In this research a method for determining 235U isotope in concentrated uranium compounds by direct measurement of 235U 186-keV gammaray was investigated. A high purity germanium (HPGe) detector of 30% relative efficiency was used to measure the gamma-ray from fine-powdered depleted and natural uranium compounds as well as from a standard natural uranium foil. The self-absorption factors of the samples were determined by transmitting the 186-kev gamma-ray from a 226Ra source. Total uranium content in the samples was determined by using the x-ray fluorescence (XRF) technique. The samples were diluted to about 2% of their original concentrations with boric acid powder then compressed with a hydraulic press. An annular 57Co was used as the exciting source. The most intense U K x-ray line, U K 1 , was detected by using a 0.6 cm ø, 0.5 cm thick HPGe detector. The mass attenuation coefficients at the U K 1, energy (98.5 KeV), obtained from transmitting 98.5 KeV x-ray from uranium secondary target, were used for correcting the matrix effects. It was found that 235U isotope concentrations in the depleted uranium samples were in the range of 0.353% to 0.432% which were close to the expected and the known values. In the natural uranium sample the 235U is tope concentration was found to be 0.716%. The results indicated the possible use of this method for determining 235U isotope concentration in uranium enrichment research and uranium fuel inspection.
