A Geiger-Müeller γ-ray Dosimeter With Low Neutron Sensitivity

It has been shown that a commercially available halogen type Geiger-Müeller counter when properly shielded with Sn and Pb provides a very practical and satisfactory device for measuring the dose due to γ-radiation in the presence of neutrons. The device measures the dose in roentgens with nearly uniform response for effective X-ray energies above about 200 keV and up to at least 1.25 MeV γ-energies. Calculations show that the fast neutron response is less than 0.15 per cent, and experiments indicate that it is less than 0.5 per cent. Experiments show that about 5 × 109 thermal neutrons per cm2 give a response equivalent to 1 r of γ-radiation. When necessary, the thermal neutron response can be decreased by a factor of 300 by using a Li shield described in the text.