Degree Type

Dissertation

Date of Award

1995

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

First Advisor

Joseph N. Gray

Abstract

Computer modeling of nondestructive inspections with x-rays is proving to be a very useful tool for enhancing the performance of these techniques. Two x-ray based inspection techniques are considered in this study. The first is "Radiographic Inspection", where an existing simulation model has been improved to account for scattered radiation effects. The second technique is "Inspection with Compton backscattering", where a new simulation model has been developed;The effect of scattered radiation on a simulated radiographic image can be insignificant, equally important, or more important than the effect of the uncollided flux. Techniques to account for the scattered radiation effects include Monte Carlo techniques, and solving the particle transport equation for photons. However, these two techniques although accurate, are computationally expensive and hence inappropriate for use in computer simulation of radiography. A less accurate approach but computationally efficient is the principle of buildup factors. Traditionally, buildup factors are defined for monoenergetic photons of energies typical of a nuclear reactor. In this work I have expanded the definition of buildup factors to include a bremsstrahlung spectrum of photons with energies typically used in radiography (keV's instead of MeV's). This expansion of the definition relies on an intensive experimental work to measure buildup factors for a white spectrum of x-rays. I have also developed a monte carlo code to reproduce the measured buildup factors. The code was then converted to a parallel code and distributed on a network of workstations to reduce the execution time;The second inspection technique is based on Compton backscattering, where photons are scattered at large angles, more than 90 degrees. The importance of this technique arises when the inspected object is very large, or when access is limited to only one side of the specimen. The downside of detecting photons from backscattering is the low cross section for Compton scattering at such angles. However, several parameters can be optimized to enhance the probability of a backscattering event. These include the x-ray tube settings, the orientation of the inspected object and the angles of the incident and backscattered radiation. Optimizing these parameters can be made fast, inexpensive and more convenient by using a simulation code.

DOI

https://doi.org/10.31274/rtd-180813-10065

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Taher Lutfi Al-Jundi

Language

en

Proquest ID

AAI9531713

File Format

application/pdf

File Size

108 pages

Share

COinS