unstable nuclei and radioactive decay

• Nuclear radiation is emitted by unstable nuclei to become more stable , this is called radioactive decay and is a random process.
• Alpha decay:

  • consists of two protons and two neutrons
  • nucleon number decrease by four and proton number changes by 2
  • has the highest ionizing power
  • range of 5cm
  • stopped by paper
• Beta minus decay:

  • a fast moving electron and an anti-neutrino
  • nucleon number stays the same but proton number increase by one
  • neutron becomes a proton
  • high ionizing power
  • 1 meter range
  • stopped by aluminum
• Gamma radiation:

  • short wavelength but high frequency electromagnetic radiation
  • loses energy
  • low ionizing power
  • range of few km
  • stopped by several cm of thick lead
• the neutrino was hypothesized to account for conservation of energy in beta decay , a certain amount of energy should be transferred by beta decay , but beta particles had a range of energies instead of one value. so another particle was suggested that may carry away excess energy. this was the anti-neutrino
• neutrino have very little mass and zero charge , making them hard to detect.
• exchange particles and corresponding forces:

  • gravity = graviton
  • electromagnetic = virtual photon
  • strong nuclear force = gluon for quarks or pions for all other hadrons
  • weak nuclear force = w+ and w- bosons
• properties of forces:

  • gravity = attractive force between any two objects due to their masses
  • electromagnetic = acts between objects with charge - repulsive when the charge is the same and attractive when charges are opposite
  • strong nuclear = only acts on a set of particles called hadrons ; holds protons and neutrons together in a stable nucleus
  • weak nuclear = extremely short range , force that acts on hadrons and leptons , involved in radioactive decay.
• what can carbon-14 be used for?


  can be used in the carbon dating of fossils to calculate age
• whats is the equation for electron capture?

  p+e- --->n+v