7 4. One second after the Big Bang the cosmic plasma has cooled to a temperatureT - 1010 K, at which point the neutron to proton ratio freezes to Ta 0.2,Прwith nn and np being the number densities of neutrons and protons, respec-tively. Estimate the primordial number abundance of Helium, assuming thatall neutrons are bound in He.

4. One second after the Big Bang the cosmic plasma has cooled to a temperature T - 1010 K, at which point the neutron to proton ratio freezes to nn 2 0.2, Пр with and being the number densities of neutrons and protons, respec- Nn Пр tively. Estimate the primordial number abundance of Helium, assuming that all neutrons are bound in He.

4. One second after the Big Bang the cosmic plasma has cooled to a temperature T - 1010 K, at which point the neutron to proton ratio freezes to nn 2 0.2, Пр with and being the number densities of neutrons and protons, respec- Nn Пр tively. Estimate the primordial number abundance of Helium, assuming that all neutrons are bound in He.