Investigation of temperature effects on electro mechanically cooled Ge detectors

Abstract The motivation for this project originated due to anecdotal evidence that Ge detectors encountered problems with energy resolution when they were located in uncontrolled environmental conditions, in which temperature variations can be as great as 30°�C. This project aims to investigate how much of an effect this temperature variation has on the resolution of the detectors and if so to what extent. Three Ge detectors were used in this project, an Ortec electro mechanically cooled Xcooler detector, an Ortec liquid nitrogen cooled detector and a Canberra cryo-cycle hybrid electro mechanical/ liquid nitrogen cooled detector. The ambient room temperature was controlled between temperatures of � 5 - 30oC and the energy resolution for the 60, 122, 779 and 1408 keV gamma peaks was determined for each of the three detectors at both low (1000counts/sec) and high (20,000counts/sec) count rates. Plots of normalised resolution versus ambient room temperature were analysed. The results for the Ortec Xcooler detector concluded that there was no significant change in resolution within error for low count rate data, however, there was evidence for a small but statistically significant change in resolution of the high energy gamma rays at high count rates. The Canberra Cryocycle detector showed a significant improvement in resolution for the low energy gamma peaks at low count rates, with some weak evidence suggesting that the resolution of the low energy gamma rays of the high count rate data may follow a similar trend. Finally, the Ortec Liquid Nitrogen cooled detector did not display any significant changes in resolution within errors at both low and high count rates. Further verification is necessary to confirm these results but the Ortec Xcooler detector and the Canberra Cryocycle detector both exhibit preliminary results that support the anecdotal evidence put forward by Sellafield, however, in the case of the Ortec Liquid Nitrogen cooled detector, this anecdotal evidence was unfounded.