Principle : The forms of neutrons is a technique of analysis based on the diffraction of neutrons on the material. it is complementary to all forms of x-rays. the measurement device used is called a diffractometer. the data collected form the diffraction pattern or diffractogramme. the diffraction does not take place only on the crystalline material, we also speak of x-ray crystallography. for materials with non-crystalline, it is called diffusion. the diffraction part of the methods of elastic scattering.
the neutrons are particles that are bound in the nuclei of almost all atoms. the diffraction of neutrons requires the use of the free neutrons, which are not normally present in nature because of their short average life span of about fifteen minutes. neutrons can be produced in two source types :
- reactor, where the neutrons are produced continuously by nuclear fission of atomic nuclei of heavy (for example, 235u, or 239pu);
- source spallation, where neutrons are produced during bombardment of a target (lead liquid, for example) by protons high-energy from a particle accelerator.
the neutrons produced are slowed down in heavy water, in order to achieve a wavelength of the order of 10-10 m, which is of the same order of magnitude as the distances interatomic in solid materials. thanks to the duality wave-corpuscle of the quantum particles that are the neutrons, it is possible to use for diffraction experiments, like x-rays or electrons.