VERIFICATION OF k0-NAA ANALYTICAL METHOD IN PAVIA LABORATORY AND DETAILED UNCERTAINTY EVALUATION

The topic of the talk involves the application of k0-NAA analytical method in the laboratory of the INRIM’s radiochemistry and spectroscopy unit located at the University of Pavia. As knowledge of flux parameters is a key step to set-up k0-NAA, f and were first evaluated in three channels of the 250 kW TRIGA Mark II reactor of Pavia, with use of Cd-covered and Cd-ratio approaches on a similar flux monitor set composed by Au, Rb, Zr and Co. Obtained values of f and  were 15.6(3) and -0.036(6), 15.7(4) and -0.041(7), 17.4(4) and -0.016(6) in Central Channel (CC), Rabbit and Lazy Susan channels, respectively [1]. Standard uncertainty is indicated in parenthesis and refers to the last digit. The verification of the applied k0-NAA method, including the assessment of flux parameters, was finally performed by irradiating standards and a reference material in CC and calculating the mass of target element from counting of -emissions using a monitor of Co. The ratio between the experimentally evaluated mass and the expected value for the same target element a, referred as a, was calcuated for each of 15 standard elements and for the 15 certified elements that were quantified in the reference material. All results appear to be in good agreement and no severe deviations from unity were registered in the experiment performed with standards confirming both the correct application of method and flux parameters evaluation. Moreover, a detailed uncertainty budget was carried out with particular focus on the major contributors (Q0 values and efficiency-related uncertainty mainly) having care to deal with all the occurring correlations among parameters. The aim was accomplished with calculation of sensitivity coefficients for each input value and with aid of the covariance matrix to resolve correlations.