The nuclear bomb

It is not difficult to construct a thermonuclear device. What is difficult is to obtain enough 235U from the uranium ore to use as fuel in the thermonuclear device. The isotope 235U must be separated from the more abundant 238U isotope. In fact the 235 isotope makes up only 0.7% of uranium metal. The 238U isotope is very stable. It can absorb neutrons without undergoing a fission reaction. This isotope mops up neutrons and prevents a chain reaction from occuring. The presence of the 238 isotope prevents nuclear chain reactions from occuring in Nature.


Above is a simple representation of a fission bomb. TNT is used to drive two pieces of fuel, of subcritical mass towards a neutron source. As the two subcritical pieces unite they form a supercritical mass of fuel. This supercritical mass can undergo a nuclear chain reaction.