Explanation

The thermal neutron beam generated by the fission of an atomic nuclear reactor is elasticity or elasticity scattered with the atomic nucleus in the sample. An experimental method for studying the molecular structure and dynamic characteristics of a sample based on the angular distribution and energy changes of scattered neutron beams. The sample can be solid or liquid, and when used for structural analysis, the scattering of neutrons with the atomic nucleus of the sample is nuclear force scattering, and the neutron scattering length of the element is independent of the atomic number. The neutron scattering length of different isotopes of the same element is different, so it has a unique function in determining the atomic position of light elements (such as lithium and hydrogen), distinguishing the atomic positions of different elements with similar atomic numbers (such as iron, cobalt and nickel) and different isotopes of the same element. Neutron has a magnetic moment. In addition to nuclear force scattering, there is also magnetic scattering with the magnetic atomic nucleus in the solid, so the distribution and magnetic moment of the magnetic atoms in the solid can be determined. In addition, there are abundant long wavelength neutrons in the thermal neutron beam, and the small angle diffraction of neutrons is often used for structural analysis of macromolecule polymer and biomolecules. The energy of thermal neutrons is in the same order of magnitude as the energy of elementary excitations (such as phonon and spin wave) generated by solid or liquid dynamics. If neutrons gain or lose certain energy from inelastic scattering, they will eliminate and generate several elementary excitations in the solid or liquid at the same time. Therefore, the elementary excitation spectrum of the sample can be determined by measuring the momentum and energy changes of neutrons before and after scattering, and a certain physical model can be used, It is also possible to calculate the energy spectra and other dynamic characteristics of solids and liquids.

Classification