Six steps from swab to signed wipe-test result.

The six-step SOP

From background reading to signed result

1. 1

   Background reading

   Place the survey meter in a low-background area, press TIMED mode, set a 10-minute count. Record the background CPM.

   A wipe-test result is meaningful only against a fresh background. The 10-minute background sits well above the statistical-noise threshold.

2. 2

   Swab the surface

   Use a dry filter-paper disc to swab a defined area of the sealed-source storage surface (typically 100 cm²).

   Wear gloves. Apply moderate pressure. Cover the full sample area with overlapping strokes.

3. 3

   Count the wipe

   Place the wipe under the pancake window at a defined distance (typically 1 cm). Press TIMED, run a 1-hour count.

   Longer counts (4 h, 8 h, overnight) reduce statistical uncertainty for low-activity samples. The 40-hour maximum supports very low-activity work.

4. 4

   Net count

   Net CPM = (wipe CPM) − (background CPM). Convert to surface activity: A (Bq/cm²) = (net CPM × efficiency factor) / (60 × area swabbed).

   Efficiency factor is isotope-specific. For Cs-137 calibrated detectors reading other isotopes, use the manufacturer cross-isotope correction or calculate from the radiopharmacy spectrum.

5. 5

   Compare against threshold

   AERB threshold for removable activity on sealed sources is typically 0.4 Bq/cm² for low-toxicity isotopes; 4 × 10⁻⁴ Bq/cm² for alpha emitters.

   Threshold values are isotope-class-specific. Check the AERB facility licence for the specific source class.

6. 6

   Document and file

   Record the result in the wipe-test log: date, source ID, area swabbed, background CPM, wipe CPM, net activity, pass/fail.

   The wipe-test log is one of the AERB inspection-ready documents. A signed-and-dated log entry per source per audit cycle.

Source: ISO 7503 — Surface contamination measurement; AERB Atomic Energy (Radiation Protection) Rules 2004; AERB Safety Code for Nuclear Medicine Facility.

Source-audit cadence

When wipes happen, what triggers escalation

• Sealed sources on the AERB facility licence get wipe-tested on a cadence the licence specifies — typically annual for the routine programme.
• When a wipe fails (activity above threshold), the source is quarantined immediately. The quarantine is documented; the source is not returned to service until cleaned and re-wiped.
• A repeat-failure on the same source is an AERB-notifiable event. The radiation-safety officer files the incident report with AERB regional office.
• Source-storage cabinets get wipe-tested even when the sources inside are not opened — surface contamination tracks back from operator handling errors during inspection, not from the source itself.
• Decommissioning wipe-test (before source return through the Source Return Service) confirms the source is wiped-clean before the transport chain accepts it.