5.3.2 Fundamental Particles

1. 5.3.2 Fundamental Particles

2. (a) explain that since protons and neutrons contain charged constituents called quarks they are, therefore, not fundamental particles

3. Fundamental particles • Until mid-20th century, it was though that all atoms consisted of electrons, protons and neutrons • Due to the increasing sophistication of the particle accelerator, and increased sensitivity of equipment measuring cosmic rays, more and more particles were being discovered • Eventually, this “particle zoo” was arranged in a more orderly way

5. Video Fundamental Particles CERN Standard model

6. (b) describe a simple quark model of hadrons in terms of up, down and strange quarks and their respective antiquarks, taking into account their charge, baryon number and strangeness;

7. Simple model Atom Hadrons Leptons Not affected by the strong nuclear force Affected by the strong nuclear force Electrons Neutrinos Protons Neutrons Quarks

8. Fermions

9. (d) describe the properties of neutrons and protons in terms of a simple quark model

10. Properties of neutrons and protons Proton Neutron u d d u u d

11. Properties of neutrons and protons • Proton • uud • total charge = ⅔ + ⅔ - ⅓ = 1 • Neutron • udd • total charge = ⅔ - ⅓ - ⅓ = 0

13. (e) describe how there is a weak interaction between quarks and that this is responsible for β decay

14. β decay • Nucleus is held together by the strong nuclear force • This explains α decay, but not β decay • There is another force, the weak interaction or weak nuclear force • Acts on quarks and leptons • Responsible for β decay

15. (f) state that there are two types of β decay (i) state that a β- particle is an electron and a β+particle is a positron

16. β decay • There are two types of β decay: • Beta-minus (β-) • electron • negative charge –e • Beta-plus (β+) • positron • positive charge +e

17. (g) describe the two types of β decay in terms of a simple quark model; (h) state that (electron) neutrinos and electron) antineutrinos are produced during β+ and β-decays, respectively

18. β-decay Electron Anti-neutrino In β- decay a neutron is changed into a proton, in other words uddchanges into uud. A d changing to a u can only happen through the weak interaction.

19. β+decay Electron neutrino In β+ decay a proton is changed into a neutron, in other words uudchanges into udd. A u changing to a d can only happen through the weak interaction.