Overlooked is a series of obituaries about remarkable people whose deaths, beginning in 1851, went unreported in The Times.
The phone call for Elizabeth Rona came to the Budapest university where she worked: Don’t go to the theater, the caller warned.
Rona, who was celebrating her 29th birthday, had planned to meet her family there in a few hours, but she learned that militants had taken control of the building. It was one of many incidents in the upheaval that was tearing at Hungary in the immediate aftermath of World War I and the disintegration of the Austro-Hungarian Empire.
It was also typical of the unsettled world that Rona — a woman who was ethnically Jewish in a male-dominated world plagued by anti-Semitism — had to navigate throughout her career as a chemist researching the strange new science of radioactivity.
Rona moved from lab to lab — often from country to country — to seize opportunities for research. As a result of her work, the world would learn fundamental details of the behavior of atoms and how radioactivity could be used as a clock in studying the earth’s history, informing the modern practice of geochronology.
The earth is threaded with radioactive isotopes that decay at a constant rate into other substances, a process that scientists can use to study the planet’s history. For example, the more recent past can be examined by measuring how much carbon-14 in a sample has decayed into nitrogen, with each stage of decay like the ticking of a second hand. For the more distant past, scientists can examine how much potassium-40 has turned into argon-40, or choose another pair that fits their needs. Radiometric dating lets scientists assign dates to objects, like fossils and ancient coral reefs, which reflect the planet’s past climate.
Elizabeth Rona was born on March 20, 1890, in Budapest to Ida Mahler and Samuel Rona. Her father was a doctor, and she wanted to become a doctor, too. But her father, fearing the work would be difficult for a woman, encouraged her to study chemistry instead. After earning her Ph.D. at the University of Budapest, she worked as a researcher with the radiochemist Kasimir Fajans at the University of Karlsruhe (now the Karlsruhe Institute of Technology) in Germany.
She returned to Hungary and worked with George von Hevesy, a chemist whose experiments used radioactive versions of elements as tracers to explore chemical reactions. Rona and von Hevesy tracked the diffusion of radioactive tracers in various materials to see how quickly atoms of a substance drifted from one area to another. With that information, it would be possible to calculate an atom’s size, which could then be used to help explain its behavior.
In those early days, radiochemistry was a kind of scavenger hunt to collect and understand these features. Every kernel of information was swiftly fed into new theories and predictions about radioactivity and atoms.
Von Hevesy and Rona’s findings were important for other scientists, but the tracers, for which von Hevesy eventually won the Nobel Prize, turned out to have even broader uses: For decades now, doctors have injected radioactive tracers into patients to aid in diagnosing conditions like cancer and heart disease.
Rona was later invited to work with the radiochemist Otto Hahn in Berlin. She arrived at the Kaiser Wilhelm Institute in 1921 to do research alongside scientific giants like Lise Meitner, who along with Hahn would contribute to the discovery of nuclear fission, the reaction at the heart of the atom bomb.
Rona set to work isolating a potential new element called ionium. The substance turned out to be an isotope of the naturally occurring radioactive metal thorium, which had already been well studied. But thorium would play an important role in Rona’s later career.
Trying to escape the hardships of post-World War I Berlin, Rona briefly worked as an industrial chemist at a textile plant in Hungary, where she developed a method to turn flax into a burlap-like material. When Stefan Meyer, the director of the Radium Institute in Vienna, offered her a research job in his lab, she moved again.
Scientists knew that exposing atoms to a radioactive element like radium would trigger reactions, revealing details of their internal structure and physics. But radium was rare and costly, with tiny quantities hoarded and chivvied between nations for experiments. Researchers soon learned that polonium could be used in these experiments instead. Rona was one of those who learned to prepare the polonium, which made her in demand by high-profile labs.
Rona traveled to Paris to work on making concentrated polonium sources alongside Irene Joliot-Curie, Marie Curie’s daughter. Rona’s polonium went on to be used in numerous experiments.
In the years following her Paris sojourn, Rona started to explore the phenomenon of radioactivity in seawater. Each summer, in an island laboratory in Sweden, she measured natural radioactivity in the ocean. She soon realized that there were important differences between the radioactivity of what was floating in the water and what settled on the seabed.
Again, politics interrupted her research. The rise of the Nazis forced her to flee Europe for the United States.
To aid in the war effort, she gave the United States her methods for concentrating polonium, which were used in the project of building an atomic bomb.
She later became a teacher at the Oak Ridge Institute of Nuclear Studies in Oak Ridge, Tenn., and a professor of oceanography at the University of Miami. She continued her work on seawater, analyzing its uranium content. Uranium levels were constant in oceans across the world, she found. Thorium, however, sinks to the sea floor.
That discovery had important implications: Anything growing in seawater, like a coral reef, will have uranium but no thorium in it — at least at first. Over the course of eons, uranium gradually breaks down into thorium. It happens at such a predictable rate that scientists can deduce the age of an ancient reef from the amount of thorium in it. Furthermore, the fact that thorium builds up on the sea floor can also be used to date deep sea sediment cores.
This set of radioactive clocks, which draw on observations that Rona made over the course of her peripatetic life, have been used around the world for more than 50 years to construct pictures of past tectonic events and measure how sea level has changed.
Rona outlived many of her colleagues, who died prematurely of ailments related to radiation exposure. She was always careful, buying a protective gas mask for herself when her supervisor declined to, and survived at least two lab explosions.
Despite the many dangers of her time — from radiation, revolutions and wars — Rona worked on radioactivity for nearly six decades, contributing to one of the most important chapters of its study.
She died on July 27, 1981. She was 91.