Dr. Stephen E. Mitchell Profile

Dr. Stephen E. Mitchell

at Natinal Security Technologies LLC

SPIE Involvement:

Author

Publications (12)

Proceedings Article | 12 September 2016 Presentation + Paper

MCNP estimate of ZLS lens sensitivity in an x-ray field

Stephen Mitchell, Stuart Baker, Russell Howe, Robert Malone

Proceedings Volume 9969, 996903 (2016) https://doi.org/10.1117/12.2235287

KEYWORDS: X-rays, Scintillators, Zoom lenses, Charge-coupled devices, Glasses, Photons, Signal to noise ratio, Silica, Visualization, Relays

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Proceedings Article | 27 August 2015 Paper

Detector blur associated with MeV radiographic imaging systems

Stuart Baker, Stephen Lutz, Duane Smalley, Kristina Brown, Jeremy Danielson, Todd Haines, Russell Howe, Stephen Mitchell, Dane Morgan, Larry Schultz

Proceedings Volume 9595, 959509 (2015) https://doi.org/10.1117/12.2191089

KEYWORDS: Sensors, X-ray sources, Point spread functions, Scintillators, X-rays, Data modeling, X-ray optics, Collimation, Imaging systems, Radio optics

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Proceedings Article | 26 August 2015 Paper

Networked gamma radiation detection system for tactical deployment

Sanjoy Mukhopadhyay, Richard Maurer, Ronald Wolff, Ethan Smith, Paul Guss, Stephen Mitchell

Proceedings Volume 9593, 959316 (2015) https://doi.org/10.1117/12.2185843

KEYWORDS: Sensors, Gamma radiation, Crystals, Detection and tracking algorithms, Data acquisition, Security technologies, Sodium, Remote sensing, Radioisotopes, Sensor networks

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Proceedings Article | 26 August 2015 Paper

Radiation anomaly detection algorithms for field-acquired gamma energy spectra

Sanjoy Mukhopadhyay, Richard Maurer, Ron Wolff, Paul Guss, Stephen Mitchell

Proceedings Volume 9593, 95930S (2015) https://doi.org/10.1117/12.2185736

KEYWORDS: Sensors, Gamma radiation, Detection and tracking algorithms, Algorithm development, Principal component analysis, Radioisotopes, Surgery, Scintillators, Calibration, Security technologies

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Proceedings Article | 5 September 2014 Paper

Scintillator efficiency study with MeV x-rays

Stuart Baker, Kristina Brown, Alden Curtis, Stephen Lutz, Russell Howe, Robert Malone, Stephen Mitchell, Jeremy Danielson, Todd Haines, Kris Kwiatkowski

Proceedings Volume 9213, 92130H (2014) https://doi.org/10.1117/12.2064028

KEYWORDS: Scintillators, X-rays, Cameras, Imaging systems, Absorption, Signal to noise ratio, Sensors, Radiography, Radio optics, X-ray imaging

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Proceedings Article | 26 September 2013 Paper

Exploitation of geometric occlusion and covariance spectroscopy in a gamma sensor array

Sanjoy Mukhopadhyay, Richard Maurer, Ronald Wolff, Stephen Mitchell, Paul Guss, Clifford Trainham

Proceedings Volume 8852, 88520H (2013) https://doi.org/10.1117/12.2019482

KEYWORDS: Sensors, Spectroscopy, Crystals, Scintillators, Gamma radiation, Compton scattering, Detector arrays, Sodium, Radioisotopes, Solids

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Proceedings Article | 26 September 2013 Paper

Real-time active cosmic neutron background reduction methods

Sanjoy Mukhopadhyay, Richard Maurer, Ronald Wolff, Stephen Mitchell, Paul Guss

Proceedings Volume 8854, 885408 (2013) https://doi.org/10.1117/12.2020895

KEYWORDS: Sensors, Scintillators, Cadmium, Boron, Logic, Manufacturing, Field programmable gate arrays, Monte Carlo methods, Picosecond phenomena, Lanthanum

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Neutron counting using large arrays of pressurized ³He proportional counters from an aerial system or in a maritime environment suffers from the background counts from the primary cosmic neutrons and secondary neutrons caused by cosmic ray‒induced mechanisms like spallation and charge-exchange reaction. This paper reports the work performed at the Remote Sensing Laboratory–Andrews (RSL-A) and results obtained when using two different methods to reduce the cosmic neutron background in real time. Both methods used shielding materials with a high concentration (up to 30% by weight) of neutron-absorbing materials, such as natural boron, to remove the lowenergy neutron flux from the cosmic background as the first step of the background reduction process. Our first method was to design, prototype, and test an up-looking plastic scintillator (BC-400, manufactured by Saint Gobain Corporation) to tag the cosmic neutrons and then create a logic pulse of a fixed time duration (~120 μs) to block the data taken by the neutron counter (pressurized 3He tubes running in a proportional counter mode). The second method examined the time correlation between the arrival of two successive neutron signals to the counting array and calculated the excess of variance (Feynman variance Y2F)¹ in the neutron count distribution from Poisson distribution. The dilution of this variance from cosmic background values ideally would signal the presence of manmade neutrons.² The first method has been technically successful in tagging the neutrons in the cosmic-ray flux and preventing them from being counted in the ³He tube array by electronic veto—field measurement work shows the efficiency of the electronic veto counter to be about 87%. The second method has successfully derived an empirical relationship between the percentile non-cosmic component in a neutron flux and the Y2F of the measured neutron count distribution. By using shielding materials alone, approximately 55% of the neutron flux from man-made sources like ²⁵²Cf or Am-Be was removed.

Proceedings Article | 24 October 2012 Paper

Direction sensitive neutron detectors in near field measurements

Sanjoy Mukhopadhyay, Stephen Mitchell

Proceedings Volume 8507, 85070S (2012) https://doi.org/10.1117/12.929975

KEYWORDS: Sensors, Mathematical modeling, Principal component analysis, Near field, Spatial resolution, Gamma radiation, Databases, Monte Carlo methods, Source localization, Homeland security

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Proceedings Article | 28 September 2011 Paper

Prompt neutron multiplicity measurements with portable detectors

Sanjoy Mukhopadhyay, Ronald Wolff, Richard Maurer, Stephen Mitchell, Ethan Smith, Paul Guss, Jeffrey Lacy, L. Sun, A. Athanasiades

Proceedings Volume 8142, 81420T (2011) https://doi.org/10.1117/12.888656

KEYWORDS: Sensors, Fermium, Frequency modulation, Data acquisition, Prototyping, Gamma radiation, Copper, Field programmable gate arrays, Environmental sensing, Manufacturing

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Proceedings Article | 12 September 2009 Paper

Multi-element neutron energy spectrometer

Sanjoy Mukhopadhyay, Richard Maurer, Ronald Wolff, Stephen Mitchell, Alexis Reed

Proceedings Volume 7449, 744914 (2009) https://doi.org/10.1117/12.824150

KEYWORDS: Spectroscopy, Sensors, Helium, Fusion energy, Multi-element lenses, Modulation, Energy efficiency, Monte Carlo methods, Solar energy, Gamma radiation

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In the area of nuclear radiological emergency response and preparedness applications, interest in neutron detection stems from several factors. Unlike gamma rays, which are abundant in nature and present serious difficulties in differentiating a signal from a changing background, whose values are location specific, neutrons are rare and nearly homogenous in spatial distribution. Additionally, many special nuclear materials (SNM) emit neutrons either directly by spontaneous fission or produce neutrons indirectly through (α, n) reactions in nearby light elements. Also of importance in detection scenarios is the fact that neutrons are not easily attenuated. Typically neutron detection is done by simply counting the low energy thermal neutrons by employing pressurized helium tubes operated at high voltages. Not much emphasis is put on determining the energy of the incident neutrons. However, critical information can be obtained by analyzing the neutron energy given off from radioactive materials. In the detection of an SNM, neutron energy information from an unknown source can be of paramount importance. We have modeled, designed, and prototyped multi-element neutron energy spectrometers that contain three to five pressurized helium tubes of dimensions 2" diam. x 10" in length. Each individual helium tube has a specific amount of high density plastic neutron moderators to slow down the incident energetic neutrons to an accurately estimated energy. A typical spectrometer is a set of moderator cylinders surrounding detectors that have high efficiency for detecting thermal neutrons. The larger the moderator, the higher the energy of incident neutrons for which the detector assembly has matched detection efficiency. If all the detectors are exposed to the same radiation field and the efficiency as a function of energy (response function) of each of the detectors is known, the neutron energy spectrum can be determined from the detector count rates. Monte Carlo simulation results of response function calculations for different arrays of helium tubes with varying amount of moderators will be shown. Experimental evidence of effectiveness of a set of moderated helium tubes to measure the hardness of the incident neutrons will be demonstrated.

Proceedings Article | 20 January 2004 Paper

Collimated step-wedge spectrometer for flash x-ray radiography sources

Fletcher Goldin, Stephen Mitchell

Proceedings Volume 5198, (2004) https://doi.org/10.1117/12.503868

KEYWORDS: X-rays, Scintillators, Aluminum, Optical filters, Collimators, Spectroscopy, Photons, Collimation, Absorption, Sensors

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Proceedings Article | 20 January 2004 Paper

End-point energy measurement in pulsed x-ray detectors

Stephen Mitchell, Joshua Friedman, Edward McCrea, Herman Utiger

Proceedings Volume 5198, (2004) https://doi.org/10.1117/12.518576

KEYWORDS: Sensors, Silicon, Diodes, X-ray detectors, Absorption, X-ray sources, Mathematical modeling, Performance modeling, Molybdenum, Manufacturing

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Showing 5 of 12 publications

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