Radioactive materials give out nuclear radiation from the nucleus of ech of their atoms. The atoms are unstable and decay naturally. During this decay, radiation can be given out in the form of alpha, beta and gamma rays:
- An alpha particle is a helium nucleus.
- A beta particle is a fast-moving electron.
- Gamma is an electromagnetic wave (energy).
Radiation is measure by the number of nuclear decays emitted per second. This number decreases with time.
Ionisation occurs when an uncharged (neutral) atom gains or loses and electrons.
Alpha radiation is highly ionising because it's missing two electrons (it has a +2 electric charge). It attracts electrons away from atoms it passes, leaving them positively charged.
During alpha emission, the atom decays by rejecting an alpha particle (a helium nucleus made up of two protons and neutrons) from the nucleus.
The nucleus of the new atom formed differs from the original one in a number of ways:
- It is a different element.
- It has two fewer protons and two fewer electrons.
- The atomic number has decreased by two.
- The mass number has decreased by four.
During a beta emission, the atom decays by changing a neutron into a proton and a electron. The high energy electron ejected from the nucleus is a beta particle.
The nucleus of a new atom formed differs from the original one in a number of ways:
- It has one more proton and on less neutron.
- The atomic number has increased by one.
- The mass number remains the same.
Half-life is the time it takes for half the undecayed nuclei in a radioactive substance to decay.
If the substance has a very long half-life then it remains active for a very long time.
Igneous rocks can contain uranium atoms which decay to produce stable atoms of lead. It's possible to date rocks by:
- Measuring the proportion of uranium and lead in the rock.
- Knowing the half-life uranium.