DiscussWorldIssues - Socio-Economic Religion and Political Uncensored Debate - View Single Post - how much water does it take to survive a nuke like in the ending of the movie Predato

**TeLMgNva** · 03-10-2009, 07:30 AM

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.

03-10-2009, 07:30 AM	#10
TeLMgNva Join Date Oct 2005 Posts 580 Senior Member	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 (810^13 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 1.2210^6 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.
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