Statement

662 keV gamma photons cannot induce nuclear transmutation; photonuclear reactions require energies ≥1.67 MeV (minimum threshold). Isotope ratios are therefore intrinsically preserved.

Evidence

Zilges et al. 2022, Progress in Particle and Nuclear Physics 122:103903. DOI: 10.1016/j.ppnp.2021.103903

• Minimum photonuclear reaction threshold: ≥1.67 MeV
• ¹³⁷Cs gamma (662 keV) is only 40% of the minimum threshold (662 keV / 1,670 keV = 0.40)

At 662 keV, photon interactions are limited to:

• Compton scattering (~90%)
• Photoelectric absorption (~10%)

No nuclear reactions are possible at this energy, the photon energy is insufficient to overcome nuclear binding.

Argument

A1: Hard physics constraint. Photonuclear reactions require photon energies ≥1.67 MeV. ¹³⁷Cs emits at 662 keV, which is 40% of the minimum threshold. This is not a statistical or dose-dependent boundary; it is a quantum-mechanical constraint.

Implication

Supports "Not Affected" for all isotopic techniques:

• TIMS × all columns
• MC-ICP-MS × all columns
• SIMS × all columns (for isotopic measurements)
• AMS × all columns
• IRMS × all columns
• NOBLE GAS MS × all columns

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