Electron spectroscopy for atoms, molecules, and condensed matter

In my thesis [1], which was presented in 1944, I described some work which I had done to study β decay and internal conversion in radioactive decay by means of two different principles. One of these was based on the semi-circular focusing of electrons in a homogeneous magnetic field, while the other used a big magnetic lens. The first principle could give good resolution but low intensity, and the other just the reverse. I was then looking for a possibility of combining the two good properties into one instrument. The idea was to shape the previously homogeneous magnetic field in such a way that focusing should occur in two directions, instead of only one as in the semi-circular case. It was known that in betatrons the electrons performed oscillatory motions both in the radial and in the axial directions. By putting the angles of period equal for the two oscillations Nils Svartholm and I [2, 3] found a simple condition for the magnetic field form required to give a real electron optical image i.e. we established the two-directional or double focusing principle. It turned out that