Unexpected result challenges nuclear fission thinking

Dr Andrei Andreyev
(Credit: University of the West of Scotland)

Assumptions about the outcome of nuclear fission reactions have been overturned by recent research which is set to continue thanks to an STFC Nuclear Physics Standard Grant.

For more than 70 years, since the discovery of fission, scientists have been attempting to identify the energy threshold at which the heavy nucleus divides into two fragments and to establish what shape changes take place as the single nucleus becomes two separate daughter nuclei. Assumptions were made that the two daughter nuclei would either have equal mass (symmetric fission), or form unstable isotopes of different sizes (asymmetric fission). A recent paper in Physical Review Letters compared theoretical results with experimental data and made an unexpected discovery for an isotope of mercury.

Dr Andrei Andreyev of the University of the West of Scotland led a multinational team using the ISOLDE beam facility at CERN (link opens in a new window). Before the study it was commonly expected that mercury-180 would split symmetrically, but the experimental data showed that it split asymmetrically into ruthenium-100 and krypton-80 – both are unstable isotopes. The results challenge current thinking.

Dr Andreyev then compared his results with those of theoretician, Peter Möller. Back in 2001, Dr Möller and colleagues at Los Alamos National Laboratory and Japan Atomic Energy Research Institute calculated the fission properties of more than 5000 heavy nuclei. Dr Möller’s results predicted that that the division of mercury-180 would be asymmetric, and the fragments would have masses of 108 and 72.

Dr Andreyev said "Whilst the theoretical results and experimental data do not correlate fully, the theoretical model did predict an asymmetric outcome. Our results demonstrate how important experimental data is when refining nuclear models."

Data from this on-going nuclear fission research will improve the control programmes that run nuclear power stations, making the reactors safer. Dr Andreyev has been awarded an STFC grant to continue his experimental work.

Page last updated: 20 December 2010 by Stephanie Hills