Marie Curie and the History of Radioactivity

During her studies Marie had heard about Henri Becquerel's discovery of some sort of radiation emitting from uranium salts and decided to investigate these mysterious 'uranium rays' for her doctoral thesis. She soon discovered that the intensity of the rays was in direct proportion to the amount of uranium in her sample. Nothing she did to the uranium affected the rays. This, she said 'shows that radioactivity is an atomic property'. She also found that two minerals, pitchblende and chalcite, were much more radioactive than uranium itself, and realised that they must contain a new radioactive element.

Her husband Pierre abandoned his research on crystals to join Marie in her work. In July 1898, using basic chemical refining methods, they isolated a product from pitchblende about 400 times more active than uranium. This they named polonium in honour of Marie's native Poland.

'It was exhausting work to move the containers about, to transfer the liquids and to stir for hours at a time, with an iron bar, the boiling material in the cast iron basin' (bibliographic reference: M. Curie, Pierre Curie, Macmillan, Science Museum Library STS Books 92 CUR)

They continued with the painstaking refining and by December 1898 the couple announced the discovery of an even more radioactive substance in pitchblende which they called radium. This discovery had far-reaching effects; opening up the fields of radiotherapy and nuclear medicine.

William Crookes designed the spinthariscope (from the Greek ‘spintharis’, a spark) in 1903 which counted alpha-particles emitted by radium. The instrument consists of a phosphorescent screen of zinc sulphide placed over a mintue trace of a radium salt (supplied to Crookes by Marie Curie). The alpha-particles cause visible flashes of light (scintillations) and these are observed through a microscope.

The examples pictured are four of the original instruments made by Crookes and show progressive stages in their development. Even after the invention of more sophisicated electric counting devices, Ernest Rutherford used these scintillation counting methods for the estimation of an activity.

Sir William Crookes is also known for his 1861 discovery of thallium, and his invention of the radiometer.