Advanced pulse-shape analysis and implementation of gamma-ray tracking in a position-sensitive coaxial HPGe detector
- Univ. of California, Berkeley, CA (United States)
A new concept in g-radiation detection utilizing highly segmented positionsensitive germanium detectors is currently being developed. Through pulse-shape analysis these detectors will provide the three-dimensional position and energy of individual γ-ray interactions and allow the full-energy and direction vectors of the incident radiation to be reconstructed in a process termed tracking. Here, a prototype segmented detector has been utilized in the assessment of theoretically modeled pulse shapes to gain insight into the factors that effect their agreement with those experimentally measured. It was found that simple modeling of the charge-collection process would provide fair agreement between calculated and experimental pulse shapes. However, in some cases significant deviations between the two were present. This was a result of insufficient modeling of all the processes involved in pulse-shape formation. Factors contributing to this include the three-dimensional spatial distribution of the charge carriers, the path of the primary electron, and fluctuations in the electric fields near electrode surfaces and due to variations in impurity concentrations. Additionally, the sensitivity of pulse shapes to changes in the interaction location has been studied. The results indicate that single interactions with energy deposition of 662 keV can potentially be localized to better than the desired position resolution of 2 mm. However, when the study was extended to two interactions totaling 662 keV a different conclusion was reached. It was shown that the pulse shapes resulting from two interactions were ambiguous with that of pulse shapes from single interactions over dimensions greater than 2 mm in the larger detector segments. The size of these segments in future detectors must be reduced in order to increase their sensitivity. Ultimately, a signal decomposition algorithm was developed and implemented to extract the position and energy of γ-ray interactions, occurring in the prototype detector, from both experimentally measured and simulated pulse shapes. For the first time, this allowed the peak-to-total ratio obtained in the energy spectra of 137Cs, 60Co, and 152Eu to be improved by preferentially removing partial-energy events in the tracking process. Larger gains in the peak-to-total ratio were obtained in the simulation as compared to the experiment. These discrepancies were largely a result of insufficient agreement between the experimentally measured pulse shapes and those theoretically calculated to form the basis pulse shapes in the decomposition process.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 807431
- Report Number(s):
- LBNL-51726; R&D Project: 463301; B& R KB0401024; TRN: US0301833
- Resource Relation:
- Other Information: TH: Thesis (Ph.D.); Submitted to the University of California, Berkeley, CA (US); PBD: 12 Nov 2002
- Country of Publication:
- United States
- Language:
- English
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