At first, I thought the title was a mistake, as the letter speaks of 'neutrons' throughout. But it turns out that the term 'neutrino' came only later: 'Pauli e

At first, I thought the title was a mistake, as the letter speaks of 'neutrons' throughout. But it turns out that the term 'neutrino' came only later: 'Pauli earlier (in 1930) had used the term "neutron" for both the neutral particle that conserved energy in beta decay, and a presumed neutral particle in the nucleus, and initially did not consider these two neutral particles as distinct from each other' (from https://en.wikipedia.org/wiki/Neutrino https://en.wikipedia.org/wiki/Neutrino)