Powdered rock versus solid rock comparisons in particle‐induced X‐ray emission measurements for planetary geochemical exploration
Bibliographic record
Abstract
Grain size is an important consideration in the determination of the bulk chemistry of Martian rocks and unconsolidated materials in situ by the alpha particle X‐ray spectrometer (APXS), deployed on the NASA‐led Mars Science Laboratory mission. We used 2.5 MeV protons to emulate the particle‐induced X‐ray emission (PIXE) branch (5 MeV alphas) of the APXS. Seven polished rock slabs (igneous and sedimentary), ranging from fine‐ to coarse‐grained, were analyzed by PIXE in their original form, then milled to powders and pressed into pellets for further analysis. The summed area (160 mm 2 ) over 10 interrogated regions on each slab is comparable to the area interrogated on the APXS; analysis of two pellets per rock, each using a 16 mm 2 region, was found to be appropriate. The mean pellet/slab concentration ratio for Na, Mg, Al, Si, K, Ca, and Fe was close to 1.0 for fine‐grained samples, but changed by ±10% for the coarser cases. The variability among PIXE concentration values across the 10 rock regions increased monotonically with coarseness in the rock slabs. Comparison of overall PIXE concentrations with values measured by borate‐fusion WDXRF provides further quantitative support to the direct comparison of pellet and slab PIXE concentrations. This work affirms the use of the APXS on fine‐grained Martian materials but recommends larger interrogation areas (including rastering) when analyzing coarser‐grained materials. It also demonstrates that the presence of relatively large mineral grains (phenocrysts) or rock/mineral fragments within fine‐grained materials can contribute to greater error for specific elements associated with those phenocrysts/fragments.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".