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Unraveling the Secrets of the Atomic Rock

Professor Studies Material From World’s First Nuclear Blast

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Prof. Nelson Eby poses next to the stone obelisk marking ground zero, the exact spot near Alamogordo, N.M., where the first atomic device was tested 68 years ago, on July 16, 1945.

By Edwin L. Aguirre

Tucked away in a corner amid stacks of books and papers in Prof. Nelson Eby’s office in Olney Hall is a box containing small shards of dark, greenish glass.

“They are called trinitite,” says Eby. “And after nearly 70 years, they are still very mildly radioactive.”

Eby, who chairs the Environmental, Earth and Atmospheric Science Department, collected the rock samples in April at the Trinity Site near Alamogordo, N.M., in what is now known as the White Sands Missile Range.

This site marks ground zero, the precise spot where the first atomic device was tested on July 16, 1945. The test went off as planned, with the plutonium device producing a blast equivalent to 21,000 tons of high explosives. Heat from the resulting fireball, which was hotter than the surface of the sun, instantly vaporized the steel tower supporting the device. It also caused the surrounding desert sand to melt into a thin layer of green, glassy material, which was later called trinitite in honor of the test site.

The successful denotation of the prototype bomb was the culmination of the U.S. government’s super-secret Manhattan Project, which paved the way for a new breed of weapons that were subsequently used against the Japanese cities of Hiroshima and Nagasaki. Military planners believed these weapons would bring World War II to a quick end, saving the lives of thousands of American troops.

From Tektites to Suitcase Bombs

Eby, together with researchers from Los Alamos National Laboratory and the University of Oxford in the U.K. as well as a mineralogist from Roxbury, Conn., analyzed the trinitite samples from a geological perspective, studying their chemical composition and morphology using scanning electron-microscopy, X-ray diffraction and neutron-activation analysis. Their findings were published in “Geology Today” in 2010.

“Contained within the glass are fused and melted fragments of the bomb and its support structures as well as various radionuclides formed during the explosion,” notes Eby. “The glass itself is marvelously complex at the tens to hundreds of micrometer scale.”

The sand at Trinity Site is composed of quartz, microcline, albite, muscovite, actinolite and calcite.

“Only quartz is found in trinitite,” says Eby. “All the other minerals had been melted.”

Eby likens the trinitites to tektites, which are dense, mostly black molten glass created by meteorite impacts.

“They are similar beasts,” explains Eby. “Like tektites, molten blobs of trinitite were transported downwind by the fireball, forming tiny beads and dumbbell-shaped particles that subsequently rained down onto the ground over a fairly wide area.” 

Shortly after the test in 1945, the Army removed most of the trinitite and buried it.

Eby says the radioactive elements distributed throughout the glasses can tell us exactly what happened during the atomic blast, data that is very helpful in the field of nuclear forensics.

“In any ground-level nuclear explosion, similar glasses will be formed,” he says. “Hence, we can use the chemistry and radioactivity of these glasses to gather information about the atomic device that was detonated, including the type of fission material used and its explosive power and, perhaps, pinpoint the bomb’s origin.”

Such forensic technique is useful especially in the face of growing terrorist threats from so-called “suitcase” bombs.