Date of Award

3-2025

Document Type

Thesis

Degree Name

Master of Science in Nuclear Engineering

Department

Department of Engineering Physics

First Advisor

Jesse C. Foster, PhD

Abstract

Neutron time-of-flight, activation foils, and spectral unfolding software were used to characterize the energy and fluence of the neutron spectrum created by the Gamble II pulsed power generator. Gamble II is a pulsed power generator that delivers a 1 MV to 2.2 MV and 800 kA electrical pulse peaking at 50 ns. This electrical release creates deuterium ions in the diode that are accelerated to a neutron converter covered with a novel lithium fluoride or deuterated polyethylene to create primarily 7Li(d,n) or D(d,n) and 12C(d,n) nuclear reactions. In October 2024, two D(d,n) shots occurred, and in November 2024, one D(d,n) and one 7Li(d,n) shot occurred. The first method of characterization used Eljen (EJ-232 and EJ-232Q) and Nuclear Enterprises (NE-111) plastic organic scintillator detectors to conduct neutron time-of-flight measurements. The second method used five activation foils and Pacific Northwest National Laboratory's unfolding software STAYSL. Using the different activation threshold reactions, these foils (aluminum, indium, nickel, cobalt, and iro0n) allow for characterization of the neutron radiation field over a wide energy range. The radioactive foils were measured using four gamma-ray spectroscopy detectors: two ORTEC GEM 100P4-108-HE-S coaxial high purity germanium semiconductor detectors, one Harshaw Integration Line 12S12/3 sodium iodide thallium-doped inorganic scintillator detector, and one H3D M400 three-dimensional cadmium zinc tellurium semiconductor detector.  The measured spectra were analyzed and used to calculate the initial number of radioactive nuclei created by the pulsed power irradiation.  These calculation values as well as a guess spectrum of the neutron fluence by energy bin, generated using the Los Alamos National Laboratory's Monte Carlo N-Particle Transport code, were input into the STAYSL software. The STAYSL software, which minimized the chi-squared values through the least-squares method, outputs an unfolded, adjusted differential neutron flux. A maximum neutron yield for a deuterated polyethylene shot with a peak voltage of 2.14 MV was determined to by 7.41 +/- 0.29*1011 neutrons, a 1 MeV(Si) equivalent yeild of 7.32*1011. This included neutrons reaching energies of 5.09 +/- 0.08 MeV and 1.54 +/- 0.02 MeV for the deuterium-deuterium and deuterium-carbon neutron-generating reactions, respectively.  A maximum neutron yield for a lithium fluoride shot with a peak voltage of 1.52 MV was determined to be 7.27 +/- 0.25 *1010 neutrons, a 1 MeV(Si) equivalent yield of 1.03 *1011 neutrons. This included neutrons reaching energies of 15.4 +/- 0.4 MeV for the deuterium-lithium neutron-generating reactions. The neutron yield for the lithium fluoride shot was artificially low due to a pulsed power problem that reduced the electrical power delivered to the diode.

AFIT Designator

AFIT-ENP-MS-25-M-208

DTIC Accession Number

AD1356637

Comments

An embargo was observed for posting this graduate work on AFIT Scholar.  Approved for public release, distribution unlimited. PA case number 88ABW-2025-0327.

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