Activity cross‐calibration of unsealed radionuclides utilizing a portable ion chamber
Bibliographic record
Abstract
Purpose: To present and evaluate an ion chamber‐based method for the cross‐calibration between sites of activity measurements of unsealed radionuclides. Notably, the method allows direct comparison of short lived (i.e., clinically used) radioisotopes and the cross‐calibration of radionuclide activity meters (also known as “dose calibrators”). Methods: A portable ion chamber has been designed which is easily shipped between sites, e.g., between a standards laboratory and a nuclear medicine department. The cylindrical chamber accommodates a syringe filled with unsealed radionuclide. Low background and staff shielding are achieved by designing the ion chamber small enough to fit into the well of a dose calibrator. The chamber's sensitivity for the clinically important unsealed radioisotopes 99m Tc, 131 I, and 18 F was measured and compared to Monte Carlo calculations. The influence of syringe fill volume, positioning, and construction (wall diameter, length) was also investigated using Monte Carlo simulations. The chamber's linearity was measured over 5.5 orders of magnitude and its constancy tested over a period of >14.5 months. An overall uncertainty budget is presented. Results: Measured chamber sensitivity was 12.1 pA/100 MBq, 12.5 pA/100 MBq and 29.4 pA/100 MBq for 131 I, 99m Tc, and 18 F, respectively. The uncertainty budget for the ion chamber alone yields an overall uncertainty of less than 1%, with the greatest contribution arising from constancy and linearity (0.5% each). Strategies to further reduce uncertainties are discussed. Conclusions: The investigation presented in this paper confirms the feasibility of the concept introduced here. To optimize its practical implementation, the concept would benefit from computerization for the purpose of data acquisition, evaluation, processing, and storage of measured values.
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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 | 0.006 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.003 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".