Knowledge Hub · TFIA-2 Air Sampler
A continuous stack monitor watches the release point in real time. A high-volume grab sampler captures a removable filter + cartridge sample that goes to laboratory gamma counting. The two answer different questions and ANSI N13.1 / N42.18 expects both on the same release point. This page unpacks why — and how the dual-cartridge cross-check turns a manufacturer-stated collection efficiency into a per-run measurement.
Why this matters
Inline monitor vs grab sample
The continuous stack monitor (a GD-53-based NaI(Tl) instrument inside or beside the duct) gives a live activity-concentration readout — fast, always-on, alarm-capable. A high-volume grab sampler gives an assay-quality integrated sample on a removable filter + cartridge that goes to laboratory gamma counting. The two answer different questions. The inline monitor catches transients in seconds; the grab sample quantifies time-integrated release with reference-grade counting. ANSI N13.1 and ANSI N42.18 both expect the two to coexist on the same release point.
Based on: ANSI N13.1 — Sampling Releases of Airborne Radioactive Substances; ANSI N42.18 — On-Site Effluent Monitoring Instrumentation.
Read source ↗Paper vs charcoal
Radioactive aerosols — particles carrying activity — collect on a paper filter. Radioiodines (I-131, I-125) are volatile and pass straight through paper; they adsorb onto activated charcoal. A TFIA configuration puts a paper-filter stage first (captures particulates without loading the charcoal) and a charcoal stage second (captures radioiodine). One sampler pass, one operator action, two contaminant classes captured separately and assayed separately. Putting the paper filter first matters: charcoal loaded with particulates loses adsorption capacity and skews the iodine-collection efficiency.
Based on: ISO 2889 — General principles for sampling airborne radioactive materials; IAEA Safety Reports 38 on radioiodine air-sampling.
Read source ↗Dual-cartridge cross-check
A single charcoal cartridge ships with a manufacturer-stated > 99 % radioiodine capture efficiency. The number is true on a fresh, well-installed cartridge with the expected flow rate. It is not necessarily true on a cartridge that has aged in storage, been over-flowed past its design, or developed a channelling defect. Two cartridges in series turn the claim into a measurement: front-cartridge activity ÷ (front + back) gives the per-run efficiency. If the back cartridge reads above the LOD, the front cartridge is breaking through and the sample is invalid. The cross-check happens on every run, not on the calibration certificate alone.
Based on: ANSI N42.18 — On-Site Effluent Monitoring Instrumentation; IAEA TECDOC on airborne radioiodine measurement.
Read source ↗I-131 therapy room air
I-131 therapy patients exhale and excrete volatile I-131 species into the room air for days after dose administration. A GM probe gives a dose-rate reading but does not quantify airborne activity concentration. The TFIA-2 collects a time-integrated charcoal-cartridge sample that goes to gamma counting; the result is activity concentration (Bq/m³) integrated over the sample run. AERB-aligned I-131 therapy programmes use the integrated number to validate room ventilation rates and to set the cleanup wait-time before the next patient.
Based on: IAEA Safety Reports 38 — Applying Radiation Safety Standards in Nuclear Medicine; AERB Safety Code for Nuclear Medicine Facility.
Read source ↗Cyclotron stack annual report
AERB cyclotron-facility licensing requires an annual environmental report — release totals per radionuclide, per release point, per quarter, against the licensed limit. The inline stack monitor produces the time series; the periodic TFIA-2 grab sample produces the assay-quality reference points the time series is calibrated against. The annual report includes both: the inline monitor curve as the year-long record, and the grab-sample assay results as the verification anchor. Drift in the inline monitor against grab-sample assay points triggers recalibration.
Based on: AERB Safety Code for Medical Cyclotron Facility; AERB environmental-monitoring reporting framework.
Read source ↗Assay chain compatibility
A high-volume air sample is only useful if the downstream assay can read it. TFIA-2 paper filters drop into standard gamma-counter sample positions and into HPGe-detector sample carriers. Charcoal cartridges sit in standard counter geometries — well counter, NaI(Tl) bench-top, HPGe high-resolution chassis. No bespoke handling, no media transfer, no contamination-risk repackaging. The sample goes from the sampler straight to the counter; the activity figure goes from the counter straight to the release record.
Based on: IAEA TECDOC on environmental radioactivity measurement; manufacturer counter-geometry compatibility specifications.
Read source ↗ANSI / ISO / IAEA documents that anchor the high-volume air-sampling workflow.
US national standard for stack effluent sampling — defines grab-sample and continuous-monitor expectations and the role of paper-filter + charcoal-cartridge configurations.
International standard defining stack and duct air-sampling design including isokinetic sampling and collection-efficiency cross-check.
US national standard for on-site effluent monitoring instrumentation; frames the role of high-volume grab samplers alongside continuous monitors.
IAEA framework for nuclear-medicine radiation protection including airborne radioiodine monitoring expectations.
Where next