Naked Science Forum
General Science => General Science => Topic started by: Herman Melville on 22/06/2009 14:33:59
-
Inspired by this story: http://news.bbc.co.uk/1/hi/world/americas/8107908.stm
What happens if a plane carrying a nuclear bomb crashes? Will the impact set off the bomb, no matter what?
-
You have to do a lot more than just dropping it to set it off.
The case is pretty strong so it is unlikely to split, I think.
The worst risk is that a terrorist will find it and make off with the nuclear material. There was a film with Ben Aflek on TV recently.. . .. The Yanks and the Ruskies ended up hugging each other, though - it was the Nazis wot dunnit.
-
Wouldn't the bomb(s) be set off if the plane exploded or crashed into a mountain?
-
No A nuclear device must itself be the result of a high energy explosion that drives two pieces of fissionable material into each other. The explosion must be of such force that it "welds" the two pieces together As there are all types of procedures to arm a device in preparation for firing that must be carried out in sequence, one of these being to enable the two parts of the fissionable materiel to come in contact with each other, there is no chance that this would happen.
There have been crashes of planes with nuclear bomb, bombs that have been lost from airplanes (I think off of Spain if my memory is correct) - all with no explosion
-
They're even safer than that JimBob, at least with regard to accidental detonation. The old and primitive two-part 'Gun' type bombs were actually quite dangerous, regarding accidental detonation, as well as being pretty inefficient.
In a 'Gun' type bomb you have two parts, as JimBob says. The two sub-critical sized parts are designed so that when brought together they they form a single super-critical mass. The two parts were either in the shape of a 'cored' sphere and a corresponding 'core', or a hollow cylinder and a solid filling cylinder or rod. This type of bomb works by firing the core or rod 'bullet' into the cored sphere or hollow cylinder by the use of an explosive charge, hence the 'Gun' moniker. It's an inefficient design though, because the high mass of the 'bullet' limits the speed it can travel with the result that fissioning starts before the bullet has fully entered the target, and it's dangerous because it relies upon a single charge, which could be fired accidentally. This was the type of bomb used on Hiroshima, and afaik, its only other use was in a cannon shell.
All other A-bombs (and A-bombs are the triggers for H-bombs), including the one that was dropped on Nagasaki, have been Implosion bombs. In this type of bomb there is effectively a single hollow sphere of fissionable material, but the hollowed sphere is of such a size that at no point within it is the local mass critical. This type of bomb is detonated, once again, by explosive charges, but in this case by many separate shaped charges arrayed around the outside of the sphere (typically > 30 individual charges iirc). When all of these charges are detonated, which must be done within fine time limit tolerances, the hollow sphere of fissionable material is said to be 'imploded' so that it now occupies a much smaller volume, which results in a critical mass. This type of bomb is more efficient because the mass is raised to super-criticality much faster and much more uniformly than with the 'Gun' type bomb. It is also much safer, regarding accidental detonation because it relies upon the tightly timed firing of many individual charges instead of just one; the accidental detonation of several of the imploding charges will only damage the bomb, not cause it to fission.
There is, therefore, little risk of current bombs detonating because of an aircraft crashing, or even from being dropped or fired without them being correctly armed to ensure that all the implosion charges fire before the bomb is damaged. Local radioactive contamination is highly probable though, of course.
-
Thanks. This is very reassuring.
-
Why? Did you find one in your back garden?
-
More importantly, if the plane were American, with an American crew and British and German observers, which took off from a UK air base and crashed in the French Alps with wreckage scattered across the border into Switzerland, where would the survivors be buried?
-
Har har.
Were we born yesterday?