The Discovery of Radioactivity


It's been 100 years since the discovery of radioactivity. Happy 100th Birthday!

This section will describe the surprise discovery of radiation and the significant contributions of several other scientists. How exciting it must have been for them to be on the forefront of such new and exciting research! Little did they know how much their discoveries would benefit mankind 100 years in the future.

Let's read about how the field of nuclear chemistry was born!

Antoine Henri Becquerel (1852-1908)

It was the month of February in the year of 1896. Antoine Henri Becquerel, a French scientist, was conducting an experiment which started with the exposure of a uranium-bearing crystal to sunlight. Once the crystal had sat in the sunshine for a while, he placed it on a photographic plate. As he had anticipated, the crystal produced its image on the plate. Becquerel theorized that the absorbed energy of the sun was being released by the uranium in the form of x-rays.

Further testing of this theory had to be put off for a few days because the sky had clouded up and the sun had disappeared. For the next couple of days he left his sample of uranium in a closed drawer along with the photographic plate.


When the weather had cleared, he returned to the drawer to retrieve his gear. He was surprised to find that the crystal had left a clear, strong image on the photographic plate.

How could this be? There was no source of energy to produce the image! What Becquerel had discovered was that a piece of mineral which contained uranium could produce it's image on a photographic plate in the absence of light. What he had discovered was radioactivity! He attributed this phenomenon to spontaneous emission bt the uranium.

If you are interested in seeing what the uranium-exposed plate
that led to the discovery of radioactivity actually looked like,
then look up the following website:
http://fysik.lu.se/~radiofys/becqfoto.htm

Although Becquerel did not pursue these findings, it wasn't long before others would.

Pierre Curie (1859-1906)
Marie Curie (1867-1934)

The husband and wife team of Pierre and Marie Curie became interested in Becquereal's discovery. While experimenting with their own uranium-containing ore, they came up with the term "radioactivity" to describe the spontaneuous emissions that they studied. This word is still used today to describe this special characteristic of some elements.(radioisotopes).

While comparing the activity of pure uranium to a uranium ore sample, they found that the ore was significantly more radioactive than the pure material. They concluded that the ore contained additional radioactive components besides the uranium. This observation led to the discovery of two new radioactive elements which they named polonium and radium.

Did you know this??

  • In 1903, Becquerel and the Curies together received the Nobel Prize in physics. This award was for their discovery of radioactivity and their other contributions in this area.
  • Marie Curie received a second Nobel Prize in 1911 for the discovery of polonium and radium. She was the first person to win two Nobel Prizes.
  • Did you know that the Curie's had a word named after them? That's right! The curie is a basic unit of measurement for describing radioactivity.

Ernest Rutherford (1871-1937)

The next important step down this road of discovery came from Ernest Rutherford. Among his many accomplishments was the fact that he named and characterized many aspects of radioactivity. He, therefore, developed the language that is in use today to describe radioactivity and atomic theory.

One cannot understand radioactivity without first understanding the atom. Rutherford's experiments, in which he bombarded gold foil with particles (alpha particles) from a radioactive source, led to the understanding of the atom. What he noted was that although most of the particles passed right throught the gold foil, a very small percentage (approximately 1 in 8000) would "bounce back". What exactly did this imply?

He interpreted this to mean that matter was made up of mostly empty space, but there was a small dense portion of matter that deflected the particles. He defined this dense area as a nucleus surrounded by electrons at a great distance away from the nucleus. His discoveries led to our current understanding of the structure of the atom. In fact, Rutherford's planetary model of the atom is essentially what we use today.

For more details on these important
Historical figures and their discoveries,
Please see website:
http://www.gene.com/ae/AE/AEC/CC/historical_background.html


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