Trinity test site. Image: United States Department of Energy
Scientists have discovered a quasicrystal, a bizarre form of matter that defies the normal rules of symmetry in crystals, in the debris of the first nuclear detonation in history. Forged on July 16, 1945 during the Trinity nuclear bomb test in New Mexico, the quasicrystal is the oldest known structure of its kind made by humans.The amazing find was achieved by a team co-led by Luca Bindi, chair of mineralogy and crystallography and head of the department of Earth sciences of the University of Florence. Bindi and his colleagues emphasized that the newly identified quasicrystal is the “the first to be identified in the remnants of an atomic blast” and contains “a hitherto unknown composition,” according to a study published on Monday in the Proceedings of the National Academy of Sciences.
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The researchers were “very excited” when they made the discovery, Bindi said in an email, as they were “not absolutely sure” of the outcome of their search. “This new study makes me think that quasicrystals could be much more common than thought,” he added.Quasicrystals have fascinated researchers for decades and ultimately earned materials scientist Dan Shechtman the 2011 Nobel Prize in Chemistry. While normal crystals contain atoms that are ordered in a periodic and repeating pattern, the atoms in quasicrystals do not repeat in regular patterns.
One way to picture the difference is to imagine a tiled floor: normal crystals correspond to neatly fitted tiles of just one repeating shape, such as triangles or squares, while quasicrystals are analogous to a mosaic of multiple shapes that don’t seamlessly fit together, like pentagons or octagons. This unusual structure challenges conventional models of matter and has yielded versatile applications in materials science. Many synthetic quasicrystals have been created in laboratories and these odd formations also form in nature, under cataclysmic pressures. For instance, Bindi and Paul Steinhardt, a theoretical physicist at Princeton University who co-led the new study, headed an effort that identified the first known natural quasicrystals inside the Russian Khatyrka meteorite. The crystals likely formed from the immense shock of two asteroids colliding in space.
“Our attempt to recreate the minerals observed in the meteorite by producing high pressure shocks in the laboratory (basically by firing a projectile at a high speed at a stack of materials) successfully reproduced the quasicrystals observed in the meteorite,” Bindi said. “This naturally led to the question: could there be quasicrystals lurking in remnants of other shock phenomena, such as an atomic blast?”That spark of inspiration led Bindi to the work of G. Nelson Eby, a professor of geosciences at the University of Massachusetts Lowell who co-authored the new study. Eby and his colleagues had meticulously studied a byproduct of the Trinity test known as red trinitite, an “atomic rock” of desert sand that had fused with artificial materials such as the copper wires of recording instruments.
Bindi and his colleagues obtained samples of the rock that had been originally collected from the blast site in 1945 by astronomer Lincoln LaPaz. The team examined the specimens using advanced techniques such as back-scattered scanning electron microscopy and single-crystal X-ray diffraction analysis. The results revealed “a heretofore unknown icosahedral quasicrystal,” made of elements including silicon, copper, calcium, and iron, that “has yet to be synthesized in the laboratory,” according to the study. The discovery demonstrates that this strange form of matter can be produced by nuclear explosions, a finding that delighted the team.
“All our searches together have been long shots, and this seemed like a long shot too,” Bindi said. “But we have learned over time that we pursue every idea, even if it seems like a long shot. Somehow, when it comes to quasicrystals, we win unreasonably often (for which we are grateful).”The new research suggests that quasicrystals may be hidden in many other sites that have experienced high pressure shocks, be they anthropogenic or natural. Finding more of these structures could help scientists better understand their formation and abundance, which can, in turn, lead to breakthroughs in pure science and applications for commercial materials. For instance, the special properties of quasicrystals have been used to develop non-stick coatings, optical technologies, and surgical equipment. To that end, Bindi and his colleagues hope to search for anthropogenic quasicrystals at other nuclear detonation sites, while also exploring impact craters, both on Earth and other celestial bodies, for natural versions of the structures. “I think an open-mind approach could reveal surprises,” Bindi concluded. “Great discoveries can only happen if we look at things differently.”