Half-Life:The Divided Life of Bruno Pontecorvo, Physicist or Spyby Frank CloseBasic Books, 2015Popular science-writer Frank Close chooses as the subject of his latest book a figure who usually merits only a line or two in even the most comprehensive histories of the Cold War; Half-Life: The Divided Life of Bruno Pontecorvo, Physicist or Spy tells in unprecedented and utterly absorbing detail the story of how Bruno Pontecorvo, one of the brightest young lights of the new nuclear age, disappeared with his family in 1950 and only re-surfaced five years later in the Soviet Union, working as a key scientist in the Soviet's burgeoning nuclear arms program. Pontecorvo had been a protege of Enrico Fermi, a worker on the United States' Manhattan Project, a smiling, congenial man of high morale and brilliant scientific insight, and it slowly became obvious that his new Soviet masters distrusted him every bit as explicitly as his earlier comrades had trusted him implicitly.Close brings a great deal of new and groundbreaking research to the question of whether or not Pontecorvo had been an active spy even before he and his family defected. His rather shabby and arm's length treatment by the Soviet authorities during the second half of his life hints that his defection had not been long-planned and wasn't welcome for anything beyond its utilitarian value, and although Close is very engaging in his sifting of the available evidence, his own skills in other areas quickly relegates the question to a back bench. Close asserts what is too often forgotten about Pontecorvo: that he even if he hadn't been a traitor, he would still have been a physicist of such a stature as to warrant a full-dress biography, and his book's main strength is in laying out that case. Close's book lacks the sparkling rhetorical skill of Alan Moorhead's 1952 The Traitors: The Double Life of Fuchs, Pontecorvo, and Nunn May, but in balance it does things Moorehead couldn't have done: it walks its layman readers right into the heart of Pontecorvo's scientific world, the better to show them the stature of the man.It's a daring gambit, since it opens the book up to the yawns of the scientifically illiterate (that is, nine-five percent of all potential readers). Pontecorvo's researches were on the farthest edge of particle physics, in abstruse theoretical regions understood by only a small handful of other scientists; the majority of Close's readers, if asked, could not pick out their home planet on a chart of the solar system and could not even vaguely say what an electron is. That's a sizable gap, and in Half-Life it's amazing how consistently and energetically Close narrows that gap, always ready to wade in and begin intelligently simplifying:

An atomic nucleus, then, is more than just a core: it is a new level of reality. Within its labyrinthine structures, powerful forces are at work, which are unfamiliar in the wider world. The presence of these forces is suggested by the otherwise paradoxical fact that nuclei exist. Why do the protons, which have all have the same electric charge, not repel each other and cause the nucleus to disintegrate? The answer is that there is a strong attractive force that grips protons and neutrons when they are in contact with one another. Within the nucleus this strong attraction between a pair of protons is over a hundred times more powerful than the electrical repulsion.

Pontecorvo's choice to defect to the Soviet Union was, among all the other things, professional suicide. Russian research was ostracized from the scientific community; Russian technical journals weren't translated, and their contents lagged behind the outside world sometimes by years. A nuclear physicist like Pontecorvo could make all the groundbreaking discoveries in the world, but as long as he was making them behind the Iron Curtain, it would be other, later scientists working in the free world who'd take the podium at Oslo. Close wants to remind his readers strongly of Pontecorvo's heartbreaking might-have-beens, and in order to do that, he has to keep right on clarifying the field:

Today, the weak force is recognized as one of the four fundamental forces of nature, along with gravity, electromagnetism, and the strong nuclear force. The discovery of the universal weak force is one of the most significant scientific advances of the twentieth century. Bruno also realized that this universality held the key to understanding how the electron, muon, and neutrino are related. Having confirmed that the muon is a sibling of the electron, he later applied this same idea to the neutrino, which he saw as having two varieties: one appears to be a sibling of the electron; the other of the muon. Bruno's pairing of these fundamental particles into distinct families was the seed for the modern Standard Model of particles and forces.These insights regarding the weak force and the choreography of particles are of Nobel Prize quality. Bruno Pontecorvo would be involved in all of them.

Involved, but not praised; the central defining choice of his life prevented that. Close is far more diffident in probing his subject's heart than his head; our science-writer is clearly far more comfortable dealing with Pontecorvo the scientist than Pontecorvo the traitor or even Pontecorvo the tortured soul, although his extrapolations in murky areas are always thought-provoking, as when he's discussing just what a heavyweight thinker like Pontecorvo could mean to the masters of his new country, intent as they were on matching and exceeding the nuclear arsenal of the West:

A hydrogen bomb's explosive power comes from the fusion of tritium and deuterium, two isotopes of hydrogen. At the start of the 1950s, when the possibility of creating this weapon arose, there was practically no tritium in the USSR. The isotope is unstable, with a half-life of twelve years. Only trifling amounts of tritium are found in nature, but it can be made in nuclear reactors, using heavy water and enriched uranium.

Since the Soviet Union had no reactors in 1950, as Close puts it, “The arrival of Bruno Pontecorvo could hardly have been more opportune.”Half-Life is a remarkably thorough analysis of that problematically opportune meeting, a grim and depressing double-history of one of the worst and most fascinating traitors of the atomic arms race that defined a generation. The fact that the book's readers will close its final page knowing much, much more about nuclear physics than they did when they started it is a very pleasing by-product, to use a loaded term.