Mr. Gabriel M. Ghita Profile

Gabriel M. Ghita

Research Assistant Scientist at Univ of Florida

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Proceedings Article | 17 April 2008 Paper

An equivalent n-source for WGPu derived from a spectrum-shifted PuBe source

Gabriel Ghita, Glenn Sjoden, James Baciak, Scotty Walker, Spring Cornelison

Proceedings Volume 6945, 694504 (2008) https://doi.org/10.1117/12.777475

KEYWORDS: Cadmium, Metals, Sensors, Monte Carlo methods, Plutonium, 3D modeling, Iron, Transform theory, Absorption, Optical filters

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We have designed, built, and laboratory-tested a unique shield design that transforms the complex neutron spectrum from PuBe source neutrons, generated at high energies, to nearly exactly the neutron signature leaking from a significant spherical mass of weapons grade plutonium (WGPu). This equivalent "X-material shield assembly" (Patent Pending) enables the harder PuBe source spectrum (average energy of 4.61 MeV) from a small encapsulated standard 1-Ci PuBe source to be transformed, through interactions in the shield, so that leakage neutrons are shifted in energy and yield to become a close reproduction of the neutron spectrum leaking from a large subcritical mass of WGPu metal (mean energy 2.11 MeV). The utility of this shielded PuBe surrogate for WGPu is clear, since it directly enables detector field testing without the expense and risk of handling large amounts of Special Nuclear Materials (SNM) as WGPu. Also, conventional sources using Cf-252, which is difficult to produce, and decays with a 2.7 year half life, could be replaced by this shielded PuBe technology in order to simplify operational use, since a sealed PuBe source relies on Pu-239 (T½=24,110 y), and remains viable for more than hundreds of years.

Proceedings Article | 24 May 2006 Paper

3D computational and experimental radiation transport assessments of Pu-Be sources and graded moderators for parcel screening

Gabriel Ghita, Glenn Sjoden, James Baciak, Nancy Huang

Proceedings Volume 6213, 62130I (2006) https://doi.org/10.1117/12.666928

KEYWORDS: Monte Carlo methods, 3D modeling, Data modeling, Sensors, Plutonium, Computing systems, Tin, Scattering, 3D displays, Photon transport

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The Florida Institute for Nuclear Detection and Security (FINDS) is currently working on the design and evaluation of a prototype neutron detector array that may be used for parcel screening systems and homeland security applications. In order to maximize neutron detector response over a wide spectrum of energies, moderator materials of different compositions and amounts are required, and can be optimized through 3-D discrete ordinates and Monte Carlo model simulations verified through measurement. Pu-Be sources can be used as didactic source materials to augment the design, optimization, and construction of detector arrays with proper characterization via transport analysis. To perform the assessments of the Pu-Be Source Capsule, 3-D radiation transport computations are used, including Monte Carlo (MCNP5) and deterministic (PENTRAN) methodologies. In establishing source geometry, we based our model on available source schematic data. Because both the MCNP5 and PENTRAN codes begin with source neutrons, exothermic (α,n) reactions are modeled using the SCALE5 code from ORNL to define the energy spectrum and the decay of the source. We combined our computational results with experimental data to fully validate our computational schemes, tools and models. Results from our computational models will then be used with experiment to generate a mosaic of the radiation spectrum. Finally, we discuss follow-up studies that highlight response optimization efforts in designing, building, and testing an array of detectors with varying moderators/thicknesses tagged to specific responses predicted using 3-D radiation transport models to augment special nuclear materials detection.

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