Re: Career != Lifetime
Radiation doses are a lot more complicated than a single number. Not only are there the various different types of radiation (alpha/beta/gamma etc. and that's ignoring things like high energy neutrons), but where on the body you're irradiated makes a big difference to the outcome. Of course, timespan also plays a part; a single high dose in one day could be less than your monthly/annual limit, but will likely be medically worse for you than someone who gets a constant low dose which sums up to be higher per month.
Hence, dosage limits are an estimation of risk, based on an aggregate of all the different radiation studies that have been done. They're deliberately simplified to a single number to make the regulations feasible. The end result is that the medical issues of (for example) an aircrew who'd reached their monthly dose and a worker in a nuclear plant who'd received the exact 'same' dose would be quite different Because they'd both likely have received different types of radiation, in different ways, over different timespans.
tl/dr radiation dose numbers are approximate and can't necessarily be directly compared between different jobs/situations.
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