The use of electron spin resonance techniques to determine gamma ray exposure of alpha-keratin in human hair
Abstract
The objective of this research was to determine the potential for using electron spin resonance (ESR) techniques with human $\alpha$-keratin (hair) as a measure of gamma ray exposure. Samples of black, brown, and blond hair from six healthy white human volunteers ages 19 to 47 were examined. Samples from each person were throughly mixed and split into 8 parts of 0.1 $\pm$ 0.01 gram each. The samples were irradiated with Co-60 gamma rays, and analyzed by electron spin resonance (ESR). Samples could be removed and replaced within the ESR cavity without statistically changing the measure of magnitude of the ESR signal (free radicals were produced isotropically). Ground samples produced an ESR signal that added to the background so whole hair strands were used for this study. Ambient humidity did not affect signal decay or response of the samples at the 95% confidence level. A linear dose response model was produced, and a correlation coefficient of greater than 0.9 was obtained from 47 Gy to 370 Gy. The models for dose response at 0.25 hours and 3 hr post irradiation are: $S\sb{0.25\rm{hr}}=0.00067\times D+0.0225$ and $S\sb{3\rm{hr}}=0.0005\times D+0.017.$ The symbol D represents the magnitude of the integrated area of the negative portion of the ESR signal first derivative and S is the dose in Gy. The lowest detectable dose, 47 Gy, the negative portion of the ESR signal after plotting, appeared to be different from background, but was not statistically significant at the 95% confidence level. A model for the decay (recombination of free radicals) of the ESR signal was also produced for doses of 47 to 740 Gy. The magnitude of the integrated area of the negative portion of the ESR signal first derivative is predicted by the following model: $A=0.46\times(S\sb{0.25\rm{hr}})\times e\sp{-0.5\times t}+0.6\times(S\sb{0.25\rm{hr}})\times e\sp{-0.0211\times t}.$ The symbol t represents the time post irradiation in hours. The rate of decay was not constant from sample to sample, possibly due to biological variation between samples. Samples must be analyzed within 24 hours of irradiation or stored in liquid nitrogen prior to analysis in order to make a dose estimate based on ESR measurements since the signal loses intensity over time.
Degree
Ph.D.
Advisors
Ziemer, Purdue University.
Subject Area
Radiology
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