On Mon, Apr 6, 2015 , meekerdb <[email protected]> wrote:
> > In general you can't assume that it takes one critical mass to make a > bomb. > You do unless you're very sophisticated, otherwise it will likely take you more than one critical mass to make a bomb, for example the critical mass of U235 is 114 pounds but the Hiroshima bomb had 141 pounds of it. If you can implode the fissile U235 or Plutonium metal and compress it to arbitrary density then you can make the critical mass arbitrarily small, but that takes great sophistication far beyond the reach of a terrorist. And even the most sophisticated bomb makers in the world on both sides of the iron curtain found that making U233 bombs to be so hard it just wasn't worth bothering with. > > the fissionable material is surrounded by other materials to act as > neutron reflectors so the fissionable mass can be considerably smaller that > the critical mass. That's the technology that went into the design of > nuclear artillery shells. > All nuclear bombs use neutron reflectors. What makes nuclear artillery shells unusual is that they used the gun method to achieve criticality and that was only tried twice, the Hiroshima bomb and one test of a nuclear artillery shell in the 1950s. The gun method is simple but is very inefficient and wasteful of super expensive U235. In the Hiroshima bomb only 1.5% of the 141 pounds of U235 actually split, 98.5% was harmlessly blasted away before it could fission because of pre-detonation, modern bombs use up nearly 100% of their U235 or Plutonium. Because of inefficiency the gun method can't achieve high enough temperatures to serve as the ignition for a H-bomb, and because of this pre-detonation problem the gun method won't work at all for Plutonium, much less for U233. All modern nuclear bombs use the implosion method. John K Clark -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
