The weak nuclear force governs the decay of quarks. The weak interaction occurs via the exchange of the intermediate vector bosons, the W and the Z bosons. This changes one flavour (type: up, down, strange, charm, top, bottom)) of quark into another. It is crucial to the structure of the universe in that:

• The sun would not burn without it since the weak interaction causes the transmutation of protons into neutrons,
• Via this route deuterium can form and deuterium is needed for fusion to take place inside the stars.
• Weak interaction is necessary for the buildup of heavy nuclei within stars.

There is a pattern of these quark decays: - a quark of charge +2/3 ( u,c,t) is always transformed to a quark of charge -1/3 (d,s,b) and vice versa.

This is because the transformation proceeds by the exchange of charged W bosons, which must change the charge by one unit. The general pattern is that the quarks will decay to the next most massive quark possible.

In all of the weak interactions you have to study for the AQA AS level examination you have up quarks changing into down quarks (or vice versa)- - they are decaying into each other ... if they throw something unknown at you - but something that involves quarks changing into other quarks - then you know that if there is a boson exchange then it is a weak interaction.