The radioactive nucleus that made History

The radium bowl
Luminescent bowl of radium bromide, photographed in 1922: Bowl containing radium bromide, photographed in the dark at some point in 1922. Radium is about a million times more radioactive than uranium and, under the influence of the heat released, emits an attractive blue colour that Pierre and Marie Curie enjoyed looking at in the evenings.

Radium is an extremely rare element that was first discovered in 1898 by Pierre and Marie Curie. They also measured its mass and atomic number, and were able to show that it filled an empty space in Mendeleyev’s periodic table. Five years after Pierre Curie’s death in 1906, Marie Curie was awarded with a second Nobel Prize in 1911 for her discovery of radium: a prize in chemistry, this time, making her the first woman to be awarded with a Nobel Prize in this particular field.

The new element was called radium, found to have 88 protons and a variety of isotopes. The most important one, radium 226, is an alpha and gamma emitter with a half-life of 1600 years.

The rue Lhomond hangar
Exterior of the ‘hangar’ of the Ecole de Physique et de Chimie de la Ville de Paris, then at 42 rue Lhomond, where Pierre and Marie Curie first isolated polonium and radium from a uranium ore known as pitchblende. Almost 400 tonnes of pitchblende had to be processed for one gram of uranium to be produced.

Traces of radium 226 can be found in uranium ore – of the order of one atom per three million. This particular radioisotope is the fifth radioactive descendant of uranium 238, which in turn transforms into a radioactive noble gas, radon 222, with a half-life of 3.8 days.

The Curie , the activity of 1 radium gram (equivalent to about 37 billion disintegrations per second), was for many years the standard unit for measuring activity. This gram of radium was the quantity that Marie Curie was painstakingly able to obtain at her rue Lhomond laboratory.

During the 1920s, the public suddenly went crazy for radium. Whereas the dangers of radioactivity are often exaggerated today, at the time none of the risks had even been considered.

The”dials painters” workshop
View of the workshop where, in the 1920s, young Americans painted alarm clock dials. The luminescent paint which contained traces of radium caused throat cancer in the workers who moistened the brushes with their tongues. It took time, tragically, once the cause of the cancers had been identified, to impose the necessary measures on the manufacturer.
© DR

As a result, one of the first uses found for radium was in luminous paint for watches, alarm clocks and compasses. In 1924, a New York doctor was surprised to find signs of jaw cancer in a large number of young women who worked in the luminous paint industry. It eventually occurred to him that the women had been licking the tips of their paintbrushes – causing them to ingest harmful quantities of radium. Marie Curie soon realized the potential dangers of her new discovery, and helped put an end to this harmful profession.

Radium was used to cure cancers for decades before finally being declared unsafe in 1976 and gradually replaced with iridium 192 and caesium 137 for brachytherapies.


– 1) : 1920’s : the radium follies
– 2) : The later uses of radium