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How Bad is How Much of What, and When?

Time to get quantitative. What kinds of radiation are there, how do we measure how much we get, and what effects can we expect from different exposures to different parts of our bodies over different times?

There are lots of kinds of radiation, from the EM spectrum we have already discussed to neutrons, alpha ($\alpha$) particles, beta ($\beta$) ``rays'' (high-energy electrons) and $\gamma$-rays - all constant companions in our environment due to natural or man-made radioisotopes - to the utterly harmless neutrinos coming from our Sun, to beams of high-energy protons, electrons, positrons, pions, muons etc., produced by accelerators like TRIUMF, to catastrophically destructive cosmic rays from which we are shielded by our atmosphere (except when we fly across country in an airliner) and so on ad infinitum. Everyone is constantly exposed to most of these types of radiation, accumulating an annual dose varying from a few hundred mR to several R. What are these units ``R'' and how can we gauge what they mean in practical terms? Time to get more technical.