What did Marie Curie call the rays emitted by uranium compounds?

Marie Curie called the rays emitted by uranium compounds “Becquerel rays.” The name honored Henri Becquerel, whose 1896 experiments showed that uranium salts could darken photographic plates even when protected from light.

Curie investigated these mysterious emissions as the subject of her doctoral research. Rather than relying only on photographic effects, she used a highly sensitive electrometer associated with Pierre Curie’s laboratory to measure the electrical conductivity produced in air by the rays. Her measurements showed that the activity was linked to the amount of uranium present and did not depend on the compound’s physical form or exposure to sunlight.

“Becquerel rays” was an early name, not the modern scientific term. Curie introduced the word “radioactivity” for the property of certain substances that spontaneously emit radiation. Her systematic measurements also revealed that thorium emitted similar rays, while unusually active pitchblende suggested the existence of previously unknown elements, eventually leading to polonium and radium.