A re-evaluation of k0 and related nuclear data for the 555.8 keV gamma-line emitted by the Rh-Rh mother–daughter pair for use in NAA

A re-evaluation is made of the k₀-factor and related nuclear data for the 555.8 keV gamma-ray of the ^104mRh-¹⁰⁴Rh mother–daughter pair that are important in neutron activation analysis (NAA). This study considers that the relevant level is also fed by the 4.34 min ^104mRh mother (with an absolute gamma-ray emission probability γ₂=0.13%) and not only, as assumed in former work, by the 42.3 s ¹⁰⁴Rh daughter isotope (with γ₃=2.0%). In view of this, generalised equations were developed for both the experimental determination and the analytical use of the k₀-factor and of the associated parameters k₀(m)/k₀(g), Q₀(m) and Q₀(g) [(m):^104mRh; (g): ¹⁰⁴Rh], requiring the introduction of the γ₂ and γ₃ data and also of the ^104mRh→¹⁰⁴Rh fractional decay factor F₂(=0.9987). The experimental determinations were based on irradiations performed in the BR1 reactor in Mol and the WWR-M reactor in Budapest. Furthermore, considering the special formation of the 555.8 keV gamma-ray, the procedure for true-coincidence correction was revised as well. All this led to the compilation and recommendation of a new set of ‘k₀-NAA’ data.