The Making of the Atomic Bomb

In 1919, Rutherford moves back to Cambridge to direct the Cavendish lab, where he makes more “astonishing discoveries.” He finds that bombarding nitrogen gas with alpha particles emitted by radon causes the nitrogen to decay into oxygen and hydrogen. He has thus discovered simultaneously that the atomic nucleus contains hydrogen ions, which he calls protons, and that alpha particles can be used to split atoms and study their insides. At the same time, a JJ Thomson protégé, Francis Aston, invents the mass spectrograph, a device that uses magnetic and electrostatic fields to sort various elements and their isotope variations. Aston finds 212 isotopes and discovers that the masses of atoms vary in whole numbers, which suggests that atomic nuclei are made of whole units, perhaps protons.

There is a very small difference between the mass of four hydrogen atoms and the mass of helium, which appears to be four hydrogen atoms packed together. Individual hydrogen atoms have a weight of 1.008, whereas Helium atoms weigh 4.002 instead of the expected 4.032. Aston realizes that, to pack together the particles that make up a larger nucleus, the particles must give up a tiny portion of their weight as “binding energy.” Very large atoms such as uranium, on the other hand, give up binding energy when split. Atoms roughly in the middle, such as nickel, iron, and tin, are tightly stable and require very little binding energy.

Since nearly one percent of hydrogen is converted to binding energy to become helium, a glass of water’s worth of hydrogen, if fused to helium, “would release enough energy to drive the Queen Mary across the Atlantic and back at full speed” (140). Aston wins the 1922 Nobel Prize in chemistry for his work. The US, having benefited from science during the war in Europe, greatly increases the training of physicists during the 1920s. This first big generation is studied later and found typically to be men of very high IQ from Protestant or Jewish families, read a lot as children, marry late but stably, decide on their career at college during a stint of independent research, are non-religious and apolitical and instead are devoted to their work. A study of Berkeley scientists reveals that they think in a manner similar to artists, and that half of them grew up with absent or emotionally remote fathers.

An exception to these types is tall, athletic, enthusiastic, salesman-like Ernest Lawrence, who in 1928 brings his newly minted Yale PhD to UC Berkeley, where he indulges his penchant for invention by building the first cyclotron, a device that uses electric fields and magnets to accelerate atomic particles in a spiral to strike a target at high speed, scattering subatomic bits for study. Lawrence and Oppenheimer each suffer privately, Oppenheimer from depression and Lawrence possibly from bipolarity. Regardless, at Berkeley they hit it off and become friends. As the atomic number rises, atomic weight goes up, but at more than twice the rate. Scientists at first think there must be extra protons bound somehow to electrons, but this makes for an awkward fit. Rutherford, as far back as 1920, theorizes that a special particle, electrically neutral, must fit the bill; he calls it a neutron. His assistant, James Chadwick, tries to find it. Years of fruitless research ensue.

In 1932, Irene Joliot-Curie, daughter of radiation pioneers and Nobel laureates Marie and Pierre Curie, teams up with husband Frederic Joliot and discovers an unusually strong emission coming from beryllium, which they believe to be high-energy photons. Chadwick discovers that the emission can penetrate nearly an inch of lead, and thus must be without electric charge; the energy of collision is on a par with something roughly the same mass as a proton. Chadwick has discovered the long-sought-after neutron. Not only does this new particle solve the problem of the excess weight atoms carry beyond their atomic number, its neutral charge allows it to penetrate to the nucleus much more effectively than can a proton; this makes neutrons excellent atomic probes. 

Albert Einstein arrives in Berlin in 1914 to take up the directorship of the new Kaiser Wilhelm Institute for Physics. In 1915, he publishes his general theory of relativity; among other things, it predicts that the light from distant stars will bend slightly as it passes the gravity of the sun. In 1919, a total solar eclipse offers a chance to test Einstein’s theory; the results vindicate him, and he becomes an instant celebrity. His work is compared in importance to that of Newton and Copernicus. After years of nominations, Einstein finally receives a Nobel for his work—not on relativity, but on the photelectric effect.

Born in 1879, Einstein as a teen rebels against authority, even renouncing his German citizenship. His nonconformity influences his unusual thinking: While working on his PhD and laboring at the patent office, Einstein has a series of breakthrough insights, including his explanation of Brownian motion, the photoelectric effect, relativity, and, in 1907, his equation E=MC2, which codifies the immense amount of energy lying dormant within matter.

Post-war German anti-Semitism is in full swing when Einstein gives public lectures on relativity; one speech is disrupted by protesters who despise a Jew for getting all this attention. In 1921, Einstein travels with Chaim Weizmann to the US to raise funds for a Jewish university in Palestine. Impressed with the vigor of American Jewry, Einstein is equally troubled by what he sees as craven behavior among German Jews. Adolf Hitler, languishing in prison in 1923 after a failed attempt by his Nazis to take over Munich, writes Mein Kampf, which spends a great deal of ink disparaging the Jews in vividly hateful terms, arguing that they are a source of evil.

These attacks aren’t new: During the late Middle Ages, under siege from Islam and increased learning, the Church demonized Jews and issued dicta that restricted them to ghettos and to certain trades. Jews are blamed for the bubonic plague that decimates Europe in the 1300s, and tens of thousands are killed. For various reasons, England, France, Spain, and Portugal expel their Jews; many, including German Jews, flee to Poland, where they live peacefully for two centuries. Poland suffers from invasions and, in the late 1700s, is divided up between several other countries, mainly Russia, which hates the Jews and pushes them west to the Pale of Settlement, where their lives are heavily restricted. Some Jews migrate back to western Europe and especially the US, where governments have become more tolerant and Jews can become citizens. Most stay in the Pale, however.

Life in the Pale slowly improves until 1881, when the Russian Czar is assassinated. Jews are blamed; riots, called pogroms, erupt against hundreds of Jewish towns; recent reforms that ease restrictions on Jews are rescinded. Though in 1900 the Pale’s Jewish population stands at 5 million, by 1920, 2.5 million European Jews have emigrated to the US.

Hitler’s sourcebook is a post-World War I bestseller, The Protocols of the Elders of Zion, a Russian made-up document that purports to be the plans of a Jewish Satanic conspiracy to take over the world. The plan is to introduce constitutional governments and science to beguile the masses; then "Liberalism will be rooted out, the masses led away from politics, censorship strict, freedom of the press abolished” and citizens will spy on each other (182-83). Ironically, these become the policies used by the Nazis in Germany, whose battle against alleged Jewish control of the government becomes an excuse to attack the government itself.

Once in power in 1933, the Nazis quickly enact laws, 400 in total, that restrict the Jews. One law forces Jewish civil servants to retire, including college professors; this includes one-quarter of German physicists. Many emigrate, including Einstein, who accepts a position in America at Princeton’s new Institute for Advanced Study. Von Neumann, Wigner, and Polish physicist Stanislaw Ulam will be there, too.

Though his mother was Jewish, Tubingen physics professor Hans Bethe didn’t think of himself as Jewish. The Nazis dismiss him anyway, and he lands at Cornell University in the US in 1935. Numerous other scientists of Jewish background make hurried work arrangements elsewhere, leaving their students scrambling to find other sponsors. Szilard and Bohr cobble together an informal rescue system for moving physics professors to other countries, especially England and the US. About 100 physicist refugees find their way to America between 1933 and 1941. 

At the Solvay Conference in Brussels in 1933, Irene and Frederic Joliot-Curie announce that, by bombarding aluminum with alpha particles, they have created radioactive phosphorus, the first artificially generated element. (After the conference, Soviet physicist George Gamow and his wife slip their handlers and defect, ending up in America.) At their Nobel Prize acceptance speech in 1935, Frederic suggests that the discovery may have literally explosive implications in the form of new weaponry.

Szilard realizes that single neutrons would be more efficient than alpha particles in attacking atomic nuclei, but he doesn’t know which elements might emit more neutrons than they absorb, starting a chain reaction that would release vast amounts of energy. Szilard is unable to cobble together money and a staff to undertake such research; the honors go to Fermi’s team in Italy.

Fermi, who studies physics and math as a child and ends up instructing his own professors at the University of Pisa, has a passion for simple, straightforward theories that can be tested in the real world. In 1933 Fermi explains beta decay, the emission of electrons and other particles during radioactivity, and introduces an accompanying phenomenon, the weak interaction, which turns out to be the fourth and final force in nature, alongside the strong force—which binds the nucleus together—electromagnetism, and gravity.

Like Szilard, Fermi realizes that neutrons are the best way to probe nuclei, and that beryllium will work fine as the source. Carefully testing each element in order, from hydrogen on up, Fermi’s team creates artificial isotopes of 20 materials, including iron, silicon, chlorine, silver, iodine, zinc, and lanthanum. Light elements tend to break down to lighter materials, while heavy elements retain the invading neutrons and become heavier isotopes and sometimes transmute into heavier elements altogether. Uranium appears to transform into an entirely new element; if so, it’s the first manmade atom.

Szilard in 1934 presents papers that predict the use of chain reactions, neutrons fired into material that releases energy and produces yet more neutrons that, in turn, strike more of the material in a self-sustaining process: “If the thickness is larger than the critical value...I can produce an explosion” (214). Szilard applies for secret patents to protect his discoveries—not for profit, but to keep them from the prying eyes of German scientists who might use them to develop their own weapons.

Neutrons can travel quickly, sometimes too fast to be captured by atomic nuclei. Fermi’s team discovers how to slow them down so they can be absorbed. In 1935, Bohr realizes that an atom’s nucleus is a collection of protons and neutrons bound tightly together, and that an incoming free neutron hurtles into the collection, causing it to wobble like a drop of water until it ejects the energy of impact and settles down, a newly made and slightly heavier isotope of the original atom.

Late in 1937, Rutherford suffers a bad fall in his garden; complications set in, and the normally robust 66-year-old dies of sepsis. His ashes are buried in Westminster Abbey, near those of Newton, “for Rutherford was the Newton of atomic physics” (230). 

By the mid-1930s, Meitner oversees the physics department at the Kaiser Wilhelm Institute, where her colleague, Otto Hahn, is now the director. Her work is interrupted when Austria becomes a province of Germany in 1938 and Meitner automatically becomes a German citizen subject to anti-Jewish laws. With the help of other scientists, she escapes to Sweden, where she gets a research position under a grant from the Nobel Foundation.

In Fascist Italy, embroiled in wars in Ethiopia and Spain, the mood darkens, and Fermi’s team members begin to emigrate, many to America. Emilio Segrè, a Jewish associate of Fermi, is visiting America when the Italian government enacts anti-Jewish laws. Segrè stays in the US and gets his wife and son out of Italy to join him. His first job is with Lawrence at Berkeley. In October 1938, the western powers cede Czechoslovakia to Hitler without a fight; in November, the Kristallnacht riots in Germany destroy Jewish businesses and kill dozens. On the same day that new restrictions against Italian Jews are announced, Fermi gets word that he has won the Nobel Prize. He uses the prize money to escape Italy with his Jewish wife and children.

Despite all the difficulties, many of the scientists continue their efforts on irradiating uranium. Some physicists wonder whether the end products aren’t new, heavier atoms at all but merely much smaller atoms, the shattered remains of collisions with neutrons. It’s hard to sort out the various by-products, and mistakes are made. The problem remains obscure for several years.

In December 1938, Hahn’s team shows that bombarding uranium with neutrons results in a barium byproduct, which proves that uranium can be split roughly in two. This seems impossible, but Meitner and her nephew, physicist Otto Frisch, work out that the heaviest atoms are loosely held together and can be split by a single neutron, the two parts flying away from each other with so much energy that it could make a grain of sand jump. Frisch calls the splitting “fission.” Fermi’s team missed it.

In America, the news gets out, and several teams manage to replicate Hahn’s experiment and discover other ways that uranium can fission—for instance, into tellurium and zirconium. Many physicists quickly realize the process can convert a small amount of uranium into a bomb of vast explosive power. Fermi, at his new Columbia University office, looks out the window at Manhattan: “He cupped his hands as if he were holding a ball. ‘A little bomb like that,’ he said simply […], ‘and it would all disappear’” (275).