Not
only have we found sub atomic particles but we also now know there is 'anti-matter'.
Anti-matter was predicted by Paul Dirac(English physicist - despite the
name!) in 1928.

He solved the equations for electron orbitals in the atom
and proposed negative energy states for electrons.

A simple example of
how he came to this conclusion is by asking ourselves,

'What is the root of 4?'

A root can produce two possible solutions +2 or -2

In 1932 Carl Anderson found experimental evidence for one in a cloud chamber (we study
those next year).

Anti-matter is the
complement to matter - it has the opposite characteristics.

Characteristics of particles are given by quantum numbers (for
charge, baryon number, strangeness etc.) - anti-particles have the opposite
sign for each one when compared to the matter particle's characteristic
quantum numbers.

Remember:

You can
have anti-matter - but there is no such thing as anti-energy!

The
rest mass of a particle is the same as the rest mass of an anti-particle - you don't have negative mass..

The
charge, baryon number and strangeness of a particle is the opposite
of the charge, baryon number and strangeness of an anti-particle.

Annihilation

An
anti-electron is a positron β+.

This
anti-particle is positive and has the same mass as an electron.

If a positron and electron
meet they annihilate one another - poof! and their combined mass (2m_{e})
is converted to electromagnetic energy (in accordance with the Einstein
equation (E = mc^{2}) ).

The energies are calculated
in terms of electron volts (eV) The eV is a very small unit of energy
- used a lot in nuclear calculations.

You need to be able
to convert from one to the other.

Remember at GCSE
you learned that:

E
= Q V

(joule) = (coulomb)
(volt)

So, a joule could
be thought of as a 'coulomb volt'

Similarly, if we
don't use a full coulomb of charge, but only the charge on an electron
'e'

eV
=
e V

(electron volt)
(charge on an electron) (Volt)

The charge on an
electron is only 1.6 x 10^{-19} C