Hans Geiger
Hans Geiger (1882-1945) invented the Geiger counter.
Hans Geiger was a German nuclear physicist best known for his invention of the Geiger counter, a device used for counting atomic particles, and for his pioneering work in nuclear physics with Ernest Rutherford.
Johannes Wilhelm Geiger was born in Neustadt ander-Haardt (now Neustadt ander-Weinstrasse), Rhineland-Palatinate, Germany, on September 30, 1882. His father, Wilhelm Ludwig Geiger, was a professor of philology at the University of Erlangen from 1891 to 1920. The eldest of five children, two boys and three girls, Geiger was educated initially at Erlangen Gymnasium, from which he graduated in 1901. After completing his compulsory military service, he studied physics at the University of Munich, and at the University of Erlangen where his tutor was Professor Eilhard Wiedemann. He received a doctorate from the latter institution in 1906 for his thesis on electrical discharges through gases.
That same year, Geiger moved to Manchester University in England to join its esteemed physics department. At first he was an assistant to its head, Arthur Schuster, an expert on gas ionization. When Schuster departed in 1907, Geiger continued his research with Schuster's successor, Ernest Rutherford, and the young physicist Ernest Marsden. Rutherford was to have a profound influence on young Geiger, sparking his interest in nuclear physics. Their relationship, which began as partners on some of Geiger's most important experiments, was lifelong and is documented in a series of letters between them.
In addition to supervising the research students working at the lab, Geiger began a series of experiments with Rutherford on radioactive emissions, based on Rutherford's detection of the emission of alpha particles from radioactive substances. Together they began researching these alpha particles, discovering among other things that two alpha particles appeared to be released when uranium disintegrated. Since alpha particles can penetrate through thin walls of solids, Rutherford and Geiger presumed that they could move straight through atoms. Geiger designed the
apparatus that they used to shoot streams of alpha particles through gold foil and onto a screen where they were observed as scintillations, or tiny flashes of light.
Manually counting the thousands of scintillations produced per minute was a laborious task. Geiger was reputedly something of a workaholic, who put in long hours recording the light flashes. David Wilson noted in Rutherford: Simple Genius that in a 1908 letter to his friend Henry A. Bumstead, Rutherford remarked, "Geiger is a goodman and work[s] like a slave… [He] is a demon at the work and could count at intervals for a whole night without disturbing his equanimity. I damned vigorously after two minutes and retired from the conflict." Geiger was challenged by the haphazardness of their methodology to invent a more precise technique. His solution was a primitive version of the "Geiger counter," the machine with which his name is most often associated. This prototype was essentially a highly sensitive electrical device designed to count alpha particle emissions.
Geiger's simple but ingenious measuring device enabled him and Rutherford to discern that alpha particles are, in fact, doubly charged nuclear particles, identical to the nucleus of helium atoms traveling at high velocity. The pair also established the basic unit of electrical charge when it is involved in electrical activity, which is equivalent to that carried by a single hydrogen atom. These results were published in two joint papers in 1908 entitled "An Electrical Method of Counting the Number of Alpha Particles" and "The Charge and Nature of the Alpha Particle."
In bombarding the gold with the alpha particles Geiger and Rutherford observed that the majority of the particles went straight through. However, they unexpectedly found that a few of the particles were deflected or scattered upon contact with the atoms in the gold, indicating that they had come into contact with a very powerful electrical field. Rutherford's description of the event as recorded by Wilson revealed its importance: "It was as though you had fired a fifteen-inch shell at a piece of tissue paper and it had bounced back and hit you." These observations were jointly published by Geiger and Marsden in an article entitled "On a Diffuse Reflection of the Alpha-Particles" for the Proceedings of the Royal Society in June of 1909.
Thirty years later Geiger recollected, "At first we could not understand this at all," Wilson noted. Geiger continued to study the scattering effect, publishing two more papers about it that year. The first, with Rutherford, was entitled "The Probability Variations in the Distribution of Alpha-Particles." The second, referring to his work with Marsden, dealt with "The Scattering of Alpha-Particles by Matter." Geiger's work with Rutherford and Marsden finally inspired Rutherford in 1910 to conclude that the atoms contained a positively charged core or nucleus which repelled the alpha particles. Wilson noted Geiger's recollection that "One day Rutherford, obviously in the best of spirits, came into my [laboratory] and told me that he now knew what the atom looked like and how to explain the large deflections of the alpha-particles. On the very same day, I began an experiment to test the relation expected by Rutherford between the number of scattered particles and the angle of scattering."
Geiger's results were accurate enough to persuade Rutherford to go public with his discovery in 1910. Nonetheless, Geiger and Marsden continued their experiments to test the theory for another year, completing them in June of 1912. Their results were published in German in Vienna in 1912 and in English in the Philosophical Magazine in April of 1913. Wilson noted that Dr. T. J. Trenn, a modern physics scholar, characterized Geiger's and Marsden's work of this period: "It was not the Geiger-Marsden scattering evidence, as such, that provided massive support for Rutherford's model of the atom. It was, rather, the constellation of evidence available gradually from the spring of 1913 and this, in turn, coupled with a growing conviction, tended to increase the significance or extrinsic value assigned to the Geiger-Marsden results beyond that which they intrinsically possessed in July 1912."
In 1912 Geiger gave his name to the Geiger-Nuttal law, which states that radioactive atoms with short half-lives emit alpha particles at high speed. He later revised it, and in 1928, a new theory by George Gamow and other physicists made it redundant. Also in 1912 Geiger returned to Germany to take up a post as director of the new Laboratory for Radioactivity at the Physikalisch-Technische Reichsanstalt in Berlin, where he invented an instrument for measuring not only alpha particles but beta rays and other types of radiation as well.
Geiger's research was broadened the following year with the arrival at the laboratory of James Chadwick and Walter Bothe, two distinguished nuclear physicists. With the latter, Geiger formed what would be a long and fruitful professional association, investigating various aspects of radioactive particles together. However, their work was interrupted by the outbreak of the First World War. Enlisted with the German troops, Geiger fought as an artillery officer opposite many of his old colleagues from Manchester including Marsden and H. G. J. Moseley from 1914 to 1918. The years spent crouching in trenches on the front lines left Geiger with painful rheumatism. With the war over, Geiger resumed his post at the Reichsanstalt, where he continued his work with Bothe. In 1920, Geiger married Elisabeth Heffter, with whom he had three sons.
Geiger moved from the Reichsanstalt in 1925 to become professor of physics at the University of Kiel. His responsibilities included teaching students and guiding a sizable research team. He also found time to develop, with Walther Mueller, the instrument with which his name is most often associated: the Geiger-Mueller counter, commonly referred to as the Geiger counter. Electrically detecting and counting alpha particles, the counter can locate a speeding particle within about one centimeter in space and to within a hundred-millionth second in time. It consists of a small metal container with an electrically insulated wire at its heart to which a potential of about 1000 volts is applied. In 1925, Geiger used his counter to confirm the Compton effect, that is, the scattering of X rays, which settled the existence of light quantum, or packets of energy.
Geiger left Kiel for the University of Tubingen in October of 1929 to serve as professor of physics and director of research at its physics institute. Installed at the Institute, Geiger worked tirelessly to increase the Geiger counter's speed and sensitivity. As a result of his efforts, he was able to discover simultaneous bursts of radiation called cosmic-ray showers, and concentrated on their study for the remainder of his career.
Geiger returned to Berlin in 1936 upon being offered the chair of physics at the Technische Hochschule. His upgrading of the counter and his work on cosmic rays continued. He was also busy leading a team of nuclear physicists researching artificial radioactivity and the byproducts of nuclear fission (the splitting of the atom's nucleus). Also in 1936 Geiger took over editorship of the journal Zeitschrift fur Physik, a post he maintained until his death. It was at this time that Geiger also made a rare excursion into politics, prompted by the rise to power in Germany of Adolf Hitler's National Socialist Party. The Nazis sought to harness physics to their ends and engage the country's scientists in work that would benefit the Third Reich. Geiger and many other prominent physicists were appalled by the specter of political interference in their work by the Nazis. Together with Werner Karl Heisenberg and Max Wien, Geiger composed a position paper representing the views of most physicists, whether theoretical, experimental, or technical. As these men were politically conservative, their decision to oppose the National Socialists was taken seriously, and seventy-five of Germany's most notable physicists put their names to the Heisenberg-Wien-Geiger Memorandum. It was presented to the Reich Education Ministry in late 1936.
The document lamented the state of physics in Germany, claiming that there were too few up-and-coming physicists and that students were shying away from the subject because of attacks on theoretical physics in the newspapers by National Socialists. Theoretical and experimental physics went hand in hand, it continued, and attacks on either branch should cease. The Memorandum seemed to put a stop to attacks on theoretical physics, in the short term at least. It also illustrated how seriously Geiger and his associates took the threat to their work from the Nazis.
Geiger continued working at the Technische Hochschule through the war, although toward the latter part he was increasingly absent, confined to bed with rheumatism. In 1938 Geiger was awarded the Hughes Medal from the Royal Academy of Science and the Dudell Medal from the London Physics Society. He had only just started to show signs of improvement in his health when his home near Babelsberg was occupied in June of 1945. Suffering badly, Geiger was forced to flee and seek refuge in Potsdam, where he died on September 24, 1945.
Further Reading
Beyerchen, Alan D., Scientists under Hitler: Politics and the Physics Community in the Third Reich, Yale University Press, 1979.
Dictionary of Scientific Biography, Volume 5, Scribner, 1972, pp. 330-333.
Williams, Trevor I., A Biographical Dictionary of Scientists, John Wiley & Sons, 1982, p. 211.
Wilson, David, Rutherford: Simple Genius, MIT Press, 1983.
"Geiger and Proportional Counters," in Nucleonics, December, 1947, pp. 69-75.
"Hughes Medal Awarded to Professor Hans Geiger," in Nature, Volume 124, 1929, p. 893.
Krebs, A. T., "Hans Geiger: Fiftieth Anniversary of the Publication of His Doctoral Thesis, 23 July 1906," in Science, Volume 124, 1956, p. 166.
"Memories of Rutherford in Manchester," in Nature, Volume 141, 1938, p. 244. □
