Statement

100 kGy gamma sterilization preserves the majority of MSR measurement objectives. The geological, geochemical, and isotopic techniques which constitute the bulk of the assessment are unaffected because gamma radiation at 662 keV cannot alter nuclear properties or significantly damage mineral crystal structures.

Life detection measurements targeting molecular biosignatures or viable organisms are most affected due to organic bond radiolysis and organism inactivation.

Dedicated atmospheric samples are unaffected by our dose and can baseline headspace gas analysis to mitigate the partial affect radiation has on those measurements.

Evidence

Synthesis of mechanism-based analysis across 280 technique × sub-objective intersections (76 unique analytical techniques × 19 sub-objectives; v8 assessment):

1. Nuclear physics precludes isotope alteration at 662 keV. Photonuclear reactions require ≥1.67 MeV, and 662 keV is only 40% of this threshold. Zilges et al., 2022, Progress in Particle and Nuclear Physics 122:103903. DOI: 10.1016/j.ppnp.2021.103903 All isotopic techniques (TIMS, MC-ICP-MS, SIMS, noble gas MS, etc.) are not affected.
2. Crystal structures stable to doses exceeding 1 MGy; ionization damage anneals rapidly. Plötze et al., 2003; Velbel et al., 2022 (see Crystal Structure Preservation claim). All crystallographic techniques (XRD, EBSD) are not affected.
3. Magnetic properties intrinsically preserved with no measurable demagnetization to 7,000 kGy. Samin, 2018, Journal of Nuclear Materials 505:82–96. DOI: 10.1016/j.jnucmat.2018.02.029 All magnetometry techniques are not affected.
4. Bulk elemental analyses unaffected. Gamma radiation does not alter elemental abundances. XRF, LA-ICP-MS, SEM-EDS are not affected.
5. Atmosphere-only samples exempt from condensed-phase radiolysis pathways. Radiolytic product yields (G-values) are defined for condensed-phase interactions (Spinks & Woods, 1990); at ~6.1 mbar (~0.22 mg gas), essentially all gamma energy passes through the tube or is deposited in the titanium tube wall. Spinks & Woods, 1990, An Introduction to Radiation Chemistry (3rd ed.), Wiley-Interscience. ISBN 978-0-471-61403-6.

What is affected:

• Organic molecular biosignatures (radiolytic fragmentation)
• Aromatic fluorescence for bio/abiotic discrimination
• Viable organism detection (organisms inactivated)
• Some redox-sensitive measurements in hydrous phases

6. Comparison to prior MSR assessment: Velbel et al., 2022, Astrobiology 22(S1):S112–S164. DOI: 10.1089/ast.2021.0113 Estimated ~50% of life-science measurements "critically sensitive" to SRF sterilization. Our intersection-level analysis shows better preservation because many technique applications within "sensitive" categories are actually preserved when examined at the specific measurement technique × sub-objective level.

Argument

A1: Mechanism-based reasoning provides physical justification. Each assessment traces to a specific physical mechanism (M1–M10 in the technical report): nuclear physics constraints, crystal lattice stability, radical chemistry, organic bond radiolysis, etc.

A2: Intersection-level analysis provides higher resolution than category-level assessment. Velbel et al. (2022) assessed broad technique categories (e.g., "spectroscopy"). Our assessment examines each technique × sub-objective combination individually, revealing that many applications within "sensitive" categories are actually preserved when the specific measurement objective is considered.

A3: Conservative methodology identifies real impacts. Where gamma radiation fundamentally compromises a specific discriminant measurement, such as fluorescence-based bio/abiotic discrimination or viable organism cultivation, our assessment assigns "Affected" regardless of whether the broad technique category might appear viable at a coarser resolution.

A4: Dedicated atmospheric samples are unaffected and preserve the baseline needed to interpret headspace gas contamination in rock tubes. Every atmospheric measurement objective is isotopic. The atmospheric tube also serves as the baseline for distinguishing radiolytic products (H₂, CO₂, CH₄) from indigenous volatiles in rock tube headspace, and any minor molecular shifts from wall-surface radiolysis are characterizable via analog experiments.

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