According to scientists, quasicrystals—so-called “impossible” materials with strange, non-repeating structures—have been discovered in leftovers of the world’s first nuclear bomb test.
The hitherto unknown structure, composed of iron, silicon, copper, and calcium, was most likely created by using vaporized desert sand and copper wires. Similar materials have been made in the lab and found in meteorites, but this is the first example of a quasicrystal with this mix of elements, according to a paper published in the National Academy of Sciences Proceedings on May 17.
SYMMETRIES THAT ARE IMPOSSIBLE
Quasicrystals are made up of atoms that do not repeat in a regular, brickwork-like pattern, unlike typical crystals. Whereas periodic crystal structures seem similar when rotated in specific directions, quasicrystals have symmetries that were previously thought impossible. For example, some have pentagonal symmetry and seem identical when turned by one-fifth of the whole twist.
Daniel Shechtman, a materials scientist at the Technion Israel Institute of Technology in Haifa, was the first to find such an impossible symmetry in a synthetic alloy in 1982. When rotated in each of the available orientations, it exhibited pentagonal symmetry, which would occur if its construction blocks were icosahedral—that is, it had a standard form with 20 faces. Many scientists first questioned Shechtman’s results, claiming that filling space with sole icosahedrons is mathematically impossible. Shechtman was awarded a Nobel Prize in the Chemistry in 2011 for his invention.
Around the same time and Paul Steinhardt, a theoretical physicist currently at Princeton University in New Jersey, and his partners began to speculate on the possibility of non-repeating 3D structures. These possessed the exact symmetry as an icosahedron but were made up of distinct sorts of building pieces that never repeated in the same way, explaining why symmetrical crystal mathematics had overlooked them. Roger Penrose, a mathematical physicist at University of Oxford in the United Kingdom, and other researchers had previously found identical patterns in two dimensions, known as Penrose tilings.
In 1982, Steinhardt recalled seeing the experimental data from Shechtman’s finding for the first time and comparing it to his theoretical expectations. He adds, “I got up from my desk and looked at our design, and you couldn’t tell the difference.” “So that was a very incredible moment.”
In the years after, materials scientists have created various quasicrystals, broadening the range of prohibited symmetries. Later, Steinhardt and his colleagues discovered the first naturally occurring icosahedrite in meteorite pieces retrieved on the Kamchatka Peninsula in Eastern Siberia. According to Steinhardt, this quasicrystal developed in the early Solar System when two asteroids collided. Because some of the lab-made quasicrystals were created by slamming materials together at high speeds, Steinhardt and his colleagues questioned if nuclear explosion shockwaves could make quasicrystals as well.
‘SLICING AND DICING’
Researchers discovered a wide expanse of greenish glassy material generated from the liquefaction of desert sand in the aftermath of the Trinity test—the first-ever detonation of a nuclear weapon, which took place on July 16, 1945, in New Mexico’s Alamogordo Bombing Range. Trinitite was the name given to this mineral.
The plutonium bomb had been detonated on the top of a 30-meter-high tower crammed with sensors and wires. According to Steinhardt, part of the trinitite that developed, as a result, included reddish inclusions. “It was a mix of natural materials and copper from transmission lines,” says the artist. Quasicrystals are made up of elements that would not ordinarily mix; therefore, Steinhardt and his colleagues felt red trinitite samples would be an excellent spot to hunt for them.
“We were slicing and dicing for ten months, looking at all kinds of minerals,” Steinhardt explains. “At long last, we discovered a little grain.” The quasicrystal has the same type of icosahedral symmetry as the one discovered by Shechtman.
Valeria Molinero, a theoretical chemist at University of Utah in the Salt Lake City, adds, “The preponderance of silicon in its structure is pretty distinct.” “What I find particularly interesting after numerous quasicrystals have been created in the lab,” she continues, “is that they are so infrequent in nature.” According to Steinhardt, this might be because the production of quasicrystals entails “strange combinations of components and unexpected layouts,” according to Steinhardt.
Like other known quasicrystals, the trinitite structure seems to be an alloy—a metal-like substance made up of positive ions amid a sea of electrons. According to Princeton geoscientist Lincoln Hollister, this is rare for silicon, which is generally found in rock in an oxidized state: reversing the oxidation would require extraordinary circumstances, such as the tremendous heat and pressure of a shockwave.
According to Steinhardt, quasicrystals might be exploited for nuclear forensic science, as they may expose the location of a clandestine nuclear test. Quasicrystals might also occur in other minerals formed in extreme settings, such as fulgurite, created when lightning strikes the rock, sand, or other sediments. “The quasicrystal tale will go on!” Hollister exclaims.