Physicist's Notes · Stack Monitor
Six metrics out of one continuous trace —the annual licence-renewal dossier.
AERB facility licence renewal at a cyclotron / PET facility centres on six release metrics derived from the continuous stack-monitor trace. This post lists the metrics, walks the in-duct vs adjacent-duct installation decision, and frames when to upgrade from the baseline variant to the spectroscopic variant.
Annual dossier metrics
Six numbers AERB inspection reads
| Metric | Source | What it reads |
|---|---|---|
| Total annual release (TBq or GBq) | Integrate the stack-monitor trace over the licence year, isotope-by-isotope | Quantitative — against authorised limit on the AERB facility licence |
| Peak release rate (MBq/h or kBq/s) | Maximum value across the licence year from the stack-monitor trace | Quantitative — flags spike events or unusual production runs |
| Isotope breakdown | Spectroscopic MCA peak analysis; or operator-assigned per run if baseline variant | F-18 / Ga-68 / C-11 / O-15 / N-13 breakdown |
| Production-run correlation | Release trace overlaid against cyclotron run log | Pattern match → expected; mismatch → anomaly investigation |
| Threshold-exceedance events | Alarm log streamed to RMS server | Count, duration, root-cause notes per event |
| Compared against authorised limit | Annual release vs the AERB-licensed authorised release figure | Percentage utilisation; trend across multiple licence years |
Source: AERB Safety Code for Medical Cyclotron Facilities; AERB Atomic Energy (Radiation Protection) Rules 2004.
Installation
In-duct vs adjacent-duct
- In-duct (preferred): detector inside the ventilation duct downstream of the cyclotron / hot-lab exhaust point. Maximum sensitivity; reads what actually leaves the building.
- Adjacent-duct (when in-duct impractical): detector beside the duct with a collimator to shape the field of view. Sensitivity lower than in-duct; needs commissioning measurement to characterise the geometric efficiency factor.
- Site-survey decision: in-duct mounting requires duct access at a stable cross-section, no flow disturbance from upstream bends or dampers, and serviceable cable routing. If any condition fails, fall back to adjacent-duct.
- Calibration: in-duct deployment uses a manufacturer-supplied geometric efficiency factor; adjacent-duct deployment usually needs site-commissioning measurement to derive the efficiency factor for the specific duct / collimator geometry.
Baseline vs spectroscopic
When to choose the spectroscopic variant
- Baseline variant (DIM-09 MCA, 1K channels with ROI analysis): sufficient when the facility produces one isotope or when run-by-run isotope assignment from the production log is reliable.
- Spectroscopic variant (DIM-15 MCA, 1K / 2K / 4K / 8K channels with peak analysis): identifies the isotope from the spectrum at the stack itself — no dependency on production-log correlation.
- When to choose the spectroscopic variant: multi-tracer cyclotron producing F-18 + Ga-68 + C-11 + O-15 in overlapping windows; theranostic-and-PET facility with mixed F-18 / Ga-68 / Lu-177 hot-lab streams; sites running investigator-initiated trials with unusual isotope production schedules.
- When the baseline variant is sufficient: dedicated F-18-only or F-18-dominant facility; sites with a robust production-log → release-trace correlation workflow; cost-sensitive deployments where the spectroscopic upgrade is not justified.