1919 Discovery of Protons
The [nucleus] is the place where radioactivity
takes place. In order to understand radioactivity, man should
first understand what is in the nucleus.
In 1919, Rutherford bombarded gases with alpha particles. This is the diagram of the apparatus used in Rutherford's investigations.
The thin silver foil at one end
could stop the alpha particles from the radioactive source. Any
other particles that penetrated through the foil would fall on
the zinc sulphide screen and produced [scintillation]. Various
gases such as oxygen, nitrogen and carbon dioxide have been used
to fill up the apparatus but scintillation was only detected when
nitrogen was used. The particles which have passed through the
silver foil were shown to have a similar range, and same charge
as protons.
Later investigations of the reaction in a [cloud chamber] gave rise
to photographs showing clearly that the alpha particle actually
entered the nitrogen nucleus which immediately ejected a proton.
This was the first occasion on which one element was changed into
another one. This process was called nuclear transmutation.
Rutherford's students nicknamed him "the crocodile"
because " the crocodile cannot turn its head... it must always
go forward with all devouring jaws."
(C)1999 ThinkQuest Team 27954