Armageddon Science (5 page)

An observer would see matter beginning to fragment into invisible particles, this decay spreading faster and faster until, in principle, the whole Earth had disappeared. The final result of this uncontrolled chain reaction could be that every speck of matter in the universe is converted into strangelets, almost as fundamental a transformation of existence as the big bang.

It sounds like scary stuff, but the CERN physicists point out that collisions of similar energy to those produced by the Large Hadron Collider are happening all the time in nature—they just don’t take place under our control and observation, as they will be at CERN—yet we don’t see matter breaking down into strangelets out in space. We also don’t even know that strange matter
can
be formed—it has never been detected. It is also believed that strangelets would be stable only at very low temperatures, and that the probability of them forming drops as the energy of the collisions involved increases, so it’s a strange worry to have for the LHC, when they haven’t formed in lower-energy colliders. In the end, an awful lot of ifs have to be assembled to make the strange-matter scenario even vaguely possible.

Opponents of the Large Hadron Collider, led by German chemist Otto Rössler, asked the European Court of Human Rights to block the use of the LHC, but the court turned down the request. The court rejected their application for an emergency injunction but allowed the case to continue being argued, implicitly dismissing the opponents’ argument, as the case would not have been heard until after the LHC was started up. As it happened, the LHC was crippled for over a year by a technical fault in September 2008 before it was fully switched on. It wasn’t until October 2009 that particles began to travel around the accelerator again, and it was late November 2009 before the first collisions occurred. This delay made it possible for the lawsuit to continue, but the European legal attempts to block the LHC were not revived.

An equivalent action in the U.S. courts, brought by retired nuclear safety officer Walter Wagner and science writer Luis Sancho, was dismissed by District Judge Helen Gillmor in Hawaii in September 2008. The judge ruled that the LHC did not fall under the court’s jurisdiction, as the United States did not contribute enough to the project to bring it under domestic environmental regulations.

These concerned individuals are not mere attention seekers or cranks. They are people with a science background who are genuinely worried about what might happen when the Large Hadron Collider is fully operational. But the vast majority of scientists would argue that the worries expressed by the protesters are so hypothetical that they don’t form a basis for stopping the research.

We can dream up hypothetical world-shattering consequences for almost anything we do. The LHC may be an extreme example, but even here, the chances are so small that arguably we should concentrate our efforts to avoid Armageddon elsewhere. There are more immediate and realistic threats of mass destruction.

Few indeed would argue about the reality of one such threat to the survival of the human race, arising from an activity that we have been engaged in since the 1940s. That’s the use, and the terrifying misuse, of atomic power.

The Second World War, of all wars, was the one that was won by science. There was the cracking of the German and Japanese codes and the breaking of the Enigma cipher machines; the development of radar, enabling a whole new ability to detect attacking aircraft and ships before they were in visible range; and the introduction of a new science, operations research, which applied the techniques of math and physics to the battlefield—for example, using statistics to deduce the most deadly spread of depth charges. But most dramatically of all, science brought nuclear energy to the battlefield.

When I was a teenager in the 1970s, there was still a real feeling of living under threat, knowing that a nuclear attack could be on the horizon. While at university I gave serious consideration to moving to the remote Scottish islands once I had graduated, on the assumption that there would be a better chance of surviving a nuclear holocaust there. Atomic weapons threatened us with destruction on an unimaginable scale. True Armageddon. It was a feeling shared by many throughout the time of the cold war. Writer Sue Guiney describes her feelings as a child in Farmingdale, New York:

The threat to the world that so terrified us then dated to a discovery made in the 1930s—the potential for destruction that lay in the nucleus of the atom. But we have to go further back, to 1909, to see how the existence of atomic nuclei was discovered, the first major step on the path to the atomic bomb.

Until then it had been thought that an atom was a ball of positive charge with negative charges distributed through it, like fruit in a pudding. But New Zealand–born physicist Ernest Rutherford and his team proved things were different. At the Cavendish Laboratory in Cambridge, England, Rutherford’s assistants Hans Geiger and Ernest Marsden were using the decay of the natural radioactive element radium to produce alpha particles—heavy, positively charged particles—which were fired at a piece of gold foil to see how the atoms in the gold influenced the flight of the particles.

Unexpectedly, a few of the alpha particles bounced back. Rutherford commented that it was “as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.” The Cambridge team’s discovery showed that the positive charge in an atom was concentrated in a small, dense nucleus. A very small nucleus indeed. If the atom were blown up to the size of a cathedral, the nucleus would be like a fly, buzzing around inside it.

Rutherford transformed our understanding of the atom’s structure, but he was to make a remark about the practical significance of his discovery that showed he hadn’t realized its potential. In 1933, in an interview with the
New York Herald Tribune,
he commented, “The energy produced by the breaking down of the atom is a very poor kind of thing. Anyone who expects a source of power from the transformation of these atoms is talking moonshine.”

What Rutherford was referring to was the concept of nuclear fission. This was a process named after the biological process of fission, where a cell splits into two. Rutherford had first split the nucleus of an atom in 1917, again using alpha particles, but in this case using the gas nitrogen as the target. In 1932 his assistants John Cockroft and Ernest Walton had taken this a stage further, using artificially accelerated protons—the positively charged particles from an atomic nucleus—to smash into lithium, splitting it into two alpha particles. This was the “breaking down of the atom” Rutherford referred to. It took a lot of energy to smash the atom, so even though energy was released in the process, it didn’t seem to have a lot of use.

What Rutherford had overlooked in his dismissal of nuclear power was that there was a way to make the process self-sustaining. The means to make his “moonshine” real was dreamed up by a Hungarian exile in London as he waited to cross the road. This was the young physicist Leo Szilard. He was staying at the Imperial Hotel in London’s Russell Square, and had been held up by the traffic lights at the corner of the square, where it adjoins Southampton Row. Thinking of Rutherford’s pronouncement as he waited for the light to change, Szilard was struck by a sudden idea that almost seemed prompted by the arrival of the green light.

“It suddenly occurred to me,” he later said, “that if we could find an element which is split by neutrons, and which would emit two neutrons when it absorbed one neutron, such an element, if assembled in sufficiently large mass, could sustain a nuclear chain reaction.” It was like getting interest on money in a bank account. You invested one neutron, and you got two neutrons back. Invest both those and you would get four—and so it went on. The process could be self-sustaining if kept in check, or could run away, doubling in its rate with every reaction.

The key concept at the heart of both the nuclear reactor and the atomic bomb had come to Leo Szilard in those few moments it took him to cross the road. (At least, this is the version he told years after the event. It wouldn’t have been the first time a scientist had exaggerated the significance of a eureka moment.)

Unusually for a theoretical physicist of the era, Szilard took out a patent on his idea, which he sent into the patent office on March 12, 1934. At the time, he thought it most likely that the substance used to produce a chain reaction would be the element beryllium. This lightweight gray metal, element 4 in the periodic table, was already associated with the production of neutrons, as it was used in the discovery of those neutrally charged particles from the atomic nucleus.

With his friend and fellow Hungarian physicist Eugene Wigner, who was visiting London from his post at Princeton, Szilard decided to take a step into the lion’s den and challenge Rutherford on the validity of his moonshine claim. After all, Rutherford had a laboratory capable of testing Szilard’s ideas, something the theoretician had no way (or inclination) to do himself. Szilard intended to win Rutherford over with his brilliance, persuading the world-famous scientist that a young Hungarian upstart had got the better of him.

The result was a failure, not helped by a clash of personalities. The older, bluff Rutherford was not impressed by the way Szilard had taken out a patent on his idea. As far as the New Zealander was concerned, this wasn’t what real scientists did—they shared information freely. Furthermore, Szilard messed up his chances in a mistaken attempt to play to Rutherford’s enthusiasms. He knew that the older man had discovered the alpha particle, so rather than describe a chain reaction as Szilard had first envisaged it, using neutrons, he made up a similar process for Rutherford’s benefit using the heavier alpha particles. Rutherford knew this wouldn’t work, and threw out the idea without having a chance to think about a reaction happening with neutrons.

Szilard had conjured up the basic premise of the atomic chain reaction. Always the purest of theoreticians, he had little interest in the nuts and bolts of making such a reaction happen. That was why he had approached Rutherford. He had put the bottle on display, but he was unable to let the genie out. That was the responsibility of the team of the Austrian Lise Meitner and the German Otto Hahn.

In 1938, Meitner and Hahn picked up on work that had been done by the Italian-born Enrico Fermi on the splitting of uranium nuclei. Uranium is a naturally occurring radioactive substance that comes in two forms. By far the more common is uranium 238, while uranium 235, with three fewer neutrons in the nucleus, is the rarer and more unstable of the two.

Meitner and Hahn pointed out that when a uranium nucleus splits, it gives off between two and four neutrons, which go flying off with high energy and could collide with another uranium nucleus. The collisions should cause
those
nuclei to split as well, giving off more neutrons. The result would be a chain reaction, just as Szilard had postulated. If handled in a controlled way, this would enable useful production of power from the fission. When the nucleus splits, a small amount of the mass in the nucleus is converted to energy according to Einstein’s iconic equation E = mc
²
, where E is the energy, m the mass that is lost, and c the speed of light. This energy, added up over millions of splitting nuclei, would make for very usable power.

But there was another possibility that also occurred to Meitner and Hahn: if the reaction was allowed to run away without control. In principle that first split could generate at least two neutrons, each of which could split another nucleus, producing at least four neutrons, then going on to release eight neutrons in the next generation and so on. In a tiny amount of time, with this doubling, a vast number of atomic nuclei would be giving off energy—in this mode there would not be a neat source of steady energy for a power station but the sudden explosion of a phenomenal bomb.

Although science did not arrive at this concept until the 1930s, British fiction writer H. G. Wells had already speculated about the use of the power locked up within the atom as early as 1913. In his book
The World Set Free,
Wells describes the destruction caused by an imaginary weapon. He called it an “atomic bomb”—the first time those words had been seen in that combination. At the time, Wells’s speculation was swept aside by the horrors of the First World War, which soon followed publication of his book. This “war to end all wars” was so horrendous even without such a weapon that Wells’s ideas seemed unnecessarily far-fetched. But years later, the term that Wells had dreamed up would return as a very real threat.

Interestingly, in
The World Set Free,
we also see the first suggestions of “mutually assured destruction”—the idea that it is rational behavior for nations to refrain from making war if a country has the means to totally destroy its enemy, and the enemy has the same capability in return. The sad reality Wells depicts is one where that assurance isn’t enough, though. It is only after a massive atomic war that the remnants of humanity can build a new and utopian society without the threat of war. Because they have experienced the true horror of nuclear warfare, they want it never to happen again. They know that the next time it would probably wipe out the human race entirely, and so they dismiss the use of war to settle any future political differences.

Producing an atomic bomb to rival Wells’s fantasy would not prove easy (probably just as well for the continued security of the world). Meitner and Hahn’s discovery pointed the way, though, and soon after, in 1939, a team at Princeton discovered a significant difference between the two different “flavors” of uranium. Uranium 238—the more stable version with three extra neutrons in the nucleus—proved to be much worse at absorbing neutrons and subsequently splitting than was uranium 235. If you wanted uranium 238 to undergo fission, you needed slow-moving neutrons, giving the nuclei a chance to absorb them, whereas uranium 235 was capable of latching onto high-speed neutrons.

The vast majority of uranium came in the 238 variety—99.3 percent of a typical chunk of uranium when dug out of the ground would be of this type. This was fine for generating nuclear power, because you could slow down the neutrons using special materials; but the slow neutrons were no good for the “all-at-once” fission required for a bomb. A bomb making use of slow neutrons would fizzle along rather than explode. So if a bomb were to be made from uranium, it would need to be mostly uranium 235, enabling the formation of a chain reaction with fast neutrons.

This proved to be a nightmare problem for anyone attempting to make such a bomb. It isn’t easy to distinguish between uranium 235 and uranium 238. There’s no point trying to chemically refine the uranium to separate the two different varieties (known as isotopes). The chemical properties of an element are determined by the electrons in the atom, and both isotopes have the same number of electrons. It’s only the number of neutrons in the nucleus, and hence the atomic weight, that differs. So to separate uranium 235, it was necessary to find a way to split off tiny amounts of a chemical with a very slightly different weight. It would take several years to discover a way to do this, proving one of the biggest difficulties faced by the atomic bomb project.

The first country to take the idea of a nuclear weapon seriously was Germany. In April 1939, the chemist Paul Harteck wrote to the German war office that nuclear fission would “probably make it possible to produce an explosive many orders of magnitude more powerful than the conventional ones…. That country which first makes use of it has an unsurpassable advantage over the others.”

The possibility of making such weapons was next picked up by Winston Churchill in the United Kingdom, while in the United States in August 1939, a letter from Albert Einstein warning of the dangers nuclear fission posed, written at the encouragement of the father of the fission reaction, Leo Szilard, was sent to the authorities, but it seems not to have raised much interest.

Initially, the difficulties of separating enough uranium 235 to make a bomb seemed insuperable. But in June 1940, American physicists Edwin McMillan and Philip Abelson, working at the Berkeley Radiation Laboratory, wrote a paper that suggested an alternative approach that would avoid the need for separating the uranium isotopes. If uranium 238 can be encouraged to absorb a slow neutron in a reactor, it becomes the unstable isotope uranium 239. This undergoes a nuclear reaction called beta decay, where a neutron turns into a proton, giving off an electron in the process (for historical reasons, the electron is called a beta particle in such circumstances).

The result of this reaction is the production of a new element, one that doesn’t exist in nature. This element was later called neptunium. But neptunium is also unstable and soon generates another electron, adding a second proton to the nucleus to become the element that would be named plutonium. This is a material that is as suitable for making a bomb as uranium 235. And because plutonium is chemically different from uranium, it is relatively easy to separate. Remarkably, the openly published Berkeley paper had shown the first step of how to use a nuclear reactor to make the principle ingredient of an atomic bomb.