how much water does it take to survive a nuke like in the ending of the movie Predator?

[Blaupanzer]

First example was 10, second example was meant to be ~ 1000 tons which is about 2,000,000 pounds.

(I have edited it, leaving Snoopy's unhooked. I got distracted apparently, as 125 tons has no contextual meaning in what I said OR what I meant to say. Numbers from the clear blue sky entering one's posting are probably not a good sign.)

[Tuberski]

Is the water being held in a fridge?

I didn't know what you were talking about, until now. I just watched the movie last night.

What is so unbelievable?

It was a lead lined fridge and everyone knows that lead is a soft metal, thereby cushioning the shock of bouncing long distances.

ACK!

[Darius871]

I didn't know what you were talking about, until now. I just watched the movie last night.

What is so unbelievable?

It was a lead lined fridge and everyone knows that lead is a soft metal, thereby cushioning the shock of bouncing long distances.

ACK!

Even IF I were to accept that the lead would A) fully shield from radiation, B) not get superheated, and C) not break apart from the shock wave, the sheer amount of kinetic energy involved would at least break multiple bones as he rattles around in there, if not liquefy him. That, and there isn't even a perfect seal, just the flimsy strip of rubber between the base and the door, which would instantly melt and let in the extreme heat. That, and there didn't appear to be any latch or other locking mechanism in place, so we have to assume he held the door shut with his fingers wrapped tenuously around the flimsy condiment shelves. Even Ahnold couldn't hold on that tight. And that's just getting started...


(Yes I know you're just being facetious, but it's fun to vent anyhow.)

[Darius871]

[KrazyHorse]

Like if you had a swimming pool with a deep end and jumped to the bottom, would that be good enough? Assume .25 mile distance from the device and a small fission device.

There are 3 key factors to consider:

1) Blast/overpressure
2) Thermal radiation
3) Ionizing radiation

Even a few feet of water would protect against lighter flying debris. I'm not sure what the overpressure effects would be underwater. My feeling is that it wouldn't be lethal.

Assuming that Hiroshima was 20 kt (8*10^13 J) and that ~50% of this was released as thermal radiation over a period of ~5 seconds an unprotected individual 400m from blast epicenter and 600 meters vertically below the blast would be exposed to an intensity of thermal radiation of 1.22*10^6 W/m^2 during this period. This is approximately 1000 times stronger than sunlight. Most of this would be released in the optical and ultraviolet. On the scale of meters water is almost perfectly transparent to optical frequencies. It is more opaque to ultraviolet frequencies, but a significant fraction of this thermal radiation would pass straight through to the individual at the bottom of the pool. Thus the water provides almost no protection from thermal radiation, and it seems to be high enough to cause almost instantaneous fatal injuries. You would be better getting behind a brick wall as a means of protecting yourself...

As far as ionizing radiation goes, alphas will be stopped cold by the water. Electrons and gammas of energy ~1 MeV (a nice nuclear energy scale) have a half-value layer in water of something like 10cm. Thus the water would actually provide significant protection against ionizing radiation of these types. Fast neutrons, on the other hand are electrically neutral and therefore interact with light nuclei via the residual strong force. Their absorption coefficient should be very low (?) therefore the water will not provide significant protection from this source of ionizing radiation.

In sum, given a few seconds warning the most important thing to do if caught near the blast zone of a nuclear weapon would be to get behind something which will absorb most of the thermal radiation and which will not collapse on you. Water provides significant protection against certain forms of ionizing radiation at nuclear energies, but will not protect against simple thermal effects in any significant way.

[Naked Gents Rut]

You would be better getting behind a brick wall as a means of protecting yourself...

What if you've covered yourself in a thick layer of mud?

[TCO]

Muddy water? What about is the light kinda bouncing around or do you need to be in los. In which case, you wouldn't be. I guess I was thinking mjore that there woujld be super heated air and such...but I guess there is not so much of that for small nuke at ground level?

[TCO]

Fast neutrons, on the other hand are electrically neutral and therefore interact with light nuclei via the residual strong force. Their absorption coefficient should be very low (?) therefore the water will not provide significant protection from this source of ionizing radiation.

Kitty, the fast neutrons interact with water by collisions and are thermalized. This is how a nuke power plant works. Tenth thickness is about one foot.

[TCO]

They interact well with water (are well thermalized) since the most advantageous collisions are with equal mass H atoms.

[notyoueither]

Use sun block before you get in the water.

[Jon Miller]

Actually, they interact with all sorts of materials, it is just that with H atoms it is more of an elastic reaction while with heavier atoms the neutrons are more likely to be absorbed or something (have lower momentum resulting scattered components).

Dense materials like Lead are good neutron shielding.

JM

[Jon Miller]

Err

that should be for high energy neutrons like what I deal with

JM

[Saras]

As far as I remember the predator was in a pit, which was in a valley, and Ahnold was already past the summit of a hill when the nuke went off.

[Darius871]

As far as I remember the predator was in a pit, which was in a valley, and Ahnold was already past the summit of a hill when the nuke went off.

That's what I thought too, but looking at the clip there was only a small ridge behind him and fireball did seem to have a straight line to him at about a 10-30 degree angle. Unless he jumped off an off-camera cliff I'd say he was toast.

[Darius871]

For comparison's sake: