A method to determine 238U activity in environmental soil samples by using 63.3-keV-photopeak-gamma HPGe spectrometer

The paper presents a method of measuring 238U activity in environmental soil samples by a low background HPGe spectrometer at the 63.3 keV gamma photopeak. The low 238U activity requires a large size soil sample with a mass of about 100 g. The geometrical and self-absorption effects as well as the density dependence of soil samples were then investigated. A procedure of analyzing environmental soil samples was established with a relative error of about 10%. Two soil samples of known activity were tested and 106 surface soil samples collected from the Southern part of Vietnam were analyzed, and then these results were compared by instrumental neutron activation analytical method.