Types of nuclear radiation
Alpha - strongly ionising, slow, not very penetrating.
Beta-minus - moderatley ionising, fast, moderatley penetrating.
gamma - very weakly ionising, travels at the speed of light, very penetrating.
where does background radiation come from?
- Radon gas released from rocks emits alpha radiation
- ground and buildings: all rock contains radioactive isotopes
- cosmic rays
- living things: plants and animals all contain carbon, some of which is radioactive carbon 14
- man-made radiation: makes up a very small portionof background radiation.
Uses of radioactive isotopes
- Radiocarbon dating (carbon-14)
- diagnose and treat medical problems
- sterilise food
Half-life and rate of decay
- Activity (number of atoms which decay each second) is proportional to the size of a sample.
- decay constant (lambda) measures how quickly an isotope will decay.
- bigger decay constant = faster rate of decay
Half-life: the average time it takes for the number of undecayed atoms to halve.(in practice it is measured by the time taken for the activity to halve)
- U-235 hit by thermal neutron
- neutron absorbed
- unstable U-236 breaks up into two smaller nuclei and some high speed neutrons
- difference in binding energy is given off as Ek of daughter products
- harnessed to drive electricity generating system
- graphite/water moderator slows emitted neutrons
- they arrive at next fuel rod at slow enough speed to be absorbed
- cadmium/boron control rods absorb excess neutrons and prevent reaction running out of control