Lise Meitner, β-decay and non-radiative electromagnetic transitions

The current activities in detecting neutrinos as carriers of information from far out in our Universe prompt us to look back on the research activities a century ago that led to the discovery of these weakly interacting particles. One of the leading researchers was Lise Meitner, who observed electrons with well-defined energy, besides the continuous energy spectrum emitted in β decay. These electron lines are well understood as radiationless nuclear transitions competing with γ-ray emission. It is proposed to name the electrons resulting out of this so-called internal conversion process after Lise Meitner and Charles D. Ellis. The equivalent process within the electronic (atomic) shell is the Auger effect , competing with X-ray emission. In this context, the radioactive decay of UX1 or 234 Th, well studied a century ago by Lise Meitner and Charles Ellis, is re-visited, and the mono-energetic electrons are ascribed entirely to the internal conversion process.