The Discovery of Radioactivity
It's been 100 years since the discovery of radioactivity. Happy 100th
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
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.
Although Becquerel did not pursue these findings, it wasn't long before
Pierre Curie (1859-1906)
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
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??
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
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
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
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