IUPAC

The single comparator calibration approach (the 'k₀-method') in neutron activation analysis is subject to various influencing factors, which might vary from laboratory to laboratory. A critical review and harmonization of measurement approaches is required to assure the highest achievable metrological comparability of results obtained.
This project aims at the development of a guidance document (protocol) for practitioners of neutron activation analysis related to calibration of the neutron fluence rate, -spectrum shapes, and full energy photo peak efficiency.

Instrumental neutron activation analysis (INAA) allows for multi-element determinations without chemical pre-treatment of the test portion. The INAA multi-elements capabilities are fully employed if the single comparator calibration is used, also known as the 'k₀-method'. In contrast to the use of reference material for calibration, the k₀-method requires very critical calibration of input quantities, including the thermal, epithermal and fast neutron fluence rate and gradients thereof in the irradiation position, as well as of the full-energy photopeak efficiency and the coincidence counting effects.

Each of these individual calibrations implies contribution to the uncertainty of measurement, and combination thereof is not always straightforward and may have to be assessed via Monte Carlo calculations.

The aim of this project is to provide practical guidance on

• preparation of standards for calibration the neutron spectrum characteristics
• assessment of correction factors for neutron self-shielding, gamma-ray self attenuation and dimensional differences during irradiation and counting
• determination of the full-energy photopeak efficiency
• assessment of correction factors for coincidence effects during counting
• asssessment of the contributions of each individual calibration step to the uncertainty of measurement
• elaboration on the traceability of the results thus obtained.

The protocol will account for differences that exist in sample packaging in various laboratories, as well as in irradiation containers and facilities, and in counting facilities. Where applicable, examples of EXCEL spreadsheet calculations will be included.

Each of the task group members will use its own network of k₀-method practioners for consultation and information on e.g. side-specific irradiation and measurement conditions. This will contribute to the development of guidance and protocols for application of the k₀-method of standardization in a broad variety of NAA facilities.