03/01/2026
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Radioactivity was discovered 130 years ago today by French physicist Henri Becquerel.
Three days before, on 26 February, it was a cloudy day in Paris, which presented a problem for Becquerel. He wanted to show that some minerals glow when exposed to strong light due to X-rays. The weather thwarted this experiment but led to a new discovery. Discouraged by the weather, Becquerel put the uranium he planned to use in his desk drawer on top of a covered photographic plate. When he returned, he found a fogged image of the uranium crystals that had been resting on it, even though the plate was wrapped in heavy black paper. He realized that the crystals were not phosphorescing from sunlight. Instead, he found that the crystals released spontaneous and penetrating rays without any external energy.
Together with his doctoral student, Marie Curie, and her husband Pierre, Becquerel studied this phenomenon, which turned out to be ‘radioactivity’ — a term that Marie Curie coined. This work earned them the 1903 Nobel Prize in Physics.
