Why are some isotopes radioactive and others are not?

1 Answer
May 22, 2018

Actually all isotopes are radioactive Some are much more radioactive than others.


The second law of thermodynamics states that everything goes from order to disorder. An atomic atom is a highly order structure.
The second law states that all highly order structure with break apart and move towards disorder. ( Someday far in the distance future there will be total disorder and no matter will be left at all)
When an atom breaks apart this causes radioactive decay.

The question is what makes some atoms more stable than others so that the rate of radioactive decay is not noticeable? The answer is the ratio of protons ( positive charges that push each other apart and cause the break up of the nucleus) and neutrons that are attracted to the charged protons and hold the nucleus together.

In small atoms a 1 :1 ratio of protons to neutrons is the most stable.
Carbon 12 with 6 protons to 6 neutrons 1:1 is very stable while
Carbon 14 with 6 protons to 8 neutrons 1;1.33 is not stable with a radioactive half live of approximately 5,700 years.

In larger atoms the ratio of protons to neutrons has to be greater than 1:1 Uranium 238 is very stable with a radioactive half-life of4.5 billion years. 92 protons to 146 neutrons. Uranium 235 is very unstable and used in atomic bombs. with a ratio of 92 protons to 143 neutrons.

The ratio of protons to neutrons is critical to the stability of the atomic nucleus. All atom will undergo radioactive decay at some point. In atoms with an unstable ratio of protons and neutrons this decay will occur at an observable and measurable rate