A Comprehensive Empirical Study of the Critical Point at N/Z = 1.55 in Heavy Nuclides: Five Independent Dimensions of Evidence

Key Points

• To investigate whether N/Z = 1.55 is a universal critical point affecting the stability and decay modes of heavy nuclides.
• Analyzed data from nuclear databases (ENDF/B-VIII.0, NuDat 3.0, ENSDF) on 577 heavy nuclides using piecewise linear regression and Chow test.
• Examined decay channels in 32 nuclides to assess phase transitions in decay mode dominance at N/Z = 1.55.
• Investigated isotopic chains for power-law scaling of beta-dominated half-lives in the supercritical region.
• Logarithmic half-life shows a significant structural break at N/Z = 1.55 (p < 0.000001).
• Shell stabilization fails for nuclides with N/Z exceeding 1.55, evidenced by the doubly magic 208Pb and control chains.
• Spontaneous fission occurs exclusively at N/Z ≥ 1.55, increasing exponentially above this threshold.