An experimental study of the relative response of plastic scintillators to photons and beta particles

A scintillation counting system has been constructed with the use of BC-400 and EJ-212 series plastic scintillators along with a subminiature photomultiplier tube to investigate the effect of increasing plastic scintillator thickness on system-integrated counts. Measurements have been carried out using four different gamma sources with different energies ranging from 6 keV to 1.332 MeV and a Ni-63 beta source with a maximum energy of 66 keV. Scintillator thicknesses ranged from 10 μm to 2500 μm. The response of the system was determined by measuring the integrated counts as a function of scintillator thickness. These experimental findings were used to empirically determine the optimum thickness of scintillator material with which to build a low energy beta detector which discriminates against high energy gamma photons in a mixed radiation field environment.

► Examined the response of thin plastic scintillators to photons and beta particles.
► Plastic scintillators used were the EJ-212 and BC-400 series.
► Positive linear correlation found for all gamma sources (Fe-55, Am-241, Cs-137, Co-60).
► 250 μm found to be the optimal scintillator thickness for photon-beta discrimination between Co-60 and Ni-63.
► A dose rate of 237 μGy/hr from Co-60 photons was used as the test of discrimination between photons and Ni-63 beta particles.