Halos and Dark Matter: A Recipe for Discovery
hubie writes:
"We started out looking for dark matter and we didn't find it," he said. "Instead, we found other things that have been challenging for theory to explain."
[...] In particular, the team confirmed that when an atom's core, or nucleus, is overstuffed with neutrons, it can still find a way to a more stable configuration by spitting out a proton instead.
[...] When people imagine a nucleus, many may think of a lumpy ball made up of protons and neutrons, Ayyad said. But nuclei can take on strange shapes, including what are known as halo nuclei.
Beryllium-11 is an example of a halo nuclei. It's a form, or isotope, of the element beryllium that has four protons and seven neutrons in its nucleus. It keeps 10 of those 11 nuclear particles in a tight central cluster. But one neutron floats far away from that core, loosely bound to the rest of the nucleus, kind of like the moon ringing around the Earth, Ayyad said.
[...] In 2019, the researchers launched an experiment at Canada's national particle accelerator facility, TRIUMF [...] It looked like the beryllium-11's loosely bound neutron was ejecting an electron like normal beta decay, yet the beryllium wasn't following the known decay path to boron.
The team hypothesized that the high probability of the decay could be explained if a state in boron-11 existed as a doorway to another decay, to beryllium-10 and a proton. For anyone keeping score, that meant the nucleus had once again become beryllium. Only now it had six neutrons instead of seven.
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