B.R. Kowash

Pacific Northwest National Laboratory

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D.K. Wehe

University of Michigan–Ann Arbor

S. S. Harilal

Pacific Northwest National Laboratory

F. N. Beg

University of California, San Diego

Mathew P. Polek

University of California, San Diego

Elizabeth J. Kautz

Pacific Northwest National Laboratory

Larry W. Burggraf

U.S. Air Force Institute of Technology

N.O. Boyce

U.S. Air Force Institute of Technology

John W. McClory

U.S. Air Force Institute of Technology

Towfiq Ahmed

Pacific Northwest National Laboratory

V. L. Kantsyrev

University of Nevada, Reno

Cooperative Institutions

University of California, San Diego

198

Manufacturing Advocacy & Growth Network (United States)

196

Sandia National Laboratories

Lawrence Livermore National Laboratory

Imperial College London

United States Naval Research Laboratory

Sandia National Laboratories California

University of Michigan–Ann Arbor

Princeton University

University of Strathclyde

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2020 IEEE International Conference on Plasma Science (ICOPS) (2023)

Eun Kyung Choi N. Riga D. Shiffler K Jensen John Petillo

Table (database)

10.1109/icops45740.2023.10481047

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Citations (0)

Experimental and theoretical comparison of ion properties from nanosecond laser-produced plasmas of metal targets

Journal of Applied Physics (2023)

Mathew P. Polek Elizabeth J. Kautz Towfiq Ahmed B.R. Kowash F. N. Beg

The ion emission properties of laser-produced plasmas as a function of laser intensities between 4–50 GW cm−2 and varying angles with respect to the target normal were investigated. The plasmas were produced by focusing 1064 nm, 6 ns pulses from an Nd:YAG laser on various metal targets. The targets used for this study include Ti, Mo, and Gd (Z=22,42,64). It is noted that all ion profiles are composed of multiple peaks—a prompt emission peak trailed by three ion peaks (ultrafast, fast, and thermal). Experimentally, it is shown that each of these ion peaks follows a unique trend as a function of laser intensity, angle, and distance away from the target. Theoretically, it is shown that simple analytical models can be used to explain the properties of the ions. The variations in the ion velocity and density as a function of laser intensity are found to be in good agreement with theoretical models of sheath acceleration, isothermal self-similar expansion, and ablative plasma flow for various ion peaks.

Nanosecond

10.1063/5.0146428

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Citations (7)

Radiation effects on YAG:Ce scintillating fiber

IEEE Nuclear Science Symposium conference record (2011)

Briana J. Singleton Bradley S. Jones Abigail A. Bickley James C. Petrosky John W. McClory

The performance of thin, cerium activated, yttrium aluminum garnet (YAG:Ce), scintillating fiber-shaped crystals were investigated following ion irradiation. The optical behavior of the YAG:Ce fibers was simulated using DETECT2000, a Monte Carlo based software program designed to model the optical properties of scintillators. The fibers were exposed to a focused beam of 0.5 and 1 MeV electrons. Fiber light output and color shift were analyzed following irradiation.

Double-clad fiber

10.1109/nssmic.2011.6154389

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Citations (0)

A rotating modulation imager for locating mid-range point sources

Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment (2009)

B.R. Kowash D.K. Wehe Jeffrey A. Fessler

Field of view

Depth of field

Modulation (music)

10.1016/j.nima.2008.12.233

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Citations (32)

Adaptive imaging using a Rotating Modulation Collimator (RMC)

Daniel T. Willcox B.R. Kowash D.K. Wehe

The Rotating Modulation Collimator (RMC) is a simple radiation imaging system that can be operated with as little as a single non-position sensitive radiation detector. While simple, its detection efficiency suffers due to necessary collimation of the incoming radiation. This paper explores adaptive techniques aimed at improving the detection efficiency and image quality for a given RMC system. Specifically, the collimating mask design, the sampling technique, and the RMC pivot angle are explored.

Collimator

Collimated light

Modulation (music)

Position (finance)

10.1109/nssmic.2010.5874032

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Citations (5)

A Modulating Liquid Collimator for Coded Aperture Adaptive Imaging of Gamma-Rays

IEEE Transactions on Nuclear Science (2013)

Jack FitzGerald Larry W. Burggraf B.R. Kowash E.L. Hull

A novel, fully reconfigurable liquid collimator device for γ-ray and X-ray imaging was built and tested as a coded aperture. The device contained a 10 × 10 grid of 5 × 5 mm ² chambers, each 5 cm long. The chambers were either grilled with an attenuating liquid, absorbing photons, or evacuated of the liquid, allowing the photons to pass. As the pattern of “on” and “off” chambers was manipulated, different, semi-independent views of the γ-ray source were found. A random mask sequence outperformed a uniformly redundant array when maximum-likelihood expectation maximization was used. Noise and reconstruction artifacts decreased as the number of masks increased. With ten mask patterns, the signal-to-noise ratio in images of point sources increased by a factor of 2. Images of a segmented, extended source are presented to demonstrate, qualitatively, that image quality increased when more masks were used. Additionally, the system crudely imaged a source using only the photons that Compton scattered within the mask.

Coded aperture

Collimator

Aperture (computer memory)

Photon Counting

Point source

10.1109/tns.2013.2259052

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Citations (6)

Thermal neutron imaging with a Rotationally Modulated Collimator (RMC)

N.O. Boyce B.R. Kowash D.K. Wehe

The Rotating Modulation Collimator has been modified to image thermal neutron sources. The components of the RMC imaging system were modified to suit thermal neutrons. The experiment compared two detectors (He3 and BF3) and two mask materials (cadmium and borated epoxy) for a 77mCi PuBe source. Preliminary results indicate that both He3 and BF3 detectors may be used with the RMC. Further efforts will be made to reduce the uncertainty in the system.

Collimator

Neutron Detection

Neutron Imaging

Particle detector

10.1109/nssmic.2009.5402407

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Citations (3)

Investigation of Ion Emission from Metal Targets

2020 IEEE International Conference on Plasma Science (ICOPS) (2023)

Mathew P. Polek Elizabeth J. Kautz Towfiq Ahmed B.R. Kowash F. N. Beg

The ion emission properties of laser-produced plasma as a function of laser intensities between 4–50 GW/cm2, and varying angles with respect to the target normal were investigated. The plasmas were produced by focusing 1064 nm, 6 ns pulses from an Nd:YAG laser on various metal targets, including Ti, Mo, and Gd (Z= 22–64). It is noted that all ion profiles are composed of multiple peaks - a prompt emission peak trailed by three ion peaks (ultrafast, fast, and thermal). Experimentally, it is shown that each ion peak follows a unique trend as a function of laser intensity, angle, and distance away from the target. Quantitatively, it is shown that simple analytical models can be used to explain the properties of the ions. The variations in ion velocity and density as a function of laser intensity are found to be in good agreement with theoretical models of sheath acceleration, isothermal self-similar expansion, and ablative plasma flow for various ion peaks.

10.1109/icops45740.2023.10481063

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Citations (0)

Parameter Study for Optimizing the Mass of a Space Nuclear Power System Radiation Shield

B.R. Kowash

Abstract : A parameter study was conducted for a space nuclear reactor radiation shield. The focus of this research was to explore alternatives to current radiation shield designs to reduce the mass while maintaining the same shielding performance. MCNP4C was used to determine the parameters necessary to build an optimum shield. A design known as the split scatter shield offered some potential for reductions in shield mass In theory, less material is required for this type of shield, which uses thin shield sections to scatter radiation away from the dose plane. The parameters for this shield design are the shield geometry, number of shield sections, and material selection. Split scatter shielding offers a potential for reducing the shield mass by allowing the gamma shield material to be moved closer to the source plane. Further research needs to be conducted on this shielding technique, however, to isolate optimum shield values. Once these optima have been identified, a split shield can be developed and compared to the original shield performance. Finally, an energy deposition study indicates that the split scatter shield will absorb less energy than the unit shield, implying that there may be less thermal stress on a scatter shield.

Source

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Citations (2)

Extended source imaging using a single rotating modulation collimator

B.R. Kowash D.K. Wehe N.O. Boyce

Rotating modulation collimators (RMC) have traditionally been most sensitive for locating point sources, but have also been used for imaging time dependent extended sources such as solar flares. Current methods for RMC imaging of extended sources have relied upon multiple RMC systems each with their own detectors, electronics, and mask sets. The difference between systems is that each mask pair has a different set of slit spacings so that different spatial frequency components of the source field can be recorded. The data from the ensemble of RMCs is then combined to produce the final extended source image. This research considers a different approach for imaging extended sources with an RMC. This method relies on a single RMC system, and takes advantage of the fact that for terrestrial imaging the separation between masks is an easily changeable and free parameter. Changing the separation between the masks effectively represents changing the spatial frequency over which the RMC is most sensitive. By measuring multiple data sets with different values of the mask separation parameter, a more complete map of the frequency domain can be recorded. This data is then used with a maximum likelihood expectation maximization algorithm to generate the final image.

Collimator

Modulation (music)

Point source

10.1109/nssmic.2009.5402165

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Citations (3)