Multipurpose Radiation Resistant Semiconductor Detectors for Alpha, Neutron & Low Energy Gamma Ray Measurements at High Temperatures in High-Intensity Gamma Ray
Work scheduled under year two of DOE Grant DE-FG02-04ER63734 is on schedule and all year-two milestones have or will be met. Results to date demonstrate that unprecedented silicon carbide (SiC) energy resolution has been obtained, and that SiC detectors may achieve energy resolution that exceeds that obtainable with the best silicon alpha spectrometers. Fast-neutron energy spectrometry measurements indicate that recoil-ion energy spectrometry should be possible with SiC detectors. Furthermore, SiC detectors have been demonstrated to perform well even after gamma-ray exposures of 1.E09 Rad. This result and the previously demonstrated capability of SiC detectors to operate in elevated-temperature environments are very promising for potential DOE EMSP applications. A new class of multipurpose, radiation-resistant semiconductor detectors that can be used in elevated-temperature and high-radiation environments is being developed under this grant. These detectors, based on silicon carbide (SiC) semiconductor are designed to have larger active volumes than previously available SiC detectors, and are being tested for their response to alpha particles, X-rays and low energy gamma rays, and fast neutrons. Specifically, SiC radiation detectors with larger areas and 100-micrometer thick active regions have been designed and manufactured according to detector-design specifications. Detectors based on a Schottky diode design were specified in order to minimize the effects of the detector entrance window on alpha particle measurements. During manufacture of the Schottky diodes, the manufacturer also provided a set of large-volume SiC p-i-n diodes for testing Extensive alpha particle measurements have been carried out to test and quantify the response of the SiC Schottky diodes. Exposures to 148-Gd, 213-Po, 217-At, 221-Fr, 225-Ac, 237-Np, 238-Pu, 240-Pu, and 242-Pu sources were used to obtain detailed alpha response data in the alpha energy range from 3182.787 keV to 8375.9 keV. The 148-Gd, 213-Po, 217-At, and 221-Fr sources provide energy-separated, mono-energetic alpha particle peaks which can be analyzed to provide detailed information on the energy response characteristics of the detectors. As was reported last year, a highly linear response was obtained between observed pulse height and alpha-particle energy over the entire energy range. Detailed full width at half maximum (FWHM) measurements were made for each of five mono-energetic peaks. The FWHM values ranged from 41.5 keV for 3182.787-keV 148-Gd (1.3% energy resolution) to 55.4 keV for 8379.5-keV 213-Po (0.66% energy resolution). Although these energy resolution values are comparable to those obtainable with silicon alpha-particle spectrometers and surpass the best values reported previously for SiC detectors, other factors in addition to the inherent SiC energy resolution contribute to the observed values and were evaluated. Details of the energy deposition processes that contribute to the FWHM were modeled with calculations using the SRIM-2003.26 code developed by Ziegler and Beirsack. Electronic and statistical broadening of the FWHM were also evaluated in order to isolate the component of the FWHM that is inherent to SiC semiconductor. It was found that the SRIM calculations systematically overestimated the range straggling component of the FWHM leading to calculated values that exceeded the measured total FWHM values. It is believed that the overestimates are a result of inherent limitations of the SRIM code. The range-straggling component of the measured energy resolution results primarily from energy-loss processes in the detector entrance window, which consists of thin layers of Au, Pt, and Ti. Therefore, it was decided to perform measurements to evaluate the range straggling component directly. For this purpose, a high-resolution (15 keV FWHM) Si alpha spectrometer was obtained.
- Research Organization:
- Washington Electric Company LLC, Monroeville, PA
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- FG02-04ER63734
- OSTI ID:
- 885081
- Report Number(s):
- EMSP-90256-2005; R&D Project: EMSP 90256
- Country of Publication:
- United States
- Language:
- English
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