Making anti-matter model 4
In beta decay, a nucleus throws out an electron as a neutron's down quark changes into an up quark making it a proton.
Particle Mass Charge Forces
electron 10-30
-1 gravity
neutrino maybe zero 0 gravity
Table 1. The leptons found in normal matter.
The electron is not the only particle given out in beta decay. There is also a particle of anti-matter - the anti-neutrino. The anti-neutrino has a corresponding particle of normal matter called the neutrino. The neutrino has a very small mass and might even have no mass at all - (neutrino means 'little light one'). It belongs to the lepton family, which is the same family of particles as the electron. The electron and neutrino are the only leptons found in normal matter and we call them the first generation of leptons (table 1).
Can you feel the force?
The neutrino does not feel the strong nuclear force (because it is a lepton) or the electrostatic force (because it is neutral). Its behaviour is affected by the weak force. The weak force describes the way in which the neutrino interacts with other matter. This force has so little effect that billions of neutrinos have passed through you in the last second without being deflected by the other particles in your body.
The need for the weak force
Family Particle charge forces
Quark Up


Lepton electron


Table 2. The quarks found in normal matter.
Two families of two sets of twins
We now have two families of fundamental particles, each with two members. The lepton family includes the electron and the neutrino and the quark family includes the up and down quark (table 2). These are the only particles found in normal matter. Each of these particles has an anti-particle, making up a total of eight fundamental particles.
The need for the weak force
Why did we need an anti-neutrino?
Beta particles from a particular decay have a range of energies. However, the energy released by the decay must be constant. So, if the beta particle does not have all the energy, where does the rest of the energy go? In the 1930s, Wolfgang Pauli suggested that the anti-neutrino was given out as well.
What does antimatter do?
The story so far
Neutrinos are the other type of lepton found in normal matter
The neutrino has an anti-particle called the antineutrino
The anti-neutrino is given out in beta decay as well as an electron
Neutrinos feel only the weak force (and gravity)
There are two families of fundamental particle: quarks and leptons
Each family has two members that are found in normal matter
Question M4

a) Apart from gravity, which force(s) is/are felt by neutrinos

b) What can you say about the range of this force?

c) Explain why millions of neutrinos are passing through you every second without you noticing.

The story so far
  • There are two types of fundamental particle: quarks and leptons
  • The electron is a lepton
  • The stong nuclear force does not affect leptons
  • The weak nuclear force affects quarks and leptons