3.5 Nuclear Decay

• alpha radiation: fast moving helium nuclei
• beta radiation: electrons with speeds just less than the speed of light
• gamma radiation: photons of high energy
• nuclear radiation: the emission of energy in the form of waves or particles from atomic nuclei
• nuclear decay: the process by which the nucleus of an atom loses energy be emitting nuclear radiation. Purely random
• properties of alpha radiation: short (3cm) range in air, stopped by a few sheets of paper. Highly ionising with poor penetrating power
• properties of beta radiation: weakly ionising, strong penetrating power (1m of air, 0.5mm of aluminium)
• properties of gamma radiation: weakly ionising, high penetrative power (15cm of lead, >100m in air)
• activity: the rate of decay (number of disintegrations per second) of a sample of radioactive nuclei

  A= λN

  where λ= decay constant, and N= number of nuclei present
• half-life: time taken for number of radioactive nuclei, N, (or the activity, A) to drop to one half of the initial value.

  A=A0/2^x and N=N0/2^x

  where x=number of half lives elapsed
• exponential decay law: A=A0e^-λt and N=N0e^-λt
• decay constant: λ=ln2/T

  where T=half life
• percentage of radioactive nuclei remaining= (1-e^λt) x 100