Replica of Rutherford and Geiger apparatus for determining the charge on the alph-particle, after original Cavendish Lab apparatus of 1908
date: label: date made
content: 1960
name: label: originator
content: Rutherford, Ernest
label: maker
content: University of Cambridge. Department of Physics. Cavendish Laboratory
notes: label: Description
content: Rutherford-Geiger alpha-particle charge apparatus 1908, replica of Cavendish Lab apparatus. Object ID EM.N-08019: length 13 in (33.1 cm) x width 13 1/2 in (34.2 cm) x depth 1 15/16 in (4.9 cm)
label: Description
content: This object consists of a cylindrical glass body with a tapered ground socket at each end. (Cylinder axis is vertical). On each side, at the middle of the glass cylinder, a glass tube extends out horizontally. The longer of the 2 tubes is provided with a stopcock.
label: Description
content: Into the lower ground socket of the main body is inserted a cylindrical glass vessel with a rounded bottom. A glass tube (emitter stem) extending at right angles from the inserted glass cylinder supports an axial brass rod, insulated with red wax. The end of this rod inside the vessel bears a horizontal brass ring, to which is soldered a thick wire across the diameter of the ring. At the center of this is soldered a vertical wire, at the upper end of which is a horizontal rectangular plate.
label: Description
content: Into the upper ground socket of the main body is inserted a second cylindrical glass vessel, this one bearing an axial glass tube (collector stem) through which passes an axial brass rod, insulated at each end with red wax. The lower end of this rod bears the collecting electrode, consisting of a short hollow brass cylinder with a disc of foil, possibly aluminum, across its lower end.
label: Description
content: History and basic principles
label: Description
content: In 1908 the New Zealand physicist Ernest Rutherford, working at the Cavendish Laboratory in Cambridge, England, was trying to understand the so-called “alpha particle,” one constituent of the radiation given off by radioactive substances. He had earlier shown that the alpha particle had a positive charge and was heavier than the previously known electron. Rutherford suspected that it was the same as the helium atom.
label: Description
content: To confirm this conjecture, he needed several pieces of evidence: the number of alpha particles given off in each radioactive decay, and the mass and electrical charge of the particles. Rutherford and his colleague Hans Geiger developed the apparatus shown here to collect the charge carried by the particles given off by a radioactive source in a given period of time. Separate experiments gave the rate of emission of the particles, from which the charge on a single particle could be computed.
label: Description
content: The radioactive material was mounted as a thin film on a holder set in the lower bulb. The emitted alpha particles passed upwards (the apparatus was evacuated to eliminate absorption by air) and struck an insulated collector plate, to which they transferred their charge. The plate was connected to a sensitive external electrometer that measured the charge delivered in a given time. The charge determined was close to twice the electron charge, supporting Rutherford’s hypothesis.
label: Description
content: Additional background on the replica of the Rutherford-Geiger alpha-particle charge apparatus
label: Description
content: At the beginning of the 20th century, Ernest Rutherford was studying the distinct types of radiation (alpha, beta, and gamma rays) emitted from radioactive elements. In 1908 Rutherford and Hans Geiger conducted a series of experiments to determine the charge and nature of the alpha particle. Their apparatus is described in the following reference: Ernest Rutherford, Radioactive Substances and their Radiations, Cambridge: 1913, p. 135, section 61, Fig. 28. Their original paper on these particular experiments is: “The Charge and Nature of the α-Particle” by Ernest Rutherford and Hans Geiger, Proceedings of the Royal Society A., Vol. 81, 1908, pp. 162-173. (This paper is reprinted in James Chadwick, ed., The Collected Papers of Lord Rutherford of Nelson, New York, 1963, Vol. 2, pp. 109-120)
label: Description
content: Object N-08019 was made at the Cavendish Laboratory, Cambridge, England, and is a copy of the original apparatus preserved in the Museum at the Cavendish Laboratory. See Cavendish Laboratory Museum photo at:
label: Description
content: <a href="http://www-outreach.phy.cam.ac.uk/camphy/museum/area4/images/cabinet_5.jpg" target="_blank">http://www-outreach.phy.cam.ac.uk/camphy/museum/area4/images/cabinet_5.jpg</a>
label: Description
content: While both our replica and the original at the Cavendish Laboratory Museum resemble the Rutherford-Geiger apparatus as described in Rutherford and Geiger’s publications, they nevertheless differ in several details, as described below.
label: Description
content: As described by Rutherford in the first of the above references, the apparatus had a short cylindrical central glass section with a ground joint at each end, into which fit closed-off glass pieces, one longer than the other. The apparatus was “exhausted to a charcoal vacuum” in order to avoid collisions of alpha particles with atoms in ambient air. Alpha particles emitted from a radioactive source in the lower of these end pieces passed up through aluminum foil mounted in the central section and were absorbed by a collector plate supported on insulators in the upper end piece. The current between the collector and the foil was measured with an electrometer. The rate of collection of alpha particles was calculated from the results of earlier experiments. These particular experiments yielded the charge on the alpha particle. Rutherford and Geiger found that each alpha particle carried a charge that was twice the “unit” charge (i.e., charge of hydrogen “atom”). They were thus able to infer that the alpha particle is an “atom” of helium.
label: Description
content: Our replica, object N-08019, is as described by Rutherford in the above references, except that the alpha emitter consists of a brass ring on an insulated stem, with a wire across the ring, to which is soldered an axial wire bearing a rectangular plate at its upper end. And in our replica, there is no foil diaphragm across the central section, as in Rutherford’s description. The collector in our replica matches that as described by Rutherford. Further details on the differences between the Rutherford-Geiger apparatus and object N-08019 are contained in notes in the Curator’s file for this accession. The reason for these differences is not known. One possibility is that Rutherford and Geiger modified their apparatus after carrying out the experiments described in their paper.
label: Location
content: Currently not on view
place: label: place made
content: United Kingdom: England, Cambridge
label: Associated Place
content: United Kingdom: England, Cambridge
topic: label: general subject association
content: Modern Physics
label: general subject association
content: Science & Scientific Instruments
setName: label: See more items in
content: Medicine and Science: Modern Physics
label: See more items in
content: Science & Mathematics
creditLine: label: Credit Line
content: Cavendish Laboratory
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: EM.N-08019
label: catalog number
content: N-08019
label: accession number
content: 224580
objectType: label: Object Name
content: apparatus, alpha charge
label: Object Name
content: apparatus, alpha charge (replica)
physicalDescription: label: Physical Description
content: glass; brass; aluminum; wax (overall material)
label: Measurements
content: overall: 13 in x 13 1/2 in x 1 15/16 in; 33.02 cm x 34.29 cm x 4.92125 cm
label: Measurements
content: projection stopcock tube from main axis: 6 9/16 in; 16.66875 cm
label: Measurements
content: projection of emitter stem from axis: 6 15/16 in; 17.62125 cm
label: Measurements
content: apparatus mounted on base (axis vertical): 13 in x 13 1/2 in x 4 1/16 in; 33.02 cm x 34.29 cm x 10.31875 cm