Bibliographic record
Abstract
Osmium is the least abundant member of the group of six elements called the PGE (platinum group elements). Like lead, osmium is an element with siderophile–chalcophile affinities, but unlike lead, osmium appears to be a strongly ‘compatible’ element during melting in silicate systems (meaning that it is strongly retained in the mantle source mineralogy). These geochemical properties mean that osmium can be used as a dating tool and a tracer in different ways from ‘lithophile’ isotope systems such as Sr, Pb and Nd, providing unique insights that complement these other systems. Osmium has seven naturally occurring isotopes, two of which ( 187 Os and 186 Os) are the decay products of long-lived radioactive isotopes, 187 Re and 190 Pt. Of these two decay schemes, the Re–Os method has been widely used as a dating tool and geochemical tracer, since its parent, 187 Re, has a half-life of ca. 42 Ga and makes up 62% of natural rhenium. Rhenium is a typical chalcophile element which behaves like molybdenum in magmatic and ore-forming systems. The Pt–Os method was developed more recently, since the radioactive parent ( 190 Pt) makes up only 0.013% of natural platinum, and has an extremely long half-life of ca. 470 Ga. This means that natural variations in 186 Os abundance are extremely small and hard to measure. However, in combination with the Re–Os couple the Pt–Os system provides unique information that justifies the effort of its analysis. Technically, 186 Os is itself radioactive, but the half-life is so long that it can be considered to be stable for geological purposes. Osmium Analysis In spite of its great potential as a geochemical tool, analytical difficulties have hindered the development of the osmium isotope method. The chief of these difficulties is the high ionization potential of Os (ca. 9 eV) which prevents the formation of positive osmium ions at temperatures attainable in conventional thermal ionization mass spectrometry (TIMS). Alternative methods of excitation therefore had to be sought. Hirt et al . (1963) analysed osmium isotopes as the gaseous species OsO 4 , but precision was low (±10% on a 200 ng sample of pure radiogenic osmium). This was probably due to dissociation of OsO 4 during thermal ionization of the molecule. Consequently, this method was not pursued for over 25 years. Instead, subsequent work focussed on the enhanced production of atomic osmium ions using more energetic ion sources.
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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 | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.002 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.061 | 0.032 |
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".