Proximity charge sensing readout in HPGe detectors

Semiconductor-based radiation detectors are routinely used for the detection, imaging, and spectroscopy of x-rays, gamma rays, and charged particles for applications in the areas of nuclear and medical physics, astrophysics, environmental remediation, nuclear nonproliferation, and homeland security. Detectors used for imaging and particle tracking are more complex in that they typically must also measure the location of the radiation interaction in addition to the deposited energy. In such detectors, the position measurement is often achieved by dividing or segmenting the electrodes into many strips or pixels and then reading out the signals from all of the electrode segments. Fine electrode segmentation is problematic for many of the standard semiconductor detector technologies. Clearly there is a need for a semiconductor-based radiation detector technology that can achieve fine position resolution while maintaining the excellent energy resolution intrinsic to semiconductor detectors, can be fabricated through simple processes, does not require complex electrical interconnections to the detector, and can reduce the number of required channels of readout electronics. Proximity electrode signal readout (PESR), in which the electrodes are not in physical contact with the detector surface, satisfies this need. Our overall project vision is to develop a prototype large-area HPGe strip detector using PESR paired with a low cost, high density spectrometer capable of real time signal processing. In earlier work we successfully demonstrated the concept of the proximity sensing in HPGe detectors by employing a small detector prototype in single sided strip configuration and reconstructing the gamma-ray energy while achieving sub-strip pitch position resolution. This proposed work seeks to demonstrate the performance potential of PESR technology on a large area HPGe detector using XIA electronics. The goal of this work is to assess performance standards of PESR versus those of well-established, conventional readout technologies. In Phase II we will develop a prototype, many channel, three-position sensitive HPGe detector based on this promising technology. Detailed characterization and modeling of the detectors will guide the optimization of the fabrication processes and permit a better understanding of complex gamma-ray interaction topologies and charge collection. Signal processing algorithms that enable the determination of energies and positions of the gamma-ray interactions will be refined and optimized. Prototype high density, high speed XIA spectrometers will be modified to allow for real-time signal processing required in high count rate applications. Existing and emerging semiconductor imaging markets have a need for a readout technology that simultaneously simplifies detector fabrication, reduces cost, expands user flexibility, improves resolution, reduces the number of readout channels and is more durable. The lack of commercially available electronics tailored to the requirements imposed by strip detectors is a further obstacle to their wider use. This problem is addressed by proximity electrodes which are not in physical contact with the detector surface readout by low cost, high density electronics tailored for imaging applications. Our overall project vision is to demonstrate the viability of a large HPGe strip detector using novel proximity sensing electrodes paired with a low cost, high density spectrometer capable of real time signal processing.