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ID number:  BIRRC-P0037
Institution:  Research and Cultural Collections
Named collection:  Historic Physics Collection
Artist / Maker:  The Cambridge and Paul Instrument Co. Ltd.
Title / Object name:  Cloud chamber for alpha particle tracks
Object type:  Physics instrument
Place made:  Cambridge, England
Date made:  1923
Materials:  Mainly metal
Measurements:  47 x 20 x 22 cm

The typed instruction sheets call this a “Ray Track Apparatus”. It uses a cloud chamber to reveal the tracks of alpha particles from a radioactive source. It is a commercial version of a design by Takeo Shimizu who was working under C.T.R Wilson at the Cavendish Laboratory.

The chamber is 6 cm in diameter with a glass top. The bottom face of the chamber is the top of a piston that is driven up and down by turning the handle, so that the height of the chamber is varied between 7 and 11 mm. The internal surfaces have to be treated with gelatine and the air kept moist. The radioactive source is mounted on a pin at the centre of the chamber and a beam of light shines in from one side. Each time the piston moves down the air becomes supersaturated and droplets form along the tracks of alpha particles. They are visible from above. Between cycles the ions and tracks in the chamber are swept out by a p.d of 200V applied across the chamber.”

Inscriptions / Translations:  THE CAMBRIDGE AND PAUL INSTRUMENT Co. Ltd.
Serial no. C37339

Notes:  T. Shimizu, Proceedings of the Royal Society A99 pp.425-431 (1921) A reciprocating expansion apparatus for detecting ionising rays.
T. Phillipson, Bulletin of the Scientific Instrument Society no.131, pp.35-38 (2016) Surviving apparatus showing the early development of the Cloud Chamber.

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