Standard unit of ionizing radiation dose is Sievert. I can get a rough idea of how dangerous absorbing various amounts is from https://xkcd.com/radiation/ and other sources. There are many other measurements related to radiation (https://www.nrc.gov/about-nrc/radiation/health-effects/measuring-radiation.html). I understand that these units measure different things and are not comparable. I would like to get a feeling for their order of magnitude, if possible.

For example, I am looking for something like (I apologize in advance for stupidity of what I am about to write, it is supposed to only illustrate the kind of answer I am looking for): 1 becquerel during 1 minute carries X to Y joules (depending on the type of decay), and when absorbed by an organ weighing 1 kilogram produces a dose of Z sieverts.

Is this at all reasonable?

  • $\begingroup$ Measures of radiation are the most confusing mess of units and meanings one will encounter. Partly this is because of the many different answers one is looking for... $\endgroup$ – Jon Custer Jun 10 at 20:38
  • $\begingroup$ Care to explain the downvotes? $\endgroup$ – Max M Jun 26 at 8:37

Given the amount of energy carried in your radiation source, if you can work out how much of that energy is deposited within the organ/tissue of interest, that will give you an absorbed dose (energy deposited per unit mass). If your units are joules and kilograms, the absorbed dose will be in units of gray (Gy). 1 Gy is a lot of dose and unless it's for radiation therapy, it would be a bad thing to receive.

To go from absorbed dose to effective dose (Sievert), you need to work out the absorbed doses from your radiation source to a specific list of organs/tissues in the body (you can see the list at https://en.wikipedia.org/wiki/Effective_dose_(radiation)). Depending on the irradiation geometry or source distribution within the body for internal radiation, some organs may receive a lot, some may get nothing at all.

Then you take the organ doses and multiply by a radiation weighting factor to take into account the type of radiation. The radiation weighting factor ranges from 1 for photons, electrons, and muons, and goes up to 20 for alpha particles and heavier particulate radiation. This gives you a quantity known as equivalent dose.

Take the equivalent doses you have, and multiply them by a tissue weighting factor that takes into account the varying sensitivities each tissue has (the tissue weighting factors are listed in the Wikipedia article...ICRP 103 values are most commonly used these days). If an organ/tissue is only partially irradiated, that can be accounted for if you know the fraction of tissue being exposed.

Take all that, add it up and you get the effective dose in Sieverts.


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