Measurement of neutron flux parameters for implementation of k0-INAA at Kyoto University Research Reactor

Neutron flux parameters at pneumatic irradiation tube Pn-1 of Kyoto University Research Reactor (KUR) were measured in order to establish k0-INAA method. The measured thermal to epithermal neutron fluxes ratio (f), shape factor of epithermal neutron flux (α), and thermal (ϕth) and fast (ϕf) neutron fluxes were 29.7 ± 2.0, − 0.015 ± 0.003, and (3.17 ± 0.11) × 1012 and (4.79 ± 0.16) × 1011 cm−2 s−1 at 1 MW, respectively. The neutron flux spectrum showed a remarkable stability over the weekly operation cycle as well as at different reactor powers. The analysis results of reference materials [multi-element liquid standard, and Oriental Basma Tobacco Leaves (INCT-OBTL-5)] revealed that the k0-INAA procedure established at the KUR can be regarded as a reliable standardization method of multi-elemental INAA; measured concentrations have zeta-score <  ± 2. Corrections due to nuclear interference resulting from fast neutron reactions must be considered for samples with relatively high concentrations of interfering elements. MCNP5 code was used to estimate the total efficiencies of gamma-rays, which might be required to calculate correction factor for the true coincidence effects.