system
Given the following post, respond as if you're commenting on Reddit:
human
What's happening during the "walking ghost" phase of acute radiation poisoning?

I read that there's a latent period after acute radiation poisoning where there are no symptoms. Like, you take a huge dose of ionizing radiation, feel sick for an hour, and then go for days in seemingly good health, before you collapse and die. How does that happen? Why does your body suddenly break down after the "walking ghost" phase? Why don't you see symptoms right away?
gpt
Acute radiation poisoning is the result of damage to very specific cell populations in the body.  Radiation is much more lethal in cells that are undergoing cellular division.  As a result, the stem cell populations that produce blood cells and intestinal tissue are most sensitive.

In short, what happens is that a large dose of radiation can destroy the underlying stem cells of the bone marrow that produce blood cells.  Normally, blood cells last about 1 month in circulation before they are removed/replaced.  After acute radiation poisoning, no more blood cells are produced, and your blood stops working when existing cells die off.  A similar effect occurs in the intestinal lining.

So the reason why there is a delay is - it isn't the functional cells that are dying.  The cells that replenish the functional cells are the ones damaged most strongly by radiation.

As an aside, this is why large doses of radiation are given as a preparatory regimen when someone receives a bone marrow transplant.  Patients with cancerous bone marrow come to us, and we give them what would ordinarily be a fatal whole-body dose of radiation.  By killing off the entire bone marrow, this destroys the cancer.  Then they are implanted with new bone marrow to resume normal blood functions.