RFID-based TLD badge control for radiation safety teams

Personnel dosimetry programs at nuclear facilities, hospitals, research labs and industrial radiography sites depend on TLD badges being issued to the right person, returned to the right slot at the end of the shift, and accounted for at every step. In practice this is one of the most error-prone routines in a radiation-safety program: badges are returned to the wrong slot, returned late, or not returned at all — and the radiation protection officer often finds out days later, during the read-out cycle.

The conventional answer is a paper register, a clipboard, or at best a spreadsheet. None of these can prevent a wrong-slot return at the moment it happens, none can chase a non-returned badge on its own, and none can give the central server a live view of who currently holds which badge.

Elementz, through its Nucleolenz product line, was asked to automate this routine end-to-end — identify the badge, validate the slot, light the right indicator, record the event centrally, and chase non-returns by SMS, without depending on the operator for any of it.

At each slot, an RFID/NFC reader identifies the badge, a mechanical limit switch confirms physical placement, a slot-wise LED indicates the correct slot and a buzzer confirms the event — while the central server logs it. A wrong-slot return triggers an immediate LED blink and audio cue, so the mistake is corrected at the rack, not in a downstream reconciliation report.

The 3 × 3 matrix of nine 16-slot racks is driven from a single PoE backbone: each rack's ESP32 controller is powered and networked through one cable from a 16-port PoE switch — no mains wiring inside the rack. A Raspberry Pi 4 runs the MQTT broker and rack server, holding every badge-to-slot mapping, every placement and every alert centrally.

Alerts that survive an outage

Routine telemetry runs over Ethernet. Critical alerts — a badge not returned within its window — go out as SMS through a Cavli C16QS LTE Cat-1 bis modem, independent of the site network. The two paths back each other up: even with facility Ethernet down, the radiation protection officer still gets the message.

Server-managed, not rack-managed

The rack itself is stateless — it reads the tag, reports, and follows the server's instruction on which LED to light. Reassigning a badge, transferring a user or auditing a slot is a server-side operation, not a physical visit. The 144-slot installation behaves as one managed system, inspection-ready at any moment.