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• The mean kinetic energy of particles at temperature T is 〈K〉 = 3kBT/2, where kB is Boltzmann’s constant, kB = 8.62 × 10−5 eV/K. (a) Given that mean energies of order 10 keV are sufficient to strip the electrons off most atoms, find the temperature Tatom above which one would find few atoms. (For its first million years or so, the universe was above this temperature and so contained just electrons and nuclei.) (b) Given that mean energies of order 1 MeV will knock most nuclei apart, find the temperature Tnuc, above which one would find few nuclei. (For its first 3 minutes or so, the universe was above Tnuc and contained just electrons, protons, and neutrons.)
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