To
investigate the structure of the nucleus, and even that of sub-nuclear particles, one particle is
usually fired at another at high energy – a method that has been compared with trying to find
out what a watch contains by throwing two watches together and seeing what bits fly
out!
A particle composed of smaller particles requires a certain amount of energy to
split it apart and this can be provided by a high-energy projectile such as another particle.
The acceleration of particles to the high energies needed in the collisions is a very important
part of nuclear physics.
All accelerators are for charged particles, the kinetic energy
of the particle being increased by an electrostatic field.
The electron gun in the
cathode ray tube used in a television (not the LCD type) or a cathode ray oscilloscope is a
simple type of accelerator – the electrons being accelerated through a potential difference of
some 10 000 to 20 000 V and reaching speeds between 107 and 108
ms-1. (relativistic effects being ignored).
You can check this using the
formula: ½ mv2 = eV where v is the maximum electron velocity, m the mass of the
electron, V the potential difference and e the electron charge.
The Van de Graaff generator was devised by the American
scientist Robert Jamieson Van de Graaff in the early nineteen thirties and patented in 1935.
His early machines were capable of generating voltages of 80 000V but this was later raised
to over 5 million volts by improved versions of the machine! Most Van de Graaff generators
that are used in schools give voltages of between 50 000 and 150 000V.