When the United States tested nuclear weapons on home turf in the 1950s, it wasn't exactly a top secret operation. In fact, word of the impending test was often listed in newspapers and discussed on the radio. Among the 30,000 residents of the growing little city of Las Vegas, news of an impending test drew the curious up onto their roofs. From there they could look across the sixty miles of desert that separated the town from the buildings, bunkers, towers, and huge expanses of impressively barren ground that made up the Nevada Test Site. Even at such a distance, the blasts were sometimes astonishingly bright, and since several were held in the hours right before dawn, more than one witness was quick to compare the momentary glare of the expanding fireballs to the glow of the rising sun (though the test site was west of Las Vegas, so it would have been a bit hard to actually get the two mixed up). A few seconds after the flare of light, a shivering rumble would pass through the ground. Residents were able to make a fair assessment of the relative strength of the weapons being tested by the way in which their household goods were rattled. They got plenty of practice.
Even in 1951, the first year the United States made use of the Nevada Test Site for nuclear weapons, the place was kept extremely busy with an even dozen explosions. Starting at the end of January, five bombs were dropped in a period of just ten days. All of the bombs were exploded in open air, and the largest was a good 25% larger than the weapon that had leveled central Hiroshima. Some observers, unsatisfied with the rooftop view, drove out of town and climbed up into the mountains for a clearer look. 6,500 Army troops, who were marshaled in the desert to conduct maneuvers while observing the blast, got an even better look. By all accounts, it was quite a show.
Other than the Trinity blast conducted during the war, these were the first nuclear explosions to be carried out in the United States. Previous tests had mostly taken place in the form of blowing the hell out of leftover World War II ships at rather obscure (at least to Americans) sites in the Pacific. Targets of these blasts included the German heavy cruiser, Prinz Eugen, which had fought alongside the Bismark, the aircraft carrier USS Saratoga which had served as the flagship for the Guadalcanal assault, and the battleship USS Nevada.
Nevada had already survived a direct hit from a torpedo and at least six bomb strikes during the Japanese raid on Pearl Harbor. She was the only battleship to get underway during the attack, causing one observer to declare the ship "the only bright spot" in an otherwise dismal morning. It sometimes seemed that the ship was everywhere in the war from the D-Day invasion of Normandy, to the assault on Iwo Jima. However, in 1946 the aging ship was painted rusty red to make it more visible against the sea, and set up as a bomb target off Bikini Atoll, a ring of tiny coral islets near the northwest edge of the Marshall Islands. USS Nevada was placed at ground zero for the first test, but the bomber wasn't perfectly accurate and the ship survived in good order. She was then dragged into place for as second test, and this time ended up only 615 yards from a 23 kiloton explosion. Nevada survived that blast, as well. Several other ships were sunk, even though they were positioned much farther from the blast.
Afterwards, the ship was towed back to Pearl Harbor, examined, and used for gunnery practice by the newer battleship, USS Iowa. The Nevada still would not go down. Finally a large aerial torpedo was dropped into the center of the hull, and USS Nevada sank into the waters south of Pearl in July of 1948. One tough ship.
Also towed to Bikini Atoll for the tests was the Japanese battleship Nagato. Nagato had been the flagship of Admiral Yamamoto, and it was from her decks he had conducted and observed the attack on Pearl Harbor. Planners took special care with Nagato. Special care consisted of placing the ship near ground zero. She sank immediately, which made for excellent and satisfying newsreel footage.
Additional blasts had been planned for Bikini, but one of the tests there was in the form of using an atomic bomb as a kind of very large depth charge. As it turned out, exploding a nuclear weapon underwater not only gave rise to so many odd effects that scientists were kept busy for weeks just pinning names on the assorted strangeness, it also caused most of the radioactive products that would otherwise have dispersed into the air to stay close at hand. The high levels of radiation would eventually force the testers to declare victory and move on to bombing Enewetak Atoll instead (though they'd get back to Bikini within a decade and eventually drop more than twenty bombs, totaling over 75 megatons, on the unlucky islands).
With all this excitement offshore, it was no surprise that the movement of US tests into the Nevada desert was big news, especially since a year earlier the Soviet Union had successfully exploded its own nuclear weapon. Following the Soviet bomb, the United States had begun stockpiling nuclear weapons as fast as they could be built, but at this stage each bomb was essentially unique. The Cold War was on, the threat of commies was everywhere, and testing a few bombs to see if this growing stash would actually work seemed like a pretty fair idea at the time.
After a break (during which the first thermonuclear weapon was tested in the Marshall Islands) explosions in Nevada resumed for the fall season. Las Vegas observers were once again ready for the flash and rumble, but on the morning of October 22, 1951 those peering off to the northwest in expectation of an announced blast saw... nothing. Some observers watching from closer vantage points in the mountains reported a brief flicker of light, but there was no massive fireball. No shaking of the ground. After awhile, the people climbed down off their roofs and went inside.
This test, test Able of Operation Buster-Jangle, was the sixteenth nuclear test conducted by the United States and it achieved something unprecedented. It was the first atomic weapon we ever triggered – so far as we're aware, the first such weapon that anyone tried to set off – that failed.
The device wasn't a complete dud. For one thing the bomb contained a good deal of convention high explosives, which went off just fine. It was the sphere of plutonium at the center of the bomb that failed to provide the expected bang. Plutonium weapons are constructed in a manner reminiscent of a evil Tootsie-Pop, where the crunchy shell consists of explosives, timers, and wiring while the not-so-chewy center is a hollow sphere of plutonium. What should happen is that the explosive force presses inward on the plutonium from all sides, momentarily increasing the density, and driving the sphere to become "supercritical." At that point a gram or so of matter is converted into energy, and if you'll remember that the 'C' part of E=MC^2 represents the speed of light, it's not surprising that the amount of energy obtained from a small amount of matter is rather a lot.
But in the case of the Buster-Able bomb, something didn't go quite right and the device produce only a partial, relatively weak moment of atomic fission in which the explosive force generated from the reaction was actually less than that of the conventional explosives used. The bomb was a "fizzle," a nuclear blast that failed to produce the expected level of destruction, but which nonetheless kicked out a nice burst of radiation.
The reason that the device failed could have been something as simple as a failure of one of the timers on the explosive shell. If all the explosives didn't fire essentially at once, then the pressure applied to the core would be uneven. But the most likely reason that Buster-Able failed to reach criticality is even simpler: it didn't have enough plutonium.
Getting enough plutonium or enriched uranium to create bombs was always the big challenge, and as the United States scrambled to produce more weapons it was anxious to get more bang for the processing buck. Weapons were designed to "do more with less" by extracting a larger explosion from a smaller lump of nuclear material. There was also a desire to come up with a "baby nuke," a tactical weapon that could be used on the battlefield. The original "Fat Man" plutonium bomb dropped over Nagasaki weighed more than 10,000 pounds – not exactly handy pocket size.
Eventually the US would produce a bomb small enough to be "man portable," with a weight below 50 pounds. There was even a special recoilless rifle created to fire these nuclear "rounds" as if they were oversized bullets. The launcher was capable of firing the round over a mile, which was a good thing. Even though the smallest of these rounds produced an explosion equivalent to only around 10 tons of dynamite (less than 1/1000 the power of the bombs dropped on Japan) the radiation from the resulting blast was almost certainly fatal in a radius of a quarter mile.
Whether through simple stinginess or in pursuit of reduced size, the effect of making do with a smaller core is the same. As the lump of plutonium was reduced, the rest of the device had to get better, with improved precision of the conventional explosives and improvements to design. The device tested on October 22, 1951 flunked. Most likely this device was designed by Ted Taylor, who designed not only many of the smallest weapons in the nuclear arsenal but also the largest fission weapon ever tested (he was also part of the team for Project Orion, a secret effort to create a spaceship the size of an skyscraper that was propelled through the release of a stream of small nuclear bombs). It was only after years of working on bomb designs that the lesson of Buster-Able came home to Taylor.
The conceptual work behind the development of atomic weapons required rare genius and insight into the implications of experimental results combined with theoretical models that were very new at the time. The Manhattan Project was a massive effort harnessing enormous resources from the government and some of the best minds of the century. Delivering those first bombs to Japan – whether you look on it as an unnecessary horror that took tens of thousands of lives, or as a necessary horror that took tens of thousands of lives – required a supreme effort of both engineering and logistical genius.
What Taylor eventually realized was that none of that remained true. The biggest breakthrough in building a nuclear weapon? Knowing it could be done. Having obtained some (though far from all) details of the Fat Man device through spies, the Soviets were able to duplicate the weapon with a fraction of the effort the United States had put into it. And Fat Man was the difficult version. The other bomb America dropped on Japan (code name: Little Boy) was a uranium weapon based on the "gun" design. Basically, the weapon contained two lumps of uranium. When triggered it brought these two lumps quickly together. There are niceties, such as adding mumble-mumblium as an initiator and using a mumble-mumblium case, but really that's all it took. If you weren't concerned about portability, precision, or engineering elegance, you could make an atomic bomb starting with some enhanced uranium, a length of pipe, and enough explosive to fling one piece at the other. How simple is a uranium bomb? So simple that we didn't bother to test one before dropping the first such weapon on Hiroshima.
If someone was making a nuclear weapon and wanted to use the bare minimum of material, they have to be pretty good. If they have enough material to get sloppy, then even a bad design is likely to work. With excess plutonium or enriched uranium, the worst you would get from a design made by people with even a modicum of understanding would still be worth noticing. And that pretty well describes what happened with the first explosion in North Korea. On October 9, 2006 North Korea conducted its first test of a nuclear weapon. It had handily announced the test to the world six days in advance, which was good, because otherwise there's some chance we would have missed it. The yield of North Korea's bomb was something less than one kiloton. Exactly how much less isn't clear. It's certainly possible to design a bomb for a yield of that size, as both the US and the Soviets demonstrated several times. However, the size of the North Korean explosion was much smaller than the initial explosions from other countries joining the nuclear club. The device exploded by India was of very simple design, but yielded 12 kilotons. Trying to build a nuclear device designed to produce less than one kiloton as a first effort, would be like starting your diving career by doing a triple somersault – with a double twist.
Instead of intentionally building a small device, it's much more likely that the North Koreans intended to explode a weapon with considerably more force. Only it fizzled. Because their bomb didn't contain just the bare minimum amount of plutonium even a fizzle resulted in a far from insignificant explosion. North Korea announced that they were going to conduct additional tests right away, but actually three years passed before they tested a second device in May of 2009. This time the yield was considerably greater – probably somewhere between one kiloton and five kilotons. And even that was probably another fizzle, with a yield far below expectations.
But what Ted Taylor had learned was: it didn't matter. Even the worst nuclear bomb was still a horrifying weapon. You don't need good design. You don't need a crowd of geniuses, or even a roomful of geniuses, or even one. In fact, you don't even need a bomb.
In 1945, the United States produced a plutonium sphere that was intended for the core of a Fat Man style bomb. About the size of a volleyball, the sphere was absolutely unremarkable in appearance – and incredibly dangerous. On August 21, 1945 physicist Harry Daghlian was conducting a test on the number of neutrons produced by the core, a test that involved surrounding the core with a loose enclose of reflective bricks. While moving the bricks around, Daghlian dropped one onto the core. It wasn't the kind of calculated compression that it took to set off a nuclear blast. It was enough to cause the core to produce an extreme burst of neutrons. Three weeks later, Harry Daghlin was dead from severe radiation sickness. Nine months after that, this same plutonium sphere was still sitting in its box at Los Alamos when physicist Louis Slotin decided to conduct another experiment. He put the plutonium ball into a beryllium bowl, then slowly lowered another bowl over the top. Beryllium reflects neutrons, and if Slotin allowed the two half-spheres to close completely around the plutonium, he knew it would become critical. So he kept the bowls apart – just apart – using the flat blade at the tip of a screwdriver. Doing so allowed measurements of the activity at a just sub-critical state. Slotin had performed this little show several times before, even though others (including Enrico Fermi) had warned him that it was a foolish risk. He should have listened. On that day, the screwdriver slipped, and in the moment before he could fling the top cover away, Slotin was washed by a warm blue light. Nine days later, Slotin died from severe radiation poisoning. Another scientist in the room at the time made it a decade before succumbing to leukemia.
What Slotin did was amazingly dangerous, but even though moving quickly to remove the top half of the beryllium cover did nothing to save his own life, it likely saved the lives of many others at the lab. Maybe everyone at the lab. The behavior of the core if it had remained covered is difficult to predict, but it had certainly gone critical the moment the halves of the cover met, and would have sleeted hard radiation for as long as the chain reaction continued. Considering the size of the core, it might even had produced a limited explosion. And that sphere of plutonium had no explosives at all. No timers and wiring. No nothing.
When it comes to nuclear weapons, the material is the weapon. When you see the concern expressed over plants that could potentially process nuclear material into a state suitable for making weapons, it may seem that there's a tendency to overreact. Yes that process is the first step in creating a bomb – but it's essentially the only step that counts. Of course, clever engineering can produce a thermonuclear bomb able to deliver staggering levels of damage, but it takes none of that to deliver horror. It takes a man with a heavy ball, staggering through a crowd.
A. Q. Kahn, the Pakistani engineer arrested for spreading nuclear secrets, wasn't handing out the blueprints to nuclear bombs. The secret that he brought first to Pakistan (and then to unknown numbers of others) was the form of uranium enrichment he learned while working for Urenco Group, a company that enriches uranium in several countries, including the United States. Learning to make enriched uranium on the cheap in limited space is the golden ticket every nervous dictator or ambitious warlord is seeking.
When you think "loose nukes," don't think about some "suitcase bomb" being ferried out of a former Soviet republic by a disgruntled night watchman, or a warhead being brokered off by a cash-starved former general. Think about the material. Anyone who can get the material can make a bomb. The United States has conducted 1,149 nuclear detonations. Only three of those were fizzles. And other than North Korea, every other nation has gotten it right the first time. In fact, so far as we know, they've gotten it right every time.
Unless you can keep nuclear material out of the wrong hands, you can't stop the proliferation of nuclear bombs. And that's the crux of the problem. North Korea is one of the poorest countries in the world. The most isolated. No other nation faces such restrictions on trade. It is, by almost any measure, backward, poor, and cut off – a country where starvation and patriotism are frequently considered synonyms. Even so, North Korea managed to obtain or create enough nuclear material to make at least two bombs.
If you can't stop the flow of nuclear material you can't stop nuclear proliferation. Unfortunately, you can't stop the flow of nuclear material.