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The possibility of the determination of U and Th concentration in the Thai monazite ore processing samples using gamma-ray spectrometry technique was investigated. The studied samples were monazite ore, tri-sodium phosphate, mixed rare earth hydroxide, enriched cerium, uranium cake, thorium cake, La2O3 and CeO2. The measured activity concentrations of 238U and 232Th were converted into the concentrations of U and Th under the assumption of secular equilibrium. The results showed that the major daughter nuclides found in the studied samples, were 214Pb 214Bi and 226Ra for 238U series with additional radionuclides of 228Ac, 212Pb, 208Tl and 212Bi for 232Th series. The concentrations of U and Th estimated via each daughter products of their series were not significantly different for all samples. Wavelength Dispersive X-ray Fluorescence (WDXRF) with different sample preparations (loose powder, pressed pellet and fused bead methods) was also used to determine the concentrations of both U and Th in these samples. A good agreement between the concentration of U and Th measured by gamma-ray spectrometry (U = 0.42 wt%, Th = 6.54) and WDXRF prepared by fused bead method (U = 0.41 wt%, Th = 7.37) was observed for monazite ore sample.
