I have always had a hard time grasping this. Radioactivity has many units of measure: Grays, Rads, Rems, Curies, Roentgen, Sieverts, Becquerels.
Why are there so many different unit types, and how do they inter-relate? I have a decent understanding of physics, but not in this specific area. To date I haven’t read or heard an explanation that gives an “ah-ha!” moment or makes me quite understand what all these measures actually mean.
Yes, I have seen the XKCD radioactivity chart.
In: Physics
Most of these aren’t units of radioactivity. Only Becquerels and Curies are. Radioactivity is a measure of how many atoms are undergoing radioactive decay each second.
Rads and Gray are units of dose, which is a measure of how much energy (per unit mass) is being absorbed from radiation. This is important, because it impacts how both materials and cells react to radiation.
Sieverts and REM are measures of biological impact from radiation. They tell us about how much cell damage and long term health impact is expected.
Roentgen is a really weird unit that measures how much ionization radiation causes in otherwise stable materials, and ionization leads to funky cell chemistry.
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