A photographic print toned with uranium, made around 1900. The discovery of uranium “rays” in 1896 led to the new science of radioactivity. (Library of Congress, LC-USZC2-6094)
Marjorie C. Malley. Radioactivity: A History of a Mysterious Science. New York: Oxford University Press, 2011. 280 pp. $21.95.
By the end of the 19th century, chemists resembled hunters, tracking and capturing many elements previously unknown. They mounted their prizes on a new invention—the periodic table of the elements. Each known element was placed according to its specific and unchanging weight and measure. The system worked so well that chemists left places at the table for those elements yet to be caught.
Chemists had no advance warning that the world of matter was less than stable. But from our modern perspective 1896 began a new era in chemistry, when Henri Becquerel discovered a ray emitted by a uranium compound, soon called a Becquerel ray. Uranium compounds had an inexhaustible supply of the mysterious ray, and no one could figure out where the energy was coming from. At first chemists paid little attention, but soon they realized they had a whole periodic table’s worth of trouble: elements that transmuted into other elements, elements whose weight fluctuated, and elements that produced far more energy than seemed possible. In Marjorie C. Malley’s book Radioactivity, scientists stumble through the wreckage of the old chemistry, finally creating a solid new science out of instability (and winning lots of Nobel prizes in the process).
Looking back in time, it’s often hard to know what all the fuss was about. What is so strange about one element decaying into another? Malley does a wonderful job of showing the uncertainty and confusion of that time and how scientists worked their way to a new understanding of the atom. By using the scientists’ frames of reference and terminology—thorium emanation, ionium, radium D—she helps us understand and sympathize as these researchers fumbled in the dark with only the faint glow of Marie Curie’s radium to light their way. The stakes were high. When Frederick Soddy (a future Nobel laureate) noted in the very early 1900s how matter seemed as transmutable as the long discredited alchemists had claimed it to be, Ernest Rutherford (also a future Nobelist) reportedly told him, “Don’t call it transmutation. They’ll have our heads off as alchemists” (p. 52).
This book is for those wanting to know more about how the science of radioactivity came to be. As such, it focuses on the major players, their research, and their scientific struggles. Malley assumes little in the way of scientific knowledge on the part of the reader but also expects the reader to work hard at digesting all the information she provides. The final section dives into the broader scientific culture of the day and the big questions raised by radioactivity. One minor quibble: the author barely touches on why these strange rays originally grabbed the public imagination. She briefly mentions how invisible rays fit into the growing spiritualist movement and leaves it at that. Yet to a few of the scientific figures of the day, this aspect of the new science was important at a time of intense religious and cultural anxiety. Chemist William Crookes even believed rays might provide a way to communicate with the dead. For some, an element that gradually vanished only to be replaced by another element was no stranger than conversing with the departed.
As soon as scientists gave up one assumption, such as the unchanging nature of an element, another challenge appeared. Chemists knew each element to be chemically distinct. But uranium, thorium, and actinium decayed into descendants that were chemically inseparable from each other. How could different elements, which by definition meant chemically separable, produce descendants that were chemically identical to each other? It was Soddy, a chemist, who showed that radiation (or “emanation” in his terms) was not connected to the chemical properties of elements. Soddy appears as quite a radical thinker in this book. He not only made “transmutation” respectable again, he also tossed out another chemical assumption, that an element’s atomic weight determined its chemical properties and so its position in the periodic table. This new approach proved justified when in 1919 Francis W. Aston built a mass spectograph and found isotopes with varying atomic weights everywhere, not just in radioactive elements. Matter seemed to do nothing but fall apart.
While radioactivity raised new questions, Malley shows how it also answered old ones, such as what powers the sun. The Curies soon realized that a tiny amount of radium produces extraordinary amounts of energy. Atomic energy appeared a better power source than comets falling into the sun, a 19th-century answer to the sun’s riddle. Radiation also solved a fundamental problem in evolution. Charles Darwin had relied on geology to determine the earth’s age, and such geologists as Charles Lyell, a contemporary of Darwin, assumed an almost infinite age. By the dawn of the 20th century, though, such physicists as Lord Kelvin had reduced the earth’s past to only tens of millions of years, not nearly enough time for Darwinian evolution. Of greater concern to many was the future: a cooling earth in which all life must come to an end. Energy from decaying elements provided planet-wide central heating. “Since the earth’s crust was riddled with radium and other radioactive substances, all bets were off on the earth’s age and its future prospects” (pp. 80–81). In the 1910s scientists turned their attention to the machinery inside the atom, the place where radioactivity originated. The rest is atomic history.
For 30 years radioactivity was a hot topic for research. Malley’s charting of its birth and growth reminds us how suddenly our assumptions about nature can be overthrown.
Michal Meyer is editor in chief of Chemical Heritage.