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Exam category: Safety → Radiation Protection
Why it matters: Two things get tested here relentlessly: the actual dose limit numbers (memorization, but precise), and which dosimeter technology does what.
Occupational dosimeters measure how much radiation a worker actually received, and NCRP recommendations set the ceiling on how much they're allowed to receive in the first place. Know both cold — the numbers and the device types are both fair game as direct-recall questions.
| Population | Effective dose limit | Notes |
|---|---|---|
| Occupational | 50 mSv/yr | Cumulative lifetime limit: 10 mSv × age in years |
| Occupational — lens of eye | 150 mSv/yr | Equivalent dose, specific organ |
| Occupational — thyroid, skin, hands, feet | 500 mSv/yr | Equivalent dose, specific organs |
| Public — frequent/continuous exposure | 1 mSv/yr | Ongoing/repeated exposure scenario |
| Public — infrequent exposure | 5 mSv/yr | Occasional/one-off exposure scenario (500 mrem) |
| Education & training (students) | 1 mSv/yr | Same as public's frequent-exposure tier |
| Embryo/fetus (declared pregnancy) | 5 mSv total | 0.5 mSv/month once pregnancy is declared |
| Negligible individual dose | 0.01 mSv/yr | Below this, protective action generally isn't warranted |
Memory cue — anchor on 50, then multiply: occupational whole-body is 50, the lens of the eye is 3× that (150), and everything-else-organs is 10× the whole-body limit (500). Fix 50 first and the other two hang off it.
Four devices are worn on the body to record the dose a worker actually received:
| Monitor | How it works | Key point |
|---|---|---|
| Film badge | Film between metal filters darkens with exposure | Oldest and cheapest; the filters estimate energy/type, but it's degraded by heat and humidity and is largely obsolete now |
| TLD (thermoluminescent) | Lithium fluoride (LiF) crystal, heated to release stored energy as light | More sensitive and accurate than film (~50 µGy); unaffected by heat/humidity; worn up to 1 year |
| OSL (optically stimulated luminescence) | Aluminum oxide (Al₂O₃), laser-stimulated to release light | Most sensitive (~10 µGy) and re-readable — today's standard occupational monitor |
| Pocket dosimeter (self-reading ionization chamber) | An ionization chamber you read immediately on the spot | The one personnel monitor with an instant reading — no lab processing, unlike film/TLD/OSL |
Where to wear it: at collar/waist level normally; if the technologist participates in fluoroscopy, the monitor goes on the collar, above the protective apron — since that's the part of the body not shielded by the apron.
These aren't worn — they measure the radiation environment or equipment output:
Memory cue — worn vs. waved: a personnel monitor (film badge / TLD / OSL / pocket) is worn to record your dose; a survey instrument is waved around the room to measure the radiation there — the wide-range ion chamber for levels and output, the ultra-sensitive GM counter for contamination.
Wearing the badge is half the topic; the exam also tests what happens to the numbers it generates.
Who gets monitored at all. You have to be monitored once there is any real chance of picking up over a tenth of any of the dose limits in section 1. In practice most imaging staff are monitored, and most of them come in well under that — typical occupational exposure runs at less than 10% of the limit.
What the report has to contain. State and federal regulation requires the results be recorded precisely and kept available for review. Monitoring periods may be annual, quarterly, monthly or weekly. Each report shows current exposure and cumulative annual exposure, and any extremity or fetal monitor is reported separately from the whole-body monitor rather than folded into it.
Lifetime exposure must be recorded — and it follows the person, not the building. When you change employers, your total exposure history transfers to the new employer's records. You should be given a report of your exposure history at that facility automatically when you leave; if you aren't, ask for it.
The control monitor is the one students miss. A control monitor travels and is stored with the batch but is never worn, so what it records is the background exposure picked up during transport, handling and storage. After processing, its reading is subtracted from every individual monitor — which is what makes each person's report represent their occupational exposure alone rather than background plus work.
That is also why a control monitor must never be stored in or next to a radiation area. Store it somewhere exposed and you subtract that spurious dose from everyone, quietly under-reporting the whole department. Return all monitors to the supplier together and on time so they're processed as a batch, and any monitor that is lost or accidentally exposed has to be evaluated and a true exposure estimated rather than simply written off.
Memory cue — the control monitor is the zero you subtract. It is never worn. It rides along to measure background, and its reading is subtracted from everyone else's. Store it near radiation and you have corrupted every report in the batch.
Students often only learn one of the two public-exposure tiers and treat it as the whole answer. Both are real, current NCRP figures — which one a question wants depends on whether it describes continuous/repeated public exposure (1 mSv) or an occasional/one-off exposure scenario (5 mSv).
Source: Bushong, Radiologic Science for Technologists, 12th ed., Ch. 40 (occupational limits; personnel monitors — film badge/TLD/OSL/pocket dosimeter, where to wear; and section 4's records material from that chapter's occupational radiation monitoring report discussion — the trigger that puts a worker on monitoring at a tenth of a limit, the requirement that results be recorded precisely and maintained for review with annual/quarterly/monthly/weekly periods acceptable, current and cumulative annual exposure on the form with extremity and fetal monitors identified separately, the requirement that lifetime occupational exposure be recorded and that exposure history transfer to a new employer, the control monitor's role in measuring background during transport/handling/storage and being subtracted from each individual monitor, the instruction never to store it in or adjacent to a radiation area, the batch return of monitors, the evaluation of lost or inadvertently exposed monitors, and the observation that occupational exposure is usually under 10% of the recommended limit) and Ch. 36 (survey instruments — ionization chamber/"cutie pie", Geiger-Müller counter), verified against the source text. Both public-exposure tiers come from Bontrager, Textbook of Radiographic Positioning and Related Anatomy, 10th ed., Ch. 1, which states them directly: 1 mSv (100 mrem) for frequent exposure and 5 mSv (500 mrem) for infrequent exposure. Bushong's NCRP summary lists only the frequent tier, which is why the 5 mSv figure is cited to Bontrager here rather than to Bushong.
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