Callaghan was a New Zealand physicist whose area of study and research was in the area of nuclear magnetic resonance (NMR). This is a way of tracking molecules using radio waves. Most people are aware of the power of large MRI machines in healthcare, where signals from the magnetic fields interacting with the atoms inside the body can be used to map the inner structure of the body.
Callaghan pioneered techniques using magnetic field gradients and achieved a number of world firsts, including the imaging of the internal structure of a microporous material and the observation of the flow profile of a complex polymeric liquid during shear banding. While that sounds (and is) difficult to understand, the techniques he developed allowed for the science to explore more varied uses, for example to look at oil production, plastics production and even food products.
Dairy giant Fonterra, working with Auckland Uniservices, recently used his techniques to develop an improved form of mozzarella cheese.