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


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

In: 25

Ionizing radiation (at least for us humans) is measured in *Sievert*, most commonly in *mSv* (MiliSivert). from there it is further differentiated with the time frame you are exposed to radiation (Immediately, per hour, per year, lifetime etc). Science differentiates between different types / sources of radiation, from normal natural background radiation to external radiation

The base assumption for many countries, depending on international regulations, is *1 mSv per year*from external sources as maximum. Natural Background radiation can be higher and comes from exposure to cosmic radiation and basically simply existing. At this level it is a normal part of human life and usually humans stay far below any dangerous levels.

From there it can go in any direction. For example Astronauts on the ISS can get up to 80 mSv for a long stay, with 1000 mSv (or simply 1 Sv) being the lifetime limit. Firefighters in Germany can be exposed to 100 mSv in a single year, to 250mSv for a single incident and only if it is for saving lives, with 400 mSv being the absolute max for their professional life (they would usually be removed from the Hazard Unit after such a dosis). Countries may regulate that a single nuclear power plant may only add 0.3 mSv per year to the radiation exposure of their employees.

Everything over 1000 mSv / 1 Sv should be firmly in the *Nope!* category.


We typically measure radiation in units of Rads or Sieverts, which indicate the amount of air kerma from the source. We use the units roentgens and gray to describe how much of the radiation is absorbed by the body or tissue.

In order to detect that radiation we use probes and various instruments. For example, an ion chamber measures how much the radiation ionizes the gas in the chamber. We also have gas filled gieger muller detectors like the pancake or hot dog probe. There’s also scintillating detectors which use a crystal to transmit ionizing events to a photomultiplier tube which is then converted to counts per second and/or milirem/hr.

The above is strictly specific to ionizing radiation. The term radiation covers all energy in the electromagnetic spectrum so I assumed you meant ionizing and not “how do we detect radio waves “…

Normal radiation varies depending on your geological location. Places with higher levels of naturally occurring radioactive elements will have higher levels. Where I am located the background radiation levels are about 10-20 microRem/hr. This is very low. Higher levels typically are considered to be 2 mR/hr and above. Very high radiation levels are considered to be 100mR/hr and above. Dose rates of 300-500 Rem/h are considered to be dangerous to your health. Does that answer your question?

In addition to the Sievert that is used for human radiation absorption, there are a few other similar units.

The Becquerel is the unit of radioactive emission, how much radiation is being thrown from the radioactive material.

The Grey is the unit of radiation absorbed per kilogram of material, this kilogram is not necessarily a human, but is general.

As others have said, the Sievert is then used to show the biological effects from a radiation source.

We have these different measurements because not all radiation is the same, and sometimes we need the information external to radiation effects on humans.

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.