Radioactivity

• The dose of radiation received is energy absorbed per unit mass.

  Dose is measured in Grays, Gy = J kg^-1
• The dose equivalent of radiation is the dose multiplied by the quality factor for the type of radiation.

  • This is measured in Sieverts, Sv = J kg^-1
  • Quality factor measures how much biological damage that type of radiation does. It goes from 1 - 20.
• Background radiation sources:

  • Rocks
  • Building materials
  • Hospitals
• When an atom undergoes alpha decay, that particles loses 2 protons and 2 neutrons, meaning a new element has formed plus an alpha particle.

  When an atom undergoes beta-minus decay, a neutron in that atom turns into a proton and an electron and an electron anti-neutrino (proton number goes up by 1)
• Nuclear decay:

  • N - number of undecayed nuclei
  • A - activity = number of decays per unit time (Units: Bq = Bequerel = s^-1)
  • t = time (s)
  • λ - decay constant = probability an individual nucleus will decay in unit time (s)
• The half-life of an isotope is the time for half of the particles in a sample to decay.

  T(1/2) = ln2/λ

  Where λ is the decay constant
• A = λN

  A = Active decay

  λ = decay constant

  N = number of undecayed nuclei

  As N decreases,

  A = - ΔN/Δt
• N = N0 e^-λt

  Where N0 = number of undecayed particles at t = 0 and λ = decay constant

  Similarly, A = A0 e^-λt