On the Applicability of <sup>48</sup>V in Positron Annihilation Lifetime Spectroscopy
Bibliographic record
Abstract
The applicability of the 48V isotope as a source of positrons for positron annihilation lifetime spectroscopy (PALS) measurements is discussed. It has been demonstrated that using such a positron source, the classical PALS setup with two detectors does not accurately determine the positron annihilation parameters of the samples being studied. This issue arises when one of the two nuclear gamma rays (of energies of 983 and 1312 keV) that are emitted almost simultaneously with the creation of a positron triggers a start signal, while the other nuclear gamma triggers a stop signal instead of the 511-keV annihilation quanta. These events manifest as prompt coincidences in the start-stop histogram, rendering the analysis of PALS spectra unreliable. To address this problem, a modification to the classical PALS spectrometer was proposed and tested. This modification involved incorporating a logic branch that significantly reduced the undesired prompt coincidences between the 983- and 1312-keV gamma rays. By conducting measurements on a series of samples utilizing 2- and 25-$\mu $m-thick Ti foils enriched with 48V, it was demonstrated that the altered setup reliably extracts accurate information on the positron annihilation states within the samples being examined.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| 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) | 0.001 | 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".