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.