Tuesday, October 5, 2010

Discovery of the Proton

            In deciphering the composition of the atomic nucleus came many experiments. In order to do so, alpha-scattering experiments were popular among scientists. In the early 20th century, Ernest Marsden was curious as to what would happen if alpha rays came in contact with light nuclei. However, Marsden moved to New Zealand for work purposes in 1914, around the beginning of World War I. He was forced to leave his experiments unfinished. Ernest Rutherford decided to take over the experiment from him. However, throughout the war, Rutherford, as well as many other scientists, were preoccupied with figuring out how to detect submarines. From 1914 to 1918, Rutherford left his experiment with the alpha particles to join the war effort. As soon as he was able to, he picked up where he left off before World War I. Rutherford shot alpha particles into nitrogen gas and noticed peculiar reactions.
            For his experiment, Rutherford had a brass box and placed a little glass tube inside at one end of the box. A zinc-sulphide scintillation screen was then placed by the glass tube. Then, radon gave off helium nuclei through the glass tube while the brass box was filled with nitrogen. There were then scintillations, or flashes of light, on the screen. Although there was no hydrogen at the beginning of the experiment, the flashes were definitely derived from hydrogen. Rutherford concluded that the nitrogen had disintegrated. Also, in conclusion, Rutherford was convinced from the evidence of his well-thought-out experiment that the hydrogen nucleus was an elementary particle due to the fact that the nitrogen nucleus was made of hydrogen nuclei. Ernest Rutherford named the particle the proton, deriving the word from the Greek word “protos”, which means “first”.
            Because Rutherford discovered the proton through a series of steps in his experiment, scientists today are able to determine which chemical element an atom is. The number of protons in the nucleus is equal to the atom’s atomic number, which would not be relevant today without Rutherford’s historical discovery.

Good video (but he means nitrogen instead of neon): http://www.youtube.com/watch?v=iqZpdrEAhTg

Rutherford’s experiment set-up:

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