Armageddon Science (6 page)

Initially work on nuclear power outside of Germany was slow, but the science community knew that one of the greatest physicists of the 1930s, Werner Heisenberg, was working on the German nuclear project. Under pressure from the United Kingdom, where the threat of invasion was becoming more and more tangible as other European countries fell to the German army, the United States began a colossal program to beat the Germans in the race to produce nuclear weapons.

In the summer of 1941, an unparalleled, industrial-scale scientific venture began. Called the Manhattan Project after the location on Broadway of the Army Corps of Engineers’ headquarters, it was an uneasy collaboration between the military and university scientists. Different subprojects included building the world’s first nuclear reactor in order to produce plutonium; attempting to separate uranium 235 using different techniques like gaseous diffusion, electromagnetism, and high-speed centrifuges (picking out the very slight difference in mass); and working out the practicalities of assembling an atomic bomb—not a trivial task even if you have the materials.

The Manhattan Project’s reactor was not the original birthplace of plutonium. The initial discovery of the element was the work of U.S. scientist Glenn Seaborg, a tireless producer of new elements, who made the first tiny sample of the material in February 1941 at the University of California, Berkeley. (Seaborg’s and Berkeley’s roles in adding to the list of elements would later be commemorated with the elements americium, californium, berkelium, and even seaborgium.)

It wasn’t until August of the next year that Seaborg, by now transferred to Chicago for the Manhattan Project, would produce enough plutonium for anyone to be able to see it. According to Seaborg, such was the demand to take a look at this wonder element that, bearing in mind its rarity and the danger it posed, he instead showed people a test tube with diluted green ink in it. There is an echo here of the miracle of the liquefaction of the blood of Saint Januarius which is said to take place in Naples, Italy, every year. Many suspect that the glass vial supposedly containing the saint’s blood in fact holds a suspension of an iron salt that gives the right effect. But to the believers it’s the real thing, just as those who saw Seaborg’s tube of ink believed they had been in the presence of a new, world-changing element.

On December 2, 1942, the first great breakthrough of the Manhattan Project occurred—at the drab location of a converted squash court in Chicago. The most modern piece of technology in the world was tucked away under the bleachers of a dusty, disused football stadium. Three years previously, the University of Chicago football team had been closed down by a college president who believed that the game was a distraction for those who should be concentrating on academic matters. Now the nineteenth-century structure of the stadium, all too like a mad scientist’s retreat with its Gothic arches and grotesque statues, would house the ultimate mad scientist’s dream.

Here, in a claustrophobic space under the stand, Fermi’s team had assembled the world’s first nuclear reactor—not built with any vision of producing cheap electricity, or for pure research. This was a structure intended only to produce plutonium for a bomb. It was referred to, almost sarcastically, as an “atomic pile” as it was constructed from a twenty-foot-high pile of carbon bricks, used as moderators to slow down the neutrons so that the six tons of uranium 238 scattered through those graphite blocks could interact with the particles. These slugs of uranium oxide were interlaced with so-called control rods made of cadmium, a material that absorbed neutrons much faster than uranium, so when the rods were in place, the reactor was damped down, preventing a runaway reaction from occurring.

Perched on a platform above this makeshift construction, three men stood ready, prepared to sacrifice their lives. If the reaction went out of control, their job was to douse the carbon bricks in neutron-absorbing chemicals. But by the time they had done this, they would already have received fatal doses of radiation. It’s hardly surprising that their hopes for a safe test of the reactor were greater than those of any of the others present.

According to project mythology, Fermi insisted that the scientists and invited guests have a lunch break before proceeding with the first live test of the reactor. All but one of the control rods were withdrawn already. The final rod was pulled back and the Geiger counters monitoring radiation from the pile began to roar. The neutron count had shot up. The pile stayed critical—generating enough neutrons to make the reaction self-sustaining—for a little over four minutes before Fermi shut it down. The production of fuel that would eventually be at the heart of the first atomic bomb had been proved possible.

In March 1943, the most famous part of the complex Manhattan Project operation was brought online. Under newly appointed director Robert Oppenheimer, what had been a ranch school at Los Alamos in New Mexico was converted into a cross between a holiday camp, a university, and a factory, where arrays of mechanical calculators could churn through the complex arithmetic required to predict the behavior of a totally new kind of weapon, and where the raw materials being assembled elsewhere would be pulled together to build the first atomic bombs.

One of the difficulties that took up much of the time of the inhabitants of Los Alamos was working out just how to make a bomb based on nuclear fission explode, rather than generate energy in a slow and steady fashion. It is easier said than done to create a nuclear explosion. In a bomb, it’s necessary to get the materials over critical mass, the amount required for the process to run away with itself, very quickly. The production of neutrons sparking the chain reaction has to peak suddenly. Otherwise, parts of the radioactive substance will go critical at different times and it will blow apart, yielding a tiny amount of its potential and leaving most of the radioactive matter intact.

Two different techniques would eventually be employed to achieve critical mass quickly enough. The bomb based on separated uranium 235 used the relatively simple gun method. Here a cylinder of uranium was shot into a hole in another piece of uranium at high speed, taking the combined mass suddenly above critical. The plutonium bomb used an alternative approach, where a hollow sphere of plutonium segments was forced in on itself by multiple simultaneous explosive blasts from different directions.

This second approach was much more complex, needing lengthy experimentation with the conventional explosive charges that would be used to drive the plutonium together. The different segments all had to arrive at the same time, requiring exquisitely precise coordination of a sphere had to be forced inward, using special shaped charges called explosive lenses that focused the blast of the conventional explosive in a particular direction. But because of differences between plutonium and uranium, the gun approach could not have achieved criticality quickly enough for plutonium, and the imploding sphere had to be attempted.

As it happened—though no one on the Allied side knew it—the race to complete an atomic weapon was one-sided. In part thanks to a successful raid on a Norwegian plant that produced a substance called heavy water, used in the German experimental reactors to slow down neutrons to enable them to work with uranium 238, the Germans didn’t even succeed in getting a reactor working properly before the war came to an end. Some of the German scientists involved claimed after the war that they had intentionally worked as slowly as they could to prevent the Nazis from getting such a devastating weapon. This has been seen by some as an after-the-event defense, by others as true—we will never be sure.

Long before the bombs were ready, the great Danish physicist Niels Bohr argued for a form of deterrence. He believed it wasn’t necessary to actually deploy the bombs, but merely to have the capability to use them. The devastating power of atomic weapons was such, he believed, that the sheer deterrent effect of what
might
be done with them should be enough to stop or prevent wars. To make the deterrent effective, it wasn’t sensible for one country alone to push ahead, as this would inevitably result in an arms race—perhaps with the Soviet Union once the war was over. Instead, he believed, it was essential to share the technology widely, building up an international state of mutual trust. Few agreed with him.

By this time the first bombs were almost complete. The alternative techniques for achieving critical mass made them very different in appearance. It was originally thought that the uranium bomb, nicknamed “Thin Man” after the hugely popular Dashiell Hammett detective novel and movie, would be extremely long and thin—perhaps 0.6 meters (two feet) wide by 5.5 meters (seventeen feet) long. Most of this length was for the gun to shoot in the uranium slug. But the gun could be made shorter if the slug didn’t need to move as fast—and it was discovered that by shielding the bomb from natural stray neutrons, the uranium would have less tendency to explode prematurely. This meant the bomb makers could take the length down to around two meters (six feet), and the bomb was rechristened “Little Boy.”

No such slimming was possible for the plutonium bomb. The need for an inner spherical casing containing the charges that would implode the segments of plutonium meant that “Fat Man,” as it was called, was never going to get much slimmer than the initial estimates of three meters by 1.5 (nine feet by five). Because of its complex mechanism, the plutonium bomb was less likely to work, but it still had to be attempted. With larger-scale reactors up and running, plutonium was relatively easy to make. The plants working on separating uranium 235 from uranium 238 were proving slow, and it was feared that only one uranium bomb could be made by early 1945, when it was thought it might be necessary to use nuclear weapons. The plutonium bomb had to be brought to completion as well—and that meant a test of that tricky implosion technique.

A site for the test had been arranged at the Air Force bombing range at Alamogordo, New Mexico. At least, that’s how the location is normally described. But the White Sands range is enormous, the size of a county. The site was a good sixty miles from Alamogordo, tucked away behind Oscura Peak.

The test was given the evocative code name “Trinity” by Oppenheimer, whose poetic leanings included a knowledge of John Donne’s
Holy Sonnet
14, which begins:

Batter my heart, three-person’d God; for You

As yet but knock, breathe, shine, and seek to mend;

That I may rise, and stand, o’erthrow me, and bend

Your force to break, blow, burn, and make me new.

Thus, Oppenheimer associated the Holy Trinity with the kind of impact it was imagined the bomb would have. That’s the usual story for the origins of the name, though Oppenheimer was less certain himself that this is where the label came from. He said in a letter that he wasn’t sure why he had used “Trinity.” He
did
have a Donne poem in his mind at the time—but it was another one that makes no reference to the Trinity. He just guessed that the one Donne poem triggered an association with another, but it’s a pretty slim connection.

The test bomb was perched on top of a 33 meters (110-foot)-high metal tower to simulate an explosion in the air as it dropped from a plane. There it sat for over thirteen hours through a thunderstorm, as the nervous team, ensconced in a concrete command center some five and a half miles away, worried about lightning strikes and the potential for the unstable weather system to carry radioactive material from the explosion into inhabited areas.

The guests and observers not directly involved in controlling the test were sited on a hill twenty miles away. They had been warned of the delay and so did not arrive until 2 a.m., ten hours after the explosion was originally due to take place. As it was, it was just before 5:30 a.m. on July 16, 1945—after an uncomfortable wait in spartan conditions—that those observers witnessed the event that was to bring Armageddon closer to a man-made possibility. The young scientist Joe McKibben switched the bomb to automatic timer forty-five seconds before detonation. Warning rockets flashed from the camp to alert those around.

In a tiny fraction of a second after the timer kicked in, the explosive lenses around the plutonium sphere sent a spherical shock wave pushing the heavy metal inward, clamping the radioactive source together into a supercritical mass. The Fat Man plutonium bomb at the Trinity site exploded, with a visual impact that would become the template for movie-effects designers for decades to come. Physicist Otto Frisch, nephew of Lise Meitner, the codiscoverer of nuclear fission, described what he experienced:

Another physicist who witnessed the test, Isidor Rabi, spoke of the aftermath:

Within days, materials for the Little Boy uranium bomb, and the physicists to assemble it, had arrived on Tinian Island in the Pacific, from where bombers based at the North Field base were already pounding Japanese cities with conventional weapons on a daily basis. The intention had been to drop the Little Boy bomb on August 1, but the weather prevented it. Instead, the world’s deployed nuclear arsenal was doubled in size the next day, when a Fat Man plutonium bomb arrived, confidently assembled after the Trinity test.