Radioactive decay and nuclear radiation
Radioactive decay
Some nuclei are unstable. They give out radiation to become more stable. This is , and it is : you can't predict when a particular nucleus will decay.
The of a source is the rate at which its nuclei decay, measured in . 1 Bq is 1 decay per second.
The is the number of decays a detector, such as a , records each second (or minute). It is less than the activity, because not all the radiation reaches the detector.
Key terms
Types of nuclear radiation
| Radiation | What it is | Range in air | Stopped by | Ionising power |
|---|---|---|---|---|
| 2 protons and 2 neutrons (a helium nucleus) | A few cm | A sheet of paper | Strong | |
| A fast electron from the nucleus | About 1 m | A few mm of aluminium | Medium | |
| An electromagnetic wave | A very long way | Thick lead or concrete (only reduced) | Weak | |
| A neutron | A long way | Thick concrete or water | Not directly; can make materials radioactive |
radiation knocks electrons off atoms, turning them into . The more strongly ionising the radiation, the shorter its range, because it loses its energy quickly.
Key terms
Nuclear equations
A nuclear equation shows what a nucleus turns into. The and must balance on both sides.
the nucleus loses an alpha particle (⁴₂He). Its mass number falls by 4 and its atomic number falls by 2.
- radium-226 (atomic number 88) → radon-222 (atomic number 86) + alpha particle
a neutron turns into a proton and a fast electron (⁰₋₁e), which leaves. The mass number stays the same and the atomic number rises by 1.
- carbon-14 (atomic number 6) → nitrogen-14 (atomic number 7) + beta particle
doesn't change the mass number or the atomic number. The nucleus just loses energy.
Common mistake
In beta decay, the atomic number goes up, not down: a neutron has become a proton.