Articles | Volume 5, issue 2
18 Dec 2014
Note |  | 18 Dec 2014

Erich Regener and the ionisation maximum of the atmosphere

P. Carlson and A. A. Watson

Abstract. In the 1930s the German physicist Erich Regener (1881–1955) did important work on the measurement of the rate of production of ionisation deep under water and in the atmosphere. Along with one of his students, Georg Pfotzer, he discovered the altitude at which the production of ionisation in the atmosphere reaches a maximum, often, but misleadingly, called the Pfotzer maximum. Regener was one of the first to estimate the energy density of cosmic rays, an estimate that was used by Baade and Zwicky to bolster their postulate that supernovae might be their source. Yet Regener's name is less recognised by present-day cosmic ray physicists than it should be, largely because in 1937 he was forced to take early retirement by the National Socialists as his wife had Jewish ancestors. In this paper we briefly review his work on cosmic rays and recommend an alternative naming of the ionisation maximum. The influence that Regener had on the field through his son, his son-in-law, his grandsons and his students, and through his links with Rutherford's group in Cambridge, is discussed in an appendix. Regener was nominated for the Nobel Prize in Physics by Schrödinger in 1938. He died in 1955 at the age of 73.

Short summary
In 1912 Hess found that the rate of production of ions in the atmosphere grows with altitude. In 1933 Regener observed a maximum rate of production above 20 km, a result later confirmed with his student, Pfotzer (Nature 1935). Final results were published in German by Pfotzer alone, probably because Regener had difficulties with the National Socialist government, and the maximum has become known as the Pfotzer maximum. An argument is made for renaming the maximum the Regener--Pfotzer maximum.