230Th assay by epithermal neutron activation analysis

Thorium-230 is an important member of the U-238 decay chain and is a major contributor to the environmental dose from actinides. The use of epicadmium neutron activation analysis (NAA) as a simple, rapid and inexpensive means of assaying 230Th in biological systems is described. The suitability of the NAA method in the presence of the 238U parent and other members of the natural uranium decay chain was examined by activating a quantity of various uranium ores with a reactor (TRIGA MK1) thermal neutron spectrum having a cadmium ratio of approximately 10. The resultant X-ray spectra in the region of 60-120 keV showed that the NAA method appeared feasible as a means of determining 230Th in the presence of natural uranium. The data suggested a sensitivity of at least 10 ng. for a 10 g sample, 100 minute counting time, and epicadmium fluence of 3 x 1012n/cm2. (UK)