The Trinity weapon, a version of which destroyed Nagasaki on Aug. 9, 1945, used plutonium. That fuel was more far more efficient than the uranium in the bomb dropped over Hiroshima on Aug. 6, but it was thought to be less certain to work.
When TNT in the Trinity device exploded, it compressed plutonium atoms inside. This set off a non-plutonium source of neutrons that split some of the plutonium atoms, triggering a chain reaction that led to the massive explosion and now famous flash of light and mushroom cloud.
J. Robert Oppenheimer and the other physicists who assembled the bomb’s core in a ranch house on-site, using tape and plastic sheets to keep the dust out, took bets on whether this process would work. No one knew how big the explosion would be if it did happen. In the end, the blast was equivalent to about 19 kilotons of TNT going off at once, and people nearly 200 miles away felt the force or saw the flash. (An official statement released in response to many concerns stated that “a remotely located ammunitions magazine containing a considerable amount of high explosives and pyrotechnics exploded” but that “there was no loss of life or limb to anyone.”)
After rupturing, the plutonium atoms transformed into a host of radioactive elements. Some, such as a form of iodine, dissipated quickly. Those still present in the sandy soil of Trinity in significant quantities today tend to be entities that will stick around for a long time, such as cesium-137, europium-152 and europium-155. One particularly long-lived isotope has a half-life of 24,100 years.
Counting the clicks
When the teenage boy swept his Geiger counter back and forth near ground zero, the instrument showed he was getting about half a millirem of radiation per hour from these materials. That measurement squared with official readings from safety officials who regularly sweep test the site and haven’t seen much change from year to year. At that rate, a two-hour visit delivered a dose of alpha particles and gamma rays equal to about a tenth of the radiation that a person soaks up during a chest X-ray.
My own Geiger counter, a yellow metal box stuffed with Cold War-era circuits, proved to be a better conversation starter than scientific instrument. As I wiggled the knobs, the needle refused to budge. That turned out to be a good thing.
“If that needle were moving right now, we’d all be dead soon,” radiation hobbyist Jim Hill told me as I struggled to get a reading. This particular model had been designed to detect only extreme radiation, he said, such as the high levels present in the immediate aftermath of a nuclear explosion or meltdown.
Hill has a long personal history with the bomb.
When the mushroom cloud billowed up, he was 18 months old and living in Albuquerque, about 100 miles away. Army officials knocked on his family’s door and said they wanted to check on his health. Every six months afterward, all through his childhood, they showed up to check on him. He has never seen the report that he suspects the military officials were compiling on the effects of radiation on people. He said that so far he has hasn’t noticed any health problems due to the bomb.
An ant mound
Brandishing his own radiation reader, Hill led the way to a particularly hot spot: an ant mound. As he passed his baton over the pile, the instrument clicked faster; the reading jumped by about 25 percent.
Ants play a special role in research being conducted at Trinity by retired physicist Robb Hermes of Los Alamos National Laboratory, a four-to-five-hour drive away.
When Hermes first visited the site as a tourist in 2003, he noticed fragments of what looked like green glass littering the ground. It was a mineral called trinitite, formed by the blast and thus named for the site.
Taking some home would have been a federal crime — as a sign at the entrance to Trinity warns — so Hermes called up White Sands officials and requested some ant hill sand. The industrious insects travel large distances to gather mineral grains for the walls of their homes. Chances were good that some of those grains would be trinitite.
“The ants don’t care about the radiation,” said Hermes. “They just care about gathering the beads.”
Hermes doesn’t care much about the radiation, either. He grabbed a handful of nickel- and quarter-size trinitite chunks for visitors to see as he explained his work. What interests him is the spherical shape of trinitite beads he has found in the ant sand, a shape that has revealed how the beads formed during the split second after the bomb detonated.
If the waves of heat issuing forth from split atoms had seared the sand like a creme brulee, as Hermes and many others have assumed, the mineral should have formed in sheets. Spheres and bubbles of trinitite, though, suggest that the blast lifted sand into the air, melted it and then showered droplets over a wide area.
Remnants of vaporization
Poking around outside the fence a day before the masses arrived for the open house, Hermes found trinitite hurled more than mile from the blast, visible on the ground. He suspects that many of the trinitite pieces he has found contain remnants of equipment used in the test.
Dark green hues in some of the pieces may be remnants of the vaporized tower that cradled the bomb, he surmises. Other pieces stained red contain residue of the copper wires that connected the bomb to instruments in bunkers.
His ant sand, described in the Trinity brochures handed out to tourists, has also proved useful to scientists who study meteorites. Microscopic balls that have turned up at possible meteorite impact sites around the world are not trinitite beads, but they have a similar shape. They might be the remnants of a hail of space stones that pelted the planet about 13,000 years ago, bursting in midair and melting the ground like miniature nuclear warheads.
Debris hurled into the sky by those explosions might have dimmed the sun and triggered conditions similar to a nuclear winter. The timing coincides with the start of the Younger Dryas, a cold snap that lasted more than 1,000 years.
Hermes and his team of international collaborators, among them a nuclear scientist and several geologists, believe that the cold conditions were triggered when a meteorite slammed into Earth, leading to the extinction of large mammals across North America and to lean times during which hunter-gatherers turned to organized agriculture.
This theory is quite controversial; most scientists credit the sudden drop in temperature to ash belched out by volcanoes.
“The subject has become very contentious,” says Mark Boslough, a physicist at Sandia National Laboratories who studies airbursts and isn’t convinced by the evidence gathered so far. Radiocarbon dating of some of the samples suggests they are far too young to fit the theory, forming a mere hundreds of years ago.
But if Hermes and his team are right, the Trinity site may hold a significance beyond its role in the beginning of the nuclear era. It may also provide a window into understanding an important chapter in the history of humanity and the planet itself.
“The Trinity site gives us a way to study air bursts,” Hermes said. “Many impacts [thousands of years ago] could have created a situation similar to nuclear winter.”
Powell is a Washington-based freelance science reporter.