Suppose the difference in rest energy of the neutron and proton were qn = (mn−mp)c 2 = 0.129 mev instead of qn = 1.29 mev with all other parameters unchanged (including the freezeout temperature for neutrinos at the time of big bang nucleosynthesis). estimate the – 2 – maximum possible mass fraction in he. you may assume all helium nuclei have two neutrons and two protons.'