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Nuclear split surprises

Physicists spot unexpected type of lopsided fission

By
3:21pm, December 2, 2010

More than seven decades after German chemists discovered nuclear fission — the splitting of an atom that is harnessed by nuclear energy and nuclear weapons — scientists still can’t describe the process in detail. A paper to appear in Physical Review Letters underscores that knowledge gap with the report of a totally unexpected type of fission in the element mercury. Instead of splitting into two equal-mass chunks as theory predicts, this bit of mercury split into uneven chunks, one lighter and one heavier than expected.

Asymmetric fission, which results in daughter fragments with different masses, has been seen before. But these earlier examples all could be easily explained. Isotopes of uranium, for instance, like to fission into one large chunk of tin-132 along with a smaller chunk. Like apartment dwellers filling each apartment in a complex, the 50 protons and 82 neutrons of tin-132 completely fill shells, or energy levels, within the nucleus

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