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38. Neutron Physics

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.

Download Getting Started in iLabs (PDF)

Download Lab Guide in PDF format

Guidelines (certificates required)

  1. Instructions for Taking Web-Based General Employee Radiological Training. (2005)
  2. iLab web page on remote operation of the experiment. (html)
    Written with the Nuclear Engineering Department in mind, this site contains much useful information.
  3. Notes on the analysis of time-of-flight data. (pdf)
  4. Properties of the neutron chopper wheel. (pdf)

References (certificates required)

  1. W.H. Bragg and W.L. Bragg, Nobel Prize Lecture "Analysis of Crystal Structure by Beams of Rontgen Rays," (1915).
  2. C. Shull (shared with B. Brockhouse), Nobel Prize Lecture "Early Development of Neutron Scattering," (1994).
  3. Chadwick, J., "Possible Existence of a Neutron", Nature, Page 245, February 27,
    1932
  4. Chadwidk, J., "The Existence of a Neutron", Proc. Roy. Sci. Vol. 136, No. 830, pp. 692-702, June 1 1932

Selected Resources

  1. Cross Sections of various detector materials
  2. Description of the MITR-II Research Reactor
  3. CYLINDRICAL BF3 NEUTRON DETECTOR specifications (LND #20135)
  4. CYLINDRICAL BF3 NEUTRON DETECTOR specifications (LND #20127)
  5. CYLINDRICAL He3 NEUTRON DETECTOR specifications (LND #25143)
  6. TGM Neutron Detectors - Background and Specifications (4-pages)
  7. Laser Diode Isolator
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