1. Feynman Diagrams
Richard Feynman invented the concept of virtual photons as part of his theory of quantum electrodynamics.
The maths is complicated – but, fortunately, Feynman depicted the theory using diagrams to represent the interactions.

2. Electron – Electron Interaction
 a photon (uncharged) e- e-

3. b- decay 1 n 1 e p + + n 1 -1

4. The Neutrino An uncharged particle. Assumed to have zero mass
Emitted in radioactive beta decay
The “weak” nuclear force is responsible
The antineutrino is the antiparticle of the neutrino = n it has opposite “spin” to a neutrino.

5. b- decay n p e- W- n

6. The Weak nuclear force
Responsible for Beta decay – as well as interactions involving electrons or neutrinos with protons or neutrons.
Carried by exchange particles known as W-bosons.
There are two types: the W+ and the W- which can also represented in Feynman diagrams like this …

7. b- decay (identical representation)W- e- n

8. Quark representation

9. Quark representation
Proton =
Neutron =

10. b- decay – Quark representationW-

11. b+ decay n n e+ W+ p

12. Electron capture n n W+ e- p

13. Neutrino – neutron collisionsp W+ n n

14. Antineutrino – proton collisionsW+ n p

15. Electron - proton collisionsW- e- p

16. Feynman Diagrams
Note – questions on the weak interaction will be limited to changes in which a proton changes to a neutron or vice versa.