Environmental Amplification of Solid Deuterium Surface Frost: A Unified Solution to the Neutron Lifetime Puzzle

The persistent ∼9-second discrepancy between bottle and proton-detection beam measurements of the free neutron lifetime is resolved by identifying progressive surface frost on soliddeuterium (SD2) ultracold neutron (UCN) converters as a systematic bias amplified by environmental conditions. Multi-site observations (LANL, PSI, NCSU) confirm frost formation,spectral hardening, and yield degradation under pulsed operation. Direct time-of-flight measurements at PSI document real-time spectral hardening consistent with frost accumulation.Marginally-trapped UCN produced by spectral hardening have measured escape times of 10100 s and cause systematic downward biases of 5–12 s, as demonstrated at NIST where removingthese neutrons recovered the correct lifetime (621 s → 833 s). LANL’s high-altitude operation(2231 m) accelerates frost formation through elevated cosmic ray heating (∼3× sea level) andlarge diurnal temperature swings (15–25 K). Critically, UCNτ’s 2017–2018 measurements occurred during solar minimum 24/25 approach, when cosmic ray flux reached near-record levels—representing maximum possible environmental stress on SD2. The December 2024 J-PARCelectron-detection beam measurement (τn = 877.2 ± 4.5 s) validates bottle measurements andidentifies a ∼10 s systematic in proton-detection experiments, not bottles. We provide falsifiable predictions including anti-correlation with temperature, dependence on source conditioningcycles, and altitude scaling, with specific recommendations for archival analysis and controlledtesting.