Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: george on 04/01/2007 04:16:45
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People talk about nuclear weapons including atom bombs and neutron bombs, but what are they? What's a hydrogen bomb, for instance?
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A hydrogen bomb works by fissioning hydrogen atoms in a chain reaction that only lasts a tiny fraction of a second. Particles released by the fissioning of 1 atom smash into other atoms causing particles from them to also be released. These in turn smash into other atoms and so on. The energy released is incredible, as given by e=mc^2.
Neutron bombs work on the same principle but, I think, it is the neutrons from the atoms that are released. I seem to remember reading that neutron bombs would not cause damage to buildings etc; they would merely smeg living things with radiation. Maybe a more qualified physicist could clarify that point for us.
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I am tempted to lecture you all on how to build nuclear weapons but I got into trouble for this on the CR4 board so my lips are sealed
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The "atom" bomb (e.g. the Hiroshima or Nagasaki bombs) is a fission bomb. The nuclei of heavy atoms are split into (nuclei of) smaller atoms, giving a lot of energy and excess neutrons, part of which trigger the splitting of other atoms.
The "hydrogen" bomb is a fusion bomb : hydrogen nuclei - actually nuclei of the deuterium isotope, which contain not only a proton but also one neutron - are made to collide, creating heavier nuclei.
In the "neutron" bomb, tritium is used rather than deuterium. The tritium nucleus has one proton and two neutrons. This sets a lot of neutrons free, creating a lot of radiation for a relatively small amount of energy.
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oops - I confused atom bombs with hydrogen bombs. Sorry [:I]
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Think nothing of it it would make little difference to me which one you dropped on me
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Neutrons have about a quarter of an hour half life, so the radiation dissipates quickly, and they were designed to not cause damage to infrastructure. The bomb got dubbed the "capitalist bomb" because you could launch one killing lots of enemy troops and then just walk in and take over their territory safely. Imagine an army just waiting a day to walk in and drive away in the enemies tanks, or live in their homes. [:-'(]
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Ever since the fifties there has been a lot of misinformation as to what nuclear bombs do to you, the emphasis has been on radiation but the people in Hiroshima and Nagasaki were either burnt to death or blown to pieces.
The motive for this propaganda seems to have been to kid us that we could survive by having brown paper over our windows.
Neutron bombs more properly known as radiation enhanced weapons blow and burn people to death in the normal way and also kill with the enhanced neutron radiation which also leaves behind induced long lasting radio activity.
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Syhprum - when you say "long lasting radioactivity", how long are we talking? Tritium has a half life of 12 years approximately, doesn't it? Surely this is nothing compared with plutonium, which takes a quarter of a million years to decay past 10 half lives...
Chris
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As a quick reply I must say I do not know at the moment just how significant this is but it is well known that many highly radioactive substances are produced by neutron irradiation.
Two that come to mind are Colbalt 60 and polonium 210 but of course it would depend how common the precursors are in the environment.
I will make a study and reply in more detail later.
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I must confess that I have probably overrated this effect, due to the short life of free Neutrons and the high temperature of weapon generated emissions the induced radioactivity is not very significant
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I heard that the high flux of neutrons from a neutron bomb would be 'good value' and selective because of the ready transfer of the neutrons' energy to the hydrogen atoms in water (and in living things). This would be because of the equal masses of the neutrons and the hydrogen nuclei.
This effect would produce a lot of ionisation from each neutron that arrives and a lot of biological damage. I understood, also that, for best results, you detonate it high overhead!
War is so sad.
Neutrons transfer less energy when colliding with more massive nuclei; they will 'bounce off' a heavier target and produce some gamma radiation . Concrete and steel would be affected much less than the inhabitants of buildings.
I do know that a relatively light water jacket around some reactors acts as a very good screen for neutrons. Apparently it 'just glows'! Of course, water does virtually nothing to screen against gamma.
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If I remember correctly, Boron is a very good neutron absorber and occurs in abundance.
Depleted boron can be used as a cheap neutron shield thus lessening the effects of a Neutron bomb.
I think it is also used in some spacecraft for its neutron absorbing abilities.
Tritium, used in theses bombs has a short half life of around 12.5 years so warheads have a "best by date" and any long term storage is not on.
Not a very practical bomb!
that mad man
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The glow in water around a running reactor isn't caused by neutrons. This is Cerenkov radiation - you can imagine it like a 'sonic boom' in light as it's caused by high energy electrons (beta particles) travelling faster than the speed of light in water (which is a good deal slower than in vacuum). It's a very impressive deep blue glow, even for fuel recently removed from a reactor.
Boron is used as a neutron absorber in Pressurised Water Reactors (PWRs) - B-10 being a strong absorber of thermal (slow) neutrons, but the by-products include tritium and alpha particles so not ideal as a radiation shield...