Seven Elements That Have Changed the World (22 page)

Hiroshima most vividly illustrates that our use of the elements holds the potential for great evil as well as great good. The atomic bomb harnessed the incomparable energy of uranium; unleashed over Hiroshima in August 1945, it changed the world forever.
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Uranium was first mined as part of a greasy mineral called pitchblende, or ‘bad luck rock’. During the Middle Ages, among the Cruel Mountains of the Kingdom of Bohemia, silver miners would thrust their pickaxes deep into the rock face only to pull out a clod of this unfortunate ore. When
pitchblende was found it usually meant the end of a particular vein of silver and so the beginning of more back-breaking work digging a new mining shaft.

For centuries, uranium was discarded as waste, but, at the turn of the twentieth century, it became an ore of great scientific interest. It was from uranium salts that, in February 1896, Henri Becquerel discovered natural radiation. He placed some uranium salt on a photographic plate and a silhouette soon appeared. This effect was not considered unusual. Uranium had long been known to affect film in this way and Becquerel thought it to be a result of a chemical reaction triggered by sunlight. Because the next few days in Paris became overcast, Becquerel decided to suspend his experiments. He placed the photographic plates and uranium salts in a drawer. Returning days later he saw that the plates had mysteriously captured the same silhouettes. There had been no sun to make the images and so something else, intrinsic to the uranium, had made them. This he called radiation.

Fellow Parisian Marie Curie heard of Becquerel’s discovery. To experiment further, Curie acquired a ton of pitchblende, still regarded as useless rock, free of charge from the Cruel Mountain region. This she used to obtain enough uranium salts to demonstrate that the amount of radiation emitted depends only on the mass of uranium. It did not matter whether it was solid or a powder, or exposed to heat or light. Her experiments led to her hypothesis that radiation comes from within the atom itself, rather than some chemical process between atoms. This radiation was the first sign of instability within the uranium atom.

Curie went on to discover two more radioactive elements, radium and polonium, and in 1903, along with her husband Pierre and Henri Becquerel, was awarded the Nobel Prize in Physics. Yet both Marie and Pierre Curie paid the price of their radioactive research. They succumbed to strange and, for Marie, fatal illnesses of a mysterious origin. Today we know that these resulted from radiation exposure, which at first was not known to be harmful.
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I first learnt of uranium’s mysterious properties while reading Natural Sciences at Cambridge in the late 1960s. It was there, forty years earlier, that many of the pioneering experiments in the newly emerging field
of nuclear physics had taken place. In 1920, Ernest Rutherford, ‘the father of nuclear physics’ and then the director of the Cavendish Laboratory, had hypothesised that the atom was made not only of negatively charged electrons and positively charged protons bound together by their opposite charges, but also of a neutral particle which he called a neutron.
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Twelve years later, James Chadwick, assistant director of the Cavendish under Rutherford, proved the neutron’s existence.
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It would turn out to be the key to splitting uranium atoms.

By the time I arrived at Cambridge, the Cavendish Laboratory had lost much of its reputation for nuclear physics. One exception was the presence of Otto Frisch, a nuclear physicist who had played an active role in the Manhattan Project which produced the bomb dropped on Hiroshima. Years before, it was Frisch’s interpretation of an unusual experimental result that, at a very basic level, provided the basis for the creation of the atomic bomb.

In 1938, Frisch was staying in Sweden over Christmas with his aunt and fellow physicist Lise Meitner. Meitner had been working at the Kaiser Wilhelm Institute for Chemistry in Dahlem, Germany, but had fled to Sweden earlier that year fearing persecution under the Third Reich. Her German colleagues, Otto Hahn and Fritz Strassmann, were keeping her updated on the progress of their research and in their latest correspondence told her of a very strange experimental result. When they fired neutrons at uranium atoms they detected signs of much lighter particles, almost half the weight of a uranium nucleus, in the debris.
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It did not make sense: the neutrons did not have nearly enough energy to break off such large chunks of atom. They decided to go for a long walk to puzzle it out.

Walking through the frozen Swedish countryside with Meitner and his aunt, it occurred to Frisch that the uranium nucleus must be very unstable. Uranium atoms are so large that the glue holding the protons and neutrons together is only just enough to withstand the repulsive force of charged protons pushing against each other.
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If a uranium nucleus absorbs a passing neutron, the energy is enough to destabilise the atom and split it. While he explained his reasoning to Meitner, both stopped and sat down on a tree trunk and began scribbling on bits of paper. They calculated that the uranium nucleus resembled ‘a very wobbly, unstable drop, ready to divide itself at the slightest provocation’.
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Frisch carried out further experiments
to confirm this idea before he and Meitner submitted two papers to the scientific journal
Nature
in February 1939. In these, Frisch gave this newly observed event of splitting the name ‘nuclear fission’.
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In nuclear fission a vast amount of energy is released. When a uranium atom splits it produces two smaller nuclei with a smaller total mass. The missing mass (m), which is about one-fifth of that of a proton, is converted into energy (E) according to Einstein’s equation E = mc
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. Because the speed of light (c) is so fast (299,792,458 metres every second) a little mass makes a lot of energy. Frisch calculated that the splitting of a single uranium atom would be enough to make a grain of sand, itself containing around one hundred trillion atoms, visibly jump in the air.

But one uranium atom does not make a bomb. The explosion in Hiroshima resulted from the simultaneous splitting of some of the thousand trillion trillion atoms contained in one kilogram of uranium.
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The splitting of a single uranium atom produces neutrons which, if travelling at the right speed, cause neighbouring uranium atoms to split as well. These produce more neutrons which in turn split more uranium atoms. This leads to an unstoppable chain reaction. Thus, uranium is literally regarded as the master of its own destruction.

Meitner and Frisch had unlocked the secret of splitting the atom. At the time, they did not understand that their discovery would enable the creation of a nuclear bomb which could be used to kill hundreds of thousands of people.

No explosion was observed in Meitner’s laboratory. It turned out that the chain reaction could only be sustained with a specific type of uranium atom, a type which is rarely found in nature. Naturally occurring uranium is almost entirely made up of the isotope uranium-238.
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However, in order to create a chain reaction, which results in a nuclear explosion, a high concentration of the fissionable isotope uranium-235 is needed. This is called ‘enriched-uranium’.
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At Columbia University in New York, Hungarian and Italian physicists Leó Szilárd and Enrico Fermi heard of Meitner and Frisch’s research and began
conducting their own experiments in nuclear fission. After moving to the University of Chicago they built the world’s first nuclear reactor, Chicago Pile-1, in an old squash court under a football stadium at the university. This did not escape the attention of the Soviet intelligence agencies, but developments got somewhat lost in translation: the Soviets mistranslated ‘squash court’ as ‘pumpkin field’, mistaking the game of squash for the eponymous vegetable. The location of the experiment was irrelevant, though, in stark contrast to its results. From the large number of neutrons released in the fission reactions, Szilárd concluded that uranium would be able to sustain a chain reaction, and so possibly could be used to create a bomb. He later recalled: ‘there was very little doubt in my mind that the world was headed for grief.’
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At the beginning of the Second World War Szilárd decided that the discovery should be urgently brought to the attention of President Roosevelt.
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He drafted a letter, which was also signed by Albert Einstein, explaining the possibility of this new type of bomb and warning that Germany could be pursuing research with this aim in mind. Roosevelt agreed to the formation of the Advisory Committee on Uranium and, later, the allocation of increased funding for uranium research. As the science behind atomic explosions became more concrete, and as the urgency of the matter increased with the Japanese attack on Pearl Harbor and America’s entry into the war, the diverse nuclear research in the US was consolidated and directed towards the single aim of producing an atomic bomb under the umbrella of the Manhattan Project.

In September 1942, the US government approved the acquisition of over 200 square kilometres of land surrounding the small town of Oak Ridge, Tennessee, to create the Clinton Engineer Works. As one of three main sites in the Manhattan Project, it was tasked with producing the enriched uranium for an atomic bomb. The other two sites under the umbrella of the Manhattan Project were Hanford, another production site for bomb material, and Los Alamos, the ‘mind centre’ of the project. Secrecy was a top priority for all three of the sites. They did not exist on maps and were referred to only by their code names of X, Y and Z.

As soon as Major General Leslie Groves, the director of the Manhattan Project, saw the site he knew it was right. Hidden away in the middle of
nowhere, Oak Ridge was perfectly positioned for the project’s secrecy and security needs. Being far from the coast reduced the risk of enemy attack and nearby rivers provided a plentiful supply of water and hydroelectric power, vital for the colossal industrial effort about to be undertaken.

With characteristic efficiency, Groves evicted 1,000 families from the area, some with only two weeks’ notice. They had no choice. The site had been chosen, and no one was going to get in the way of America building the bomb. It was ‘child’s play’ according to one official from the US Army Corps of Engineers.
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Scale was everything for the Clinton Engineer Works. At its peak it employed 80,000 workers. The small town of Oak Ridge quickly grew to become the fifth largest city in the state of Tennessee and held a greater concentration of PhDs per capita than any other city in the country. Twelve thousand people worked in the K-25 uranium-processing building alone. At the time, it covered more area than any structure ever built. Inside K-25, uranium was enriched by passing it, in gaseous form, through a series of membranes. Lighter molecules pass through a fine membrane faster than heavier molecules, so that the percentage of uranium-235, which was lighter than uranium-238, gradually increased.
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The US did not know whether their prodigious experiment would work, but they had to try. Only an atomic bomb, harnessing the incomparably destructive energy of uranium, held the potential to win the war in an instant. They also understood that speed in this endeavour was essential. They feared that Germany might beat them to it and unleash the devastating power of uranium on them.

To the US, these uniquely dark circumstances justified the enormous expense of the project and the forced evictions at Oak Ridge. They also enabled it to enlist the world’s brightest and best scientific minds at the Los Alamos site, the ‘mind centre’. Robert Oppenheimer, the director at Los Alamos, was among the first to witness the success of the US’s endeavours at the Trinity bomb test site on 16 July 1945. Later he recalled that, as he watched the bright atomic flash in the New Mexico desert, he was reminded of a line from Hindu scripture: ‘Now, I am become Death, the destroyer of worlds.’
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Today, scientific challenges are more diverse and the solutions less clear. This was evident when I visited the site of the Clinton Engineer Works, now called Oak Ridge National Laboratory, in March 2009. The square industrial buildings sit out of place among Tennessee’s rolling forest landscape and the expansive countryside belies the true size of the Laboratory. On a tour of the site I was shown the X-10 graphite reactor, the second nuclear reactor in the world, and now a National Historic Landmark. The K-25 uranium enrichment facility is currently being demolished.

Research priorities have long since moved on, and these were the reason for my visit. I was there in my role as a partner in a private equity firm, which at the time managed the world’s largest renewable and alternative energy investment fund. I came to learn about the Laboratory’s recent approaches to the production of biofuel from crops, such as grasses and trees, which are obviously not used for food. Biofuel can be made from the sugars contained in plant cellulose. But non-food crops also contain a lot of lignin, which forms strong bonds with these sugars, making them difficult to extract. A particular interest at the laboratory was poplar trees, which have a wide variation in many natural traits. Researchers were searching over 1,000 poplar tree varieties for traits that would produce the greatest amounts of sugar.
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By producing economically competitive biofuels sources, the US had hoped to reduce further their dependency on foreign oil. Oak Ridge may have moved on from uranium, but once again it was working in the interests of national security.

On 25 July 1945, the last shipment of enriched uranium needed for the Hiroshima bomb left Oak Ridge, arriving at the Pacific island of Tinian two days later. Here the three-metre-long atomic bomb, called ‘Little Boy’, which was soon to be dropped on the city of Hiroshima, was assembled. From this point on, the science was frighteningly simple. Lumps of enriched uranium would be slammed together to form a critical mass, initiating an uncontrollable, runaway nuclear reaction.