Answer to Question #34453 in Atomic and Nuclear Physics for junaid iqbal

Question

what are the difficulties in making the fission chain reaction (go)?

Answer 1

The principle of operation of an atomic bomb or power plant, utilizing uranium fission is quite simple. If one neutron causes division, which leads to the release of several new neutrons, the number of fissions can increase tremendously with the release of enormous amounts of energy. The possibility of such growth determined by the relative probability of a number of processes. Neutrons in the fission process may escape entirely from the uranium, may be captured by uranium in the process leading to the division, or they may be captured by an impurity. Thus, the question of whether or not a chain reaction depends on the result of a competition between the four processes:
1. Escape of neutrons from uranium,
2. Capture by uranium without division,
3. Capture by impurities.
4. Capture by uranium division.
If the lossof neutrons in the first three processes than the number of neutrons produced by the fourth, the chain reaction occurs, otherwise it is impossible. Obviously, any of the first three processes may have a greater chance in this location that the extra neutrons in the fission, unable to keep the reaction going. For example, in the case where the process 2 - capture by uranium without division - has a much higher probability than fission capture chain reaction impossible.

An additional difficulty is that the natural uranium is composed of three isotopes: U- 234, U- 235 and U- 238 contained in amounts of approximately 0.006, 0.7 and 99.3 %, respectively. We have already seen that the probability of the 2 and 4 are different for different isotopes. We have also seen that the probabilities are different for neutrons of different energies.