Read more: 鈥�Rewriting the textbooks: When science gets it wrong鈥�
We鈥檝e built the bomb. We鈥檝e built the reactors that provide us with vast amounts of low-carbon power. If that seems remarkable, it becomes all the more so when you realise that the whole enterprise of nuclear fission is based on a misunderstanding.
This much we thought we knew: when a susceptible element undergoes fission, it will split into roughly equal parts, and if it doesn鈥檛, it is down to 鈥渕agic鈥� numbers. These numbers spring from an elaborate, but slightly shaky, construction for understanding atomic nuclei. It starts off by imagining a nucleus as a . When this doesn鈥檛 quite deliver the desired results, it adds on that, like the electron shells envisaged to form an atom鈥檚 outer coat, can each hold a certain number of protons and neutrons.
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Just as an atom with a full outer electron shell is a peculiarly unreactive noble gas, an outer shell with the right number of protons and neutrons makes a nucleus magically stable. So if an atom doesn鈥檛 split in exact halves, it will preferentially split to make a magic nucleus or two.
Last year, these ideas were put to the test at ISOLDE, a facility for making rare radioactive isotopes at CERN near Geneva, Switzerland, to predict the outcome of fissioning mercury-180. Dividing mercury-180 evenly gives two zirconium-90 nuclei, which just happen to have a magic number of neutrons and an almost magic number of protons. Given all that, says of the University of Surrey in Guildford, UK, to expect exactly that outcome is 鈥渁 no-brainer鈥�.
Sadly, mercury-180 doesn鈥檛 play by the rules. It divides asymmetrically into the distinctly unmagical nuclei ruthenium-100 and krypton-80 ().
鈥淚t鈥檚 surprising that a process as basic as fission so obviously does not agree with what is expected,鈥� says Walker. The forgotten factor, the ISOLDE team proposes, is time. As a nucleus splits, it elongates and a neck appears between two lobes. Some nuclei, perhaps, simply cannot reach a symmetrical equilibrium before that neck breaks. But as for what nuclear factors determine that 鈥� there, the experts are split.
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