Neutron spectrometry

Article By:

Harvey, John A. Oak Ridge National Laboratory, Oak Ridge, Tennessee.

Last reviewed:June 2020

DOI:https://doi.org/10.1036/1097-8542.451100

A generic term applied to experiments in which neutrons are used as the probe for measuring excited states of nuclides and for determining the properties of these states. The term neutron spectroscopy is also used. The strength of the interaction between a neutron and a target nuclide can vary rapidly as a function of the energy of the incident neutron, and it is different for every nuclide. At particular neutron energies the interaction strength for a specific nuclide can be very strong; these narrow energy regions of strong interactions are called resonances. The strength of the interaction, expressing the probability that an interaction of a given kind will take place, can be considered as the effective cross-sectional area presented by a nucleus to an incident neutron. This cross-sectional area is expressed in barns (1 barn = 10⁻²⁸ m²) and is represented by the symbol σ. The neutron total cross section of the nuclide ²³¹Pa from 0.01 to 10 eV is shown in Fig. 1. Even though the neutron has zero charge, neutron energies are measured in electronvolts (1 eV = 1.60 × 10⁻¹⁹ joule). Neutron spectroscopy covers the vast energy range from 10⁻³ eV to 10³ MeV.

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