On the earlier and more recent history of the neutrino

The continuous energy spectrum of beta rays discovered by J. Chadwick in 1914 immediately posed difficult problems with respect to its theoretical interpretation. Was it directly due to the primary electrons emitted from the radioactive nucleus or was it to be attributed to secondary processes? This paper discusses the first hypothesis, which was proved to be the correct one, was advocated by C. D. Ellis, the second one by L. Meitner. Meitner appealed to the fact that nuclear posses discrete energy states, as was known from alpha and gamma rays. She focused attention on the discrete energies of electrons, which had been observed for many beta-radioactive nuclei. Ellis interpreted them as electrons being ejected from the outer shells by inner conversion of monochromatic nuclear gamma rays and assigned them to the observed X-ray lines. According to Metiner's theory, however, at least one of the electrons of discrete energy should be a genuine primary electron from the nucleus, which, in a secondary process, could then emit from the outer shells more electrons with smaller energies