2012 Rutherford medal and prize

Professor Peter A Butler, University of Liverpool.

For his outstanding work in the field of experimental nuclear physics and his dynamic contributions to the future direction of the field.

Peter Butler has made an outstanding contribution to our understanding of nuclear structure, especially properties of nuclei far from the line of beta stability, elucidating many aspects of nuclear behaviour. He is most closely associated with investigations of nuclear shapes and deformations, from fission isomers to octupole deformation, where he has led some of the most important experiments on octupole deformation and reflection asymmetry. He pioneered the technique of collinear conversion-electron spectroscopy and led the construction of the SACRED system at the University of Jyväskylä, Finland. This device has proven extremely important in the study of heavy nuclei. Peter has been leading experiments over the last 25 years to study such nuclei.

Amongst many achievements, he found evidence of reflection-asymmetric intrinsic states in atomic nuclei, including pear-shapes that give rise to transitions with large electric dipole and octupole moments. The nuclei with pear-like shapes may have enhanced Schiff moments, the quantity that determines the static electric-dipole moment of the corresponding atom if time-reversal invariance is violated. He observed strongly-converted transitions between deformed excitations in the heaviest elements, up to high angular momentum. These observations confirm that the stability of transfermium nuclei, nuclei with atomic number beyond 100, is partly derived from deformation. The stability of nuclei around Nobelium-254 to rotation means that their fission barriers persist to unexpectedly high angular momentum. His team’s studies of isomers in this region are crucial for understanding the single-particle structure of super-heavy elements. 

He has been a key figure in defining the future directions of nuclear physics worldwide.