Publications

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A. Asghari, S. Dazeley, A. Bernstein. “Applications of water-based neutron detectors for nuclear safeguards and security,” 56th INMM Annual Meeting in Indian Wells, CA. 2014.

The depletion of national helium-3 stockpiles has necessitated the development of non- helium-3 based neutron detectors. The Water Neutron Detector (WaND) is a novel concept that utilizes gadolinium-doped water as a neutron multiplicity counting medium for special nuclear material. The detection system meets standards set forth by the IAEA for helium-3 replacement technologies. It has high efficiency (28%), a short neutron capture time (~15 microsecond, tunable based on the gadolinium percentage), high gamma rejection (108:1 for cobalt-60), and is robust, nontoxic, and non-flammable. The active detector volume is 1.02 m3 deionized water doped with 0.25% of the neutron capture agent gadolinium, in a soluble chloride compound. The detection principle relies on the Cherenkov light created following a gamma cascade from a neutron capture on gadolinium. Recently, the WaND system has been investigated for applicability to neutron multiplicity counting for International Atomic Energy Agency (IAEA) safeguards purposes. Research will be presented describing the detector’s technical merits as outlined by the 2013 IAEA Workshop on Requirements and Potential Technologies for Replacement of 3He Detectors in IAEA Safeguards Applications. Overall, the WaND system compares favorably, especially as a dedicated assay tool for low plutonium quantities.


S. Dazeley, A. Asghari, A. Bernstein, N.S. Bowden, V. Mozin. “Performance Characterization of a Water-based Multiplicity Counter,” 55th INMM Annual Meeting in Atlanta, GA. 2014.

We report the performance characteristics of a water-based neutron detecting multiplicity counter for the non-destructive assay of fissile sources. This technique could replace or supplement existing 3He-based multiplicity counters. The counter is a 1.02 m3 tank containing pure deionized water doped with 0.5% GdCl3. It has highly reflective walls and eight 10-inch PMTs mounted at the top. An unshielded source well of 19 cm diameter, mounted at the top and center, extends 73 cm down into the detector. The counter was evaluated using low intensity 252Cf and 60Co sources, and a fast pulsing LED to simulate higher intensity backgrounds. At low gamma ray intensities (~200 kBq or less) we report an absolute neutron detection efficiency of 28% and a 60Co rejection/suppression factor of ~108 to 1. For sources with high gamma ray intensities, the neutron efficiency was 22±1 up to a 60Co equivalent activity of 4 MBq. The detector background event rate, primarily due to muons and other cosmogenic particles, was found to be stable over a period of almost three months. The minimum detectable neutron source intensity above background was 3.1 neutrons/second, assuming a one-hour data acquisition.


S. Dazeley, A. Asghari, A. Bernstein, N.S. Bowden, V. Mozina. “A Water-Based Neutron Detector as a Well Multiplicity Counter.” Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, January 2015.

We report the performance characteristics of a water-based neutron detecting multiplicity counter for the non-destructive assay of fissile sources. This technique could replace or supplement existing 3He- based multiplicity counters. The counter is a 1.02 m3 tank containing pure deionized water doped with 0.5% GdCl3. It has highly reflective walls and eight 10-in. PMTs mounted at the top. An unshielded source well of 19 cm diameter, mounted at the top and center, extends 73 cm down into the detector. The counter was evaluated using low intensity 252Cf and 60Co sources, and a fast pulsing LED to simulate higher intensity backgrounds. At low gamma ray intensities (200 kBq or less) we report an absolute neutron detection efficiency of 28% and a 60Co rejection/suppression factor of 108 to 1. For sources with high gamma ray intensities, the neutron efficiency was 22±1% up to a 60Co equivalent activity of 4 MBq. The detector background event rate, primarily due to muons and other cosmogenic particles, was found to be stable over a period of almost three months. The minimum detectable neutron source intensity above background was 3.1 neutrons/second, assuming a one-hour data acquisition.

C. Neher, R. L. Lander, A. Moskaleva, J. Pasner, M. Tripathi, M. Woods. “Further Developments in Gold-stud Bump Bonding.” Journal of Instrumentation, 2011.

As silicon detectors in high energy physics experiments require increasingly complex assembly procedures, the availability of a wide variety of interconnect technologies provides more options for overcoming obstacles in generic R&D. Gold ball bonding has been a staple in the interconnect industry due to its ease of use and reliability. However, due to some limitations in the standard technique, alternate methods of gold-stud bonding are being developed. This paper presents recent progress and challenges faced in the development of double gold-stud bonding and 0.5 mil wire gold-stud bonding at the UC Davis Facility for Interconnect Technology. Advantages and limitations of each technique are analyzed to provide insight into potential applications for each method. Optimization of procedures and parameters is also presented.

M. Woods, R. G. Fields, B. Holbrook, R. L. Lander, A. Moskaleva, et al. “Development of Readout Interconnections for the Si-W Calorimeter of SiD.” Journal of Instrumentation, 2011.

The SiD collaboration is developing a Si-W sampling electromagnetic calorimeter, with anticipated application for the International Linear Collider. Assembling the modules for such a detector will involve special bonding technologies for the interconnections, especially for attaching a silicon detector wafer to a flex cable readout bus. We review the interconnect technologies involved, including oxidation removal processes, pad surface preparation, solder ball selection and placement, and bond quality assurance. Our results show that solder ball bonding is a promising technique for the Si-W ECAL, and unresolved issues are being addressed.

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