Advent Calendar of Science Stories 18: Third Time's the Charm

The winter solstice holidays are a time for family and togetherness, so building off yesterday's post about the great Marie Skłodowska Curie, we'll stay together with her family. Specifically her daughter Irène Joliot-Curie and her husband Frédéric. The Joliot-Curies are possible answers to a number of Nobel Prize trivia questions-- only mother and daughter to win, one of a handful of married couples, etc.-- but the scientific story about them that I find most fascinating is that their Nobel was for the third thing they did that could've earned them the prize, after they just missed out on two other Nobel-worthy discoveries.

Their two near-misses came in 1932. One was a paper they published on some intriguing new radiation originally noticed by Walther Bothe in Germany. Bothe had noticed some odd effects when alpha particles from polonium hit light elements, and the Joliot-Curies expanded on his experiments showing that the new radiation had unusual penetrating power, and knocked protons with fairly high energies out of materials containing hydrogen. The new radiation wasn't affected by an electric field, so it was initially believed to be a new type of gamma rays (that is, high-energy light), but the Joliot-Curie results were hard to fit with that theory.

In England, James Chadwick heard of the Paris results, and immediately realized the significance, because he and his boss, Ernest Rutherford, had been looking for it for almost twenty years. The new radiation wasn't an unusual gamma ray, but a new, neutral particle with about the mass of a proton. Chadwick quickly threw together an experiment-- he was the assistant director of the Cavendish Laboratory, and thus had ample resources to command-- and within a few weeks had demonstrated the existence of the neutron. This won him the 1935 Nobel Prize in Physics.

As if that weren't enough, 1932 also saw the Joliot-Curies miss out on the discovery of antimatter. They were photographing particle tracks to study the effects of alpha particle bombardment of various targets, and in May produced some very clear photos showing particles that appeared to have the same mass as an electron, but curved in the wrong direction in response to a magnetic field. As the tracks left by the particles don't indicate the direction of motion, they interpreted this (with some input from Niels Bohr) as ordinary electrons moving in the opposite direction from their particle beam, presumably produced by collisions in the back wall of their detection chamber.

Of course, there's another way to produce such tracks, namely a particle going in the right direction, but with the opposite charge. The Joliot-Curies didn't consider this, as no such particle was known, but Carl Anderson at Caltech did, and in August of that same year produced the famous photograph confirming the existence of the positron, the antimatter equivalent of the electron. This got Anderson half of the 1936 Nobel Prize in Physics.

You would think, then, that 1935 would've been a real bummer of a year for the Joliot-Curie family, watching Chadwick win a Nobel Prize that could've been theirs, had they correctly interpreted their results. Luckily for them, though, in the intervening three years they had done the work that would secure them their own prize, in Chemistry, that very same year. In 1934 they showed that the same sort of experiments that produced the neutrons they might've discovered, namely bombarding light elements with alpha particles, also produced unstable isotopes of other elements. They demonstrated that they could make radioactive nitrogen from boron, radioactive phosphorus from aluminum, and radioactive silicon from magnesium.

This discovery of "artificial radioactivity" richly deserved the Nobel Prize they won for it, because it opened a huge range of new experiments. Rather than spending weeks distilling naturally occurring radioactive elements out of pitchblende ore, the way Marie and Pierre Curie had, physicists could use particle bombardment to create new isotopes. Given the right projectile and the right target, you can make almost anything you might care to study. Modern nuclear physics would be impossible without the Joliot-Curie's discovery. And if you like your physics to have practical applications, well, they have that, too: most of the isotopes used in nuclear medicine are manufactured in accelerators, using a version of the Joliot-Curie process.

So, the Joliot-Curies had a fascinating career in science, and probably deserve to be more widely known. As great as their contributions to physics were, the most interesting part of their story might be what came after-- when France fell to the Nazis in 1940, Frédéric stayed in Paris, where he used his physics work as cover for manufacturing radios and chemicals for the french Resistance. Irène was in Switzerland for much of the war, being treated for tuberculosis, but made several trips to Paris to visit her husband and children, eventually taking the children to safety in Switzerland in 1944. The photo I grabbed from Wikimedia for the featured image doesn't have a specific date, just "1940's," and I haven't tried too hard to find a more specific attribution, because it's sort of romantic to imagine that it was taken during one of her wartime visits.

(And, of course, their whole relationship is a good story-- neither appeared especially brilliant as students, and they seemed an unlikely match when he first started working at the Radium Institute. Marie Curie was sufficiently skeptical that she insisted that control of the Institute should pass to Irène alone. It all worked out pretty well, though... Somebody should totally make a movie about these two.)

Anyway, take a moment to celebrate the Joliot-Curies, whose work is essential for everything from basic science to cancer therapy to smoke detectors. They're also a great demonstration of the importance of persistence in science-- if you miss out on your first chance at a Nobel, well, just keep at it, and maybe everything will work out in the end...

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(Part of a series promoting Eureka: Discovering Your Inner Scientist, available from Amazon, Barnes and Noble, IndieBound, Powell’s, and anywhere else books are sold.)