Technical Note: Sensitive volume effects on ion chamber responses in longitudinal magnetic fields
Bibliographic record
Abstract
PURPOSE: It has been shown that ion chamber dose response Monte Carlo simulations, in transverse magnetic fields, are susceptible to small changes in the scored sensitive volume. Changes in sensitive volumes have been investigated as a surrogate for modeling the true collection volume governed by the electric field. This work has not been fully extended to longitudinal fields. This study investigates the effect of the sensitive volume of ion chambers on magnetic field dose response within longitudinal magnetic fields. METHODS: The egs_chamber application within EGSnrc was used to model the Exradin A19, A28, and A1SL ion chambers within a uniform longitudinal magnetic field. The sensitive volume of the ion chambers was varied by removing portions of the air volume (from 0.2 to 3 mm) closest to the chamber stem from the dose scoring region; the dose to the scoring volume as a function of magnetic fields strength was normalized to 0 T in all cases. RESULTS: With the chamber long axis oriented parallel to the radiation and magnetic fields, for every magnetic field strength, all investigated chambers' dose response remained inside statistical variations for all investigated chamber sensitive volumes. When the chamber long axis is oriented perpendicular to the radiation and magnetic fields, the A28 and A1SL show negligible sensitive volume effects, while the A19 under responded by 0.5% for the largest removed volume of 3 mm. CONCLUSIONS: When the ion chambers' long axis is parallel to the radiation and magnetic fields, the magnetic field dose response is unaffected by small changes in sensitive volume. When oriented perpendicularly, only the A19 exhibits sensitive volume based magnetic field dose response changes, and only with ≥ 1 mm of assumed insensitive volume. We can therefore safely assume complete charge collection in Monte Carlo calculated correction factors involving similar chambers in similar conditions.
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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 | 0.003 | 0.010 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.005 | 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".