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.