Who discovered radioactivity?
Quick answer
French physicist Henri Becquerel discovered radioactivity in 1896 while studying uranium salts. He found that uranium gave off invisible rays that could expose a photographic plate even in the dark, without any sunlight. Marie and Pierre Curie continued the research, and the three shared the 1903 Nobel Prize in Physics.
Key facts
- Discoverer
- Henri Becquerel (1852–1908)
- Year
- 1896
- Nobel Prize
- Physics, 1903 (with Marie and Pierre Curie)
- Unit named after him
- The becquerel (Bq)
A cloudy-day accident
Inspired by the discovery of X-rays a few months earlier, Becquerel wondered whether glowing minerals gave off similar rays after being exposed to sunlight; see who discovered X-rays. He placed uranium salts on photographic plates wrapped in black paper and left them in sunlight.
In late February 1896, the weather was cloudy, so he put the plates in a drawer. When he developed them anyway, he found strong images. The uranium was giving off radiation on its own, without needing sunlight.
The Curies take it further
| Year | Discovery |
|---|---|
| 1898 | Marie Curie coins the word “radioactivity” |
| 1898 | The Curies discover polonium and radium |
| 1903 | Nobel Prize in Physics for Becquerel and the Curies |
| 1911 | Marie Curie wins a second Nobel, in Chemistry |
See the first woman to win a Nobel Prize.
What is radioactivity?
Some atoms have unstable nuclei. They release energy as radiation as they change, or decay, into other elements.
| Type | What it is | Stopped by |
|---|---|---|
| Alpha | Two protons and two neutrons | A sheet of paper |
| Beta | Fast electrons | Thin aluminum |
| Gamma | High-energy light | Thick lead or concrete |
The rate of decay is steady, which makes it useful for dating; see how carbon-14 is used in the element with atomic number 6.
A dangerous discovery
Early researchers didn’t know radiation could harm the body. Becquerel got a burn from carrying radium in his pocket, and Marie Curie’s notebooks are still too radioactive to handle without protection.
Uses today
Radioactivity is used in medicine (cancer treatment and imaging), nuclear power, smoke detectors, and dating rocks and fossils. The neutron, key to nuclear power, is described in who discovered the neutron.
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