Benford, Gregory. The Berlin Project. New York: Saga Press, 2017. ISBN 978-1-4814-8765-8.
In September 1938, Karl Cohen returned from a postdoctoral position in France to the chemistry department at Columbia University in New York, where he had obtained his Ph.D. two years earlier. Accompanying him was his new wife, Marthe, daughter of a senior officer in the French army. Cohen went to work for Harold Urey, professor of chemistry at Columbia and winner of the 1934 Nobel Prize in chemistry for the discovery of deuterium. At the start of 1939, the fields of chemistry and nuclear physics were stunned by the discovery of nuclear fission: researchers at the Kaiser Wilhelm Institute in Berlin had discovered that the nucleus of Uranium-235 could be split into two lighter nuclei when it absorbed a neutron, releasing a large amount of energy and additional neutrons which might be able to fission other uranium nuclei, creating a “chain reaction” which might permitting tapping the enormous binding energy of the nucleus to produce abundant power—or a bomb.

The discovery seemed to open a path to nuclear power, but it was clear from the outset that the practical challenges were going to be daunting. Natural uranium is composed of two principal isotopes, U-238 and U-235. The heavier U-238 isotope makes up 99.27% of natural uranium, while U-235 accounts for only 0.72%. Only U-235 can readily be fissioned, so in order to build a bomb, it would be necessary to separate the two isotopes and isolate near-pure U-235. Isotopes differ only in the number of neutrons in their nuclei, but have the same number of protons and electrons. Since chemistry is exclusively determined by the electron structure of an atom, no chemical process can separate two isotopes: it must be done physically, based upon their mass difference. And since U-235 and U-238 differ in mass only by around 1.25%, any process, however clever, would necessarily be inefficient and expensive. It was clear that nuclear energy or weapons would require an industrial-scale effort, not something which could be done in a university laboratory.

Several candidate processes were suggested: electromagnetic separation, thermal or gaseous diffusion, and centrifuges. Harold Urey believed a cascade of high-speed centrifuges, fed with uranium hexafluoride gas, was the best approach, and he was the world's foremost expert on gas centrifuges. The nascent uranium project, eventually to become the Manhattan Project, was inclined toward the electromagnetic and gaseous diffusion processes, since they were believed to be well-understood and only required a vast scaling up as opposed to demonstration of a novel and untested technology.

Up to this point, everything in this alternative history novel is completely factual, and all of the characters existed in the real world (Karl Cohen is the author's father in-law). Historically, Urey was unable to raise the funds to demonstrate the centrifuge technology, and the Manhattan project proceeded with the electromagnetic and gaseous diffusion routes to separate U-235 while, in parallel, pursuing plutonium production from natural uranium in graphite-moderated reactors. Benford adheres strictly to the rules of the alternative history game in that only one thing is changed, and everything else follows as consequences of that change.

Here, Karl Cohen contacts a prominent Manhattan rabbi known to his mother who, seeing a way to combine protecting Jews in Europe from Hitler, advancing the Zionist cause, and making money from patents on a strategic technology, assembles a syndicate of wealthy and like-minded investors, raising a total of a hundred thousand dollars (US$ 1.8 million in today's funny money) to fund Urey's prototype centrifuge project in return for rights to patents on the technology. Urey succeeds, and by mid-1941 the centrifuge has been demonstrated and contacts made with Union Carbide to mass-produce and operate a centrifuge separation plant. Then, in early December of that year, everything changed, and by early 1942 the Manhattan Project had bought out the investors at a handsome profit and put the centrifuge separation project in high gear. As Urey's lead on the centrifuge project, Karl Cohen finds himself in the midst of the rapidly-developing bomb project, meeting and working with all of the principals.

Thus begins the story of a very different Manhattan Project and World War II. With the centrifuge project starting in earnest shortly after Pearl Harbor, by June 6th, 1944 the first uranium bomb is ready, and the Allies decide to use it on Berlin as a decapitation strike simultaneous with the D-Day landings in Normandy. The war takes a very different course, both in Europe and the Pacific, and a new Nazi terror weapon, first hinted at in a science fiction story, complicates the conflict. A different world is the outcome, seen from a retrospective at the end.

Karl Cohen's central position in the Manhattan Project introduces us to a panoply of key players including Leslie Groves, J. Robert Oppenheimer, Edward Teller, Leo Szilard, Freeman Dyson, John W. Campbell, Jr., and Samuel Goudsmit. He participates in a secret mission to Switzerland to assess German progress toward a bomb in the company of professional baseball catcher become spy Moe Berg, who is charged with assassinating Heisenberg if Cohen judges he knows too much.

This is a masterpiece of alternative history, based firmly in fact, and entirely plausible. The description of the postwar consequences is of a world in which I would prefer to have been born. I won't discuss the details to avoid spoiling your discovery of how they all work out in the hands of a master storyteller who really knows his stuff (Gregory Benford is a Professor Emeritus of physics at the University of California, Irvine).

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