[QUOTE=OtakuLoki]
A couple of caveats - I was trained as a rad tech, not a scientist, nor engineer. I’m also going to be using general cases. When dealing with gamma rays, a lot depends on the initial energy of the photons being emitted. Some energy levels pass through shielding better than others. (And others are much, much less able to penetrate.) I’m also going to be using radcon math in my reasoning - so don’t expect numbers to be exact.
I haven’t seen the movie, so I can’t comment on the scenes shown with all that much confidence, but while water is a coolant, it’s also a pretty effective shield. It’s not magic, of course, but I can imagine a scenario where someone vertically suspended in a pool shielding a rad source could get a lethal dose, while someone a few meters above him with only a little more water between the center of his body and the rad source, got out without any immediately visible effects.
First off, IIRC the general rule of thumb is that for every 24 inches of water gamma rays have to pass through the dose rate drops by 90%. So the guy in the water would have the center of his body almost a full tenth thickness less shielding than the guy in the air, even if they were the same distance from the rad source. Which translates to effectively ten times the dose for the guy in the water.
Now, the way I’m seeing this in my mind, the guy in the air would be on some cat walk say, two or three meters above the pool. Radiation strength varies at the inverse square of the distance from the emission source. So, those extra two or three meters could be almost as effective in reducing the dose to the guy on the catwalk, as the extra shielding tenth thickness of water was. So, for easy calculations (radcon math - always choose your numbers for easy calculations!) let’s say that the guy on the catwalk is now three times as far from the source as the deader in the water - which means that the guy in the catwalk is only getting one tenth of the unshielded dose that the guy in the water got. And because of the extra shielding the guy on the catwalk gets only one tenth of what he’d have gotten without that shielding. So the guy on the catwalk could be getting as little as 1% of what the guy in the water is getting.
Now, let’s plug in some numbers to that: the LD 50 dose for ionizing radiation is about 400 REM. But that’s usually after a lovely time fighting rad sickness in a hospital. If the guy in the water has to die quickly, let’s zap him with, say 1000 REM. It’s still probably too little to really kill him immediately, but it’s in the right ballpark, I’d think.
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Nah. You need a hell of a lot more radiation than 1,000 REM to actually incapacitate someone. (Much lower dosages will indeed kill someone, but it takes a few days.) This 1971 study (with the catchy title of “Survival Time and Dose-Response Following Supralethal Irradiation of Dogs”) indicates that it took dosages of up to 20,000 rads (approximately equal to REM) to incapacitate dogs within 100 minutes. The guy in the movie was incapacitated almost immediately. Lets be generous and say it took 10 seconds. Lets also assume that 20,000 REM will incapacitate a person. This means that the guy in the water was being exposed to a gamma flux of 20,000 REM/10 seconds = 2,000 REM/sec.
[QUOTE=OtakuLoki]
If the guy on the catwalk is getting 1% of that dose, he’s only gotten 10 REM. Measurable blood changes don’t even start until about 25 REM. So the guy on the catwalk could be okay, even if the guy in the pool goes belly-up.
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I’ll buy your radcon math for the dose fraction of 1% (taking into account the distance and shielding) for the guy higher up in the maintenance shaft. So 1% of 2,000 REM/sec works out to 20 REM/sec.
The guy up in the maintenance shaft spent a lot of time fucking around in there. However, let’s say he spent just one minute in there. His dose then is 20 REM/sec x 60 sec = 1,200 REM. That’s it, he’s dead. He won’t be incapacitated for hours or days, but he almost certainly will not survive a week.
[QUOTE=OtakuLoki]
Whether I think that geometry is likely is another question altogether. I’m making a number of assumptions about the shape of the source in the pool that probably can’t be considered accurate for close proximity. AIUI there’s usually a LOT of water over the stuff kept in containment pools. Heck, when I toured a 10 KW thermal reactor at WPI their itsy, bitsy, teeny, weenie core was covered by at least a meter of water.
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This whole exercise brings up my original point again, which is: what type of hard gamma source do you leave at the bottom of a maintenance shaft in the first place? :dubious: I know! Maybe that’s why they were warned to stay out of the maintenance shaft! Anyone who attempts to circumvent the security between levels is dead! Makes as much sense as anything else in this stupid movie… :rolleyes:
P.S. IIRC from my nuke training, it takes a great deal of radiation to actually incapacitate someone in a short-term time frame because the only thing that will really drop a person in their tracks is neural damage (i.e. actually killing nerve cells). It takes a great deal of radiation to cause this damage (in the tens of thousands of REM). Much lower dosages will kill a person (500-1,000 REM), but it takes a few days, because the mechanism of death in this case is the fact that much of a person’s DNA has been damaged, so cells can no longer reproduce. This effect is first seen in the quickly reproducing cells, such as cells in the gastrointestinal tract, bone marrow/blood cells, and hair follicle cells. So the doomed person’s hair falls out, their whole GI tract sloughs off (resulting in vomiting and diarrhea), and they get anemic and can no longer fight off infection. Fun way to go… 