Neutrons are thus sensitive to light atoms in the presence of heavy ones and they are suited to application of the technique of isotopic substitution. In particular, H and D have very different scattering lengths and substitution of one for the other, contrast matching, is a powerful technique in fields such as biology and polymer chemistry. Neutrons are non-destructive and highly penetrating, so they probe the interior of bulk materials, largely independent of the surface condition. Consequently, the use of complex sample environments such as cryostats, furnaces, pressure cells etc. is routine. However, neutron scattering techniques are now developed that permit investigation of surfaces and interfaces and this is a growing field of neutron scattering research.
Neutrons are a weak probe of matter.
As a consequence, the cross-section contains terms dependent on the neutron interaction, which are known, and terms dependent on the properties of the system under investigation. This greatly facilitates the theoretical interpretation of neutron scattering data, for the experimental results thus give direct information about the microscopic properties of the system of interest.