SBIR-STTR Award

Semiconductor-based radiation detectors are routinely used for the detection, imaging, and spectroscopy of x-rays, gamma rays, and charged particles in nuclear and medical physics, astrophysics and Homeland Security applications. Imaging with HPGe, Si or CdZTe is an increasing segment of radiation detection. Position sensitive implementations needed for imaging or tracking of radiation are most often realized by segmenting the electrical contacts in one or two dimensions. In order to achieve sufficient position resolution, many segments have to be implemented which is associated with complex fabrication processes to obtain a reliable and high-resolution detector and a complex and costly readout scheme to process the signals from each segment. The yield in the fabrication as well the reliability of operation, and the performance of high-energy and position resolution and large-volume semiconductors suffer due to these complexities. We propose to develop and demonstrate an alternative approach to obtain a position-sensitive detection of radiation, which is significantly easier to realize and provides excellent position resolution, reliability, and superior flexibility in adjusting segmentation and readout schemes according to experiment-specific requirements. The proposed approach of employing close-proximity electrodes to obtain energies and positions of radiation interaction will enable a significantly simpler detector fabrication process and readout configuration. It will provide the ability to adjust the resolution according to experimental requirements without re-fabricating the detector. In addition, close proximity electrodes can be used to measure specific charge losses due to charge collection on non-contact surfaces. Such processes are observed in semiconductor detectors due to imperfect surfaces and passivation techniques. Employing proximity electrodes close to these non-contact surfaces will allow us to observe these events which deteriorate the performance of the detector. These events can then be further processed to improve the response of the detector. Another major benefit of the proximity sensor approach is that charge appears and is fully integrated on all electrodes, dispensing with the need for computationally expensive spectator signals. Commercial Applications and Other

Benefits:
If this concept can be successfully demonstrated for imaging as well as particle tracking applications, we envision developing a marketable product available for commercial applications, basic and applied research, and for several branches of the federal government. Estimates: Biomedical research field is large in instrumentation ( & gt$100M), nuclear security is medium ( & gt$10M), Research demands in imaging is medium ( & gt$10M)

Semiconductor-based radiation detectors are used in 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 as they typically must also measure the location of the radiation interaction in addition to he deposited energy. In such detectors, the position measurement is generally achieved by dividing or segmenting the electrodes into many strips or pixels and then reading out the signals from all electrode segments. This requires complex detector fabrication and signal readout processes and is often associated with high cost, low yield, and high power requirements. There clearly is a need for a 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, in which the electrodes are not in physical contact with the detector surface, satisfies these needs. On equal footing is the need to develop low cost, high density readout electronics adapted to the unique demands required in a proximity electrode readout detector. 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. Phase I allowed us to successfully refine the concept of the proximity sensing in HPGe detectors by employing a large area detector prototype in single sided strip configuration and reconstructing sub-strip pitch position resolution. In Phase II we will further develop and optimize this promising new technology resulting in a fully operational, multi-dimensional position sensitive HPGe detector with real-time processing and display of energies and positions. We will achieve this goal through detailed characterization and modeling of the detectors, which will guide the optimization of the fabrication processes and implementation of proximity sensing HPGe detectors. In parallel we will refine and optimize signal processing schemes that enable the determination of energies and positions of the gamma-ray interactions in real time. Commercial Applications and Other

Benefits:
If this concept can be successfully demonstrated for imaging as well as particle tracking applications, XIA and our commercialization partner ORTEC will develop benchtop and portable products intended for medical and mining industries, basic and applied research in within DOE and DHS offices.