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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