by Richard Ellis
Born in the North of England 100 years ago, John Cockcroft became a
world figure in 1932, the year in which he and his Irish partner,
Ernest Walton, split the atomic nucleus at the Cavendish Laboratory
at Cambridge University. Twenty years later, he and Walton were
awarded the Nobel Prize for Physics.
In the view of Professor Archie Howie, the present head of the
Cavendish Laboratory, the significance of Cockcroft's work lies not
only in his atomic experiment, momentous though it was. It lies also
in the way he and Walton opened up a new scientific area by devising
an accelerator as a means of investigating nuclear physics.
''The whole idea of using accelerators and manipulating nuclei
artificially dates from the 1932 experiment, and that was a really
significant legacy,'' says Professor Howie. ``Cockcroft and Walton
transformed the nuclear physics of Rutherford into an engineering
subject in which matter could be manipulated. Rutherford had to make
do with what nature provided.''
Professor Howie believes that Cockcroft's genius lay in discernment,
in seeing an opportunity. He had a very important meeting with George
Gamov in 1929, when he realised that Gamov's theory about collisions
between atoms and fast protons - namely that particles could get into
the nuclear of an atom by quantum mechanics - opened the way to an
''Cockcroft saw that it should be possible to get a nuclear reaction
going without resorting to the use of very high voltages to
accelerate the protons, as had previously been thought. He foresaw
the possibility of managing with perhaps half a million volts in the
accelerator instead of having to use about five million, which was
unthinkable in those days.''
Ernest Rutherford, then Professor of Physics at the Cavendish
Laboratory, had in 1919 made the first nuclear transformations, using
particles emitted by natural radioactive nuclei. But even after
Cockcroft and Walton's experiment he was sceptical about any
practical use for nuclear energy.
History has shown otherwise. Not only did Cockcroft's work contribute
directly to the success of the atomic bomb but also to a host of
beneficial applications, especially in medicine and in the
manufacture of semiconductor devices.
''Nuclear medicine is entirely dependent on the nuclear industry,
either in the production of X-rays by collisions of particles with
nuclei or in the production of the nuclear isotopes which are used in
all kinds of medical treatments nowadays,'' says Professor Howie.
''Magnetic resonance imaging, for example, is entirely dependent on the
properties of nuclei and if people had not been uneasy about the word
'nuclear', this scanning technique would probably still be known, as
it was initially, as nuclear magnetic resonance imaging.''
In material science there are many nuclear processes, basically using
atom smashing techniques, says Professor Howie. ``In the manufacture of
silicon chips, crucial stages are often done with ion beams to etch
different areas. And when doping atoms are inserted into
semiconductors, this is done by firing them in with an accelerator
not unlike the one designed by Cockcroft and Walton.
"In addition to being the source of all these techniques, nuclear
physics underpins a whole variety of methods for precise radioactive
dating of the remote past.''
During the 1939-45 war John Cockcroft was influential in the
development of radar. Later he was appointed director of Britain's
Atomic Energy Research Establishment. He retired from this post in
1960 to become the first Master of Churchill College, Cambridge. His
energy was undiminished. He saw his mastership as an opportunity not
only to build an impressive new college, a process in which he became
deeply involved, but also to establish the college as a centre for
the training of scientists and engineers. He broke down conventional
ways when they seemed to be a barrier to progress, creating a college
that attracted academics of distinction from many parts of the world.
Cockcroft was quiet and laconic but people who knew him sensed they
were in the presence of a remarkable man. "He had a great force of
personality,'' says Professor Howie. "He had a very dry style and did not
believe in wasting words, but people understood what he wanted. And
he had the ability not to listen to something he did not want to
hear. He somehow inspired a great deal of loyalty and admiration,
even though people never really felt they knew him very well. They
could sense an integrity in him.''