particle physics

particle physics

1. Alpha scattering

   • Rutherfords gold foil experiment
     • observations: 1) most particles don't deflect. 2) very few are deflected by over 90 degrees 3) even fewer are repelled
     • conclusions: 1) most of atom is empty space 2) very small point with a concentrated mass 3) nucleus and alpha particle both have positive charge
     • method: use radioactive nsample to emit alpha particles at gold foil and surround it with a zinc sulfide shield to see where the particles land

2. Electrons from atoms

   • Photoelectric effect: photoelectrons are emitted from surface after light above a threshold frequency shines on it> photoelectrons are emitted as electrons near surface of metal absorb photon and gain energy to leave surface
   • Thermionic emission: metal is heated until free electrons gain energyand are emitted. electrons are accelerated using electric fields or magnetic fields radially

3. Particle accelerators

   • LINACS: 1) pathshape- straight line 2) fields-electric only 3) where charged particles increase speed- between drift tubes 4) what is used to increase speed- a p.d 5) particles are at constant speed inside drift tubes 6) extra info- as charged particle accelerates drift tubes length increases 7) maths- in between drift tubes : KE gain= Q x change in V 1/2mv^2-1/2mu^2= Q x change in V
   • Cyclotron: 1) pathshape- semi-circular and straight between dees 2) fields- alternating elec and constant mag 3) where charged particles increase speed- between the dees 4) what is used to increase speed- a p.d between dees 5) particles are at constant speed inside the dees 6) extra info- as charged particles increase speed radius within dees increases 7) maths- between dees:KE gain= Q x change in V 1/2mv^2-1/2mu^2= Q x change in V inside the dees: BQv= force = (mv^2)/r
   • Synchrotons: 1) pathshape- circular 2) fields- alternating elec fields in accelerating gap frequency increases as time period decreases with increasing velocity of particle. 3) where charged particles increase speed- accelerating gap 4) what is used to increase speed?- a p.d across accelerating gap 5) particles at constant speed- in evacuated tubes 6) extra info- radius of tube is fixed so mag field must be steadily increased ad energy increases to keep radius constant. there are some staright sections and some sections with many magnets to deflect particles into a virtually circular course

4. particle detectors