The author says "an ordinary beryllium nucleus, 8Be, is made of 4 protons and 4 neutrons". This is absolutely untrue as 9Be is the "ordinary" beryllium nucleus

The author says "an ordinary beryllium nucleus, 8Be, is made of 4 protons and 4 neutrons". This is absolutely untrue as 9Be is the "ordinary" beryllium nucleus. It is in fact one of the best and lowest mass examples of nuclear "magic numbers" having inconsistencies. 8Be has a halflife of attoseconds and a mass greater than two alpha particles therefore isn't even a bound state. I'd be hard pressed to even attach the label nucleus to it in the sense that an atom could form around it. https://en.wikipedia.org/wiki/Beryllium-8 https://en.wikipedia.org/wiki/Beryllium-8 That extra neutron is somewhat important.