How would you describe becquerel experiments?

Answer 1

Antoine-Henri Becquerel discovered and experimented with radioactivity, and also experimented with phosphorescence (the phenomenon in which certain compounds glow after being exposed to direct light).

One experiment with phosphorescence went as such:

Wrap a Lumiere photographic plate with a bromide emulsion in two sheets of very thick black paper, such that the plate does not become clouded upon being exposed to the Sun for a day.

Place on the sheet of paper, on the outside, a slab of the phosphorescent substance, and expose the whole to the Sun for several hours.

When one then develops the photographic plate, one recognizes that the silhouette of the phosphorescent substance appears in black on the negative.

From this simple experiment, Becquerel concluded that the phosphorescent substance had to be emitting a type of ray that was passing through the paper and reducing the silver in the emulsion. This would seem to make sense, as the production of X rays, discovered a few years earlier by Wilhelm Röntgen, is accompanied by a soft glowing spot at the surface of the cathode ray tube. Becquerel decided to probe his unusual rays a little further. One week later, on March 2, 1896, Becquerel was back before the French Academy with the results of his further experiments. He had continued his experiments using a double sulfate salt of uranium and potassium (potassium uranium sulfate monohydrate), which has a strong but short-lived phosphorescence.

He carefully wrapped his photographic plates in black paper, coating the paper with a crust of the uranium double salt, and upon exposure to sunlight he once again observed the "signature" of the phosphorescence-induced rays. However, repeating the experiment on Wednesday, February 26, and Thursday, February 27, he was frustrated by two days of only intermittent sunlight. And because the Sun made no appearance on the two days following, on March 1 he developed his plates. Expecting to see only a faint silhouette resulting from the wrapped plates' intermittent exposure to sunlight, he was surprised to see that the silhouettes appeared with great intensity.

Becquerel suspected that the rays that produced the silhouettes emanated from the uranium salt itself, and that the small amount of sunlight was of no consequence. He arranged three more experiments, in which photographic plates were kept completely in the dark but put in direct contact with: (1) the salt; (2) a thin sheet of glass; and (3) a thin sheet of aluminum. He surmised that the glass would eliminate any possibility that a silhouette was the consequence of a chemical reaction, and that the aluminum would block the mysterious rays.

Developing the photographic plates, Becquerel observed an intensely defined silhouette on the first two plates, and a clear but considerably weaker silhouette on the third. Because he had double-boxed his plates inside his dark room, and had placed the ensembles inside a drawer that he then closed, he was able to conclude that his mysterious rays were not related to phosphorescence and were not induced by sunlight.

It was another four years before Becquerel's radiation became understood as the production of β -rays (high energy electrons), but, by then, there was no question that Becquerel had discovered the instability of some atomic nuclei, and that he was richly deserving of the 1903 Nobel Prize that he shared with Pierre and Marie Curie.

Answer 2

Antoine-Henri Becquerel discovered and experimented with radioactivity, and also experimented with phosphorescence (the phenomenon in which certain compounds glow after being exposed to direct light).

One experiment with phosphorescence went as such:

Wrap a Lumiere photographic plate with a bromide emulsion in two sheets of very thick black paper, such that the plate does not become clouded upon being exposed to the Sun for a day.

Place on the sheet of paper, on the outside, a slab of the phosphorescent substance, and expose the whole to the Sun for several hours.

When one then develops the photographic plate, one recognizes that the silhouette of the phosphorescent substance appears in black on the negative.

From this simple experiment, Becquerel concluded that the phosphorescent substance had to be emitting a type of ray that was passing through the paper and reducing the silver in the emulsion. This would seem to make sense, as the production of X rays, discovered a few years earlier by Wilhelm Röntgen, is accompanied by a soft glowing spot at the surface of the cathode ray tube. Becquerel decided to probe his unusual rays a little further. One week later, on March 2, 1896, Becquerel was back before the French Academy with the results of his further experiments. He had continued his experiments using a double sulfate salt of uranium and potassium (potassium uranium sulfate monohydrate), which has a strong but short-lived phosphorescence.

He carefully wrapped his photographic plates in black paper, coating the paper with a crust of the uranium double salt, and upon exposure to sunlight he once again observed the "signature" of the phosphorescence-induced rays. However, repeating the experiment on Wednesday, February 26, and Thursday, February 27, he was frustrated by two days of only intermittent sunlight. And because the Sun made no appearance on the two days following, on March 1 he developed his plates. Expecting to see only a faint silhouette resulting from the wrapped plates' intermittent exposure to sunlight, he was surprised to see that the silhouettes appeared with great intensity.

Becquerel suspected that the rays that produced the silhouettes emanated from the uranium salt itself, and that the small amount of sunlight was of no consequence. He arranged three more experiments, in which photographic plates were kept completely in the dark but put in direct contact with: (1) the salt; (2) a thin sheet of glass; and (3) a thin sheet of aluminum. He surmised that the glass would eliminate any possibility that a silhouette was the consequence of a chemical reaction, and that the aluminum would block the mysterious rays.

Developing the photographic plates, Becquerel observed an intensely defined silhouette on the first two plates, and a clear but considerably weaker silhouette on the third. Because he had double-boxed his plates inside his dark room, and had placed the ensembles inside a drawer that he then closed, he was able to conclude that his mysterious rays were not related to phosphorescence and were not induced by sunlight.

It was another four years before Becquerel's radiation became understood as the production of β -rays (high energy electrons), but, by then, there was no question that Becquerel had discovered the instability of some atomic nuclei, and that he was richly deserving of the 1903 Nobel Prize that he shared with Pierre and Marie Curie.