Mark Megahan
Physicists claim there are some peculiar fruits on the atomic vine and their new FRIB particle accelerator will blast them into a magnetic jar for a more intense study than ever before. We all know that stars make the basic elements up to iron but where do the rest of the periodic table’s elements come from? The answer may lie with a symbol once used as a family crest.
The atomic House of Borromeo
When the Borromeo family adopted the three rings which only remain linked when all are together, as their family crest, they had no idea it was a concept which would drive atomic physicists bananas centuries later. The potent symbol is a master key to the secret of Lithium-11’s nucleus. Atoms come in different configurations based on the number of neutrons packed into their nucleus. For instance, most of the lithium atoms here on planet Earth have 7 neutrons, making them billiard table steady, while others have 11 neutrons. Those are unstable as a rap band.
That particular atomic flavor of lithium gives physicists mental problems because the nucleus “is separated into a main cluster of protons and neutrons flanked by two neutrons, which form a halo around the core.” Just like Borromean rings, “remove any one piece and the trio disbands.”
Those extra two neutrons make the atomic nucleus swell up like it was stung by bees. “With its wide halo, it is the same size as a lead nucleus, despite having nearly 200 fewer protons and neutrons.” There “wasn’t a prediction of this,” theorist Filomena Nunes explains.
“This was one of those discoveries that was like, ‘What? What’s going on?'” Lithium-11 is just one example of what happens when nuclei get weird she notes. There are a whole class of nuclei which “have properties that are mind-blowing.” They “can become distorted into unusual shapes, such as a pear. Or they can be sheathed in a skin of neutrons — like a peel on an inedible nuclear fruit.”
They have a brand new peeler which will “soon help scientists pluck these peculiar fruits from the atomic vine.” At Michigan State they built the Facility for Rare Isotope Beams. FRIB, which they pronounce “eff-rib.” It’s a blast to work with.
After stripping off the useless electrons to create ions, FRIB flings them around a paper-clip shaped track until they reach the speed of light, then smash them into a block of carbon. The groovy part is what happens next.
The neutron drip line
There are only so many marbles that can fit in a jar before they start to roll on the floor. It works that way with neutrons in an atomic nucleus. Things get freaky at the borderline where one more neutron is one too many. They like to call that “the neutron drip line.” FRIB lets them “have a new look into an unexplored territory,” says nuclear physicist Brad Sherrill.”
After the big slam into the graphite target, the “hard hit knocks protons and neutrons off the nuclei of the incoming ions, forming new, rarer isotopes. Then, the specific one that a scientist wants to study is separated from the riffraff by magnets that redirect particles based on their mass and electric charge.”
After that, the atomic particles of interest are then sent to the experimental area, where scientists can use various detectors to study how the particles decay, measure their properties or determine what reactions they undergo. It isn’t as large or powerful as the Large Hadron Collider at CERN near Geneva but it doesn’t need to be.
“FRIB will be able to slam 50 trillion uranium ions per second into its target. As a result, it will produce more intense streams of rare isotopes than its predecessors.” According to Dr. Nunes, “you can’t have a shower if it’s just trickling. FRIB is going to come in with a fire hose.” FRIB is “expected to determine the neutron drip line up to the 30th element, zinc, and maybe even farther.”
“That’s right out at the limits of existence,” Dr. Heather Crawford explains. “Out there, theories that predict the properties of nuclei are no longer reliable. Theoretical physicists can’t always be sure what size and shape a given nucleus in this realm might be, or even whether it qualifies as a bound nucleus.” One helpful factor is that the “spacing of these energy levels acts as a kind of fingerprint of an atomic nucleus, one that’s highly sensitive to the details of the nucleus’ shape and other properties.”
They’re trying to solve one of the biggest mysteries in the universe “As large stars age, they fuse progressively larger atomic nuclei together in their cores, creating elements farther along the periodic table — oxygen, carbon, neon and others. But the process halts at iron. The rest of the elements must be born another way.” Not all have been explained by neutron stars or magnetars.
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