Nuclear weapons

Essay by laraa March 2005

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Good morning, ladies and gentlemen. First, let me introduce myself. My name is Lenny and I'm student at Faculty of Manufacturing Technologies of Technical University in Kosice. I'm going to talk today about nuclear weapons. I would like to divide my presentation into two parts. Firstly, I'll talk about the A-bomb and fission. Secondly, I'll define the H-bomb and fusion reactions. If you don't mind, we'll leave the questions until the end.


The simplest fission bomb, or A-bomb, consist of two pieces of 235U such that separately their masses are less than the critical mass, but jointly their masses add up to more than the critical mass. To detonate such a bomb, the two pieces of 235U, initially at a safe distance from one another, are suddenly brought closely together. The assembly of two subcritical masses into a single supercritical mass must be carried out very quickly; if the two are brought together slowly, a partial explosion (predetonation) will push them apart prematurely, before the chain reaction can release its full energy - the explosion fizzles.

The device commonly used for the assembly of the two pieces of uranium toward the other at high speed (Figure 1); the propellant is an ordinary chemical high explosive.

Fig. 1. A fission bomb using a gun deviceFig. 2. An implosion device

A more sophisticated fission bomb consist of a (barely) subcritical mass of 239Pu; if this is suddenly compressed to a higher than normal density, it will become supercritical. The sudden compression is achieved by the preliminary explosion of a chemical high explosive such as TNT. If this explosive has been carefully arranged in a shell around a sphere of 239Pu (Figure 2), then its detonation will crush the sphere of 239Pu into itself; this implosion of the plutonium very...