Physicist's Notes · Personal Dosimeter
Two instruments doingtwo different jobs.
A common procurement question: "do we need the EPD if every worker already wears a TLD / OSL badge?" The answer is yes — the two instruments do different jobs. The badge is the legal cumulative-dose record; the EPD is the real-time behavioural feedback. This post unpacks the comparison and walks the AERB-compliant combined dose dossier.
Passive badge vs active EPD
Six dimensions, six different answers
| Dimension | Passive badge (TLD / OSL) | Active EPD | Verdict |
|---|---|---|---|
| Read-out latency | Monthly (after lab read-out) | Real-time on the device LCD | EPD wins for behavioural feedback |
| Legal-record status | AERB-recognised cumulative record | Supplementary record; not the legal cumulative document | Badge is the legal record |
| Energy range covered | Broad — calibrated for the radiopharmacy isotope mix | Specified energy window; check manufacturer spec | Badge is broader; EPD is more specific |
| Dose-rate alarm | None — passive integrator only | Configurable cumulative-dose AND instantaneous-dose-rate alarms | EPD only |
| Operating cost | Per-badge subscription + lab read-out fee | One-off purchase + battery + annual calibration | Different cost models |
| Workplace fit | Clipped to lab coat; forgotten between months | Active reminder mid-shift; vibration alarm for patient-care environments | Both wear in the same place |
Source: ICRP Publication 75; IAEA Safety Reports Series 16; AERB Atomic Energy (Radiation Protection) Rules 2004.
Threshold setting
Cumulative-dose + dose-rate alarms — indicative values
- Cumulative-dose warning at 1 mSv per quarter (5 % of the 20 mSv/year limit) — early flag for a worker accumulating dose faster than expected.
- Cumulative-dose action at 5 mSv per quarter (25 % of the annual limit) — triggers a workload review by the radiation-safety officer.
- Dose-rate warning at 100 µSv/h — typical hot-lab dispensing-area background is below this; an alert points at an unshielded vial or a hot spot.
- Dose-rate action at 1,000 µSv/h — operator should step back, add shielding or request help. Typical only during high-activity dispensing or theranostic patient bedside care.
- Site-specific calibration: indicative thresholds above; final values from the radiation-safety officer in consultation with the AERB facility licence.
AERB inspection dossier
Six items the combined EPD + badge record produces
- EPD shift log: per-worker daily / weekly dose-rate trace, downloaded via IR or USB to the radiation-safety officer's PC
- EPD calibration certificate: annual NIST-traceable calibration record
- EPD threshold-configuration log: documented alarm settings per worker class (RSO, radiopharmacist, ward nurse, trainee)
- Passive badge monthly record: per-worker cumulative dose from the dosimetry lab
- Cross-reconciliation log: badge cumulative dose vs EPD-derived cumulative dose, monthly check
- Annual dose-record summary per worker: combined badge + EPD-derived figures, signed off by the RSO
Source: AERB Atomic Energy (Radiation Protection) Rules 2004; AERB Safety Code for Nuclear Medicine Facility — occupational-dose section.