Why is large-scale nuclear fission a rare phenomenon on Earth? A. There isn't enough energy to start a chain reaction in nature. B. There are no naturally occurring atoms that can undergo fission left on Earth. C. Atoms that undergo fission aren't concentrated enough to sustain a chain reaction. D. Atoms that undergo fission tend to decay more slowly on Earth than in stars.

The answer is; C

The radioisotopes in the interior of the earth are not in pure form and have many embedded impurities and are interspersed. Therefore when a neutron is released by a decaying atom, its chances of hitting another radioisotope atom (to continue the chain reaction) are lower than in a manmade nuclear reactor. This way, the radioactive chain reaction in the earth's interior is not well sustained.

The answer is: C. Atoms that undergo fission aren't concentrated enough to sustain a chain reaction.

For example, the decay chain of U-238 is called the uranium series.

Decay start with U-238 and ends with Pb-206. There are several alpha and beta minus decays.

The half-life for the radioactive decay of U-238 is 4.5 billion years and is independent of initial concentration.

Uranium is find in ores on Earth with very law mass percentage in it, so fission is not possible.

Nuclear reactions do not require heat or an input of energy to occur.