Abstract
The halogen quench gas present within a Geiger-Müller detector will govern its operational lifetime. Such halogen gases are highly corrosive and are very likely to interact with their surroundings. This factor must be taken into account when designing GM detectors to extend their lifetimes. The quench gas depletion is thought to be linked to the current resulting from the gas ionisation from each detection event. As such, GM detector lifetimes are typically expressed in units of total counts accumulated. At elevated temperatures, the molecules will possess more thermal energy and become more likely to interact. To preserve the amount of halogen gas in each detector, three different corrosion-resistant techniques have been considered for investigation; the samples used are ZP1200 GM detectors that consist of 446 stainless steel components. The surface treatment techniques used to prepare each sample were labeled as “raw” for an oxygen plasma process, “passivated” for a combination of a nitric acid passivation and an oxygen plasma process and, finally, “plated” for a combination of a chromium plating process and an oxygen plasma process. The effectiveness of each process has been studied at temperatures of up to 175 oC. A Caesium-137 source was used to age all detector samples by irradiating them with dose rates of 1.3 mSv/hr. 32 samples were aged at room temperature and another 32 samples were aged in parallel at an elevated temperature of 125 oC. At room temperature, all detector types produced stable detectors with operational parameters that did not change significantly with age. The plated samples did show an initial rise in their starting voltage (Vs) measurements. At 125 oC, the plated detectors produced the most stable lifetime performance after an initial Vs conditioning period. The passivated and raw detector samples, however, showed a drop in their Vs values. Preliminary studies carried out at 175 oC confirm the superiority of the chromium plating process at resisting performance degradation at elevated temperatures. After investigating the surfaces of the detector components, no changes with age in the bromine content were observed. The plated cathodes showed no bromine deposits when investigated using Energy Dispersive X-Ray Spectroscopy. Bromine was detected on the passivated and raw cathode surfaces, but its quantity remained unchanged with age. The impact of contamination on the performance of gas-filled radiation detectors was also investigated in collaboration with the Institut Laue-Langevin in Grenoble, France.