Physicist's Notes · Personal Dosimeter

Two instruments doing two 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.