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and the Earth's internal heat as it was known at the time was soon
changed. He spent a brief interlude away from England when he took
up a professorship at McGill University in Montreal, but by 1908 he
was back, first at Manchester and then from 1919 in Cambridge again
where he accepted the Chair of Physics in 1919. In the following year
he took over as Director of the Cavendish Laboratory, succeeding his
mentor J. J. Thomson. Rutherford was responsible for some major
scientific discoveries but it was his work on radioactivity, and his
investigations from 1909 into the internal structure of the atom, that
were his most important. He visualised the atom as having a nucleus
around which whizzed electrons: a structure similar, on a much smal-
ler scale, to that of the Sun and its revolving attendant planets.
Rutherford published a landmark book in 1904 that was simply
entitled Radio-activity, and this was instrumental in bringing the
infant subject to a whole new audience of academics and students.
The subject was progressing so fast that he had to produce a second
edition of the topic the following year, and it was 181 pages longer than
the first. In 1908 he received the Nobel Prize for Chemistry; twenty-
three years later he was raised to the peerage and thereafter was styled
'Baron Rutherford of Nelson'.
RADIOACTIVITY AND THE DISINTEGRATION SEQUENCES
In 1902 Rutherford and Soddy had a brilliant insight into the nature of
radioactivity: they suggested that during radioactive decay of an ele-
ment it becomes transformed into another, and these transformations
became known as 'radioactive decay series'. Within a year the decay
series of uranium, thorium, radium and actinium were known. The
sequence for thorium was:
Thorium (the initial starting product) ! thorium X ! thorium-
emanation (a gas now called thoron) ! thorium-excited I !
thorium-excited II ! unknown (the resultant material)
and each step was accompanied by emissions of different rays at
varying intensities. Rutherford also was the first to arrive at the
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