Hans Geiger

Early Life and Education

Hans Geiger was born on 30 September 1882 in Neustadt an der Weinstraße, Germany. He grew up in an academic family — his father was a university professor. Geiger studied physics at Munich and Erlangen, receiving his PhD at Erlangen in 1906 for research involving electrical discharges through gases.

That doctoral work on electrical discharges would prove surprisingly relevant. The techniques he learned for detecting tiny electrical signals in gases became the foundation of his later work on radiation detection.

Counting Alpha Particles

Soon after his PhD, Geiger went to the University of Manchester to work in Ernest Rutherford's laboratory. An important problem in early radioactivity research was simply being able to detect and count individual particles reliably. Early experiments sometimes required researchers to sit in darkness and count tiny flashes of light on a screen by eye.

Geiger worked with Rutherford on electrical methods that made counting radioactive particles much more practical. In 1908 Rutherford and Geiger published an electrical method for counting alpha particles. Geiger continued improving radiation detection techniques throughout his career.

The Geiger–Marsden Experiment

At Manchester, Rutherford asked Geiger and undergraduate Ernest Marsden to investigate how alpha particles behaved when fired at very thin metal foils. In 1909 they found that while most alpha particles passed through with only small changes in direction, a very small number were scattered through surprisingly large angles — with some effectively bouncing back toward the source.

This was completely unexpected under the prevailing 'plum pudding' model of the atom. Rutherford later interpreted these results as evidence that most of an atom's positive charge and mass were concentrated in a tiny central nucleus. Geiger and Marsden performed the crucial experiments; Rutherford interpreted the results and developed the nuclear model. It was not any one person's discovery alone.

The Geiger–Nuttall Law

Geiger also worked with John Mitchell Nuttall. Their research established the Geiger–Nuttall relationship, which linked characteristics of alpha-particle emission with radioactive decay rates. As with his other work, this was a collaborative finding — not Geiger's alone.

Coincidence Counting with Walther Bothe

In the 1920s Geiger also worked with physicist Walther Bothe on coincidence counting — detecting whether two events occurred at the same time. Their experiments on the Compton effect provided important evidence that interactions between radiation and electrons occurred as individual, connected events, strengthening the developing quantum description of light.

The Geiger–Müller Counter

Geiger developed early electrical devices for detecting radioactive particles, but the familiar instrument people call a 'Geiger counter' was actually the result of collaboration with his doctoral student Walther Müller. In 1928, while working at Kiel, Geiger and Müller published work on an improved gas-filled counting tube.

The improved Geiger–Müller counter could detect several forms of ionising radiation and became far more practical than earlier radiation counters. The device that people commonly call a Geiger counter is properly associated with both Geiger and Müller.

Later Career

Geiger returned to Germany in 1914. His later academic career included positions at Kiel, Tübingen and the Technische Hochschule Berlin. In 1936 he became director of the Physics Institute at the Technische Hochschule Berlin, where he continued research in nuclear physics and cosmic radiation.

He died on 24 September 1945 in Potsdam, Germany. His legacy lives on every time someone uses a radiation detector — a direct descendant of the counting tube he developed with Walther Müller.