Different methods for the determination of thermal-to-epithermal neutron flux ratio are reviewed and nuclear data for commonly
used monitor materials and for Zr isotopes are tabulated. It is shown that the use of the94Zr−96Zr isotope pair gives significant improvement in precision while measuring Φth/Φe ratios in the 20<Φth/Φe<200 range. When the single comparator method is applied, the use of the94Zr isotope is suggested as a comparator with the94Zr−96Zr isotope pair for simultaneous flux ratio determination. Theoretical calculations show that the Zr comparator-flux ratio
monitor gives better precision and accuracy than does Ru for two-thirds of the isotopes used for analysis in well thermalized
(Φth/Φe>100) channels. The Io/σth-values for the mentioned Zr isotopes have been experimentally determined and compared with previously published data.