| Popis: |
Primordial terrestrial radiation is mainly a consequence of the radioactive decay of nuclei in three naturally occurring decay series known as uranium series, actinium series, and thorium series. The parent nuclei along with the progeny (decay products) of these decay series can be found in various concentrations in Earth’s crust. Among the progeny, 226Ra is of greatest concern. 226Ra is water soluble and it decays to 222Rn which is a gas, which allows these two radionuclides to migrate considerable distances. 226Ra is found in shale at relatively high concentrations compared to other rock formations making shale a naturally occurring radioactive material (NORM). One concern with hydraulic fracturing is that the extraction of the gas embedded in the shale formation buried deep within Earth’s crust is bringing radioactive nuclides to Earth’s surface. This thesis is focused on the development of gamma-ray spectroscopic methods to determine the radium concentration in drill cuttings and water that is produced by hydraulic fracturing. The methods rely upon the development of secular equilibrium between 226Ra and its progeny. Only the countrate of the 214Bi 609 keV gamma-rays is counted and compared to the countrate of 137Cs activity doped in standards. Measurement methods are unique in that two factors are used to correct for the varying sample attenuation of the 214Bi 609 keV gamma-ray resulting from varying compositions and densities in each sample. Measurements are made with a 137Cs point source that is placed on top of the sample and is used for one correction factor, and Monte Carlo simulations of the response of an HPGe gamma-ray detector are used for the other correction factor. For a representative drill cutting sample, the product of the correction factors equals approximately 0.89. For a representative water sample, the product of the correction factors equals approximately 1.17. |
