Development of a negative helium ion source with non-metallic charge exchange
Bibliographic record
Abstract
Abstract Negative helium ion (He − ) beams are required for tandem accelerators used at research centers and implanter facilities. The common production method of such beams involves charge exchange between a positive helium ion (He + ) source or beam, with a low pressure alkali metal vapour. However, the efficiency of this reaction is poor (only a small percentage) and the alkali metal vapour increases the potential flammability of the interior surfaces of the reaction chamber, as well as contributing to unwanted electrostatic discharge and target contamination downstream. In this paper we describe initial results from experiments using a focused He + ion microscope (HIM) to measure charge uptake efficiencies after transmission through carbon membranes. The He + beam (15 keV to 30 keV, 50 fA to 10 pA) collides with a non-metallic foil, and transmitted particles (He + , He 0 , and He − ) are separated electrostatically into discrete beam spots and detected using a radiation camera (AdvaCam MiniPIX). A He − percentage uptake of 0.05 was observed using a 20 nm exfoliated graphite membrane consistent with previous reports. Future work will investigate the efficiency of charge exchange through other suitable membrane materials.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| 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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".