The Life History Of One Uranium Nuclei

One final nugget from E = mc²

Uranium²³⁵ is a nuclei which can undergo spontaneous fission. Radioactivity is a stochastic process and it is not possible to predict exactly when any one particular nuclei will decay. However "mean lifetime" (T) or "decay constant" (reciprocal of mean lifetime) is a measure of the longevity of a nuclei and is proportional to the half life of the isotope; t1/2 = Tln2. U²³⁵ has a half life (t1/2) of about 700 million years. That means that any one U²³⁵ nuclei may remain stable without decaying for hundreds of millions to few billion years....unless it is made to decay by inducing fission...

...which is what happened to a few U²³⁵ nuclei when the bomb hatches of the Enola Gay opened and Little Boy began hurtling towards Hiroshima:

The uranium atoms mined on Earth were each over 4.5 billion years old. Only a very powerful force , before the Earth was formed had been able to squeeze their electrically crackling protons together. Once that uranium had been formed, the strong nuclear force had acted, gluelike, to hold these protons in place over all that long span; while the Earth cooled, and continents formed; as America separated from Europe, and the North Atlantic Ocean slowly filled; as volcanic bursts widened on the other side of the globe, forming what would become Japan. A single extra neutron unbalanced that stability now...

... the density of uranium was enough that a chain reaction started, and soon there weren't just two speeding fragments of uranium nuclei, there were four, then eight, then sixteen, and so on. Mass was "disappearing" within the atoms, and coming out as the energy of speeding nuclei fragments. E = mc² was now under way.

1900 feet over Hiroshima, a few billion years of stable existence for those U²³⁵ nuclei ended. Nature hangs by a precarious balance...