The photon sensitivity of a moderated activation neutron detector

A method is described for estimating the overresponse produced by neutrons generated in the hydrocarbon moderator of a neutron dosimetry system by photon reactions. It is shown that photon interactions in the moderator produce an apparent neutron fluence per unit absorbed dose of 1.40 X 10(6) n/cm2/Gy-x for a flattened 33-MV x-ray beam and 2.66 X 10(6) n/cm2/Gy-x for the same beam without the flattening filter in place. The photon response of the moderated activation neutron detector was found to decrease rapidly with end point energy of the x-ray beam in the range 33 to 18.7 MeV.