1. Particles and how they interact

2. Particles e-, νe µ-, νµ τ-, ντ All particles hadrons leptons baryons
Feel the strong nuclear force
Don’t feel the strong nuclear force
Are made up of quarks (u, d, s, c, t, b)
hadrons
leptons
Decay into protons
Don’t decay into protons
e-, νe µ-, νµ
τ-, ντ
Consist of a quark +
an anti-quark
Consist of 3 quarks, or 3 antiquarks
mesons
baryons
pions
kaons
proton (uud), and anti-proton
neutron (udd), and anti-neutron

3. Fundamental forces
gravitational (for particles with mass) – infinite range
electromagnetic (for particles with charge) – infinite range
Weak nuclear (particles in nucleus) – short range < fm
Strong nuclear (particles in nucleus) – short range 3-4 fm

4. The electromagnetic force
Interaction between particles with charge
Can be repulsive (like charges) or attractive (opposite charges)
Interactions involve the exchange of an ‘exchange particle’ which, for the electromagnetic force, is the (virtual) photon
virtual
photon
exchange
proton
proton

5. A model to explain exchange - repulsive

6. A model to explain exchange - attractive

7. The Feynman diagram (proton-proton interaction)ɣ
time p p
position

8. The Feynman diagram (electron-electron interaction)

9. The weak nuclear force
The exchange (virtual) particles involved in the weak nuclear force are call the W bosons.
They have a non-zero mass and carry a charge.
The W- boson carries a negative charge
The W+ boson carries a positive charge

10. The weak force is involved in beta decay
Beta-minus decay involves a neutron changing to a proton in a nucleus in which there are too few protons (i.e. neutron rich)
neutron -> proton + β- + anti-electron neutrino

11. proton -> neutron + β+ + electron neutrino
Beta positive decay involved a proton changing to a neutron in a nucleus in which there are too many protons (proton rich). Note that this doesn’t occur in naturally occurring isotopes.
proton -> neutron + β+ + electron neutrino

12. Other examples of weak force interaction
Although neutrinos rarely interact
neutron + electron neutrino -> proton + β-

13. What is happening here?

14. The strong nuclear force
The force that binds nucleons (protons and neutrons)
Short range (3-4 fm)
Same between proton-proton, proton-neutron, neutron-neutron
Attractive down to 0.5 fm, repulsive below this
The exchange particle is the gluon

15. The strong nuclear force

16. Competing forces

17. Nuclei attempt to become more stable in several ways:
Proton rich nuclei can become more stable by alpha particle decay, beta plus emission, and electron capture.
Example: alpha decay

18. Proton poor nuclei can become more stable by gaining protons in beta minus decay
Example: iodine-131 changes to xenon-131 plus a beta minus plus an anti-electron neutrino

19. Gamma emission
There are energy levels in the nucleus, just like energy levels for electrons in their orbitals.
When transitions occur between these energy levels, gamma rays are emitted.