Matter and Radiation

Matter and Radiation

1. Stable and unstable nuclei

   • Alpha Decay
   • Beta Decay
   • Strong Nuclear Force: Keeps the nucleus together (by keeping protons and neutrons together)
     • Attractive untiil about 0.5fm, repulsive after that
   • Gamma Decay

2. Photons

   • E = hf
   • Wavelength = c/f
   • Power of beam = nhf
     • n = number of beams passing a fixed point each second
     • h = plank's constant
     • f = frequency of photons
   • Electromagnetic waves consist of an electric wave and magnetic wave which travel together and vibrate,,,
     • ...in phase with each other (reach peak together and trough together)
     • ...at right angles to each other and the direction they are travelling
     • In a vacuum they travel at the speed of light (c)
     • There is a wide spectrum of waves, dependant on wavelength
       • Radio waves (>0.1 m)
       • Microwaves (0.1 m - 1 mm)
       • Infrared (1 mm - 700 nm)
       • Visible (700 nm - 400 nm)
       • Ultraviolet (400 nm - 1 nm)
       • X-rays (10 nm - 0.001 nm)
       • Gamma rays (<1 nm)

3. How particles interact

   • Electron Capture
     • W+ boson changes the electron into a neutrino
     • A proton in a proton rich nucleus turns into a neutron through the weak interaction
     • Can also occur when a proton and electron collide at very high speeds
     • For an electron with sufficient energy, the overall change would occur as a W- exchange from electron to proton
   • Weak nuclear force
     • Causes a neutron to change to a proton or vice versa
     • W Bosons
       • Positively or negatively charged
       • Have a non-zero rest mass
       • Have a range of around 0.001fm
   • EM force - momentum is conserved due to exchange of virtual photons
   • Beta decay
     • W+ decays to a B+ and a neutrino
     • W- decays to a B- and antineutrino
   • Charge and mass is always conserved

4. Particles and antiparticles

   • Particle and anti-particle...
     • ...have opposite charges
     • meet... annihilation
     • meet... total rest mass converted to photons
     • ...have exactly the same rest mass
   • Pair production: when a photon with sufficient energy changes into a particle-antiparticle pair which then seperate
     • Minimum energy of the photon: 2E = hf
   • 1 eV = the energy transferred when an electron is moved through a potential difference of 1V

5. Inside the atom

   • Proton: Charge = +1.6x10^-19 C Mass = 1.67x10^-27kg
   • Neutron: Charge = 0 C Mass = 1.67x10^-27kg
   • Electron: Charge = -1.6x10^-19 C Mass = 9.11x10^-31kg
   • m/z ratio = specific charge
   • Isotopes = atoms with the same number of protons and different number of neutrons