Date of Award

12-26-2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Department of Engineering Physics

First Advisor

Benjamin R. Kowash, PhD.

Abstract

The design parameters of a Time-of-Flight (TOF) neutron spectrometer composed of BCF-12 plastic scintillating fibers were investigated. A GEANT4 transport model was developed for analyzing the interaction of 2.5 MeV neutrons with a 14 x 14 BCF-12 fiber bundle. The bundle simulation demonstrated that 0.359% of all neutrons incident on the bundle will double scatter. The timing and data collection e efficiencies of a Tektronix DPO7104 series digital oscilloscope were examined to determine the signal processing requirements for future fiber bundle measurements. The minimum detectable neutron energy was computed by taking into account the bundle scintillation e efficiency, light collection e efficiency, photodiode quantum e efficiency, and quenching. For a BCF-12 fiber coupled to dual-readout Hamamatsu S10362-11-025C series Silicon Photomultipliers (SiPMT), the minimum detectable neutron energy was calculated to be 300-700 keV, depending on the fiber cladding and geometry. The spatial and timing uncertainties were set to 1 mm and 0.1 ns, respectively, to determine the overall energy uncertainty associated with a TOF neutron spectrometer. The uncertainties of 1 mm and 0.1 ns were chosen as the optimal capabilities of the SiPMT and digital oscilloscope. Finally, analysis of a SiPMT in a light-tight box was performed to validate dark counts, determine light leakage and other detection system background noise. An experiment involving a 14 x 14 BCF-12 fiber bundle connected to dual-readout SiPMTs is recommended for future research to compare to the GEANT4 double scatter event probability.

AFIT Designator

AFIT-ENP-13-D-01

DTIC Accession Number

ADA603828

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