Ionising effect of radiation
Extended tier only
- The relative ionising effects of nuclear radiation depend upon their:
- kinetic energy
- electric charge
Ionisation
- Ionisation is when an atom becomes negatively or positively charged by gaining or losing electrons
- Nuclear radiation can ionise the atoms that it hits
- This is mostly done by removing an electron so the atom loses a negative charge and is left with an overall positive charge
Nuclear radiation ionising an atom
When radiation passes close to atoms it can knock out electrons, ionising the atom
Effects of kinetic energy and charge on ionising power
- The greater the charge of the radiation, the more ionising it is
- This means alpha radiation is the most ionising as it has a charge of +2
- A beta particle has a charge of –1 so it is moderately ionising
- This means gamma radiation is the least ionising as it has a charge of 0 (no charge)
- The higher the kinetic energy of the radiation, the more ionising it is
- This means the alpha particle is still the most ionising because it has the greatest mass
- However, a beta particle is very light (it is an electron) but travels at high speeds, therefore, it has a lot of kinetic energy and is still moderately ionising
- Gamma radiation has virtually no mass so it is weakly ionising
Exam Tip
Remembering the properties of alpha, beta and gamma radiation helps to deduce how much ionising power they have. E.g. An alpha particle is a helium nucleus which contains two protons and two neutrons. It therefore has a charge of +2 since each proton has a charge of +1 and a neutron has no charge.
Kinetic energy is defined by the equation mv2 therefore it depends on the mass m of the particle and its velocity v.