Who Discovered Radioactivity and What two elements are naturally radioactive?

Marie Curie’s discovery of two naturally radioactive elements, polonium and radium, made headline news, but her real discovery was that atoms were not small solid balls and that there must be even smaller particles inside them. This discovery opened the door to all atomic and subatomic research and even to the splitting of the atom.

Curie carried out her research with radioactive elements before the dangers of radioactivity were understood. She suffered from ill health (radiation sickness) for most of her adult life. Indeed, for many years after her death, her notebooks were still highly radioactive.

Marie Curie’s studies rank as one of the great turning points of science. Physics after Curie was completely different than before and focused on the undiscovered subatomic world. She cracked open a door that penetrated inside the atom and has led to most of the greatest advances of twentieth-century physics.

In 1896 Marie Curie decided to complete her doctoral dissertation in a totally new field: radiation. It was exciting.

It was something no one had ever seen or studied before. Scientists knew that electrically charged radiation flooded the air around uranium, but not much else was known. Marie used a device her husband, professor Pierre Curie, invented to detect electric charges around mineral samples. She named this process radioactivity and concluded that radioactivity was emitted from inside a uranium atom.

Since the Curies had had no money of their own to pay for her research, and since the university refused to fund a woman’s graduate-level physics research, Marie scrounged for free lab space. She found an abandoned shed that had been used by the Biology Department to hold cadavers. It was unbearably hot in the summer and freezing cold in the winter, with a few wooden tables and chairs and a rusty old stove.

In 1898 Marie was given a puzzling uranium mineral ore called pitchblende, which her tests showed gave off more radioactive emissions than expected from the amount of uranium it contained. She concluded that there must be another substance inside pitchblende that gave off the extra radiation.

She began each test with 3.5 ounces of pitchblende. She planned to remove all of the known metals so that ultimately all that would be left would be this new, highly active element. She ground the ore with mortar and pestle, passed it through a sieve, dissolved it in acid, boiled off the liquid, filtered it, distilled it, then electrolyzed it.

Over the next six months Marie and her husband, Pierre, chemically isolated and tested each of the 78 known chemical elements to see if these mysterious radioactive rays flowed from any other substance besides uranium. Most of their time was spent begging for tiny samples of the many elements they could not afford to buy. Oddly, each time Marie removed more of the known elements, what was left of her pitchblende was always more radioactive than before.

What should have taken weeks, dragged into long months because of their dismal working conditions. In March 1901, the pitchblende finally gave up its secrets. Marie had found not one, but two new radioactive elements: polonium (named after Marie’s native Poland) and radium (so named because it was by far the most radioactive element yet discovered). Marie produced a tiny sample of pure radium salt. It weighed .0035 ounces, less than the weight of a potato chip, but it was a million times more radioactive than uranium.

Because the dangers of radiation were not yet understood, Marie and Pierre were plagued with health troubles. Aches and pains. Ulcer-covered hands. Continuous bouts of serious illnesses like pneumonia. Never-ending exhaustion. Finally, the radiation Marie had studied all her life killed her in 1934.

Female Nobel Prize laureates accounted for only 34 out of a total of 723 prizes awarded as of 2005. Marie Curie is not only the first woman to be awarded a Nobel Prize, but also one of four persons to have been awarded the Nobel Prize twice.