Neutron Energy Measurement with a Crystal Spectrometer

7 NEUTRON ENERGY MEASUREMENT WITH A CRYSTAL SPECTROMETER 

The measurement of neutron energy with a crystal spectrometer is based on the same principle of Bragg diffraction as is the measurement of X-ray energy (see Sec. 12.10). 

A neutron with kinetic energy E has a de Broglie wavelength equal to 

Monoenergetic neutron sources at the energy range provided by crystal spectrometers are necessary for the study of low-energy neutron cross sections with resonances. Consider, as an example, the total neutron cross section of iridium shown in Fig. 14.20. To be able to measure the resonances of this cross section, one needs neutron energy resolution less than 0.1 eV, resolution that can be achieved only with crystal spectrometers or time-of-flight measurements (see Sec. 14.8). 

Most of the discussion presented in Sec. 12.10 for X-ray crystal spectrometers is also valid for neutron spectrometers (i.e., rocking curve, alignment, higher order reflections, types of spectrometers). There are some differences, however, which are discussed next. 

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