International key comparison of thermal neutron fluence measurements - CCRI(III)-K8

After more than thirty years a new key comparison of thermal neutron fluence measurements was organized by section III of CCRI. The comparison was carried out by rotating four transfer instruments among the four participants (CIAE, PTB, NMIJ and NPL). The stability of the detectors was repeatedly verified by the pilot laboratory between the measurements. Each of the four transfer devices had a different dependence of the fluence response on the neutron energy. Hence the comparison was also sensitive to the knowledge of the spectral distributions of the facilities used by the participants for their measurements. The results of the comparison showed signs of inconsistencies which could not be resolved during the analysis. Therefore the arithmetic mean of the results was used to calculate the key comparison reference value. (authors)