Determination of the f parameter for k 0-neutron activation analysis at the Australian 20 MW OPAL research reactor

In the k ₀ method of standardisation in neutron activation analysis (k ₀-NAA), the ratio of thermal to epithermal neutrons, a value known as f, is fundamental in accurately determining the concentration of elements within the sample. Research into determining this f value via the cadmium ratio method was undertaken for two positions within the 20 MW Open Pool Australian Light water (OPAL) research reactor (Lucas Heights, NSW, Australia). A short irradiation and long irradiation position were assessed via two methods; the conventional cadmium ratio method based on the Høgdahl formalism, with f values of 2,666 ± 255 and 1,538 ± 258 being calculated respectively for the short and long positions, and an ASTM-INVAP-based cadmium ratio method, which allows for the higher neutron temperature of OPAL to be accounted for, with f values of 3,057 ± 318 and 1,755 ± 312 being calculated respectively. These values were validated by analysis of NIST standard reference materials (SRM™), with good agreement between experimental values and reference and literature values being observed, showing the accuracy and suitability of these values for OPAL. Additionally, the high values of f shown endorse the strength of performing k ₀-NAA at OPAL. This manuscript publishes the first values of f from OPAL and provides a detailed description of the method employed.