‘On a diffuse reflection of the [alpha]-particles,’ pp. 495-500 in: Proceedings of the Royal Society, Series A, Vol. 82, No. 557, July 31, 1909.

London: Harrison and Sons, 1909.

First edition, journal issue in original printed wrappers, of Geiger & Marsden’s famous alpha-particle scattering experiment, which demonstrated for the first time the existence of the atomic nucleus, leading to the downfall of Thomson’s plum-pudding model of the atom, and the development of the Rutherford (or planetary) model. Rutherford's description of the atom laid the foundation for all future atomic models and the development of nuclear physics. “One of the most important experiments in physics took place in 1909 when Hans Geiger (1882-1945) and the undergraduate student Ernest Marsden (1889-1979), under the direction of Rutherford, sent alpha particles towards a very thin film of gold, and discovered that the majority of them passed through the foil without hitting anything. Only a tiny number of particles were scattered back (towards the source) after hitting the nucleus of a gold atom. The results of the experiment were analyzed by Rutherford and led to several far-reaching conclusions. The first was that most of the atom is empty! The nucleus occupies only the 10-15th part of the volume of the atom (a radius 105 times bigger than the newly found radius of the nucleus). Thus, the orbits of the outer-most electrons (which define the radius of the atom) are far away from the nucleus. The second conclusion was that the force acting between the positive charge in the nucleus and charged scattered projectiles obeys the Coulomb law” (Shaviv). Rutherford wrote: “It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you. On consideration, I realized that this scattering backward must be the result of a single collision, and when I made calculations I saw that it was impossible to get anything of that order of magnitude unless you took a system in which the greater part of the mass of the atom was concentrated in a minute nucleus. It was then that I had the idea of an atom with a minute massive center, carrying a charge”. “In many respects this picture is one of the most fundamental in physics. We note that at this time Wien's discovery of the proton had not yet been approved. The nucleus was found to contain the positive charge, but its breakdown was not clear. Note also that Rutherford got his Nobel Prize [in chemistry] before he analyzed the alpha scattering experiment and made this fantastic contribution, for which he definitely deserved the Nobel in physics” (ibid).

In the first decade of the twentieth century atoms were a reality to nearly every scientist. It was also known that they were not indivisible since, by ionization, one or more electrons could be removed from an atom. That meant that an atom contains one or more electrons … But nothing was known about their inner structure. Several models of the atom were proposed but could not be subjected to severe experimental tests. The most popular model was one by J. J. Thomson, sometimes called the plum-pudding model. It described the atom as a sphere filled out evenly with positive charge which contained the point-like electrons …

“The true structure of the atom was revealed by Rutherford and his collaborators by scattering α-particles on atoms and, in particular, by Rutherford’s theoretical analysis of the scattering process. Rutherford discovered α-scattering in 1906 when he was still in Montreal. In an evacuated tube he let a beam of collimated α particles pass through a slit and then fall onto a photo- graphic plate on which he could observe the image of the slit. When he placed a thin foil of mica between slit and plate, the image was blurred.

“In Manchester, Rutherford chose the scattering of α-particles as one of the first research subjects in his new laboratory and asked Geiger and a young research student, Marsden to study it in detail. To measure the scattering angle, i.e., the angle by which an α-particle was deviated from its original direction, instead of a photographic plate a zinc-sulphide screen was used. On it the position, where each α-particle hit the screen, could thus be observed under the microscope. It was found that the average scattering angle was small but that there were exceptions. Geiger wrote in 1910:

‘It is also of interest to refer here to experiments made by E. Marsden and myself [described in the offered paper] on the diffuse reflection of the α-particles. It was found that some of the α-particles falling upon a metal plate appear to be reflected, i.e., they are scattered to such an extent that they emerge again on the side of incidence. It was shown that from gold 1 in about 8000 of the incident α-particles suffers reflection, and that this reflection takes place within a relatively thin surface layer equivalent to about 5 mm. of air.’

“Rutherford was very much intrigued by these large scattering angles. Until then it had been thought that larger angles came about by multiple scattering off electrons while the α-particles traversed one or several atoms. But Rutherford realized that larger forces than those of a single electron were needed. He therefore assumed a large central charge within the atom. Only later he used the word nucleus. In addition to its charge the nucleus was to contain essentially the complete mass of the atom. He thought at first that the central charge must be negative so that it attracted an α particle, which could swing around it like a comet coming from far outside is swung around by the sun. But he realized that the α-particle could just as well be deflected by a large positive central charge” (Brandt, pp. 66-68).

Hans Geiger (1882-1945) studied physics at the University of Munich and served in the German military before pursuing graduate studies at Erlangen, earning his PhD in 1906 with a thesis on electrical releases through gases. He then moved to England to become a laboratory assistant in Rutherford’s laboratory at the University of Manchester. In 1909 he conducted the famous ‘gold foil experiment’ with Ernest Marsden, and in 1911 he and John Nuttall discovered the ‘Geiger-Nuttall law’ relating the rate of radioactive decay to the energy of the emitted α-particles. In 1914, Geiger returned to Germany, initially to take charge of radiation research at the National Institute for Science and Technology. After World War I, during which he served as an artillery officer, Geiger returned to research, finding a position at the University of Kiel where he collaborated with one of his doctoral students, Walther Muller, on improving his original Geiger counter device, making it more efficient, responsive, durable and portable. Unlike the earlier version, which could detect only α-particles, the new improved Geiger-Muller counter could detect many different kinds of ionizing radiation. He used the new device to confirm the existence of light quanta in 1925, and later to discover cosmic ray showers, which would claim his scientific attention for the remainder of is career. Geiger was a member of the so-called Uranium Club, a clandestine German effort to develop and produce atomic weapons after the discovery of atomic fission in 1939. The program splintered in 1942, with its scientists moving to other areas of research deemed more urgent, after it was determined (incorrectly) that nuclear fission would not play a major role in ending the war.

Born in Manchester, Ernest Marsden (1889-1970) conducted the Geiger-Marsden experiment while still an undergraduate student under Rutherford. In 1915, with Rutherford’s recommendation, he moved to Victoria University College in Wellington, New Zealand, as Professor of Physics. He spent the rest of his life in New Zealand.

DSB, V, 331; XII, 31; Brandt, The Harvest of a Century, 2009. Shaviv, The Life of Stars, 2009.

8vo (257 x 175 mm), pp. 453-533. Original printed wrappers. Very fine.

Item #3587

Price: $1,850.00

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