Cadmium cyanide is a negative thermal expansion material: it shrinks – rather than expands – when heated. We are proposing to carry out an inelastic neutron scattering experiment on the MARI spectrometer. This experiment will allow us to work out exactly how the structure of cadmium cyanide responds to temperature. We are trying to answer the question: when the material is heated, how do its atoms vibrate? Answering this will allow us to work out the mechanism responsible for its negative thermal expansion effect. This question might have been asked (and answered) many years ago, were it not for the fact that cadmium absorbs neutrons incredibly strongly. What's changed is that we now have access to a sample made from a single isotope of cadmium that is actually a good neutron scatterer, rather than a good neutron absorber.