Electrical and Computer Engineering ETDs

Publication Date

4-27-1973

Abstract

The purpose of this effort is to evaluate several types of dosimeters being used with the 2-MeV flash X-ray facilities at The University of New Mexico and the Air Force Weapons Laboratory (AFWL). The types include lithium fluoride and calcium fluoride thermaluminescent dosimeters (TLD's), thin foil calorimeters, p-i-n diodes, cobalt glass chips, and #25 purple Cinemoid. The evaluation includes a comparison of dose measurements, repeatability, and useful ranges. This report describes fundamental physical mechanisms by which photons and high energy electrons interact with matter, the physical mechanisms of different dosimeters, and techniques for using the dosimeters. The calcium fluoride TLD's yield repeatable measurements, but the lithium fluoride TLD measurements are not repeatable. A one-sided, nonparametric median test and a Wilcoxin two-­sample rank test were used to test the TLD data. Thin foil calorimeters, purple Cinemoid, and cobalt glass chips were used to measure doses between 0.3 and 10 megarads(Si). The calorimeter and Cinemoid results agree well at doses of from 1 to 10 megarads(Si). However, the cobalt glass chips yielded lower dose readings and saturated at about 1.8 megarads. Although they have been used at up to 15 megarads on radioactive sources having low dose rates, the upper limit of utility for cobalt glass chips is between 1.0 and 1.8 megarads(Si) when exposed at the high dose rates generated by flash X-ray machines. The lower end of the usable range for cobalt glass chips is 2 kilorads. The thin foil calorimeters connected directly to a high-gain oscilloscope have a usable range of from 50 kilorads to the machine's maximum output of about 10 megarads. Purple Cinemoid has a usable range of from 0.5 to greater than 10 megarads. It was used to measure the cross section of an electron beam propagating in a 5-inch drift tube. p-i-n diodes were used to successfully measure pulses of gamma radiation, but when they were used in the electron beam, electrical noise obscure the signals. Calibration curves for copper-constantan calorimeters, cobalt glass chips, and purple Cinemoid are included. Weighted electron stopping powers for the electron beam spectrum of the 2-MeV flash X-ray machines were calculated for eight materials used in dosimeters. The ratio of these stopping powers to that of silicon was also calculated. The method by which the weighted stopping powers were calculated is described.

Document Type

Thesis

Language

English

Degree Name

Electrical Engineering

Level of Degree

Masters

Department Name

Electrical and Computer Engineering

First Committee Member (Chair)

Harold Dean Southward

Second Committee Member

Wayne Willis Grannemann

Third Committee Member

Roy Arthur Colclaser

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