Zakopane 2026 Conference on Nuclear Physics

The isomeric cross-section ratio R = σm/σg for the ¹⁹⁷Au(p,n)¹⁹⁷m,gHg reaction is analyzed over the proton energy range 6.5–32.0 MeV using selected published experimental datasets retrieved from the EXFOR nuclear reaction database and primary publications. Cross-sections calculated with the TALYS-1.9 nuclear reaction code, taken from the TENDL-2019 evaluated nuclear data library (Plompen et al., 2020), are compared with the experimental data. The analysis reveals that TENDL-2019 systematically underestimates the isomeric ratio above 14 MeV by 15–25%, motivating a detailed examination of the angular momentum and spin-cutoff parameter physics that govern isomeric state population. The large spin asymmetry between the isomeric state (¹⁹⁷mHg, Jπ = 13/2+, T½ = 23.8 h) and the ground state (¹⁹⁷gHg, Jπ = 1/2⁻, T½ = 64.14 h) makes this reaction an extreme example of spin-dependent level density sensitivity, directly connecting to the conference theme of nuclear extremes. The spin-cutoff parameter σ² is evaluated analytically using three published level density parameterizations, namely, Gilbert–Cameron, back-shifted Fermi gas, and microscopic HF-BCS—and its role in controlling the energy dependence of R is discussed in the context of the TENDL-2019 discrepancy.