In addition to uranium, which elements were known to emit radioactive "rays" before M. Curie discovered radium?
Marie Curie's discovery of radium was indeed a significant milestone in the field of radiation research. However, there were several other elements known to emit radioactive "rays" prior to her discovery.
To find out which elements were known, we can refer to historical information and scientific experiments conducted during that time. One of the key experiments involved the study of uranium salts by German physicist Wilhelm Conrad Roentgen in 1895. He observed that these salts emitted a type of radiation that he called "X-rays." Although X-rays are not caused by the element itself, this discovery demonstrated that certain substances could emit radiation.
Around the same time, French physicist Henri Becquerel was working with uranium compounds and accidentally discovered that they could also expose photographic plates even in the absence of sunlight (a property later termed radioactivity). This led him to conclude that uranium emitted its own form of radiation.
After these discoveries, other scientists began investigating various substances. In 1898, Marie Curie and her husband Pierre Curie focused their research on the mineral pitchblende, which contains uranium. During their work, they discovered two new radioactive elements, polonium and radium. These findings demonstrated that radioactivity was not limited to uranium and opened up new avenues of exploration in the field of radiation.
In summary, before Marie Curie's discovery of radium, uranium was known to emit radiation, as demonstrated by Wilhelm Roentgen and Henri Becquerel. Curie's own research eventually led to the discovery of additional radioactive elements, such as polonium and radium.