Why does plutonium-238 undergo radioactive decay?

AUTHOR'S NOTE: This is a VERY simplified version of what actually happens. There is a complex exception to most of what I say below, but the general story is still useful as written! read more

Sometimes the product of that nuclear decay is unstable itself and undergoes nuclear decay, too. For example, when U-238 (one of the radioactive isotopes of uranium) initially decays, it produces Th-234, which decays to Pa-234. The decay continues until, finally, after a total of 14 steps, Pb-206 is produced. read more

Silicon does exist in space near very active stars, supernovas,etc. in the form of isotopes that undergo radioactive decay. The longest lived silicon isotope (32) that will undergoradioactive decay, has a halflife of roughly 700 years and thuswill effectively completely decay to stable sulfur-32 in less than4000 years. read more

When Plutonium-239 undergoes alpha decay with a half-life of 24110 years, there will remain an alpha-particle (Helium-4) and Uranium-235, that are called "daughter nuclei". The excess energy is 5244.50 keV, which is distributed to the kinetic energy of the daughter nuclei and the excitation energy of Uranium-235. read more