Motion Of Particles

Motion Of Particles

1. Cyclotrons

   • Circular Motion - Velocity is constantly changing
     • Velocity = Speed & Distance
       • Changing direction means it is accelerating
         • Thus a result force must be acting on it
           • This force acts towards the centre
             • A force that keep something moving in a circle is called a centripetal force
               • Radius of path decreases as particle loses energy
     • A charged particle in a magnetic field will experience a force
       • This force acts perpendicular to the direction of travel
         • Making the path curved
           • Path of positive & negative particles are opposite
   • Is a Circular Particle Accelerator
     • Particle accelerator uses magnetic field to accelarate particles to high energies
       • Charged particle (E.g Proton) starts at the centre
         • Two hollow semi-circle electrodes used to accelerate particles across a gap
           • Alternating Potential difference applied in the gap
             • As the particles are attracted from each side the energy increase (I.e They accelerate)
               • A magnetic Field makes particles spiral outwards as energy increases

2. Uses Of Particle Accelerators

   • Medical
     • Proton Enrichment forms isotopes that emit positrons
       • Some radioactive isotopes are produced by bombarding stable elements with protons
         • Protons need lots of energy to be absorbed
           • Positron Emitter are used in PET Scanners
   • Astronomy
     • Big accelerators smash particles at high speeds to see what happens
       • What kind of radiation is released, new particles, e.t.c
         • Big research is done internationally to save money
           • Large Hadron Collider in Geneva. Set up by European Organisation for Nuclear Research
           • Combines expertise of many

3. Momentum & Kinetic Energy

   • Momentum is always conserved
     • Total Momentum Before = Total Momentum After
       • Momentum = Mass x Velocity
   • Collisions can be Elastic or Inelastic
     • Elastic
       • Momentum is conserved
       • Kinetic energy is conserved
     • Inelastic
       • But Momentum is always conserved
       • Some (or all) of the Kinetic energy is converted into other forms on collision
       • Bouncing Ball is and example of an Inelastic collision

4. Annihilation & PET Scans

   • Annihilation
     • Particle meets its antiparticle = Annihilation
       • Similar: Electron + Positron = Annihilation
     • All the mass is converted into energy (gamma rays)
       • Emitted in opposite directions
         • Same velocities
       • Charge is conserved
   • E = m x c2
     • E = Energy m = Mass c = Speed of light 3 x 10 8 m/s
     • Einstein said mass is a form of energy
       • Thus Mass can be converted into other types of energy (and vice versa)
         • Mass Energy is conserved in Annihilation reactions
           • All the mass of the of the Electron & Positron is converted into energy
   • PET scans involve Positron/Electron annihilation
     • Gamma rays released in opposite directions
       • Detectors detect gamma rays & at least 3 pairs help find tumour using triangulation

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