February 26 – Glowing with pride

Today’s Factismal: Henri Becquerel discovered that uranium was radioactive when he forgot about an experiment.

In 1896, not much was known about radioactivity. Physicists knew that you could generate x-rays using vacuum tubes, but they didn’t know exactly what X-rays were or if there were other types of rays that could be created. About all that they did know was that X-rays could produce an image on a photographic plate even when the plate was covered in paper to prevent all light from getting through.

Based on that hint, Becquerel thought that X-rays and other possible forms of radiation might be a type of phosphorescence. He knew that if you exposed uranium to sunlight, it would glow for a brief period thanks to a phenomenon called phosphorescence. Becquerel thought that uranium might actually “glow” with X-rays. In order to test his idea, he wrapped photographic plates in paper and then put a lump of uranium on top before putting it all in the sunlight for a couple of hours. He had been doing the experiment for a few weeks when a cloudy day rolled around on February 26, 1896. He put the plates away in the back of his laboratory and forgot about them for a few days while he worked on other experiments. When he did finally remember them, he developed the plates even though they hadn’t had the sun treatment. Much to his surprise, the plates were just as dark as if those which had been exposed to the sun. Based on that, he deduced that the rays were coming from the uranium itself and had nothing to do with phosphorescence. He had discovered naturally-occurring radioactivity.

The photograph Becquerel "took" using uranium

The photograph Becquerel “took” using uranium

Becquerel spent the next few months working with his doctoral student, Marie Curie. Because Marie was married to another chemist, Becquerel got two lab assistants for the price of one. And he and his assistants were able to show that uranium was naturally radioactive as were thorium, polonium and radium. Indeed, it was the radioactivity of polonium and radium that allowed Marie Curie to isolate them from uranium. The new elements were so radioactive that they have made her laboratory notebooks too dangerous to handle even now.

Thanks to the trio’s efforts, they were jointly awarded the Nobel Prize in Physics in 1903. Unfortunately, they were awarded another prize as well – radiation poisoning. Because they didn’t understand the dangers associated with radioactivity, all three of them ended up with severe radiation burns; it is likely that their exposure to radioactive elements contributed to the deaths of Becquerel and Marie.

Their discovery of radioactivity led to a new theory of the universe, one which is being tested right now in “atom smashers” across the globe. If you would like to help physicists with their research by donating unused time on your home computer, then why not join LHC@home?

6 thoughts on “February 26 – Glowing with pride

  1. Pingback: March 25 – Jupiter Calling – Little facts about science

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