CBSE Class 12-science Answered

In the following we are trying to see how we can assemble masses greater than critical masses.When the actual critical mass is reached nothing happens, so that to produce a nuclear explosion you need several critical masses—about three. In that case more neutrons will be produced in the interior than will leak through the surface; as a result a self-sustaining chain reaction will occur. This poses an apparent dilemma. How do you assemble several critical masses if you start with an amount of material that is less than a critical mass, which you must do to avoid pre-detonation? The secret has to do with the density of the material. What you call the critical mass depends on the density. If you increase the density, the critical mass becomes dramatically smaller. If, for example, you increase the density by a factor of two, the critical mass is decreased by q factor of four. In a bomb what happens is that the material is rapidly compressed so that this compressed material has a smaller critical mass and hence you can achieve several critical masses at these compressed densities.