- Main
Position Sensitive Proximity Charge Sensing Readout of HPGe Detectors
- Priest, Anders Peterson
- Advisor(s): Vetter, Kai
Abstract
Electrode segmentation is a necessity to achieve position sensitivity in semicon-
ductor radiation detectors. Traditional segmentation requires decreasing electrode
sizes while increasing channel numbers to achieve very fine position resolution. These
electrodes can be complicated to fabricate, and many electrodes with individual
electronic channels are required to instrument large detector areas. To simplify
the fabrication process, we have moved the readout electrodes onto a printed cir-
cuit board that is positioned above the ionization type detection material. In this
scheme, charge from radiation interactions will be shared amongst several electrodes,
allowing for position interpolation. Because events can be reconstructed in between
electrodes, fewer electrodes are needed to instrument large detector areas. The prox-
imity charge sensing method of readout promises to simplify detector fabrication
while maintaining the position resolution that is required by fields such as home-
land security, astrophysics, environmental remediation, nuclear physics, and medical
imaging.
We performed scanning measurements on a proof of principle detector that we
fabricated at Lawrence Berkeley National Laboratory (LBNL). These measurements
showed that position resolution much finer than the strip pitch was achievable using
the proximity charge readout method. We performed analytic calculations and Monte
Carlo modeling to optimize the readout electrode geometry for a larger detector to
test the limits of this technology. We achieved an average position resolution of 288
μm with eight proximity electrodes at a 5 mm pitch and 1 mm strip width, set 100
μm away from the detector surface by a Kapton spacer. To achieve this resolution
using standard technologies, 300 μm pitch strips are necessary, and would require
100 channels to instrument the same area. Through our optimization calculations,
we found that there is a trade-off between position resolution and energy resolution,2
and this system provided comparatively poor energy resolution by HPGe standards,
with 4.7 keV FWHM at 59.5 keV. With another electrode geometry, we were able
to achieve 2.9 keV FWHM at 59.5 keV. This dissertation describes the work we
completed to achieve these results.
Main Content
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