Examining the exotic

Nuclear physics is at the heart of all science. “The atomic nucleus is responsible for more than 99.9% of the mass of all the matter we can see,” said Professor Paddy Regan from the University of Surrey. “100 years after the experimental verification of the nucleus and we are still uncovering its mysteries.”

The atomic nucleus at the centre of an atom contains combinations of neutrons and protons. The discovery of different isotopes of specific elements – atoms of the same element but with differing numbers of neutrons – has transformed a range of scientific disciplines. For instance, a radioactively unstable isotope of carbon, Carbon-14, is routinely used for dating archaeological biological remains. “There are fewer than 300 stable isotopes that make up the material of everyday life but closer to 7,000 possible radioactive combinations of nuclei that can exist,” Professor Regan said. “The science behind radioactive beam physics is to chart and study these, effectively to complete a nuclear ‘genome’ project where each form of nuclear excitation and decay is noted and registered.”

Physicists create and study exotic nuclei with highly unusual ratios of protons and neutrons to learn more about our universe and the fundamental forces that hold the nucleus together. They want to know which nuclei can exist and why, and how heavier elements were originally created. In the process, the science produces instruments and techniques that can be applied to a wide range of other areas including energy generation, medical diagnosis and treatment, the study of evolution and human anthropology. Exotic nuclei often only exist for fractions of a second before they decay but their existence and internal structure can be studied using a gamma-ray spectrometer called RISING (Rare Isotopes Spectroscopic INvestigation at GSI).

Designed and built by Daresbury Laboratory and the University of Liverpool, RISING is based at the GSI Helmholtz Centre for Heavy Ion Research in Germany. It is the most powerful instrument of its kind in the world and UK scientists played leading roles in two recent experiments to study the most exotic forms of the elements cadmium and platinum. “The first aim was to prove that such exotic forms of cadmium and platinum existed at all and could be synthesised,” said RISING collaboration spokesperson Professor Regan. “The second was to use RISING as a microscope to see the internal nuclear structure of these new, exotic isotopes.”

“These experiments allow us to detail and revise our understanding of the quantum shell structure in the atomic nucleus,” he added, “and further our understanding of the fundamental forces which govern how protons and neutrons form nuclei. This research will also help explain the creation of more than half of the elements heavier than iron via the rapid neutron capture process in exploding stars.” The University of Surrey team led four of the main RISING experiments, paving the way for further UK science programmes at the future international FAIR accelerator (Facility for Antiproton and Ion Research) on the GSI site in Germany. The UK will play a significant role in this growing area of atomic science through a collaboration called NuSTAR (Nuclear Structure Astrophysics and Reactions).

Nuclear physics research information

• Nuclear physics research is applied to energy generation, medical imaging and treatment, cosmology, geology, industrial processing, remote sensing and the study of human evolution and anthropology
• The GSI accelerator centre, where the UK-designed and built instrument RISING is based, has also been used for new treatments of inoperable cancers
• STFC is contributing to experiments at NuSTAR involving 9 UK institutions Professors Jim Al-Khalili and Paddy Regan of the University of Surrey regularly communicate nuclear physics to the public through festivals, talks and the media The UK will also participate in the PANDA experiment at FAIR