Calibration of the fission-track dating method: Is Cu useful as an absolute thermal neutron fluence monitor?

Thermal neutron fluence measurements have been performed with Au and Co standard monitors at the one side and Cu monitors (foils and wires) at the other. using three reactor channels with different neutron energy spectra and two calibrated Ge detectors. Care was taken to eliminate errors caused by epithermal activation and neutron self-shielding while special attention was also paid to the problem of incomplete annihilation of the ⁶⁴Cu β⁺ radiation. Our new measurements reveal consistent fluences between Cu and the Au and Co standard monitors, when using the recommended and/or recently evaluated nuclear parameters for the ⁶³Cu(n,γ)⁶⁴Cu reaction. However, we do not endorse the usage of Cu as a standard fluence monitor for fission-track dating because from a metrological standpoint too large uncertainties still exist on some of its relevant nuclear parameters such as the thermal neutron activation cross-section (σ₀) of ⁶³Cu.