Boffins challenge shape of neutron neutrality

Pick a team, dammit

Neutrons. You might very well think (unless you are a physics buff, or associated geek) they are neutral, that is to say, without charge. After all, they even sound like the word neutral.

Well, yes, and no.

Back in 1947, Enrico Fermi proposed that in fact neutrons do have charge, but that it cancels out, so the overall effect is as if they have no charge at all. He suggested that a neutron carries a positive charge on the inside, offset by a negative charge on its outer envelope.

Now researchers at the University of Washington have challenged this idea, suggesting instead that the charge is negative at the core and on the edge, with a sliver of positive charge in between, balancing it all out.

"Nobody realised this was the case," said Gerald A Miller, the professor who led the research. "It is significant because it is a clear fact of nature that we didn't know before. Now we know it."

The discovery is significant because the neutron is the particle responsible for the strong force, one of four fundamental forces that are at work in our universe. It is the strongest force known in nature, and is responsible for binding atomic nuclei together, but exactly how it works is still poorly understood.

"Without the strong force you wouldn't have atoms - or anything else that follows from atoms," Miller said.

Miller's team used data from the Thomas Jefferson National Accelerator Facility in Newport News, Va., the Bates Linear Accelerator at the Massachusetts Institute of Technology, and the Mainz Microtron at Johannes Gutenberg University in Germany.

He says one of the key findings was confirmation of Fermi's idea that the neutron carries a negative charge on its outer shell. He also does not rule out a further refinement of the picture of the charge distribution, as the data is analysed further.

His analysis is published in the 13 September edition of Physical Review Letters. ®

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