RADIOACTIVE DECAY Preliminary information: --alpha decay ejects a He nuclei --when an nucleus emits an alpha particles, the atomic number goes down by two (two fewer protons) while its atomic mass goes down by four (two neutrons, two protons) --beta decay produces high energy electrons--these are ejected when one neutron in a nucleus turns itself into a proton (and electron, which gets emitted) --when an nucleus emits a beta particles, the atomic number goes up by one (one more proton than before) while its atomic mass stays the same --gamma decay produces a high energy photon --when an atomic nucleus is “excited” (same as when an atom is excited), the nucleus will de-excite by emitting a photon in the keV to MeV range

FISSION --U-238 is a non-fissionable form of uranium--it is also the most common form of uranium --U-235 is a fissionable material --in being fissionable, a neutron that strikes U-235 can make the atom elongate and split (why will it split if elongated?) --the reaction looks like 1 235 91 142 1 n U Kr Ba 3 ( n) 92 36 56 --in other words, with fusion diminishing at the core, the star gets brighter

--a TNT reaction produces 30 eV’s worth of energy --a typical fission reaction produces 200,000,000 eV’s worth of energy --when critical mass is generated, every fission reaction that occurs will spawn one other reaction --when super critical mass is generated, every fission reaction produces multiple reactions and energy is released --Enrico Fermi, on Dec. 2, 1942, generated the first controlled fission reaction in the world on a squash court located underneath Stagg Field at the University of Chicago --in other words, with fusion diminishing at the core, the star gets brighter

-plutonium is more fissionable than U-235 --to produce plutonium --make a U-238 atom absorb a neutron making U-239 --U-239 has a half-life of 24 minutes--it goes through beta decay producing Np-239 --Np-239 has a half-life of 2.3 days--it also goes through beta decay producing Pu-239 --Pu-239 has a half-life of 24,000 years and is more fissionable than U-235 --in other words, with fusion diminishing at the core, the star gets brighter