Atomic bomb

[ludwig]

When they tested the A bomb for the very first time, how did they know how far back to stand?

[jake-the-peg]

They had calculated (estimated ) the amount of matter that would be destroyed and hence the power and did a test with conventional explosives before hand.

You can read all about Trinity here:

http://nuclearweaponarchive.org/Usa/Tests/Trinity.html

[kempie]

Castle Bravo was a lithium-deuteride fuelled H-bomb exploded 1st March 1954 at Bikini Atoll. It yielded 15 megatons and had a fireball 4 miles in diameter. It was much bigger than the test crews had been expecting (6 megatons). It engulfed its 7,500 foot diagnostic pipe array all the way out to the earth-banked instrument bunker, which barely survived. Test crews were trapped in experiment bunkers well outside the expected limits of its effects. It menaced task force ships, one of which held Marshall Rosenbluth, a U.S. theoretical physicist, "I was on a ship that was thirty miles away, and we had this horrible white stuff raining down on us. I got 10 rads [100 chest x-rays] of radiation from it'. The 'horrible white stuff' was calcium precipitated from vaporised coral.

http://nuclearweaponarchive.org/Usa/Tests/Castle.html

[Peter Pedant]

The web site is a good one.

I think they were not sure how far back to stand as they were not sure if it would work or not. The scientists opened a book on the power of the blast with the lowest estimate being the power of the priming charge. I think they all underestimated the power of the blast.

[landie]

They didn't know until they tried a smaller version which they made a scale model from a 500th of an atom.