How do we measure radiation? Like the unit of measurement, what’s considered normal and what’s considered high.

Question

How do we measure radiation? Like the unit of measurement, what’s considered normal and what’s considered high.

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Answer 1

Measuring radiation via physical device is accomplished through a Geiger counter or Dosimeter.

The measurements for radiation exposure are the Gray (Gy) and the Sievert (Sv). Gray is a measure of the actual dose of radiation, and Sievert is a measure of equivalent dose. The difference is that Gray is what you actually received, Sievert is what that’s equivalent to. For example, 1 Gy of Gamma radiation is 1 Sv, whereas 1 Gy of Alpha radiation is 20 Sv (because Alpha radiation is considerably more dangerous than Gamma.)

We’ll utilize Sieverts for this explanation, since that’s the unit utilized in exposure thresholds and the one most people are likely to be familiar with.

Sievert calculation is complex, but suffice to say it’s used to represent the random array of health effects that occur as a result of ionizing radiation exposure. Ionizing radiation is the bad stuff (it knocks electrons out of atoms/molecules.) Exposure limits are scaled – you may receive more or less exposure depending on what you’re doing and where you work, and the legal limits depend on your field and activity. In general, the US limits public exposure to 1 mSv. For reference, airport X-Rays are limited to 250 nSv (nanoSieverts) a set of dental X-Rays is about 5-10 μSv (microSieverts), whereas a full body CT is 10-30 mSv (milliSieverts.)

In general, radiation is everywhere all the time, so exposure is pretty regular and normal. The higher up you go in altitude, the more exposure you receive. Flight attendants receive about 1.5-1.7 mSv annually for instance. Astronauts have a career max exposure limit of 1 Sv, with the average 6 month stint on the ISS netting an exposure of 80 mSv.

4-5 Sv is the LD50/30 for humans, when received over a short period. This means that if you’re exposed fairly suddenly to 4-5 Sv of radiation you have a 50% chance of dying in 30 days. In general, between 50-150 nSv is normal. As you can see, time frame of exposure matters too. Albert Stevens, for example, *involuntarily* received 64 Sv over a period of 21 years at an average of 3 Sv per year as part of a research effort during the Manhattan Project. So, while he received an *extraordinarily* high exposure, he survived because the rate of exposure was slow and sorta-low.