Statement

Raman carotenoid biosignatures show significant diminishment at 15 kGy and complete erasure by 150 kGy gamma radiation.

Evidence

Dartnell et al., 2012, Analytical and Bioanalytical Chemistry 403(1):131–144. DOI: 10.1007/s00216-012-5829-6 Dartnell et al., 2011, Astrobiology 11(10):997–1016. DOI: 10.1089/ast.2011.0663

Dose-response for carotenoid Raman peaks (ν₁ C=C ~1510–1518 cm⁻¹, ν₂ C-C ~1152–1155 cm⁻¹):

• 15 kGy: 33–67% carotenoid peak retention (Dartnell et al., 2012)
• 60 kGy: Complete carotenoid degradation by absorption spectroscopy (Dartnell et al., 2011)
• 150 kGy: Complete erasure of Raman carotenoid biosignatures (Dartnell et al., 2012)

Argument

A1: 100 kGy falls between measured brackets. Carotenoid Raman peaks show significant diminishment at 15 kGy (Dartnell et al., 2012), complete degradation by absorption spectroscopy at 60 kGy (Dartnell et al., 2011), and complete Raman erasure at 150 kGy (Dartnell et al., 2012). The 100 kGy reference dose sits above the 60 kGy destruction threshold.

A2: The degradation mechanism is bond scission in conjugated polyene chains. Carotenoid Raman signal depends on intact conjugated C=C chains. Gamma radiolysis breaks these bonds stochastically.

Implication

At 100 kGy, expect significant carotenoid loss. Supports "Affected" for:

• RAMAN SPECTROSCOPY × SCI 2.2 (Biosignatures)
• RAMAN SPECTROSCOPY × SCI 2.3 (Martian Life)
• RAMAN SPECTROSCOPY × SSA 1.2 (Abiotic Baseline)

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