Whatever his reason for developing the plates, Becquerel realized he had observed something significant. Perhaps he was under pressure to have something to report at the next day’s meeting. Possibly he was motivated by simple scientific curiosity. Many people have wondered why Becquerel developed the plates at all on that cloudy March 1, since he didn’t expect to see anything. The next day, March 2, Becquerel reported at the Academy of Sciences that the uranium salts emitted radiation without any stimulation from sunlight. On March 1, he opened the drawer and developed the plates, expecting to see only a very weak image. Thinking he couldn’t do any research without bright sunlight, Becquerel put his uranium crystals and photographic plates away in a drawer. But the weather in Paris did not cooperate it became overcast for the next several days in late February. Seeking further confirmation of what he had found, he planned to continue his experiments. He reported this result at the French Academy of Science meeting on February 24, 1896. He also placed objects such as coins or cut out metal shapes between the crystals and the photographic plate, and found that he could produce outlines of those shapes on the photographic plates.īecquerel took this as evidence that his idea was correct, that the phosphorescent uranium salts absorbed sunlight and emitted a penetrating radiation similar to x-rays. When he developed the plates, he saw an outline of the crystals. He then placed the crystals of uranium salt on top of the wrapped plates, and put the whole setup outside in the sun. To test this idea (which turned out to be wrong), Becquerel wrapped photographic plates in black paper so that sunlight could not reach them. Becquerel thought that the phosphorescent uranium salts he had been studying might absorb sunlight and reemit it as x-rays. After learning about Roentgen’s finding, Becquerel began looking for a connection between the phosphorescence he had already been investigating and the newly discovered x-rays. The newly discovered x-rays also penetrated the body’s soft tissue, and the medical community immediately recognized their usefulness for imaging.īecquerel first heard about Roentgen’s discovery in January 1896 at a meeting of the French Academy of Sciences. Wilhelm Conrad Roentgen had found that the Crookes tubes he had been using to study cathode rays emitted a new kind of invisible ray that was capable of penetrating through black paper. In early 1896 the scientific community was fascinated with the recent discovery of a new type of radiation. Like his father, Henri was especially interested in uranium and its compounds. In 1883 Becquerel began studying fluorescence and phosphorescence, a subject his father Edmond Becquerel had been an expert in. Following in his father’s and grandfather’s footsteps, he held the chair of applied physics at the National Museum of Natural History in Paris. Becquerel was born in Paris in1852 into a line of distinguished physicists. Henri Becquerel was well positioned to make the exciting discovery, which came just a few months after the discovery of x-rays. In one of the most well-known accidental discoveries in the history of physics, on an overcast day in March 1896, French physicist Henri Becquerel opened a drawer and discovered spontaneous radioactivity. March 1, 1896: Henri Becquerel Discovers Radioactivity
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