Abstract This thesis discusses 226Ra distribution in the seawater of the East China Sea and the sea off northeastern Taiwan. Six profiles and fifteen surface water samples were measured. Water samples were collected during cruises 493 and 523 in July, 1997 and July, 1998, respectively. 226Ra measurements were performed by the regenerated 222Rn method that had been widely used for seawater samples. The surface water 226Ra activities vary between 8.7 and 15.9 dpm/100kg in the East China Sea. There is an increase in surface water 226Ra northward toward the estuary of the Changjiang. This variation is somewhat similar to that observed in the East China Sea by Nozaki et al. (1976). The surface water 226Ra activities vary between 9.1 and 10.8 dpm/100kg in the area off northeastern Taiwan. There values are higher than KEEP-MASS cruise of July, 1992. The Kuroshio Current not easy to enter shelf, so the dilution effect of Kuroshio is smaller. Otherwise, There are 226Ra in profiles were measured from six stations on Cruise 493 (13 and 15) in Kuroshio area and Cruise 523 (5, 7, 13 and 15) in shelf. The deep water profile on Cruise 493 (st.13) displays a phenomenon 226Ra increase from about 9.7 dpm/100kg at 5m to about 14.3 dpm/100kg at 500m, station 15 from Cruise 493 displays a phenomenon 226Ra increase from about 9.8 dpm/100kg at 5m to about 17.7 dpm/100kg at 800m. 226Ra profile at station 7 showed that the gradient from 600m to 750m is large, and 226Ra concentration does not increase below this depth. 226Ra maybe associated with nepheloid layer due to lateral or horizontal transport of the water mass. Each 226Ra profile shows a downward increase from less than 10 dpm/100kg at the surface, and shows the underlying sediments as the main source. Based on the radioactive disequilibrium observed between 210Pb and 226Ra, all the ratios of Pb-210/Ra-226 in Station 13 are greater than 1, except at 400m. The 210Pb concentration is high and the ratio of Pb-210/Ra-226 is greater than 1 at 800m.

Radium contamination in the lakes near uranium mines and its intake by fish and other aquatic species are of great concern in environmental radiation protection. As an alternative technique to Liquid Scintillation Counting, we present a gamma-ray spectrometric method for low level 226Ra analysis, particularly in live fish. The HyperPure Ge and a 4π NaI(Tl) array were employed as gamma-ray spectrometers. The 226Ra spectra for each spectrometer were collected in order to compare their analytical performance. From the HPGe 226Ra spectra, a detection limit of 6.81 Bq with 99% confidence was determined for an hour counting with the three strongest peaks combined. For the 4π NaI(Tl) 226Ra spectra, in order to optimize the spectral analysis, a method applied to nine different energy regions was attempted and it turned out that the detection limit is best when the total integral count subtracted by the corresponding background is used. The detection limit of the 4π NaI(Tl) was 0.99 Bq with 99% confidence for one hour counting. A benchmark simulation for point source position dependence on relative peak efficiency showed a good agreement with the experimental data. To extend 226Ra analysis to volumetric aqueous samples, MCNP Monte Carlo simulations showed that for three cylindrical volume sources, as the simulated volume source size increased from 60 ml to 125 ml to 250 ml, the full-energy peak efficiency in the energy range of interest for 226Ra decreased by approximately 3% for each size increase, due to attenuation in the source volume. A method has been proposed in order to demonstrate this technique for a live fish, whereby a fish injected with 226Ra would be kept in its own special aquarium and its gamma-ray spectrum collected. / Thesis / Master of Science (MSc)

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