system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the difference between sievert, roentgen, and gray? Why is radiation measured with different units? What other units are used to measure radiation?
gpt
These aren't direct measures of radiation, but measures of impacts of radiation. The roentgen is a measure of how much gamma and xray radiation ionises air, but isn't a measure of anything else. Gray is a measure of how much energy is absorbed by a thing, and is useful in measuring doses of radiation (different things absorb radiation in different amounts, so will receive different doses of radiation even when the amount of radiation you fire at the thing is the same for each). Sievert is a measure of the health effects of radiation, ie, how much damage this much radiation does to people. They're different units because they measure different things.