In the Footsteps (Part 8) August 24, 2011Posted by Lofty Ambitions in Science.
Tags: In the Footsteps, Museums & Archives, Nuclear Weapons, Radioactivity, WWII
On this date in 1945, Japanese actress Midori Naka died from radiation sickness. She had been in a building not far from the Hiroshima bomb blast on August 6. After digging herself out from the collapsed structure, she thought she had suffered no serious injury. Soon, though, she became ill with a variety of symptoms, including vomiting and bleeding. By the time she was admitted to a hospital, she was in terrible shape. Her death was the first ever recorded as “A-bomb disease.”
Only three days earlier, a Los Alamos physicist named Harry Daghlian was working alone on a criticality test. As he piled tungsten carbide bricks, a neutron counter warned that, if he added the last brick, the stack would go supercritical. When he starting pulling the brick away, he dropped it on the stack. He stopped the reaction by disassembling the pile, all the while absorbing what would be a lethal dose of radioactivity. He died twenty-five days later.
In May of the following year, a similar accident at Los Alamos killed physicist and chemist Louis Slotin. He had already been working with uranium, then plutonium, and had assembled the core for the Trinity test on July 16, 1945. On May 21, 1946, with seven others in the room (after Daghlian’s accident criticality tests were not conducted alone), Louis Slotin was placing two halves of a beryllium sphere around the same core of plutonium that had irradiated Harry Daghlian. Though a screwdriver wasn’t recommended for the task, that’s the tool Slotin was using when his hand slipped and the gap maintained by the screwdriver closed. Slotin pulled his other hand, which he felt burning, and the half-sphere it held away from the core, stopping the reaction. But the room had already been doused with a blue-colored blast of radioactivity. Slotin died nine days later, having received four times the lethal dose of radioactivity. His was the last hands-on criticality test; the task was thereafter done by remotely controlled machines.
On Friday of last week, inspectors in Japan discovered that rice is among the foods contaminated by the accident at Fukushima Daiichi, though officials assure the public the radiation levels are within safe limits. Radioactivity had already been found in beef, spinach, and green tea. In April, TEPCO warned that radioactivity levels from Fukushima Daiichi, which hasn’t stopped leaking, could eventually exceed those of Chernobyl. One study puts Chernobyl-related deaths at 985,000 worldwide, with 170,000 of those in North America. Earlier this month, TEPCO measured record-setting radiation levels, and decommissioning the nuclear power plant will take decades.
Accidents happen. We’ve written before about risk and our inability to calculate it well or to use our calculations wisely. Nuclear weaponry and nuclear power are not without risks, and we’ve known that for 66 years. Some of those accidents are called broken arrows, a term that refers to nuclear weapons accidents that don’t pose a risk of starting nuclear war.
On January 17, 1966, this type of nuclear accident occurred: a B-52 bomber carrying four Mk-28 hydrogen bombs collided with a KC-135 during mid-air refueling off the coast of Spain. The KC-135, which was full of fuel, incinerated with its four crewmen aboard. Three crew from the B-52 were killed; one of those men ejected but was unable to open his parachute. Four crew parachuted safely, one to the ground without separating from his seat and three to the ocean.
The four bombs fell, too, near a small village named Palomares. Within a day, three of the bombs were found. One was in pretty good shape, but the conventional explosives in the other two had detonated. No nuclear explosion had occurred, but radioactive material—plutonium—had caught fire and been spread by a good wind, contaminating a couple of square miles. Decades later, traces of radioactivity remain there.
After five days, the fourth bomb had not been found, so the Navy started looking for it in the Mediterranean Sea. Using a carefully mapped grid of probabilities and an eyewitness account by a local fisherman of the bomb entering the water, an 80-day underwater search turned up the fourth bomb. DSV-Alvin located the missing nuclear weapon at a depth of 2550 feet. Unfortunately, as the Navy tried to raise the bomb, it slipped away. Alvin found it again on April 2 at a depth of 2900 feet. When a torpedo recovery submersible, not Alvin, became entangled in the weapon’s parachute, the two had to be raised together by the USS Petrel.
Two of these bomb casings are now on display at the National Museum of Nuclear Science and History (whose website link we haven’t included because the site has been hacked and is currently being used to advertise pharmaceuticals). When we looked at the two casings (the casings from the two bombs that didn’t explode) and thought about what had happened in 1966, we were amazed at what good shape they were in. Their rounded tips were dented, but both otherwise looked to be fully intact. We were also taken aback by how small a powerful nuclear weapon can be. The Mk-28 is just 22 inches in diameter and between eight and about fourteen feet long, depending on the model.
Two other accidents involving the same kind of nuclear weapon occurred. On March 14, 1961, a B-52 carrying two Mk-28s crashed in California. Neither bomb detonated. In 1968, a B-52 carrying four bombs caught fire, and the crew ejected before they could land back at Thule Air Base in Greenland. The plane crashed into the ocean, breaking apart and spreading radioactive contaminants. In the nine-month cleanup, the secondary section (which contained the fusion fuel, not plutonium) for one bomb was never found. Contaminated ice and debris were shipped to the United States for storage.
The Mk-28 thermonuclear bomb was part of our NATO arsenal for about a decade, from 1962 to 1972. Production started in 1958, and about 4500 individual Mk28s were made. Depending on the model, it packed a wallop of between 70 kilotons and 1.45 megatons. (The atomic bombs used on Hiroshima and Nagasaki ranged only from 13 to 22 kilotons.) The detonation could be set for the air or the ground. The Mk-28 was retired in 1991, thereby becoming another artifact in our nuclear history. We saw two of those artifacts in Albuquerque earlier this year as we retraced footsteps in nuclear history.