TY - JOUR

T1 - Effect of prolonged annealing on the performance of coaxial Ge gamma-ray detectors.

AU - Owens, A.

AU - Brandenburg, S.

AU - Buis, E.-J.

AU - Kozorezov, Alexander G.

AU - Kraft, S.

AU - Ostendorf, R. W.

AU - Quarati, F.

PY - 2007/1/11

Y1 - 2007/1/11

N2 - 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.

AB - 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.

KW - Cryogenic detectors

KW - Gamma detectors (scintillators

KW - CZT

KW - HPG

KW - HgI etc)

KW - Radiation damage to detector materials (solid state)

U2 - 10.1088/1748-0221/2/01/P01001

DO - 10.1088/1748-0221/2/01/P01001

M3 - Journal article

VL - 2

JO - Journal of Instrumentation

JF - Journal of Instrumentation

SN - 1748-0221

IS - P01001

ER -