Marie Curie (4 page)

Four months into their marriage came a remarkable scientific discovery. Not, however, made by either Curie, but by a reclusive German physicist named Wilhelm Röntgen. In November 1895, he accidentally discovered a new kind of ray. These rays had the ability to travel through opaque material that was impenetrable to ordinary light—they could travel through wood, even flesh. The rays were invisible but revealed themselves on a special phosphorescent screen that was standing nearby. very mysterious. He labeled them X-rays, “X” as in the math term used when a quantity is unknown.

He wrote to a friend that initially he told no one except his wife Bertha about the discovery. He feared people would say, “Röntgen is out of his mind.” One of the very first X-ray pictures he made was of Bertha’s hand—not only was the wedding ring on her fourth finger visible, but so were her bones. It was to become one of the most famous pictures in the world. Röntgen finally announced his discovery in a dramatic lecture in 1896, capping his performance by x-raying onstage the hand of an eighty-year-old man. Seeing the entire bone structure beneath the skin, the audience rose as one in a standing ovation. Here was a new way of looking
inside
nature, seeing what had never been visible before.

Röntgen refused to patent X-rays for private gain, wanting them to benefit humanity. He later died broke.

Meanwhile, only a few months after Röntgen’s X-ray discovery, a French physicist discovered what appeared to be yet another kind of ray. Henri Becquerel, who came from four generations of illustrious scientists, was studying X-rays and working with uranium. This element had been discovered in 1789 and named for the then-newest planet, Uranus. Becquerel observed that uranium salts, in spite of being wrapped in a protective envelope, left a visible image on a photographic plate. Continuing to experiment, he discovered something really odd—a constant stream of rays were emitted from uranium in all directions. It seemed impossible to measure these rays or to do anything further with them. He assumed he’d reached a dead end.

Röntgen’s X-rays thrilled scientists, especially medical doctors, who leapt on them with great energy. Anyone who has ever broken a bone clearly understands their value. One year after the announcement of his discovery, there were forty-nine books or pamphlets published about X-rays, plus over a thousand papers.

Becquerel’s discovery, on the other hand, caused no such sensation. His rays were mostly ignored. They seemed much the same as X-rays, only weaker. Just a day or so after his discovery, he reported on them to the Monday meeting of the French Academy of Sciences, the most powerful organization for science in France. His colleagues listened, then went to the next item on the agenda. Becquerel himself sort of dropped the ball and drifted for the time being into other areas of research.

Back in the Curie apartment, the nightly discussions were centering on the work of both Röntgen and Becquerel. Marie had published her first article on the magnetism of tempered steels and was casting about for a subject for her doctoral thesis. To earn her doctorate, she had to present original research and make a significant discovery.

Ambitious, enterprising, and always practical, she was attracted to Becquerel’s rays by their very neglect. There was so little work on them—only four other papers besides Becquerel’s own—she could skip that whole business of reading lengthy lists of background material.

And in her estimation, these “uranium rays” were a new phenomenon that deserved attention. She decided to make a systematic investigation. Uranium had a mysterious way of electrifying the air around it—why? What was the effect of these rays, and where did their energy come from? Were the kinds of rays in uranium to be found in other elements as well?

It was quite stimulating—a new area where she could start experimenting immediately and try to discover something interesting. Even something important.

CHAPTER FOUR

Mr. and Mrs. Radioactive

T
HE BIRTH OF her daughter Irène in September 1897 barely interrupted the flow of Marie’s work. The baby was delivered by Marie’s father-in-law, who reported that she never once cried out during the entire labor. It didn’t seem to occur to either Marie or Pierre that she might give up research for motherhood. Instead, Pierre’s father came to live with them. They also hired a nanny, although according to legend, Marie
never
missed giving the baby her nightly bath. However, little Irène was much closer to her grandfather. He helped enormously with child care as well as housekeeping. When she was old enough to ask why Marie was gone every day while other mothers stayed home, it was her grandfather who explained that Marie was doing important work.

Indeed she was, despite one big problem. Marie had no lab of her own. Pierre solved it by arranging for her to take over a drafty, drab storage space at his school. A closet, really. (On cold days, the room’s temperature could drop as low as a frigid forty-four degrees.) Still, it was all hers, a lab she was essentially starting from scratch. Had she worked in a fancy setup within the scientific establishment—say, at the Sorbonne—she might have had to focus on what professors told her to do. Here she was out of the loop, free to explore what she pleased: Becquerel’s rays. Passing her during the day, Pierre sometimes would stop to caress her hair.

Pierre was busy with his own work on crystals. Beyond that, his electrometer device was of critical help to her now. With it, Marie could measure very small currents of electricity that the weaker rays of uranium produced.

Pierre also helped Marie construct a chamber out of old wooden grocery crates. Inside they placed two circular metal plates, one at the bottom with a positive charge and another with a negative charge three centimeters above it. A thin layer of uranium was placed on the lower plate.

Marie already knew that the uranium rays would make the air conduct an electric current to the top plate. The more radiation, the stronger the current would be. Using the electrometer to measure the strength of the electric current, she could work out how much radiation was being emitted.

What she discovered was that the amount of uranium was the sole factor determining the amount of radiation emitted (and also the strength of the electric current). Nothing else mattered—not changing the temperature of the uranium, for instance.

The work required incredible dexterity and concentration, painstaking hours of sitting in one position using very precise devices while manipulating a stop-watch and weights. Think of someone juggling while reading a newspaper and you get some idea of the multitasking involved. But this was a job tailor-made for Marie Curie, so careful a worker that at the Sorbonne she was known for never shattering glass tubes the way other students did. She succeeded in obtaining the measurements that gave her the relative power of the uranium.

Now that she’d measured the amount of radiation given off by uranium, the next question was: did other elements besides uranium emit these strange rays? The only way to find out was to examine all the known elements. very persuasive when she needed something for her work, she begged and borrowed samples of elements from other scientists, including some of her old professors. She now went through Mendeleyev’s periodic table of elements, testing them one by one. The mystery rays weren’t just peculiar to uranium—she discovered that they came in a weaker form from thorium (a mineral element discovered in 1828) as well. Her findings were that only the elements uranium and thorium gave off this radiation.

In April of 1898, Marie made a report to the all-important French Academy of Sciences. The eminent men at the meeting listened to a report on frog larvae. Then Marie’s report, called “Rays Emitted by Uranium and Thorium Compounds,” was read aloud by one of her professors. She couldn’t read it herself because she wasn’t a member—no women were allowed. Then came a report on hydraulics. . . .

Marie returned to the lab and kept experimenting. Now that she had tested all the elements for Becquerel rays, she turned her attention to compound minerals, ones containing some uranium and thorium.

She tested ores just as she had tested each element. Her interest was piqued in particular by a heavy black ore called pitchblende. Pitchblende contains a huge variety of minerals, including uranium and thorium. What she discovered was intriguing: pitchblende gave off four to five times more rays than could have been predicted by the amount of uranium and thorium in it.

Why?

Her leap in thinking was straightforward and brilliant at the same time.

She came up with a hypothesis, a possible explanation that could be tested. A new element, considerably more active than uranium, must be present in the ore. She set out to look for an unknown substance of unusually high activity. “The element is there and I’ve got to find it,” she told Bronia. She was doing something completely new, looking for an unknown element with the only clue to its existence being its strange rays—rays that she called radioactive, meaning active in emitting rays.

To Marie, time was of the essence. “I had a passionate desire to verify this hypothesis as rapidly as possible,” she wrote. She was aware of other scientists working in this area already, though perhaps not as precisely and systematically as she was. G. C. Schmidt in Germany, for example, was investigating the activity of thorium. There was a race on—all terribly polite, but still . . . Marie was determined to be first.

At this point, Pierre showed what a generous spirit he had: he could see his wife was on the verge of discovering something major. As brilliant as he was, Marie’s work was leading in a more important direction. For a man raised in the nineteenth century, when the second-place status of women—both intellectually and physically—was a given, Pierre did something extraordinary. He stopped his work on crystals and joined her. Marie, who had something of a notebook obsession, had all along been keeping rigorous records of her work. Now her meticulous handwriting was interspersed with his childlike scrawl.

Isolating this theoretical new element involved a process of elimination. All other elements in the pitchblende had to be separated out chemically. After weeks of attacking and reattacking their supply of pitchblende with all the chemicals available to them, the Curies produced something they suspected was their new element.

How could they prove it? Possibly by looking at the light pattern produced by the substance. during Newton’s famous 1666 experiments, he first worked with sunlight and a prism, proving that light contains all the colors. By Marie’s time, a whole science—spectroscopy—had developed. In spectroscopy, when an element is heated to a gaseous state and the light it emits is studied through a prism, it produces unique lines along the spectrum of colors. The pattern of spectral lines supplies a sort of signature for that element. Already, eight new elements (including helium) had been identified through their unique spectral lines.

The Curies called in Eugène demarcay, a French spectroscopy specialist, to help. Alas, no unique spectral lines appeared when their substance was tested. Whatever they had could not be labeled a new element . . . not yet.

As usual, Marie was undeterred. It was her hunch that the substance just needed more purification. After more chemical investigation, on July 13, 1898, she had what she wanted. A new element. She felt secure enough to give it a name—“polonium,” with the abbreviation “Po.” Pierre wrote it down in their notebook. Patriotic Pole Marie came up with the name to honor her native land.

Five days later, at the French Academy, Henri Becquerel himself read a report by the Curies, called “On a New Radio-Active Substance Contained in Pitchblende.” (Pierre couldn’t read it because he wasn’t a member, either.) It announced the Curies’ discovery of polonium, a substance well over four hundred times as radioactive as uranium—a new element. It was also the first use of “radioactive” in print. She wrote that it was “necessary at this point to find a new term to define this new property of matter.” She had discovered a new element in a completely new way—by its rays.

The scientific establishment understood it was not dealing with an amateur. Marie was awarded a prize, money, and a statement that conceded, “The research of Madame Curie deserves the encouragement of the Academy.”

At long last, the Curies took a three-month summer vacation to get out of the hot city. Talk and planning did not cease, especially a hunt for a supplier of enormous amounts of pitchblende.

Even after the polonium was isolated, pitchblende still gave off an incredible amount of radiation. did this mean there was yet another new element waiting to be discovered? It certainly seemed that way. After being back at work for six weeks of experiments, the Curies discovered a substance
nine hundred times
as radioactive as pure uranium.

And it produced new and unique spectral lines.

Six days later, on december 20, 1898, she sent off a new paper to the Academy announcing the discovery of another new element. In it she concluded, “The various reasons we have just enumerated lead us to believe that the new radioactive substance contains a new element which we propose to give the name of RADIUM.” The name came from “radius,” the Latin for
ray
, used for the element’s intense radioactivity. discovering the two elements had taken one year. Marie couldn’t have done it without Pierre’s help. They were inseparable. “We really have the same way of seeing everything” was one of his most frequent comments. It wasn’t one of those marriages where one spouse’s obsessions made the other one feel neglected or envious—they shared exactly the same obsessions to an equal extent. Marie wrote to Bronia (who was in the process of founding a state-of-the-art treatment center for tuberculosis patients back in Poland): Pierre is “the best husband one could dream of. . . . He is a true gift of heaven, and the more we live together the more we love each other.”

The lab was a place of beauty, love—and serious accomplishment. By age thirty-one, Marie had discovered two new elements through the rays they emitted and coined the word that described those rays. One way in which she did differ significantly from Pierre was her drive to succeed. He was all but indifferent to competition or taking credit. She was just the opposite—she wanted her gold medals.