A method to deal with correlations affecting gamma counting efficiencies in analytical chemistry measurements performed by k(0)-NAA

The ratio of gamma counting efficiencies is very important in trace element analysis carried out by prompt- and delayed-gamma neutron activation based on k(0) standardization. Although the effect of correlation between counting efficiencies is well known and methods have been developed and adopted in prompt-gamma neutron activation analysis to correctly evaluate the uncertainty, proposals and applications in delayed-gamma neutron activation analysis are still lacking. To fill the gap, we developed a new method based on the use of reference gamma-sources to determine the detection efficiency ratio and its uncertainty by taking full account of correlations. A measurement model that differs to some extent from the classical k(0) formulation widely used in delayed-gamma neutron activation analysis is required. A detection system was characterized to test the suitability of the method in a double-counting position setup, where the standard is placed far from the detector end-cap and the sample is placed close to it. The present paper is a significant expansion of a relevant abstract presented at the 'Mathematical and Statistical Methods for Metrology' Workshop, Torino, Italy, 30-31 May 2019 (pp 27-28 in ).