Optimization of the Canberra UltraRadiac GM Tube Wrapping

The UltraRadiactrade personal radiation monitor is a ruggedized handheld dose rate and total dose monitoring device intended for use by first responders in the harsh environments that firefighters, Hazmat teams, paramedics and military personnel may encounter. The device is based on Geiger-Mueller (GM) tubes with lead and tin wrappings. Different options exist for different dose ranges. The photon radiation interacts with the GM tube wrapping through Compton scattering and the scattered electrons are counted through ionization in the fill gas. The amount of the ionization created in the Geiger discharge saturates and becomes independent of the initial energy deposit in the gas. The thickness of the wrapping material must be carefully optimized however in order to obtain a fairly uniform energy response to the incident photons that give rise to the secondary ionizing electrons which are actually counted. MCNP simulations and benchmark measurements were performed to establish a suitable energy compensation filter design. The results of the study will be presented and the performance of the selected design summarized in this paper.