Chapter Twenty-Seven

BRANCA (Boron)

A STEADY RAIN beat on the train carrying Marie and Ève south to Spain in April 1931. They saw little of the passing countryside but found entertainment in conversation with physicist Blas Cabrera of the University of Madrid—and with his companion, who spun tales of traveling the world by zeppelin—till they crossed the Pyrenees and the skies cleared.

“When we arrived at the station in Madrid,” Marie wrote to Irène, “we were welcomed kindly with a magnificent bouquet of red carnations, then we collapsed at our lodgings in the women’s residence, only to be frozen solid because the heat wasn’t working.” The present moment, she said, found her “next to a warm radiator, without shivering,” and hoping to avoid a second night of poor sleep troubled by nightmares. “I dreamt I had fled Madrid in secret, and, realizing what I had done and the inconvenience it would cause, I was trying desperately to return.”

Ève added her own colorful account of the frigid night in a postscript: “I screamed, broke furniture, and committed acts of war until someone finally turned on the heat.”

Abundant sunshine on the following day, luncheon with Mme. Cabrera, and a tour of the physics laboratories did much to warm the travelers. Naturally Ève was not expected to assist in any scientific demonstrations, as Irène would have done, but simply to escort their mother through a series of guest lectures and social engagements in Madrid, Toledo, Granada, Málaga, Almería, Murcia, Alicante, Valencia, and Barcelona. King Alfonso XIII, whom Marie met in 1919 while teaching her radioactivity course to his subjects, had just been deposed, and the former monarchy was changing radically to a republic.

“We are very well received,” Marie wrote Irène again on April 24, after giving two presentations in Madrid. “We meet people rejoicing in their young republic, and it is very moving to see such confidence in the future among the youth, and among many of their elders as well.” The gracious Ève had made “conquests, as usual” during student encounters and visits to the French and Polish embassies.

Once they left the capital, their busy itinerary, coupled with the slow pace of mail, kept them a step or two ahead of letters from home. “I am without news of you and of the Laboratory,” Marie rued to Irène, “and this makes me feel uneasy, as though I were on another planet.”

Of course she knew she could trust Irène, André Debierne, Sonia Cotelle, Catherine Chamié, and Léonie Razet to run things in her absence. But it had become more difficult for Marie to be absent from the lab, even as the reasons for her absences multiplied.

“I arrived here this morning,” she notified Ève from Geneva in mid-July, at a meeting of the International Committee on Intellectual Cooperation, “after a pleasant enough journey with an adequate amount of sleep. I dreamt, I don’t know why, that the public had invaded the wagon-lit, making it impossible for me to dress myself in the morning.” Her committee duty was getting to be “a very heavy task,” she allowed, but one that she deemed indispensable and worthy of personal sacrifice.

She got back to Paris just in time to serve as honorary president of the Third International Congress on Radiology, chaired by Dr. Antoine Béclère, and held at the Sorbonne the last week of July. In the years since the Great War, X-rays and radioactivity had become integral to medical diagnosis and treatment. Physicians were now looking beyond ampoules and needles of radon gas implanted inside the body to “teletherapy,” or the irradiation of cancerous tumors from without, using radium positioned somewhere near the patient. A contingent of doctors from the United States took the occasion of the Paris congress to bestow on Mme. Curie the gold medal of the American College of Radiology.

No Solvay Council was scheduled for 1931, but an International Congress on Nuclear Physics drew Marie and most of her Solvay associates to Rome in October. Enrico Fermi, a new name in the nuclear community, organized the congress to signal Italy’s serious entry into this burgeoning field of research. “I don’t know everyone here,” Marie told Irène on the thirteenth, though at least twenty of the fifty participants were acquaintances, among them Niels Bohr, Max Planck, Arthur Holly Compton, and Werner Heisenberg. In addition to Mme. Curie, usually the only woman at such get-togethers, Fermi had invited Lise Meitner of the Kaiser Wilhelm Institute for Chemistry in Berlin. The Vienna-born Fraulein Meitner, a co-discoverer of the element proto-actinium, was the first woman to be elected physics professor at the University of Berlin—the first, in fact, in all of Germany.

“I try to follow the reports as much as possible,” Marie continued in her letter to Irène, “which is not always easy, considering the extreme technicality and above all the lack of clear elocution among certain speakers. I think I’ll have a few words to say when the discussion turns to radioactive phenomena.” She had not taken in the sights of Rome, nor did she expect to. “I have little else to tell you at this point, except that Bohr strongly insists on the impossibility of actually applying quantum mechanics to the interior of the nucleus. Love, Mé.”

Niels Bohr had successfully connected quantum mechanics—the new understanding of events at the atomic and subatomic scale—to the exterior of the atom, that is, to the orbiting electrons. As he envisioned the atom, electrons could occupy only certain orbits, representing discrete energy levels. When an electron absorbed a specific quantum of energy, it instantly shifted to a higher orbital shell, and when it dropped down again to its accustomed level, it emitted that quantum of energy as a specific wavelength of light. This activity accounted for the colors of lines in the visible spectra of elements.

Marie, a close witness to the growth of quantum mechanics, well appreciated the theory’s departures from classical physics. As a human being in the realm of ordinary experience, she had traveled from Paris to this meeting in Rome along a continuous stretch of railroad tracks. At the scale of an electron in the subatomic realm, where discreteness trumped continuity, she would have been either in Paris or in Rome, and never anywhere in between.

Each orbital shell of Bohr’s atom had its own population limit: two electrons at most could inhabit the lowest one, eight apiece in the next two, and eighteen in each of the following two. Atoms with outermost shells filled to capacity could not engage in chemistry with other atoms. This limitation explained the inactivity of the inert, or “noble,” gases. The completion of each electron shell coincided with the end of a period, or horizontal line of elements on the periodic table.

The nucleus within the electron shells—the interior of the atom, the seat of radioactivity—remained elusive. Known only as the locus of positive charge, it somehow managed to expel negative electrons in the course of beta decay. Some of the scientists present in Rome had already tried to poke at the nucleus by various means in the hope of exposing its secrets. Perhaps the most riveting talk Marie heard was the one presented by Walther Bothe, director of the Institute of Physics at the University of Giessen. He and a student collaborator, Herbert Becker, had used beams of alpha particles from polonium to bombard targets made of lightweight elements such as lithium, beryllium, and boron. Bursts of penetrating radiation fled the struck targets with enough energy to pierce a piece of lead several centimeters thick. The emitted radiation resembled gamma radiation, in that it carried no charge, and its measured energy exceeded that of the bombarding alpha particles. Apparently, the target materials, although not radioactive, had undergone some type of nuclear decay. Neither Bothe nor anyone else could explain this strange outcome.

MARIE RETURNED FROM her international travels to the international milieu of the Institut du Radium. The forty men and fifteen women now working in the expanded Laboratoire Curie represented nearly every European country, as well as Russia, China, and India. “La patronne” had begun holding weekly meetings to afford researchers a chance to report their progress or bemoan a setback. Her newest trainee, Branca Edmée Marques, came from the University of Lisbon, having taught courses for six years there in physical, organic, and analytical chemistry. At age thirty-two, she was one of several talented young career scientists selected to staff the new Portuguese radiological institute, and had been awarded a government fellowship to acquire the necessary experience abroad. Branca Edmée Marques chose to learn the measurement of radioactivity and the chemistry of radioelements in Mme. Curie’s lab, even though her husband and former professor, António Sousa Torres, could not accompany her to Paris. She brought her mother instead.

Irène had recently shown several years’ worth of her chest X-rays to a new doctor, who reassured her as to the condition of her lungs. It seemed her tuberculosis was in remission, though anemia continued to weigh on her. Thus far that year she had sought relief at three mountain retreats, beginning in April at the Jura range on the Swiss border. In August, upon her arrival in the Chartreuse Mountains just north of Grenoble, she complained of feeling “very tired and incapable of walking for as much as an hour.” She rallied as the days passed, however, and moved on to meet her colleague and hiking pal Angèle Pompéï at le Monêtier-les-Bains, a resort area that offered them mineral baths as well as the beneficial altitude of the Hautes-Alpes.

Irène rested some more in September with her husband and daughter at l’Arcouest. She had been warned, while pregnant with Hélène, that she should not attempt to have a second child, given the precarious state of her health. Nevertheless, she was expecting again when she and Frédéric resumed their research in the fall.

Lately they, too, had been using beams of alpha particles from polonium to probe the atomic nucleus. The Curie lab’s enviable and constantly replenished stockpile of polonium put them at an advantage over most other researchers. When they decided to repeat and extend the recent experiments of Walther Bothe and Herbert Becker, they began by preparing a polonium source of ninety-eight millicuries—far more intense than the seven-millicurie source that the German researchers had employed. They channeled its diffuse emission of alpha particles into a narrow, collimated beam and aimed it alternately at targets of boron, beryllium, and lithium, to see whether these nonradioactive elements could really be made to release radiation.

In each case, copious radiation streamed from the target into the ionization chamber, where its strength was registered on an electrometer. They tried deflecting the emission with magnets but could not. Since it proved neutral—neither positively nor negatively charged—they took it for gamma radiation. They placed thin metal screens in the radiation’s path, and it punched right through them. When they replaced the metal screens with others made of hydrogen-rich material such as paraffin, the ionization actually increased in strength.

How to explain this result? It was surprising enough to elicit gamma radiation from lightweight elements. Now it seemed that the gamma radiation was actually knocking hydrogen nuclei out of the paraffin screen, and these ions of hydrogen were adding their power of ionization to that of the gamma rays from the targets.

Irène and Frédéric prevailed on physicist and Curie family friend Jean Perrin to deliver their news to the Académie des Sciences.