Rutherford Electroscope

Physics

Accession Number: 2011.ph.577

Description:

The instrument consists of two separable black metal boxes stacked one upon the other. with an arm attached to the bottom box holding a microscope. The bottom box contains a stand with an adjustable pedestal on a plate which slides out of the box through a side door. The top box has two parallel glass windows on opposite sides and another side composed of aluminum foil. Attached to the roof of the top box is a metal rod attached to a gold leaf (missing). The rod touches a contact, which can be controlled by a lever on the top of the box. There is a copper mesh grate on the top of the bottom box.

Alternative Name:

Primary Materials: Metal, Copper alloy, Glass

Markings:

Plaque fastened to the top: “CHAS. W. COOK & SONS LTD. ENGINEERS & SCIENTIFIC APPARATUS MAKERS, 97. WALSALL ROAD. BIRMINGHAM, 22.”

Microscope reads “W. G. PYE &Co. CAMBRIDGE. ENG.”

Dimensions (cm): Height = 29, Length = 16, Width = 33

Function:

This instrument is a “Rutherford” electroscope and was likely used for measuring the intensity of radioactive substances, probably sources of weak alpha rays.

The rod protruding from the top of the top box would be charged, causing the (missing) gold leaf to move away from the rod. Radioactive material would be then inserted into the bottom box, and over time the radiation emitted would cause the gold leaf to lose its charge and drop towards the rod. The microscope is used to observe this event. The rate of fall of the the gold leaf corresponds to the intensity of the radioactive source.

Condition:

Good: Gold leaf element is missing; Minor abrasions; The foil shield has some perforations.

Associated Instruments:

Manufacturer: Chas. W. Cook & Sons Ltd.

Date of Manufacture: Early 20th Century

Provenance:

University of Toronto Physics Department.

Additional Information and References:

The University of Toronto Report of the Board of Governors for the Year Ending June 30th, 1938 ( p. 238) may indicate that this instrument was acquired in 1938 for $95.03.

For more on Rutherford’s own microscope, see:

1) McGill University, Department of Physic “Measurement Techniques”

2) W. Makower and H. Geiger. 2012. Practical Measurements in Radio-Activity.London: Longmans, Green, & Co. pp. 21-22.

Historical Notes: