 MeV we observe the appearance of a detection mechanism involving charged particles in the exit channel. (orig.)