Uranium
Uranium-238 is the most stable isotope of uranium, with a half-life of about 4.468 years, roughly the age of the Earth. Uranium-235 has a half-life of about 7.13 years, and uranium-234 has a half-life of about 2.48 years.
For natural uranium, about 49% of its alpha rays are emitted by each of U atom, and also 49% by U (since the latter is formed from the former) and about 2.0% of them by the U. When the Earth was young, probably about one-fifth of its uranium was uranium-235, but the percentage of U was probably much lower than this.
Nihonium
All nihonium isotopes are unstable and radioactive; the heavier nihonium isotopes are more stable than the lighter ones, as they are closer to the centre of the island. The most stable known nihonium isotope, Nh, is also the heaviest; it has a half-life of 8 seconds. The isotope Nh, as well as the unconfirmed Nh and Nh, have also been reported to have half-lives of over a second. The isotopes Nh and Nh have half-lives of 1 and 0.1 seconds respectively. The remaining two isotopes have half-lives between 0.1 and 100 milliseconds: Nh has a half-life of 70 milliseconds, and Nh, the lightest known nihonium isotope, is also the shortest-lived, with a half-life of 1.4 milliseconds. This rapid increase in the half-lives near the closed neutron shell at "N" = 184 is seen in roentgenium, copernicium, and nihonium (elements 111 through 113), where each extra neutron so far multiplies the half-life by a factor of 5 to 20.