Simultaneously, this tranquil administration oversaw the rapid development of the hydrogen bomb, a weapon 1,000 times more powerful than those used to wipe out entire cities in Japan with single drops, and the exotic hardware to deliver it. Nuclear rockets capable of sending a fully equipped colony to Mars in one shot were designed. Most of the nuclear power research effort went into submarine propulsion, with civilian electrical plants a minor sub-topic. Enormous scientific and engineering development efforts, such as the nuclear-powered strategic bomber and earth-moving by atomic bombs, call into question the enthusiasm of this ten-year span. Some projects were so insanely reckless, the public perception of anything nuclear was permanently damaged.
A case in point is Castle Bravo, the code name for the first test of a practical H-bomb at Bikini Atoll in the Marshall Islands archipelago. The concept of a nuclear fusion weapon had been resoundingly confirmed on November 1, 1952, with the explosion of the Ivy Mike thermonuclear device on what used to be Elugelab Island in the adjacent Enewetak Atoll. That bomb weighed 82 tons, sat in a two-story building, and required an attached cryogenic refrigeration plant and a large Dewar flask filled with a mixture of liquefied deuterium and tritium gases. It erased Elugelab Island with an 11-megaton burst, making an impressive fireball over 3 miles wide, and the test returned a great deal of scientific data concerning pulsed fusion reactions among heavy hydrogen isotopes, but there was no way the thing could be flown over enemy territory and dropped.[59]
The Castle Bravo shot on March 1, 1954, tested a lighter, far more compact H-bomb named “Shrimp.” It used “dry fuel” or lithium deuteride as the active ingredient, and it needed no liquefied gases or the cryogenic support equipment, yet it gave the same deuterium-tritium fusion explosion in an “F-F-F” sequence: first a RACER IV plutonium implosion bomb (fission), followed by a large deuterium-tritium compression event (fusion), and finally a fast-neutron chain reaction in the uranium-238 tamper (fission). Sixty percent of the power from this and subsequent thermonuclear devices came not from the hydrogen fusion, but from the fission of the humble uranium tamper, a mechanical component with a lot of inertia intended to keep the bomb together for as long as possible while it exploded.
The tritium used in the fusion event was made during the explosion from the lithium component of the dull gray lithium deuteride powder.[60] The light isotope of natural lithium, lithium-6, captures a surplus neutron from the explosion of the RACER trigger device and immediately decays into tritium plus an alpha particle, or a helium-4. This tritium plus the deuterium nucleus in the same molecule fuse, being caught between the severe x-ray pressure front from the fission explosion and a plutonium “spark plug” in the center of the fusion component.[61]
The explosive yield of this arrangement was predicted to be 5 megatons, with no possibility of exceeding 6 megatons. It could not be as efficient as the Ivy Mike device using liquid hydrogen isotopes, because the lithium was not all lithium-6. Natural, out-of-the-ground lithium is only 7.5 percent lithium-6; the rest is lithium-7. Lithium-6 has an enormous neutron activation cross section, or probability of capturing a neutron and exploding into tritium plus helium. Lithium-7 has an insignificant cross section and would not participate. With great effort, the bomb makers were only able to enrich the natural lithium to 40 percent lithium-6, and the rest would be inert and wasted.
In the week before the Castle Bravo test, the wind was blowing consistently north. That was good. Any fallout kicked up by the explosion would be blown out over a large Pacific range, empty of islands and inhabitants. Early in the morning of the test, the wind shifted, blowing east. That was bad. From 60 to 160 miles east of ground zero were inhabited islands that could be hit with a load of radioactive debris. Delaying the detonation until the wind direction improved was debated, but the operations director vetoed it. There were too many time-dependent experiments set up, and it would cost too much to interrupt the tight schedule. The countdown continued.
The Shrimp was set up on an artificial island on the reef next to Namu Island, and at 6:45 local time it was detonated, becoming the first nuclear accident involving a weapon test. We will never know exactly how powerful the Castle Bravo was, because all the measuring equipment, close-in cameras, and recorders were blown away in the blast, but it is believed to be between 15 and 22 megatons, making it the biggest explosion ever staged by the United States, and much larger than what was planned for. In one second it made a fireball four and a half miles in diameter, visible on Kwajalein Island 250 miles away. The top of the mushroom cloud reached a diameter of 62 miles in ten minutes, expanding at a rate of four miles per minute and spreading radioactive contamination over 7,000 square miles of the Pacific Ocean. Did they do anything like that in the sixties? Not even close.
All hell broke loose. The Rongelap and Rongerik atolls had to be evacuated. Men were trapped in control and observation bunkers, sailors suffered beta burns, and fallout rained down on Navy ships in the area. The bomb had cleaned out a crater 6,500 feet in diameter. The coral in the reef was pulverized and neutron-activated to radioactivity, mixed with radioactive fission debris, and in 16 hours spread into a dense plume, 290 miles long and heading due east in the wind toward inhabited islands. Permanently installed testing facilities at the atoll were knocked down, and radioactive debris fell on Australia, India, and Japan. Circling the world on high-altitude air currents, the dust from the test was detected in England, Europe, and the United States. American citizens were alarmed when warned of milk contaminated with strontium-90, a major product of the uranium-238 fissions in the tamper.
What happened? The expectation of no action from the lithium-7 component of the lithium deuteride was incorrect. The neutron density in a thermonuclear bomb explosion is inconceivably large, and in this condition it does not really matter how small the activation cross section is. Neutrons will interact with the lithium-7, producing tritium, and helium-4, plus an extra neutron. All of the lithium deuteride was therefore useful in the explosion, and the yield was three times the expected strength. Not only was more energy released in the deuterium-tritium fusion, but the unexpected neutron excess increased the third-stage fission yield in the tamper, made of ordinary uranium. While the fusion process was considered clean, producing no radioactive waste products, the uranium-238 fission was unusually dirty.
A complicating problem was the choice of the Director of Operation Castle, Dr. Alvin C. Graves. As you recall from the previous chapter, he was standing close behind Louis Slotin when he made his fatal slip with a screwdriver and a plutonium bomb core went prompt critical. Graves caught 400 roentgens right in the face. He could have died easily from the acute exposure, but he lived on to rise in the ranks at Los Alamos.[62] Graves therefore could see no particular problem putting men close to atomic blasts in several experiments, from the Marshall Islands tests to the above-ground explosions in Nevada.[63] This peculiar tendency is similar to the case of Bill Bailey and his Radithor, noticing no ill effects from his elixir while subjecting Eben Byers to a horrible death. Both men, Graves and Bailey, endured later condemnation for exposing so many people to so much radiation.
59
Or, at least you would think that a rational military-industrial complex would have ruled it impractical. The Sandia Committee in New Mexico proposed the design of a weaponized Ivy Mike device designated TX-16/EC-16, to be carried aloft in a B-36 “Peacemaker” 10-engine strategic bomber. The “EC” in the designation referred to “emergency capability” version, meaning that it was to be used only in the dire situation of an enemy attack, which was anticipated to occur at any time. The problem with the liquid hydrogen isotopes slowly boiling off and being lost was solved by installing large Dewar flasks in the airplane with piping to replenish the cold liquid as it gassed off into the atmosphere. Only five of these monsters were built, and it was never tested. It looked as big as an Airstream house trailer, and it was named “Jughead.”
60
At 8 grams per mole, lithium-6 deuteride is the second lightest compound known to chemistry. Lithium-6 hydride is the lightest.
61
This extreme force, capable of bending atomic structure, exerted by an x-ray front is completely outside human experience. Imagine sitting in the dentist chair and being blown through the wall of the building when the technician pushes the button on his x-ray machine. There are other forces at work in an H-bomb, such as the gamma front, the neutron front, the beta front, the alpha front, and, of course, the shock wave caused by the explosion, but the x-rays are the first out of the box. The x-rays are caused by accelerating electrons originating in the loosely coupled outer orbitals of the atoms. Before the atomic nuclei have time to fully react, the electrons have been bounced and are sending off x-rays at the speed of light in an extremely dense mob.
62
Alvin C. Graves, Ph.D. physics, became head of the Test Division at the Los Alamos National Laboratory. The accident with Slotin made him temporarily sterile, and his eyesight was never the same. He appeared in the documentary motion picture
63
Subjecting soldiers and village people to radiation from above-ground nuclear weapons tests just to see what would happen was not unique to the United States. In September 1954, large-scale human response tests were performed at the Totskoye Military Range in Orenburg Oblast, Russia. In the military exercise “Light Snow,” about 45,000 Soviet soldiers and officers were exposed to the radiation from an above-ground detonation of a 30-kiloton nuclear device, dropped from a Tu-4 bomber for realistic effect. This was a complete surprise to the test subjects, who, unlike their American military counterparts, were given no protective gear or a hint as to what was going to happen. Deputy Defense Minister Georgy Zhukov observed from a safe distance in an underground bunker. The medical records of the thousands of people affected seem to have disappeared.