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Famous scholars from Kiel:

Hans Geiger

The “father“ of the famous Geiger counter taught in Kiel from 1925 to 1929. On 17th June 2009 a physics lecture theatre will be named after him on the occasion of a scientific colloquium. Professor Alexander Piel tells us more about this famous physicist.

Depending on your point of view, the clicking of the Geiger counter is either the heart-beat of the atomic age or the symbol of menacing radiation. In 1928, when Hans Geiger and his doctoral student Walther Müller recognised the extraordinary sensitivity of their radiation counter to alpha, beta and gamma radiation during their work at Kiel University, they were bestowing the young sciences of atomic and high energy physics with powerful new systems of measurement.

Hans Geiger was born in Neustadt an der Weinstrasse on 30th September 1882. His father was an upper secondary school (Gymnasium) teacher and later Professor of Indo-Germanic Languages at the University of Erlangen where the young Hans Geiger commenced his studies of mathematics and physics in 1902. After taking his doctorate in 1906 he moved to the Physics Institute at Manchester to study under Arthur Schuster, a specialist in geomagnetism. However, the crucial factor for his later career was his meeting with Ernest Rutherford (1871 - 1937) who took over the Institute in 1907 and was later awarded the Nobel Prize for Chemistry. Rutherford, a pioneer in the new field of radio-activity, recognised Geiger's gift for experimentation and appointed him to be his assistant.

During his collaboration with Rutherford, Geiger's studies focussed on how alpha radiation penetrated material. Alpha radiation consists of alpha particles which arise as radio-active elements decay. They are 8,000 times heavier than electrons. It became evident in the course of experiments that the radiation was sometimes reflected and scattered by thin metal foils. At the time this phenomenon was completely incomprehensible - it was as if a mountain of cushions was deflecting a cannon-ball. Rutherford was seeking an explanation for this observation and finally developed his model of an atom. Geiger therefore played an essential part in our present understanding of the structure of atoms.

During these early years in Manchester Geiger was looking for electrical methods of measurement with which alpha radiation could be proved. His "pointed counter", a precursor of the radiation counter, is still in use. These electrical methods of counting replaced the difficult and time-consuming observations during which scientists had to resort to a fully darkened room to count the extremely faint flashes of light created by radio-active radiation on zinc sulphide fluorescent screens.

In the meantime Geiger had become famous in the field of radio-activity. He left England in 1912 and accepted a position at the German Physical-Technical Institute (Physikalisch-Technische Reichsanstalt) in Berlin (today the Federal Physical-Technical Institute based in Brunswick). In Berlin he built a radio-activity laboratory and received his "Habilitation" (a prerequisite for teaching at a university) in 1924. In 1925 he accepted the offer of a Chair in Experimental Physics at Kiel University and moved to Kiel. Geiger appreciated the greater independence offered by this university and quickly made himself at home here. He held the "Great Experimental Lecture" as early as the 1926 summer semester and offered experimental work in physics. What is probably his most famous development belongs to his time in Kiel - the Geiger radiation counter that bears his name and that of his first doctoral student Walther Müller. In the years that followed the device became one of the essential and widespread tools of modern physics and technology.

Geiger probably recognised the significance of this discovery. It clearly opened up completely new possibilities for research into cosmic radiation. Geiger made this branch of research into his main field of activity when he was appointed to positions at Tübingen in 1929 and later to the Technical University of Berlin in 1936. He published his experiments and the properties of the "Geiger-Müller counter" in detail in scientific papers.

Geiger was an enthusiastic experimental scientist who was also an expert in understanding how to inspire a sense of enthusiasm for physics in those who listened to his instructive and entertaining lectures which were filled with clear and convincing arguments as well as light-hearted remarks. He died in Potsdam on 24th September 1945.

Alexander Piel

The author, Alexander Piel,

is a Professor of Atomic and Plasma Physics at the Institute for Experimental and Applied Physics.

Key word: Geiger counter

The Geiger counter or the Geiger-Müller counter is a measuring instrument for precisely gauging the intensity of alpha, beta and gamma radiation. It consists of a metal tube with a diameter of several centimetres which is filled with argon or a mixture of air and alcohol vapour. A wire conductor is positioned along the middle of the tube with a high tension between the wire and the metal tube. If ionizing radiation (the radiation generated during radio-active decay) penetrates the inside of the tube, the particles with a positive or negative charge (ions) which the radiation generates cause an electrical discharge which can be made audible or visible by the use of a loud-speaker (the Geiger counter's ticking noise) or by activating a counter.
It is certainly true that other types of radio activity detectors exit today but when it is necessary to detect extremely small amounts of radiation, what the world knows as the Geiger counter is still unsurpassed.

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