The Maxwell-Boltzmann distribution and Bragg scattering of thermalized neutrons; the DeBroglie relation; neutron absorption cross sections. The technique of time-of-flight spectroscopy with a mechanical beam chopper is used to study the properties of thermal neutrons in a beam emerging from the MIT research reactor.
First, the distribution in velocity of the neutrons is measured, and the results are compared with the Maxwell Boltzmann distribution for the temperature of the reactor.
Second, the DeBroglie relation between wavelength and momentum of neutrons is determined from measurements of the angle of Bragg reflection of the beam from a copper crystal as a function of the velocity measured by time-of-flight. Third, the absorption cross sections of several elements are measured, and the 1/v dependence of the boron cross section is observed.
Lab Guide (PDF)
Mechanical beam chopper. (Image courtesy of Junior Lab staff.)
References
Bragg, William H., and William L. Bragg. "Analysis of Crystal Structure by Beans of Rontgen Rays." Nobel Prize Lecture. Stockholm, Sweden, 1915.
Shull, Clifford (shared with Bertram Brockhouse). "Early Development of Neutron Scattering." Nobel Prize Lecture. Stockholm, Sweden, 1994.
Chadwick, J. "Possible Existence of a Neutron." Nature 129, no. 3252 (1932): 312.
———. "The Existence of a Neutron." Proceedings of the Royal Society of London 136, no. 830 (1932): 692-708.