2. PARTICLE PHYSICS Summary

3. Alpha Scattering & Electron Diffraction

4. The angle of deflection is determined by the K.E. of the alpha particle. The “no – go “ zone behind the nucleus gets smaller the larger the K.E. of the alpha particles

5. Electron diffraction sin  =1.22λ d Airy Disk Airy disk produced by electron diffraction around a spherical object (nucleus) Diameter of nucleus λ = h p (de Broglie) Utilising wave qualities of electrons i.e. diffraction Remember:  is the angle from 0 th order to 1 st minimum

6. Rutherford scattering and electron diffraction Angle No of electrons 1/r curve predicted by Rutherford scattering Actual curve for electron scattering Quantum feature of e - makes it

7. Ch 17 Probing Deep into Matter 17.2 Scattering and scale Particle Zoo

8. Hadron Made up of quarks i.e. protons, neutrons Lepton Fundamental particle i.e. electrons, neutrinos Categorisation of sub-atomic particles Meson Quark – antiquark i.e.  0 Baryon 3 quarks i.e. proton, neutrons Fermion Half integer spin Subject to exclusion principle Boson Whole integer spin Not subject to exclusion principle Transmit a force i.e. photons, gluons,

9. Flavours of Quark (exam only requires up and down) (⅔ e) -(⅓ e) Charge

10. Quarks are never seen on their own have anti-versions of themselves Everything, other than mass, is opposite Hadron rules Quark combinations must have… Net integer charge Zero colour charge

11. Ch 17 Probing Deep into Matter 17.1 Creation & annihilation Particle – Antiparticle

12. Particles and antiparticles Same mass, everything else is opposite Electron Antielectron (Positron) Charge /C Mass /kg Spin -e+e -½-½½ 9.11 x 10 -31

13. -e +e Mass destroyed and turned into energy (& vice versa) All collisions must:- Conserve energy, linear momentum and charge Conserve lepton and baryon number More of this later Annihilation & Creation What happens if particle-antiparticles meet

14. e - + e +  +   - gamma ray (photon) (no charge) e - = electron e + = positron Mass converted into energy Example interactions

15. In theory…(but very rarely happens) e - + e +  +  Energy converted into mass More commonly… e - + e +  Photon interacts with a nearby nucleus producing mass Example interactions

16. The energy of a photon must be sufficient to create the mass of a particle & an antiparticle E rest = mc 2 So, if mass is to be created, photon energy must = 2mc 2 (at least) E = hf Provided by photonElectron produced 1 photon producing electron-positron pair It also works the other way around – knowing the mass of the particle-antiparticle pair that annihilate you calculate the energy of the photons produced.

17.  decay occurs due to weak force Random radioactive decay event due to exchange of Z 0 or W ± boson Nuclei with excess n undergo  - decay Nuclei with excess p undergo  + decay Beta decay Theoretical requirement for electron neutrino

18. Beta decay In the nucleus a neutron turns into a proton β-β- d u u uud d d u udd down quark → up quark Change in quark charge - ⅓ e → ⅔ e = e + e - must be emitted to conserve charge

19. np+ e - Interaction must also conserve baryon and lepton number e.g.n & p have baryon number = 1 e - has lepton number = 1 1 0 1 1 0 Beta decay n & p have baryon number = -1 e + ( e - ) has lepton number = -1

20. Charge 01 + -1 Baryon 11 + 0 Lepton 00 + 1 + -1 anti electron neutrino +  e 0 0 Beta decay np+ e - 1 0 1 1 0 Problem – doesn’t balance so create new particle

21. Work out the decay of a proton into a neutron Beta decay β+β+ +  e 0 0 pn+ e + 1 1 1 0 0 1 electron neutrino

22. Another reason why neutrino’s needed to exist… Experimentally β particle energy varied – problem as decay releases fixed amount Conservation of energy Beta decay (anti) neutrino has energy left over

23. Pauli Exclusion Principle Within an atom, two identical particles cannot be in the same quantum state Applies only to Fermions – i.e. hadrons and leptons Explains why objects are solid, periodic table and electron shells

24. Spin A quantum number that comes in lumps of ½ The closest to identical, two particles can be is to have all the same quantum numbers but opposite spin To be aware of…

25. Think of an alpha particle… 2 protons, 2 neutrons Both protons/neutrons have identical quantum states but opposite spins This makes alpha particles very stable