Vertical variations of flux parameters in irradiation channels at the TRIGA Mark II reactor of Pavia

The knowledge of neutron flux parameters, both in terms of value and gradient, in irradiation channels of nuclear
reactors is required to avoid biased results when applying Neutron Activation Analysis. To this aim, the Au Zr
bare triple-monitor method with the addition of Lu as a temperature monitor was used to collect experimental
data in irradiation channels of three facilities at the TRIGA Mark II reactor of Pavia. Twenty-four monitors were
placed in as many positions to determine the vertical variations of the neutron flux parameters. The results obtained
in three different activation experiments pointed out a decrease of the conventional fluxes up to 70% in
some cases. Nevertheless, the epithermal neutron flux correction factor, the thermal to epithermal neutron flux
ratio and the modified spectral index were constant throughout the entire length of the channels within the core
whereas trends were identified in channels outside the core.