Effect of prolonged annealing on the performance of coaxial Ge gamma-ray detectors.

Owens, A. and Brandenburg, S. and Buis, E.-J. and Kozorezov, Alexander G. and Kraft, S. and Ostendorf, R. W. and Quarati, F. (2007) Effect of prolonged annealing on the performance of coaxial Ge gamma-ray detectors. Journal of Instrumentation, 2 (P01001). ISSN 1748-0221

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The effects of prolonged annealing at elevated temperatures have been investigated in a 53cm3 closed-end coaxial high purity germanium detector in the reverse electrode configuration. The detector was multiply annealed at 100°C in block periods of 7 days. After each anneal cycle it was cooled to 77 K and the relative efficiency, peak channel location and FWHM energy resolution measured at 6 gamma-ray energies. At the present time, the detector has completed 16 anneal cycles. It was found that above ~ 662 keV the photopeak efficiency decreased almost linearly at a rate of ~ 1.5% per anneal cycle, although the energy resolution and centroid (and therefore charge collection efficiency) remained unchanged. The change in detection efficiency is attributed to the expansion of the inner n+ contact due to the thermal drive-in of Li ions into the bulk. The rate is found to follow a power-law dependence in agreement with that expected from Fick's diffusion laws. Using these data, we have derived a simple 1-D phenomenological model in which the n+ contact thickness is simply related to the Li diffusion length. For annealing at 100°C, the thickness of the n+ contact, d, as a function of the annealing time, t, can be described semi-empirically by d(mm) = 0.231 × t(days)1/2.

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Journal of Instrumentation
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31 Oct 2008 10:12
Last Modified:
01 Jan 2022 08:40