The properties of materials are determined by how they work at the microscopic, atomic level.
Understanding how atoms behave helps us to explain things such as why some materials conduct electricity and others don’t; why some are magnetic and others are not; why some are hard, some soft, and so on.
But it’s very hard to see atoms directly. One way to find out where atoms are and what they are doing is to use neutron scattering. Another way to find out about materials on an atomic level is to implant particles called muons into the material.