Characteristics of an ethylene-polyethylene high-pressure ionization chamber and its potential for deriving radiation dose and quality information in neutron-gamma radiation fields.

A recently developed method for measuring dose and quality parameters in mixed neutron-gamma radiation fields is extended for neutron energy regions relevant to current neutron therapy. It is theoretically shown that if a polyethylene high-pressure ionization chamber filled with a gas mixture of 95% ethylene and 5% carbon dioxide is used at suitable gas pressures, it may overcome the limitations found for a similar tissue-equivalent chamber and measure both the gamma ray absorbed dose-fraction and the mean incident neutron energy for neutrons between 0.1 and at least 30 MeV, if certain conditions exist. The simultaneous use of the polyethylene high-pressure ionization chamber as a conventional neutron dosimeter also allows determination of both the neutron and gamma ray absorbed doses. Estimated accuracies are 15% for the mean incident neutron energy and 15%-30% for the doses determination. The present method may complement currently available techniques as it presents certain advantages in situations where the neutron spectrum is poorly known. If coupled with other dosimeters, the accuracy of the method can be improved.