Date of Award

2004

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Physics

Advisor

C.T. Hess

Second Committee Member

C.W. Smith

Third Committee Member

G.P. Bernhardt

Abstract

Soil contains many radionuclides, occurring both naturally and from man-made nuclear reactions. The radiation exposure to humans from these radionuclides can be measured with radiation detectors. Measuring radiation from soil near a body of water requires consideration of the shielding effect of water. Shielding occurs when a material absorbs radiation. This work models the amount of exposure measured on a tidal flat throughout the tide cycle. Understanding how the exposure rate changes during the tide cycle provides accurate calculations of the total exposure absorbed by humans when on a tidal flat. We derive a theoretical model to predict the behavior of exposure rate in time for a detector placed one meter above ground on a tidal flat. The numerical integration involved in this derivation results in an empirical formula that implies exposure rate is proportional to tan^-1 (sin t), where t is in minutes. With this formula we propose that calculating the total exposure incurred on a tidal flat requires measurements of only the slope of the tidal flat, the exposure rate when no shielding occurs, the cosmic exposure rate, and an empirical constant. Experimental results are consistent with the model.

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