RUTHERFORD, E. (ERNEST) and T. ROYDS. - THE FINAL PROOF OF THE NATURE OF ALPHA-PARTICLES.

The Nature of the alpha Particle.

Manchester, 1909. 8vo. Contemp. full cloth. Orig. printed paper label on spine (a bit chipped). In: "Memoirs and Proceedings of the Manchester Literary & Phlosophical Society. (Manchester Memoirs.). Volume LIII. (1908-09). Entire volume offered. The volume contains 24 papers, all with seperate pagination. Rutherford's paper: pp. 1-3.

First printing of the paper which Rutherford and Royds gave the final proof that the alpha particle are atoms of helium. The present paper was read on November 3rd 1908 and published on the 19th. It was reprinted in Philosophical Magazine and that paper is dated November 13, 1908 and published February 1909.

"After nearly a decade of labor, Rutherford was finally prepared to state... what the alpha particle really was "We may conclude that an alpha-particle is a helium atom, or, to be more precise, the alpha-particle, after it has lost its positive charge, is a helium atom". In a paper together with Royds, completed in November 1908, he was even more emphatic: "We can conclude with certainty... that the alpha-particle is a helium atom... They had shown that a discharge sent through a volume in which alpha-particles from radium had been collected produced the characteristic helium spectrum !"(Pais "Inward Bound", p. 61).

"Rutherford’s early conviction that the alpha particle was a doubly charged helium atom, but he had not succeeded in proving that belief. In 1908 he and Geiger were able to fire alpha particles into an evacuated tube containing a central, charged wire and to record single events. Ionization by collision, a process studied by Rutherford’s former colleague at Cambridge, J. S. E. Townsend, caused a magnification of the single particle’s charge sufficient to give the electrometer a measurable "kick." By this means they were able to count, for the first time accurately and directly, the number of alpha particles emitted per second from a gram of radium.

This experiment enabled Rutherford and Geiger to confirm that every alpha particle causes a faint but discrete flash when it strikes a luminescent zinc sulfide screen, and thus led directly to the widespread method of scintillation counting. It was also the origin of the electrical and electronic methods of particle counting in which Geiger later pioneered. But at this time the scintillation technique, now proved reliable, was more convenient. This counting work also led Rutherford and Geiger to the most accurate value of the fundamental electric charge e before Millikan performed his oil-drop experiment. They measured the total charge from a radium source and divided it by the number of alphas counted to obtain the charge per particle. Since this figure was about twice the previous values of e. they concluded that the alpha was indeed helium with a double charge. But Rutherford still desired decisive, direct proof; and here his skilled glassblower came to his aid. Otto Baumbach in 1908 was able to construct glass tubes thin enough to be transparent to the rapidly moving alpha particles yet capable of containing a gas. Such a tube was filled with emanation and was placed within a larger tube made of thicker glass. In time, alpha particles from the decaying emanation penetrated into and were trapped in the space between inner and outer tubes: and when ROYDS SPARKED THE MATERIAL IN THIS SPACE, THEY SAW THE SPECTRUM OF HELIUM." (DSB).

The volume contains 2 other importent papers by Rutherford 1. "Some Properties of the Radium Emanations" (issued Nov. 19th, 1908) and 2. together withY. Tuomikoski "Differences in the Decay of the Radium Emanations" (issued April 7th, 1909).

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