| Citation | Distinguished particularly for his pioneering development of the nuclear refrigeration technique and its application to the investigation of superfluid helium-3 in the ballistic excitation regime below 200uk. Early heat capacity measurements at Oxford were follwed at Helsinki by investigations of rare earth hyperfine heat capacities as well as precision measurements of the lambda-point and phase separation anomalies in liquid helium isotopic mixtures.At Lancaster Pickett and Guenault developed a novel form of nuclear refrigeration, using finely divided copper immersed in liquid helium-3 to overcome thermal boundary reistances. This led in due course to the lowest temperatures yet achieved in pure helium-3, in isotopic solutions, and in metals. The vibrating wire viscometer was ingeniously exploited to discover new non-linear effects in superfluid helium-3 associated with the ballistic propagation of excitations, and satisfying explanations of the phenomena were devised. |