Inscribed on an Italian family’s 15th century coat of arms and decorating an ancient Japanese shrine, the Borromean rings are symbolically potent. Remove one ring from the trio of linked circles and the other two fall apart. It’s only when all three are entwined that the structure holds. The rings have represented the concepts of unity, the Christian Holy Trinity and even certain exotic atomic nuclei.
A rare variety, or isotope, of lithium has a nucleus that is made of three conjoined parts. Lithium-11’s nucleus is separated into a main cluster of protons and neutrons flanked by two neutrons, which form a halo around the core. Remove any one piece and the trio disbands, much like the Borromean rings.
Not only that, lithium-11’s nucleus is enormous. With its wide halo, it is the same size as a lead nucleus, despite having nearly 200 fewer protons and neutrons. The discovery of lithium-11’s expansive halo in the mid-1980s shocked scientists (SN: 8/20/88, p. 124), as did its Borromean nature. “There wasn’t a prediction of this,” says nuclear theorist Filomena Nunes of Michigan State University in East Lansing. “This was one of those discoveries that was like, ‘What? What’s going on?’ ”
To read more, click here.