Safety · Radiation protection and dose2 min read5-question check
Personnel Dosimetry
Wear your dosimeter at the collar, outside the apron, in fluoro. A declared pregnant worker adds a second one at the waist, under it.
The devices
A personnel dosimeter records the occupational dose you receive over a wear period, usually one month or one quarter. The OSL dosimeter is the most common. Its aluminum oxide strip is read by laser light, it measures doses as low as 0.01 mSv, and it can be reread. A TLD uses lithium fluoride crystals that give off light when heated. It is often used in ring badges, and heating erases the reading. Film badges are older, fog with heat and humidity, and miss doses below about 0.1 mSv. A direct ion storage (DIS) dosimeter holds a tiny ion chamber that can be read on demand. A pocket ionization chamber gives an immediate reading for short, high-exposure tasks.
Where to wear it
Wear the primary dosimeter on the front of the body at collar level, outside the lead apron, during fluoroscopy and mobile work. The collar is closest to the unshielded thyroid and eyes, so the reading estimates their dose. Without an apron, wear it on the front between the chest and waist. A declared pregnant worker gets a second dosimeter worn at waist level under the apron to estimate fetal dose. Ring badges go on the hand nearest the beam, label facing the source.
Reading the report
Reports list deep dose at 1 cm, eye dose at 0.3 cm, and shallow or skin dose at 0.007 cm. An M means the dose was below the minimum detectable level. Worked example: an annual deep dose of 0.8 mSv is 1.6 percent of the 50 mSv limit. Many facilities also set ALARA investigation levels well below the limits. A common scheme puts Level I at 10 percent of the limit, about 1.25 mSv per quarter whole body, and Level II at 30 percent, about 3.75 mSv per quarter. Crossing Level I prompts a review by the radiation safety officer. Crossing Level II prompts a formal investigation.
On the job
A dosimeter measures dose. It does not protect you. Never wear it during your own medical exam, never share it, and leave it at work. Report a lost or damaged badge right away.
Clinical Example
A radiographer's quarterly report shows 2 mSv deep dose, far above her usual readings. The radiation safety officer finds she hung her apron, badge attached, inside the fluoro suite between cases. The reading is corrected, and she is reminded to store her badge away from the room.
Common Mistakes
- Wearing the collar badge under the apron during fluoroscopy, which hides the thyroid and eye dose.
- Wearing the fetal badge outside the apron instead of under it.
- Thinking a TLD can be reread like an OSL.
- Reading M as maximum instead of minimal.
Why It Matters
The registry tests badge placement, device features and how to read a report. These are quick points if you know the collar and waist rules.
Key Relationships
- Fluoroscopy → collar badge outside the apron
- Declared pregnancy → second badge at waist under the apron
- OSL → laser read, rereadable, most sensitive
- Investigation level crossed → radiation safety officer review