How does radiation poisoning kill you, and why does it sometimes take weeks?
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Other explanations in this thread are really great. To add to this, it often isn’t the radiation itself that does the job. You are about 2/3 water, so it is overwhelmingly likely that what a gamma ray will hit (external radiation is almost always gammas, because betas and alphas have very poor skin penetration) is the electron clouds of water molecules, knocking those loose. Those accelerated electrons in turn cascade into other electrons, etc, and for every primary gamma interaction, you can have 10,000+ secondary events, creating all sorts of short-lived, very nasty particles called free radicals and superoxides, like H2O+, H202, OH-, etc. Those nasty critters tear and shred all the complex molecules they encounter, like proteins, which can immediately kill the cell, and DNA, which can kill the cell via self-regulation failure, or by failure to divide. (Source: nuclear medicine specialist)
Radiation releases energy that damages the “code” inside of your cells (DNA). Those cells fail to reproduce – or reproduce incorrectly – and with nothing to replace your old cells as they die, your body literally falls apart, like an old wood board rotting because it’s no longer part of a living tree that can grow new wood cells.
This is why radiation poisoning is a particularly gruesome way to die.
Radiation damages your cells’ ability to replicate. As cells die, the aren’t replaced.
Imagine it’s the opposite of Wolverine’s healing ability. You’ve lost the ability to heal anything, including replacing dead cells.
Imagine your cells are like a windshield and the radiation is like rocks on the highway.
Some rocks are fine not big enough to do damage, like X rays or just basic background radiation.
Higher levels of radiation is like faster bigger rocks they cause actual damage, some people get chips but sometimes it shatters and the body can’t fix it like you can’t fix a shattered windshield.
If it takes weeks it’s like a crack that you watch grow and grow until it’s too much for the weight and crumbles to dust.
Radiation causes damage to your DNA. Your cells can survive for some time with damaged DNA but they can’t properly replicate. So as old cells die there are no new cells to replace them. This results in dysfunction/death of all of the fastest replicating cells (e.g. skin, intestinal, bone marrow, etc). The bone marrow is probably the most important as it produces your immune cells as well as your blood cells and platelets. So you simultaneously have no immune system, severe anemia and problems with clotting.
Nuclear Engineering Professor here, I have a [YouTube video on this very topic!](https://youtu.be/Pd7j5pEqcAU)
Radiation damages your cells on a molecular level. If it damages enough of your body you will die. Your body will try and survive for as long as possible. Sometimes the damage is just enough and it takes a few weeks before your body has exhausted all its options and you die. Sometimes it’s much shorter
All right all of you…
What’s a Roentgen, is 3.6 really not great not terrible, and how fast would fifteen thousand kill you?
Your body rebuilds itself over time, some systems in hours, others days and some months or years.
Radiation messes with the code that is responsible for newer cells to meet the same or similar function and health as the ones they’re replacing, after a while the copy of a copy of a copy gets so much worse and your body or part of it can’t maintain itself.
In a way it’s essentially aggressively and painfully doing in a short time frame what old age does to us all.
That’s why you should always wear sunscreen and or be under shade and stay hydrated when the UV rate is higher, regardless if it’s sunny or not, so you decrease your chances of having skin cancer.
DNA is the instructions on how our body makes things. This includes regrowing/replacing/repairing damage to parts. Radiation poisoning messes up these instructions.
As a result, someone affected might not immediately show symptoms like you might expect in a horror movie. That’s because the body hasn’t had to regrow/replace/repair those cells yet. When the time comes inevitably to replace those cells, those instructions now damaged, are still being followed, if they aren’t destroyed completely.
So, this is why you can seemingly survive the initial dose, only to die in agony weeks later. There was a Japanese man who took a massive dose of radiation, but because of this process taking some time to be noticeable, some thought he was recovering. Sometime after the first week it all went down hill.
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