Chadwick's Neutron Chamber, replica of Cavendish Lab apparatus

Chadwick's Neutron Chamber, replica of Cavendish Lab apparatus

Usage conditions apply
Chadwick's Neutron Chamber, replica of Cavendish Lab apparatus. Object ID EM.N-08022. Overall: length 15.5 cm x width 6 cm x height 14 cm.
Object consists of a brass tube. In the original apparatus, the tube contained a polonium (source of alpha particles) at one end and a berylium target.
(See 1st object on right in accompanying image).
History and basic principle
In their attempts to excite and transform atomic nuclei physicists were limited throughout the 1920s to bombarding them with the particles--chiefly alpha-particles -- spontaneously emitted by naturally radioactive substances. This was irksome to physicists, not least because of the limited supply and great expense of radium and similar substances, but also because of the limited energy and uncontrollability of these spontaneous radiations. However, the era of hamstrung nuclear physics before the advent of accelerators ended on an unexpected upbeat: the discovery of the neutron in 1932.
Object EM.N-08022 is a replica of the neutron chamber used by James Chadwick in 1932 at the Cavendish Laboratory, Cambridge University, England in his first experiments demonstrating the existence of the neutron. In his experiments, the neutron chamber served as the neutron source and was used in conjunction with a separate ionization chamber.
Rutherford had long anticipated the existence of an uncharged particle of about the mass of a proton, and members of his Cambridge research group had repeatedly sought for it. Chadwick recognized evidence of it in I. and F. Joliot-Curie’s description of phenomena resulting from the bombardment of beryllium by alpha-particles.
At one end of the chamber's brass tube, polonium emiited alpha particles, which then struck a berylium target causing particles to be emitted from the other end of the tube. The emitted particles entered an adjacent ionization chamber in which their identity could be confirmed as Rutherford's hypothesized neutron.
See: - for a brief historical account of Chadwick's career, including his association with Ernest Rutherford at the Cavendish Laboratory, as well as his experimental confirmation of Rutherford's speculation on the existence of the neutron (for which Chadwick was awarded the Nobel Prize in 1935).
Also see Chadwick's publication:
Chadwick, James, The Existence of a Neutron, Proceedings of the Royal Society, A.136(830) 692-708.
Currently not on view
Object Name
Neutron Chamber
Date made
ca. 1960 (original 1932)
University of Cambridge. Department of Physics. Cavendish Laboratory
Chadwick, James
place made
United Kingdom: England, Cambridge
Associated Place
United Kingdom: England, Cambridge
overall: 14 cm x 6 cm x 15.5 cm; 5 1/2 in x 2 3/8 in x 6 3/32 in
ID Number
catalog number
accession number
Credit Line
Cavendish Laboratory
Science & Scientific Instruments
Modern Physics
See more items in
Medicine and Science: Modern Physics
Science & Mathematics
Data Source
National Museum of American History
Nominate this object for photography.   

Our collection database is a work in progress. We may update this record based on further research and review. Learn more about our approach to sharing our collection online.

If you would like to know how you can use content on this page, see the Smithsonian's Terms of Use. If you need to request an image for publication or other use, please visit Rights and Reproductions.


Add a comment about this object