Trinitite

Trinitite, also known as atomsite or Alamogordo glass, is the glassy residue left on the desert floor after the plutonium-based Trinity nuclear bomb test on July 16, 1945, near Alamogordo, New Mexico. The glass is primarily made of arkosic sand composed of quartz grains and feldspar (both microcline and smaller amount of plagioclase with small amount of calcite, hornblende, and augite in a matrix of sandy clay) that was melted by the atomic blast. It was first academically described in American Mineralogist in 1948. It is usually light green, although red trinitite was also found in one section of the blast site, and rare black trinitite was also formed. It is mildly radioactive but safe to handle. Pieces of the material remain at the Trinity site as of 2018, although most of it was bulldozed and buried by the United States Atomic Energy Commission in 1953.

Formation

In 2005, it was theorized by Los Alamos National Laboratory scientist Robert E. Hermes and independent investigator William Strickfaden that much of the glass was formed by sand which was drawn up inside the fireball and then rained down in a liquid form. In a 2010 article in Geology Today, Nelson Eby of University of Massachusetts Lowell and Robert Hermes describe trinitite: Contained within the glass are melted bits of the first atomic bomb and the support structures and various radionuclides formed during the detonation. The glass itself is marvellously complex at the tens to hundreds of micrometre scale, and besides glasses of varying composition, also contains unmelted quartz grains. Air transport of the melted material led to the formation of spheres and dumbbell-shaped glass particles. Similar glasses are formed during all ground-level nuclear detonations and contain forensic information that can be used to identify the atomic device. This was supported by a 2011 study based on nuclear imaging and spectrometric techniques. Dark green, grey, and black trinitite is theorised by researchers to contain varying concentrations of material from the bomb's steel support structure, while red trinitite contains material originating from copper electrical wiring. An estimated 4,300 gigajoules (4.3×1019 erg) of heat energy went into forming the glass. As the temperature required to melt the sand into the observed glass form was about 1,470 °C (2,680 °F), this was estimated to have been the minimum temperature the sand was exposed to. Material within the blast fireball was superheated for an estimated 2–3 seconds before solidification. Relatively volatile elements such as zinc are found in decreasing quantities the closer the trinitite was formed to the centre of the blast. The higher the temperature, the more these volatile elements evaporated and were not captured as the material solidified. The detonation left large quantities of trinitite scattered around the crater, with Time writing in September 1945 that the site took the appearance of "[a] lake of green jade," while "[t]he glass takes strange shapes—lopsided marbles, knobbly sheets a quarter-inch thick, broken, thin-walled bubbles, green, wormlike forms." The presence of rounded, beadlike forms suggests that some material melted after being thrown into the air and landed already formed, rather than remaining at ground level and being melted there. Other trinitite, which formed on the ground, contains inclusions of infused sand. This trinitite cooled rapidly on its upper surface, while the lower surface was superheated.

Composition

The chaotic nature of trinitite's formation has led to variations in both its structure and composition. The glass has been described as "a layer 1 to 2 centimeters thick, with the upper surface marked by a very thin sprinkling of dust which fell upon it while it was still molten. At the bottom is a thicker film of partially fused material, which grades into the soil from which it was derived. The color of the glass is a pale bottle green, and the material is extremely vesicular with the size of the bubbles ranging to nearly the full thickness of the specimen." The most common form of trinitite is green fragments of 1–3 cm thick, smooth on one side and rough on the other; this is the trinitite that cooled after landing still-molten on the desert floor. Around 30% of trinitite is void space, though their porosity varies widely between samples. Trinitite exhibits various other defects such as cracks. In trinitite that cooled after landing, the smooth upper surface contains large numbers of small vesicles, while the lower rough layer has lower vesicle density but larger vesicles. It is primarily alkaline. One of the more unusual isotopes found in trinitite is a barium neutron activation product, the barium in the Trinity device coming from the slow explosive lens employed in the device, known as Baratol. Quartz is the only surviving mineral in most trinitite. Trinitite no longer contains sufficient radiation to be harmful unless swallowed. It still contains the radionuclides 241Am, 137Cs and 152Eu owing to the Trinity test using a plutonium bomb.

Variations There are two forms of trinitite glass with differing refraction indices. The lower-index glass is composed largely of silicon dioxide, while the higher-index glass has a mixed composition. Red trinitite exists in both variants and contains glass rich in copper, iron, and lead as well as metallic globules. Black trinitite's colour is a result of being rich in iron. In a study published in 2021 a sample of red trinitite was found to contain a previously undiscovered complex quasicrystal, the oldest known manmade quasicrystal, with a symmetry group in the shape of an icosahedron. It is composed of iron, silicon, copper and calcium. The quasicrystal's structure displays fivefold rotational symmetry. The quasicrystal research was led by geologist Luca Bindi of the University of Florence and Paul Steinhardt, after he theorised red trinitite was likely to contain quasicrystals as they often contain elements that rarely combine. The structure has a formula of Si61Cu30Ca7Fe2. A single 10μm grain was detected after ten months of work examining six small samples of red trinitite.

Nuclear forensics

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