MEASUREMENT OF NEUTRON AND GAMMA-RADIATION IN A MIXED FIELD

This paper describes a study of dosimeters with a range of 0 to 0.2 mG y that were developed by the authors and built by the Federal Emergenc y Management Agency (FEMA), These instruments are a type of air-filled ion chamber that is self-reading by means of an internal carbon fiber electrometer. Two types of these dosimeters were constructed: one wit h an ion chamber wall made of a conductive hydrogenous material, and t he other device made with a conductive wall lining of non-hydrogenous material. Both types of dosimeters have the same sensitivity for gamma radiation, but greatly different sensitivities for fast neutrons, thu s making it possible to measure gamma radiation and neutron doses sepa rately in a mixed radiation field. The results indicate that such pair s of dosimeters can be used for the first time to accurately monitor p ersonnel for gamma ray and neutron doses in real time, Since the diffe rence in neutron sensitivities is due to the properties of wall materi als, periodic calibrations of the dosimeter system can be accomplished using only gamma rays after the material constants are measured. The absolute number of neutron induced transmutations in sulfur was requir ed for this work. Methods and techniques which were applied to determi ne this quantity are described in the text. This approach was one of s everal dosimetric procedures utilized in this investigation.