Anthony D. Lavietes

A Germanium Orthogonal Strip Detector System for Gamma‐Ray Imaging

A coded aperture, germanium‐detector based gamma‐ray imaging system has been designed, fabricated, and tested. The detector, cryostat, and signal processing electronics are discussed in this paper. The latest version orthogonal strip planar detector is 11‐millimeters thick, having 38×38 strips of 2‐millimeter pitch. The planar detector was fabricated using amorphous germanium contacts. The strips on each face of the detector lie in a chorded‐circular pattern to more efficiently utilize the area of the 10‐cm diameter germanium crystal. The detector is held in a mount that allows convenient installation and removal of the detector, lending itself to eventual tiling of such detectors into large arrays. The cryostat includes provisions to install a large volume coaxial germanium detector immediately behind the planar detector in the same cryostat. Many gamma rays Compton scatter from the planar detector into the coaxial detector. The energies of these coincident interactions are summed to increase the gamma‐r...

Portable system for nuclear, chemical agent, and explosives identification

The FRIS/PINS hybrid integrates the LLNL-developed Field Radionuclide Identification System (FRIS) with the INEEL- developed Portable Isotopic Neutron Spectroscopy (PINS) chemical assay system to yield a combined general radioisotope, special nuclear material (SNM), and chemical weapons/explosives (CWE) detection and identification system. The PINS system uses a neutron source and a high- purity germanium (gamma) -ray detector. The FRIS system uses an electromechanically cooled germanium detector and its own analysis software to detect and identify SNM and other radioisotopes. The FRIS/PINS combined system also uses the electromechanically-cooled germanium detector. There is no other currently available integrated technology that can combine an active neutron interrogation and analysis capability for CWE with a passive radioisotope measurement and identification capability for SNM.

CADMIUM ZINC TELLURIDE SPECTRAL MODELING

Cadmium Zinc Telluride (CZT) detectors are the highest resolution room-temperature gamma ray detectors available for isotopic analysis. As with germanium detectors, accurate isotopic analysis using the spectra requires peak deconvolution. The CZT peak shapes are asymmetric, with a long low energy tail. The asymmetry is a result of the physics of the electron/hole transport in the semiconductor. An accurate model of the physics of the electron/hole transport through an electric field will allow the parameterization of the peak shapes as a function of energy. In turn this leads to the ability to perform accurate spectral deconvolution and therefore accurate isotopic analysis. The model and the peak-shape parameterization as a function of energy will be presented.

Development of a portable ambient temperature radiometric assaying instrument

There is a strong need for portable radiometric instrumentation that can accurately confirm the presence of nuclear materials and allow isotopic analysis of radionuclides in the field. To fulfill this need we are developing a hand-held, non-cryogenic, low-power gamma- and X-ray measurement and analysis instrument that can both search and then accurately verify the presence of nuclear materials. We will report on the use of cadmium zinc telluride detectors, signal processing electronics, and the new field-portable instrument based on the MicroNOMAD Multichannel Analyzer from EG&G ORTEC. We will also describe the isotopic analysis that allows uranium enrichment measurements to be made accurately in the field. >

Germanium orthogonal strip detector system for gamma-ray imaging

A germanium-detector based, gamma-ray imaging system has been designed, fabricated, and tested. The detector, cryostat, electronics, readout, and imaging software are discussed. An 11 millimeter thick, 2 millimeter pitch 19x19 orthogonal strip planar germanium detector is used in front of a coaxial detector to provide broad energy coverage. The planar detector was fabricated using amorphous germanium contacts. Each channel is read out with a compact, low noise external FET preamplifier specially designed for this detector. A bank of shaping amplifiers, fast amplifiers, and fast leading edge discriminators were designed and fabricated to process the signals from preamplifiers. The readout system coordinates time coincident x-y strip addresses with an x-strip spectroscopy signal and a spectroscopy signal from the coaxial detector. This information is sent to a computer where an image is formed. Preliminary shadow and pinhole images demonstrate the viability of a germanium based imaging system. The excellent energy resolution of the germanium detector system provides isotopic imaging.

A Portable System for Nuclear, Chemical Agent and Explosives Identification

The FRIS/PINS hybrid integrates the LLNL-developed Field Radionuclide Identification System (FRIS) with the INEEL-developed Portable Isotopic Neutron Spectroscopy (PINS) chemical assay system to yield a combined general radioisotope, special nuclear material, and chemical weapons/explosives detection and identification system. The PINS system uses a neutron source and a high-purity germanium γ-ray detector. The FRIS system uses an electromechanically cooled germanium detector and its own analysis software to detect and identify special nuclear material and other radioisotopes. The FRIS/PINS combined system also uses the electromechanically-cooled germanium detector. There is no other currently available integrated technology that can combine a prompt-gamma neutron-activation analysis capability for CWE with a passive radioisotope measurement and identification capability for special nuclear material.

Preliminary Uranium Enrichment Analysis Results Using Cadmium Zinc Telluride Detectors

Lawrence Livermore National Laboratory (LLNL) and EG&G ORTEC have jointly developed a portable ambient-temperature detection system that can be used in a number of application scenarios. The detection system uses a planar cadmium zinc telluride (CZT) detector with custom-designed detector support electronics developed at LLNL and is based on the recently released MicroNOMAD multichannel analyzer (MCA) produced by ORTEC. Spectral analysis is performed using software developed at LLNL that was originally designed for use with high-purity germanium (HPGe) detector systems. In one application, the CZT detection system determines uranium enrichments ranging from less than 3% to over 75% to within accuracies of 20%. The analysis was performed using sample sizes of 200 g or larger and acquisition times of 30 min. The authors have demonstrated the capabilities of this system by analyzing the spectra gathered by the CZT detection system from uranium sources of several enrichments. These experiments demonstrate that current CZT detectors can, in some cases, approach performance criteria that were previously the exclusive domain of larger HPGe detector systems.

Technical Review of the Domestic Nuclear Detection Office Transformational and Applied Research Directorate's Research and Development Program

At the request of the Domestic Nuclear Detection Office (DNDO), a Study Committee comprised of representatives from the American Physical Society, Panel on Public Affairs, the IEEE, and Nuclear and Plasma Sciences Society performed a technical review of the DNDO Transformational and Applied Research Directorate (TARD) R&D program. TARDs principal objective is to address gaps in the Global Nuclear Detection Architecture (GNDA) through improvements in the performance, cost, and operational burden of detectors and systems. The charge to the Study Committee was to investigate the existing TARD R&D plan and portfolio, recommend changes to the existing plan, and recommend possible new R&D areas and opportunities. This report is the result of an independent, detailed analysis of the current R&D plan and includes, for each application area, observations, and recommendations to focus future investments within the context of the TARD mission.

Pulse Height Analyzers

The sections in this article are 1 Pulse Processing with the PHA 2 Principles of Operation 3 Acknowledgement

Radiation detection in a marine environment

We have performed radiation detection measurements to explore the feasibility of radioisotopic analysis and detection of a neutron source in a marine environment. We determined the maximum range in seawater through which complex (gamma) -ray emitting materials could be accurately assayed for isotopic content. Additionally we used the gamma rays from neutron capture on chlorine to detect a neutron source. Results from our experiments have been used to determine the greatest distance at which the presence of a neutron emitter can be confirmed. The measurements used an electromechanically-cooled high-purity germanium detector system in both laboratory and fielded seawater conditions. The laboratory experiments used a variety of sources in an arrangement where both the source and detector were surrounded by seawater. The field experiments were performed underwater with the detector in a sealed container that was separate from the source.