On the limits of the Influence Method in the determination of the intrinsic efficiency of liquid scintillators

The limitations of the Influence Method for the determination of the intrinsic efficiency of a EJ-301 liquid scintillator to gamma-rays and neutrons in the MeV range is presented. Discrepancies between the intrinsic efficiencies, measured according to the Influence Method, and their accepted values are reported and investigated using MCNP6. It was found that this discrepancy is caused by multiple scattering of both gamma-rays and neutrons in the detector, effects which are not properly accounted for in the Influence Method. Correction factors have been calculated in MCNP6 for different detector geometries and different gamma-ray and neutron energies. A simple correction factor is derived, which can be used to calculate the correct intrinsic efficiency for similar detectors using the Influence Method without having to recur to Monte Carlo simulation.