Diana Preston - Before the Fallout

Just like the neutron, the positron had previously been glimpsed but misinterpreted by others. Chadwick had come close to it but, fixated on the neutron, had missed the significance of some observations. The Joliot-Curies had photographed electrons in a magnetic field “going backwards the wrong way,” but had not recognized them as positrons until they read of Anderson’s work. Piqued by their failure to identify the positron, the Joliot-Curies had launched a series of experiments to discover more about it. Placing a cloud chamber in a strong magnetic field, they bombarded elements with alpha particles. The bombardment caused elements in the middle of the periodic table to release protons, but light elements like aluminum sometimes ejected a neutron and a positron instead. This finding caused them to wonder whether a proton might be a compound of a neutron and a positron. However, their suggestion met fierce opposition at the Solvay Conference, particularly from Lise Meitner. Undeterred by the hostile gaze of Marie Curie, who resented her daughter’s work being criticized, she stated, “My colleagues and I have done similar experiments. We have been unable to uncover a single neutron.”

Deflated and anxious, the Joliot-Curies hurried back to Paris to recheck their results but could find no mistakes. The light elements had definitely emitted neutrons. Encouraged, they resumed their experiments and so stumbled upon one of the most significant discoveries so far.

After bombarding ordinary aluminum with alpha particles, Frederic Joliot-Curie used a Geiger counter to measure the results. To his surprise, when he moved the radioactive source emitting the alpha particles away from the aluminum, the counters, instead of immediately falling silent, continued noisily clicking. He could not believe it and repeated the maneuver. The results were the same. He fetched Irene, who was equally puzzled. That evening, having to attend a dinner engagement, they asked a colleague to check that the counters were not faulty. Hastening back to their laboratory the next morning, they found his note: The counters were operating perfectly.

Painstakingly, the Joliot-Curies worked out what had happened. Until then, all reactions that scientists had produced had occurred immediately and ceased as soon as the bombarding source was removed. However, on being bombarded with alpha particles, the aluminum had transmuted into an intermediate radioactive isotope of phosphorus, which, as it decayed back to its stable state, silicon, continued to emit radioactivity (positrons) for some time after the bombarding source of alpha particles had been removed. They had induced a new phenomenon: “artificial radioactivity.” An exultant Joliot told his assistant, “With the neutron we were too late. With the positron we were too late. Now we are in time.” Until then, physicists had known that by bombarding it with a particle of sufficient energy, a nucleus could be disintegrated and a new, stable one formed. No one had realized that in certain circumstances, an unstable element in the process of nuclear decay could be created. In other words, man could force the elements to release their energy in the form of radioactive decay. The Joliot-Curies rushed to publish the news of “A New Type of Radioactivity.”

The discovery caused consternation and disappointment at Berkeley. As one of Lawrence’s team observed, “We could have made the discovery any time.” If, rather than concentrating on continued improvement of the performance parameters of their accelerators, they had only thought to run a Geiger counter over one of their targets, they too would have heard the telltale click announcing the creation of a new radioactive element. This had not happened for practical reasons: The laboratory’s Geiger counter and the cyclotron worked on the same switch, so that the team had never had the chance to explore whether the counters kept registering after the cyclotron was switched off. It was an irritating thought. As another man admitted, “We felt like kicking each other’s butts.” They altered the wiring, left the Geiger on after taking the cyclotron down, and sure enough heard the counter’s rhythmic tick—“a sound that none who was there would ever forget,” recalled Stanley Livingston.

The discovery brought Marie Curie great satisfaction. Joliot wrote of “the expression of intense joy which overtook her when Irene and I showed her the first [artificially produced] radioactive element in a little glass tube. I can see her still taking this little tube… in her radium-damaged fingers. To verify what we were telling her, she brought the Geiger counter up close to it and she could hear the numerous clicks…. This was without a doubt the last great satisfaction of her life.” Marie told a friend, “We’re back in the fine days of the old laboratory.”

“La Patronne” was still a powerful presence at the Curie laboratory. When the young chemist Bertrand Goldschmidt arrived for an interview in June 1933, sn e told him in a strong Polish accent, “For a year or two you will be my slave in chemistry and do everything for me.” He was in awe of this “rather small old lady with big hairs on her chin” and dressed entirely in black who looked much older than her sixty-five years. He was also fascinated by the stories still circulating of a once-active love life. There were, he recalled, “many rumours,” including that Eve Curie, born in 1904 and with her blue eyes and dark hair so different from her older, fairer sister, Irene, was not Pierre Curie’s daughter “but Andre Debierne’s,” but that Debierne had later been “succeeded in Madame Curie’s heart by Langevin.”

However, any such passions were long spent. Marie’s life was ending. She died, aged sixty-six, at dawn on 4 July 1934 in a sanatorium in the mountains. The cause of death was extreme pernicious anemia “of rapid, feverish development. The bone marrow did not react, probably because it had been injured by a long accumulation of radiations.” She had insisted on reading her own temperature, holding the thermometer “in her shaking hand,” and recognizing from the sudden fall in her fever that her end was near.

Her coffin was buried above Pierre Curie’s. There was no priest and no prayers, as befitted a devout skeptic, but her brother and sister cast a few grains of Polish soil on her coffin.

The following year, the Joliot-Curies were awarded the Nobel Prize for Chemistry for their finding of artificial radioactivity. In his acceptance speech, Frederic Joliot-Curie remarked that “scientists who can construct and demolish elements at will may also be capable of causing nuclear transformations of an explosive character.” Few paid much public attention to these prophetic words. In 1933, at a meeting of the British Association for the Advancement of Science, Ernest Rutherford had insisted that anyone who believed that atomic energy could be released on a large scale was “talking moonshine.” Niels Bohr believed that even if a release of explosive power from the nucleus was possible in theory, in practical terms it was unattainable: “Not only are such energies at present far beyond the reach of experiments, but it does not need to be stressed that such effect would scarcely bring us any nearer to the solution of the much discussed problem of releasing nuclear energy for practical purposes. Indeed the more our knowledge of nuclear reactions advances the remoter this goal seems to become.” To Einstein, the chances of achieving a massive release of energy were like “a blind man in a dark night hunting ducks by firing a shotgun straight up in the air in a country where there are very few ducks.”