Bibliographic record
Abstract
The cosmogenic isotope 36Cl (half-life of 3.01 x 105 years) has been applied to problems in hydrogeology and surface exposure dating for a number of years. However its measurement in natural samples is complicated by its low abundance with respect to the stable isotopes of chlorine (36Cl/Cl = 10-10 to 10-16), and the presence of the isobar 36S (0.02% of S). Conventional Accelerator Mass Spectrometry (AMS) techniques for measuring 36Cl require tandem accelerators of 5 MV or larger. Only these machines can accelerate the 36Sn+ ions to high enough energies for them to be separated in gas-filled magnets, or in dE/dx analysis in the final detector. The present work investigates the possibility of 36Cl analysis on smaller, more economical machines. It is demonstrated that 36Ar3+ and 36S3+ ions, generated from argon and SF6 gas within the 2 MV tandem accelerator at the University of Toronto, will not preclude 36Cl measurements. A gas ion source was developed in which Cl- ions are created when a negative ion beam transfers its charge to the gas ICl, and the Cl- ions are then extracted. The efficiency of Cl- generation was about 20% for a Cu- beam. Because of the instability of sulphur iodide (S2I2) at room temperature, and the resonant charge transfer reaction to ICl, this gas source should discriminate against 36S. It was also shown that in the collision of S - and Cl- ions with NO2 gas at about one milliTorr pressure, the S- was attenuated by about two orders of magnitude relative to the Cl-. Finally, the 25 MV Holifield accelerator at Oak Ridge, Tennessee was used to measure 36Cl with the completely stripped 36Cl 17+ ion. Because the completely stripped sulphur species has a charge of 16+, it was possible to separate this isobar from 36Cl in a magnet. These measurements detected 36Cl in seawater for the first time, and showed, unexpectedly, that the 36Cl/Cl ratio varies in the world ocean.
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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 | 0.004 | 0.004 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
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".