Chapter 1

Chapter 1

1. Structure Of An Atom

   • Proton
     • Charge/C - +1.60x10-19 Mass/kg - 1.67x10-27
   • Neutron
     • Charge/C - 0 Mass/kg - 1.67x10-27
   • Electron
     • Charge/C - -1.60x10-19 Mass/kg - 9.11x10-31

2. Specific Charge

   • Specific Charge = Charge/Mass

3. Isotopes

   • Isotopes are atoms with the same number of protons and a different number of neutrons

4. Strong Nuclear Force

   • In a stable isotope there is a strong nuclear force which overcomes the electrostatic force of repulsion between the protons in the nucleus and keeps the protons and neutrons together.
   • It is an attractive force from 3-4fm sown to around 0.5fm. At smaller seperations it is repulsive.

5. Radioactive decay

   • Alpha Radiation
     • Alpha particles consist of 2 protons and 2 neutrons
   • Beta Radiation
     • Beta radiation consists of fast moving electrons. The symbol is -1β as the electrons charge is equal and opposite to that of a proton. A neutron is then changed into a proton, which is why the proton number goes up by 1. An antineutrino is also emitted.
     • Beta Decay
       • The W- boson decays into a β- particle and an antineutrino
       • The W+ boson decays into a β+ particle and a neutrino
   • Gamma Radiation
     • Gamma Radiation is electromagnetic radiation emitted by an unstable nucleus. It can pass through thick metal plates. It has no mass and no charge. It is emitted by a nucleus with too much energy, following alpha or beta emission.

6. Electromagnetic Waves

   • wavelength = wavespeed/frequency
   • Photons
     • Elecromagnetic waves are emitted as short bursts of waves
       • Each burst of waves are referred to as a photon
       • EM waves are emitted when
         • A fast moving electron is stopped or slows down or changes direction
         • An electron in a shell of an atom moves to a different shell of lower energy
     • Photon energy E = hf
       • h = Plancks Constant - 6.63x10-34
       • f = frequency

7. Laser Power

   • Laser beam consists of photons of the same frequency
     • The power of the beam = nhf
       • n = number of photons passing a fixed point each second
       • h = Plancks Constant - 6.63x10-34
       • f = frequency

8. Antimatter

   • When antimatter and matter particles meet, they destroy each other and radiation is released.
   • Antiparticles
     • Electron / Positron
     • Proton / Antiproton
     • Neutron / Antineutron
     • Neutrino / Antineutrino
     • A particle and its antiparticle have equal and opposite properties e.g. Charge
       • They have the same mass as you cannot have a negative mass
   • Energy of a particle or antiparticle is expressed in MeV
     • 1 MeV = 1.60x10-13
   • Annihilation And Pair Production
     • Pair Production
       • A photon creates a particle and a corresponding antiparticle, and vanishes in the process
       • Minimum energy of a photon needed = hfmin = 2Eo
         • A photon with less energy couldn't create a positron and an electron
     • Annihilation
       • Occurs when a particle and corresponding antiparticle meet and their mass is converted into radiation energy.
         • In the process 2 photons are created.
       • Minimum energy of photon produced = hfmin = Eo

9. Particle Interactions

   • Weak Nuclear Force
     • Causes neutrons to change into protons in β- decay, or a proton into a neutron in β+ decay
     • Weaker than the strong nuclear force, otherwise it would affect stable nuclei
     • A neutrino can interact with a neutron and make it change into a proton and a β- particle is created and emitted as a result
     • An antineutrino can interact with a proton and make it change into a neutron. A β+ particle is created and emitted as a result
       • These interactions are due to the exchange particles referred to as W bosons
         • Have a non-zero rest mass
         • Have a very short range of no more than about 0.001fm
         • Are positively charged (the W+ boson) or negatively charged (the W- boson)
   • Electron Capture
     • Sometimes a proton in a proton rich nucleus turns into a neutron as a result of interacting through the weak interaction with an inner shell electron from outside the nucleus
       • The same change can happen when a proton and an electron collide at very high speed. In addition, for an electron with sufficient energy, the overall change could also occur as a W- exchange from the electron to the proton.
     • Force Carriers
       • The photon and the W boson are know as force carriers, as theyre exchanged when the electromagnetic force and the weak nuclear force act respectively.