Kai Vetter | University of California, Berkeley (original) (raw)
Papers by Kai Vetter
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2022
Spatial localization of special nuclear materials (SNM) via their neutron signatures amidst backg... more Spatial localization of special nuclear materials (SNM) via their neutron signatures amidst background requires knowledge of the background neutron environment or a means of separating a source from background based on low amounts of information. This requirement has created the need for characterizing the spatial distribution of the cosmogenic neutron background. Neutron scatter cameras have been developed and optimized for rapid detection of high activity sources, but have low imaging efficiency, making it difficult to use them to characterize low rate diffuse sources, such as the neutron background. The Low Intensity Neutron Imaging System (LINIS) is a collimated neutron imager that has been designed and optimized for imaging diffuse cosmogenic neutron background in the energy range of 0.5−15 MeV. LINIS operates using 16 liquid scintillation detectors shielded by ultra-high molecular weight polyethylene cylindrical collimators in a staggered orientation and rotates to 7 discrete positions, giving it roughly 2π sensitivity. LINIS has been characterized using (α, n) and fission neutron sources using two imaging techniques for neutron source localization, simple backprojection and Maximum Likelihood Expectation Maximization.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2017
In an effort to characterize the fast neutron radiation background, 16 EJ-309 liquid scintillator... more In an effort to characterize the fast neutron radiation background, 16 EJ-309 liquid scintillator cells were installed in the Radiological Multi-sensor Analysis Platform (RadMAP) to collect data in the San Francisco Bay Area. Each fast neutron event was associated with specific weather metrics (pressure, temperature, absolute humidity) and GPS coordinates. The expected exponential dependence of the fast neutron count rate on atmospheric pressure was demonstrated and event rates were subsequently adjusted given the measured pressure at the time of detection. Pressure adjusted data was also used to investigate the influence of other environmental conditions on the neutron background rate. Using National Oceanic and Atmospheric Administration (NOAA) coastal area lidar data, an algorithm was implemented to approximate sky-view factors (the total fraction of visible sky) for points along RadMAPs route. Three areas analyzed in San Francisco, Downtown Oakland, and Berkeley all demonstrated a suppression in the background rate of over 50% for the range of sky-view factors measured. This effect, which is due to the shielding of cosmic-ray produced neutrons by surrounding buildings, was comparable to the pressure influence which yielded a 32% suppression in the count rate over the range of pressures measured.
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Dec 11, 2012
Scientific Reports, 2021
The ability to map and estimate the activity of radiological source distributions in unknown thre... more The ability to map and estimate the activity of radiological source distributions in unknown three-dimensional environments has applications in the prevention and response to radiological accidents or threats as well as the enforcement and verification of international nuclear non-proliferation agreements. Such a capability requires well-characterized detector response functions, accurate time-dependent detector position and orientation data, a digitized representation of the surrounding 3D environment, and appropriate image reconstruction and uncertainty quantification methods. We have previously demonstrated 3D mapping of gamma-ray emitters with free-moving detector systems on a relative intensity scale using a technique called Scene Data Fusion (SDF). Here we characterize the detector response of a multi-element gamma-ray imaging system using experimentally benchmarked Monte Carlo simulations and perform 3D mapping on an absolute intensity scale. We present experimental reconstru...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2004
Due to advances in manufacturing large and highly segmented HPGe detectors along with the availab... more Due to advances in manufacturing large and highly segmented HPGe detectors along with the availability of fast and high precision digital electronics it is now possible to build efficient and high-resolution Compton cameras. Two-dimensionally segmented semiconductor detectors along with pulse-shape analysis allow to obtain three-dimensional positions and energies of individual gamma-ray interactions. By employing gamma-ray tracking procedures it is possible to determine the scattering sequence in the detector and ultimately to deduce the incident direction of gamma rays without the use of a attenuating collimator. These advanced gamma-ray tracking based Compton cameras are able not only to image gamma-ray sources with higher sensitivity than collimator-based systems but can increase the sensitivity in finding gamma-ray sources over non-imaging detectors, particularly in complex radiation fields. We have implemented a Compton camera built of a single doubule-sided strip HPGe detector with a strip pitch size of 2mm. A three-dimensional position resolution of 0.5mm at 122keV by using simple pulse-shape analysis is achieved. We have implemented image reconstruction procedures for search scenarios, which are of interest for national security applications. In addition, we have developed reconstruction procedures to optimize image quality which potentially finds applications in other areas as well.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2016
Glenn Knoll was one of the leaders in the field of radiation detection and measurements and shape... more Glenn Knoll was one of the leaders in the field of radiation detection and measurements and shaped this field through his outstanding scientific and technical contributions, as a teacher, his personality, and his textbook. His Radiation Detection and Measurement book guided me in my studies and is now the textbook in my classes in the Department of Nuclear Engineering at UC Berkeley. In the spirit of Glenn, I will provide an overview of our activities at the Berkeley Applied Nuclear Physics Program reflecting some of the breadth of radiation detection technologies and their applications ranging from fundamental studies in physics to biomedical imaging and to nuclear security. I will conclude with a discussion of our Berkeley Radwatch and Resilient Communities activities as a result of the events at the Dai-ichi Nuclear Power Plant in Fukushima, Japan more than 4 years ago.
IEEE Transactions on Nuclear Science, 2009
We present a new standoff imaging technique able to provide 3-dimensional (3D) images of gamma-ra... more We present a new standoff imaging technique able to provide 3-dimensional (3D) images of gamma-ray sources distributed in the environment. Unlike standard 3D tomographic methods, this technique does not require the radioactive sources to be bounded within a predefined physical space. In the present implementation, the gamma-ray imaging system is based on two large planar HPGe double sided segmented detectors, which are used in a Compton camera configuration. A LIDAR system is used in conjunction with the gamma-ray imaging system to confine the gamma-ray image space to the interior of physical objects situated within the detection range of the gamma-ray imager. This approach results in superior image contrast and efficient image reconstruction. Results demonstrating the operating principle are reported.
Proceedings of International Symposium on Radiation Detectors and Their Uses (ISRD2016)
Recent developments in the detector fabrication, signal readout, and data processing enable new c... more Recent developments in the detector fabrication, signal readout, and data processing enable new concepts in radiation detection that are relevant for applications ranging from fundamental physics to medicine as well as nuclear security and safety. We present recent progress in multi-dimensional radiation detection and imaging in the Berkeley Applied Nuclear Physics program. It is based on the ability to reconstruct scenes in three dimensions and fuse it with gamma-ray image information. We are using the High-Efficiency Multimode Imager HEMI in its Compton imaging mode and combining it with contextual sensors such as the Microsoft Kinect or visual cameras. This new concept of volumetric imaging or scene data fusion provides unprecedented capabilities in radiation detection and imaging relevant for the detection and mapping of radiological and nuclear materials. This concept brings us one step closer to the seeing the world with gamma-ray eyes.
Annual Review of Nuclear and Particle Science
The accident at the Fukushima Daiichi Nuclear Power Station (FDNPS) following the Great East Japa... more The accident at the Fukushima Daiichi Nuclear Power Station (FDNPS) following the Great East Japan Earthquake and the subsequent tsunami in March 2011 changed people's perceptions regarding nuclear power generation in Japan and worldwide. The failure to prevent the accident and the response to it had an enormous impact specifically on the communities close to the site but also across Japan and globally. In this review, I discuss radiation detection technologies, their use and limits in the immediate assessment and response, and improvements since then. In particular, I examine recent developments in radiation detection and imaging systems that, in combination with the enormous advances in computer vision, provide new means to detect, map, and visualize radiation using manned and unmanned deployment platforms. In addition to smarter and more adaptable technologies to prevent and minimize the impact of such events, an important outcome of this accident is the need for informed and...
AIP Conference Proceedings
ABSTRACT Gamma-ray tracking is a new concept for the detection of γ radiation. One proposed imple... more ABSTRACT Gamma-ray tracking is a new concept for the detection of γ radiation. One proposed implementation of this concept, called GRETA for Gamma Ray Energy Tracking Array, aims at an improvement in nuclear physics and is based on an array of highly segmented HPGe detectors. We have developed new techniques to determine three-dimensional positions and energies of interactions based on pulse-shape analysis in a two-dimensionally segmented Ge detector and algorithms which use this information to reconstruct the scattering sequence of γ rays, even if many γ rays hit the array at the same time. Such a detector will have a high efficiency and a good peak-to-background ratio, an excellent Doppler-shift correction and high count rate capability, as well as a high polarization sensitivity. However, the concept will not only improve the sensitivity for γ rays in nuclear physics but large potential gain is also possible in other areas, such as γ-ray imaging used in astrophysics or medicine. Only recently we have shown the proof-of-principle of the proposed concept based on the measured position resolution of better than 1 mm in three dimensions in a 36-fold segmented Ge detector at an γ-ray energy of 374 keV. © 2001 American Institute of Physics.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
IEEE Transactions on Nuclear Science
IEEE Transactions on Nuclear Science
Sensors
The enormous advances in sensing and data processing technologies in combination with recent deve... more The enormous advances in sensing and data processing technologies in combination with recent developments in nuclear radiation detection and imaging enable unprecedented and “smarter” ways to detect, map, and visualize nuclear radiation. The recently developed concept of three-dimensional (3-D) Scene-data fusion allows us now to “see” nuclear radiation in three dimensions, in real time, and specific to radionuclides. It is based on a multi-sensor instrument that is able to map a local scene and to fuse the scene data with nuclear radiation data in 3-D while the instrument is freely moving through the scene. This new concept is agnostic of the deployment platform and the specific radiation detection or imaging modality. We have demonstrated this 3-D Scene-data fusion concept in a range of configurations in locations, such as the Fukushima Prefecture in Japan or Chernobyl in Ukraine on unmanned and manned aerial and ground-based platforms. It provides new means in the detection, mappi...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
High-purity germanium (HPGe) radiation detectors with segmented signal readout electrodes combine... more High-purity germanium (HPGe) radiation detectors with segmented signal readout electrodes combine excellent energy resolution with fine spatial resolution, opening exciting possibilities in radiation imaging applications. Segmenting the electrodes provides the ability to determine the positions of radiation interactions in the detector, but it also brings potential challenges that can inhibit performance. A challenge unique to segmented electrode detectors is collection of charge carriers to the gap between adjacent electrodes rather than to the electrodes themselves, which gives a deficit in the summed energy. While amorphous semiconductor electrical contacts have enabled a simplified fabrication process capable of fine electrode segmentation, the amorphous semiconductor passivation layer between electrodes is prone to inter-electrode charge collection. This article presents a study of the impact of fabrication process parameters on the energy deficit due to inter-electrode charge collection for double-sided strip detectors. Eight double-sided strip HPGe detectors were fabricated with amorphous germanium (a-Ge) and amorphous silicon (a-Si) contacts formed by sputter deposition. Each detector was evaluated for interelectrode charge collection performance, using as a metric the deficit in the summed signal of two adjacent electrodes. It is demonstrated that both aGe and a-Si contacts can be produced with nearly non-existent inter-electrode charge collection when the appropriate combination of sputter gas hydrogen content and gas pressure are selected.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Amorphous semiconductor electrical contacts on high-purity Ge radiation detectors have become a v... more Amorphous semiconductor electrical contacts on high-purity Ge radiation detectors have become a valuable technology because they are simple to fabricate, result in thin dead layers, block both electron and hole injection, and can readily be finely segmented as needed for applications requiring imaging or particle tracking. Though significant numbers of detectors have been successfully produced for a variety of applications using the amorphous semiconductor contact technology, there remains a need to better understand the dependence of performance characteristics, particularly leakage current, on the fabrication process parameters so that the performance can be better optimized. To this end, we have performed a systematic study of leakage current on RF-sputter-deposited amorphous-Ge (a-Ge) and amorphous-Si (a-Si) contacts as a function of process and operational parameters including sputter gas pressure and composition, number of detector temperature cycles, and time spent at room temperature. The study focused primarily on the current resulting from electron injection at the contact. Significant findings from the study include that a-Si produces lower electron injection than aGe , the time the detector spends at room temperature rather than the number of temperature cycles experienced by the detector is the primary factor associated with leakage current change when the detector is warmed, and the time stability of the aGe contact depends on the sputter gas pressure with a higher pressure producing more stable characteristics.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Progress in Particle and Nuclear Physics
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
This paper presents the concept of real-time fusion of gamma-ray imaging and visual scene data fo... more This paper presents the concept of real-time fusion of gamma-ray imaging and visual scene data for a hand-held mobile Compton imaging system in 3-D. The ability to obtain and integrate both gamma-ray and scene data from a mobile platform enables improved capabilities in the localization and mapping of radioactive materials. This not only enhances the ability to localize these materials, it provides important contextual information of the scene, which once acquired, can be reviewed and further analyzed subsequently. To demonstrate these concepts, the High-Efficiency Multimode Imager (HEMI) is used in a hand-portable implementation in combination with a Microsoft Kinect sensor. This sensor, in conjunction with open-source software, provides the ability to create a 3-D model of the scene and to track the position and orientation of HEMI in real-time. By combining the gamma-ray data and visual data, accurate 3-D maps of gamma-ray sources are produced in real-time. This approach is extended to map the location of radioactive materials within objects with unknown geometry.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2022
Spatial localization of special nuclear materials (SNM) via their neutron signatures amidst backg... more Spatial localization of special nuclear materials (SNM) via their neutron signatures amidst background requires knowledge of the background neutron environment or a means of separating a source from background based on low amounts of information. This requirement has created the need for characterizing the spatial distribution of the cosmogenic neutron background. Neutron scatter cameras have been developed and optimized for rapid detection of high activity sources, but have low imaging efficiency, making it difficult to use them to characterize low rate diffuse sources, such as the neutron background. The Low Intensity Neutron Imaging System (LINIS) is a collimated neutron imager that has been designed and optimized for imaging diffuse cosmogenic neutron background in the energy range of 0.5−15 MeV. LINIS operates using 16 liquid scintillation detectors shielded by ultra-high molecular weight polyethylene cylindrical collimators in a staggered orientation and rotates to 7 discrete positions, giving it roughly 2π sensitivity. LINIS has been characterized using (α, n) and fission neutron sources using two imaging techniques for neutron source localization, simple backprojection and Maximum Likelihood Expectation Maximization.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2017
In an effort to characterize the fast neutron radiation background, 16 EJ-309 liquid scintillator... more In an effort to characterize the fast neutron radiation background, 16 EJ-309 liquid scintillator cells were installed in the Radiological Multi-sensor Analysis Platform (RadMAP) to collect data in the San Francisco Bay Area. Each fast neutron event was associated with specific weather metrics (pressure, temperature, absolute humidity) and GPS coordinates. The expected exponential dependence of the fast neutron count rate on atmospheric pressure was demonstrated and event rates were subsequently adjusted given the measured pressure at the time of detection. Pressure adjusted data was also used to investigate the influence of other environmental conditions on the neutron background rate. Using National Oceanic and Atmospheric Administration (NOAA) coastal area lidar data, an algorithm was implemented to approximate sky-view factors (the total fraction of visible sky) for points along RadMAPs route. Three areas analyzed in San Francisco, Downtown Oakland, and Berkeley all demonstrated a suppression in the background rate of over 50% for the range of sky-view factors measured. This effect, which is due to the shielding of cosmic-ray produced neutrons by surrounding buildings, was comparable to the pressure influence which yielded a 32% suppression in the count rate over the range of pressures measured.
OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Dec 11, 2012
Scientific Reports, 2021
The ability to map and estimate the activity of radiological source distributions in unknown thre... more The ability to map and estimate the activity of radiological source distributions in unknown three-dimensional environments has applications in the prevention and response to radiological accidents or threats as well as the enforcement and verification of international nuclear non-proliferation agreements. Such a capability requires well-characterized detector response functions, accurate time-dependent detector position and orientation data, a digitized representation of the surrounding 3D environment, and appropriate image reconstruction and uncertainty quantification methods. We have previously demonstrated 3D mapping of gamma-ray emitters with free-moving detector systems on a relative intensity scale using a technique called Scene Data Fusion (SDF). Here we characterize the detector response of a multi-element gamma-ray imaging system using experimentally benchmarked Monte Carlo simulations and perform 3D mapping on an absolute intensity scale. We present experimental reconstru...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2004
Due to advances in manufacturing large and highly segmented HPGe detectors along with the availab... more Due to advances in manufacturing large and highly segmented HPGe detectors along with the availability of fast and high precision digital electronics it is now possible to build efficient and high-resolution Compton cameras. Two-dimensionally segmented semiconductor detectors along with pulse-shape analysis allow to obtain three-dimensional positions and energies of individual gamma-ray interactions. By employing gamma-ray tracking procedures it is possible to determine the scattering sequence in the detector and ultimately to deduce the incident direction of gamma rays without the use of a attenuating collimator. These advanced gamma-ray tracking based Compton cameras are able not only to image gamma-ray sources with higher sensitivity than collimator-based systems but can increase the sensitivity in finding gamma-ray sources over non-imaging detectors, particularly in complex radiation fields. We have implemented a Compton camera built of a single doubule-sided strip HPGe detector with a strip pitch size of 2mm. A three-dimensional position resolution of 0.5mm at 122keV by using simple pulse-shape analysis is achieved. We have implemented image reconstruction procedures for search scenarios, which are of interest for national security applications. In addition, we have developed reconstruction procedures to optimize image quality which potentially finds applications in other areas as well.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2016
Glenn Knoll was one of the leaders in the field of radiation detection and measurements and shape... more Glenn Knoll was one of the leaders in the field of radiation detection and measurements and shaped this field through his outstanding scientific and technical contributions, as a teacher, his personality, and his textbook. His Radiation Detection and Measurement book guided me in my studies and is now the textbook in my classes in the Department of Nuclear Engineering at UC Berkeley. In the spirit of Glenn, I will provide an overview of our activities at the Berkeley Applied Nuclear Physics Program reflecting some of the breadth of radiation detection technologies and their applications ranging from fundamental studies in physics to biomedical imaging and to nuclear security. I will conclude with a discussion of our Berkeley Radwatch and Resilient Communities activities as a result of the events at the Dai-ichi Nuclear Power Plant in Fukushima, Japan more than 4 years ago.
IEEE Transactions on Nuclear Science, 2009
We present a new standoff imaging technique able to provide 3-dimensional (3D) images of gamma-ra... more We present a new standoff imaging technique able to provide 3-dimensional (3D) images of gamma-ray sources distributed in the environment. Unlike standard 3D tomographic methods, this technique does not require the radioactive sources to be bounded within a predefined physical space. In the present implementation, the gamma-ray imaging system is based on two large planar HPGe double sided segmented detectors, which are used in a Compton camera configuration. A LIDAR system is used in conjunction with the gamma-ray imaging system to confine the gamma-ray image space to the interior of physical objects situated within the detection range of the gamma-ray imager. This approach results in superior image contrast and efficient image reconstruction. Results demonstrating the operating principle are reported.
Proceedings of International Symposium on Radiation Detectors and Their Uses (ISRD2016)
Recent developments in the detector fabrication, signal readout, and data processing enable new c... more Recent developments in the detector fabrication, signal readout, and data processing enable new concepts in radiation detection that are relevant for applications ranging from fundamental physics to medicine as well as nuclear security and safety. We present recent progress in multi-dimensional radiation detection and imaging in the Berkeley Applied Nuclear Physics program. It is based on the ability to reconstruct scenes in three dimensions and fuse it with gamma-ray image information. We are using the High-Efficiency Multimode Imager HEMI in its Compton imaging mode and combining it with contextual sensors such as the Microsoft Kinect or visual cameras. This new concept of volumetric imaging or scene data fusion provides unprecedented capabilities in radiation detection and imaging relevant for the detection and mapping of radiological and nuclear materials. This concept brings us one step closer to the seeing the world with gamma-ray eyes.
Annual Review of Nuclear and Particle Science
The accident at the Fukushima Daiichi Nuclear Power Station (FDNPS) following the Great East Japa... more The accident at the Fukushima Daiichi Nuclear Power Station (FDNPS) following the Great East Japan Earthquake and the subsequent tsunami in March 2011 changed people's perceptions regarding nuclear power generation in Japan and worldwide. The failure to prevent the accident and the response to it had an enormous impact specifically on the communities close to the site but also across Japan and globally. In this review, I discuss radiation detection technologies, their use and limits in the immediate assessment and response, and improvements since then. In particular, I examine recent developments in radiation detection and imaging systems that, in combination with the enormous advances in computer vision, provide new means to detect, map, and visualize radiation using manned and unmanned deployment platforms. In addition to smarter and more adaptable technologies to prevent and minimize the impact of such events, an important outcome of this accident is the need for informed and...
AIP Conference Proceedings
ABSTRACT Gamma-ray tracking is a new concept for the detection of γ radiation. One proposed imple... more ABSTRACT Gamma-ray tracking is a new concept for the detection of γ radiation. One proposed implementation of this concept, called GRETA for Gamma Ray Energy Tracking Array, aims at an improvement in nuclear physics and is based on an array of highly segmented HPGe detectors. We have developed new techniques to determine three-dimensional positions and energies of interactions based on pulse-shape analysis in a two-dimensionally segmented Ge detector and algorithms which use this information to reconstruct the scattering sequence of γ rays, even if many γ rays hit the array at the same time. Such a detector will have a high efficiency and a good peak-to-background ratio, an excellent Doppler-shift correction and high count rate capability, as well as a high polarization sensitivity. However, the concept will not only improve the sensitivity for γ rays in nuclear physics but large potential gain is also possible in other areas, such as γ-ray imaging used in astrophysics or medicine. Only recently we have shown the proof-of-principle of the proposed concept based on the measured position resolution of better than 1 mm in three dimensions in a 36-fold segmented Ge detector at an γ-ray energy of 374 keV. © 2001 American Institute of Physics.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
IEEE Transactions on Nuclear Science
IEEE Transactions on Nuclear Science
Sensors
The enormous advances in sensing and data processing technologies in combination with recent deve... more The enormous advances in sensing and data processing technologies in combination with recent developments in nuclear radiation detection and imaging enable unprecedented and “smarter” ways to detect, map, and visualize nuclear radiation. The recently developed concept of three-dimensional (3-D) Scene-data fusion allows us now to “see” nuclear radiation in three dimensions, in real time, and specific to radionuclides. It is based on a multi-sensor instrument that is able to map a local scene and to fuse the scene data with nuclear radiation data in 3-D while the instrument is freely moving through the scene. This new concept is agnostic of the deployment platform and the specific radiation detection or imaging modality. We have demonstrated this 3-D Scene-data fusion concept in a range of configurations in locations, such as the Fukushima Prefecture in Japan or Chernobyl in Ukraine on unmanned and manned aerial and ground-based platforms. It provides new means in the detection, mappi...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
High-purity germanium (HPGe) radiation detectors with segmented signal readout electrodes combine... more High-purity germanium (HPGe) radiation detectors with segmented signal readout electrodes combine excellent energy resolution with fine spatial resolution, opening exciting possibilities in radiation imaging applications. Segmenting the electrodes provides the ability to determine the positions of radiation interactions in the detector, but it also brings potential challenges that can inhibit performance. A challenge unique to segmented electrode detectors is collection of charge carriers to the gap between adjacent electrodes rather than to the electrodes themselves, which gives a deficit in the summed energy. While amorphous semiconductor electrical contacts have enabled a simplified fabrication process capable of fine electrode segmentation, the amorphous semiconductor passivation layer between electrodes is prone to inter-electrode charge collection. This article presents a study of the impact of fabrication process parameters on the energy deficit due to inter-electrode charge collection for double-sided strip detectors. Eight double-sided strip HPGe detectors were fabricated with amorphous germanium (a-Ge) and amorphous silicon (a-Si) contacts formed by sputter deposition. Each detector was evaluated for interelectrode charge collection performance, using as a metric the deficit in the summed signal of two adjacent electrodes. It is demonstrated that both aGe and a-Si contacts can be produced with nearly non-existent inter-electrode charge collection when the appropriate combination of sputter gas hydrogen content and gas pressure are selected.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Amorphous semiconductor electrical contacts on high-purity Ge radiation detectors have become a v... more Amorphous semiconductor electrical contacts on high-purity Ge radiation detectors have become a valuable technology because they are simple to fabricate, result in thin dead layers, block both electron and hole injection, and can readily be finely segmented as needed for applications requiring imaging or particle tracking. Though significant numbers of detectors have been successfully produced for a variety of applications using the amorphous semiconductor contact technology, there remains a need to better understand the dependence of performance characteristics, particularly leakage current, on the fabrication process parameters so that the performance can be better optimized. To this end, we have performed a systematic study of leakage current on RF-sputter-deposited amorphous-Ge (a-Ge) and amorphous-Si (a-Si) contacts as a function of process and operational parameters including sputter gas pressure and composition, number of detector temperature cycles, and time spent at room temperature. The study focused primarily on the current resulting from electron injection at the contact. Significant findings from the study include that a-Si produces lower electron injection than aGe , the time the detector spends at room temperature rather than the number of temperature cycles experienced by the detector is the primary factor associated with leakage current change when the detector is warmed, and the time stability of the aGe contact depends on the sputter gas pressure with a higher pressure producing more stable characteristics.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Progress in Particle and Nuclear Physics
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
This paper presents the concept of real-time fusion of gamma-ray imaging and visual scene data fo... more This paper presents the concept of real-time fusion of gamma-ray imaging and visual scene data for a hand-held mobile Compton imaging system in 3-D. The ability to obtain and integrate both gamma-ray and scene data from a mobile platform enables improved capabilities in the localization and mapping of radioactive materials. This not only enhances the ability to localize these materials, it provides important contextual information of the scene, which once acquired, can be reviewed and further analyzed subsequently. To demonstrate these concepts, the High-Efficiency Multimode Imager (HEMI) is used in a hand-portable implementation in combination with a Microsoft Kinect sensor. This sensor, in conjunction with open-source software, provides the ability to create a 3-D model of the scene and to track the position and orientation of HEMI in real-time. By combining the gamma-ray data and visual data, accurate 3-D maps of gamma-ray sources are produced in real-time. This approach is extended to map the location of radioactive materials within objects with unknown geometry.