Physics - Atoms and Radioactivity
Alpha radiation has the strongest ionising power. This means that it will ionise lots of particles as they travel. Because of this, they get 'used up' quickly, so also have the shortest range. They can only penetrate a few cm of air.
Alpha radation is emitted as alpha particles. Each alpha particle is made of 2 neutrons and 2 protons, giving it the greatest mass out of the three types of radiation. Because it has 2 protons but no electrons, it has a relative charge of +2.
It is important to remember that an alpha particle (a particle that has two neutrons and two protons) is the same as a helium atom without the electrons, so expect to see it written as α or 4He2.
Beta radiation - Ionising radiation is the result of an unstable nucleus, and in beta radiation a neutron splits into a proton and an electron so that the electron can be ejected and leave only a proton left. This will increase the relative charge of the nucleus by +1, which will help restore balance in the nucleus.
The electron that is emitted is called the beta particle. It is many thousands of times lighter than an alpha particle, and has a relative charge of -1 (because of the electron).
Beta particles are not as strongly ionising as alpha particles, but are stronger than gamma particles. They lie in the middle. As a result, their range is also between that of alpha particles and gamma particles. They can be stopped by 1- 2mm of aluminium.
Gamma radiation is an electromagnetic wave, so has no mass at all. It is the weakest in terms of ionising power, so has the longest range. A thick lead sheet is needed to stop gamma radiation.
It emitted in packets of energy called photons.
Summary: the stronger the ionising power, the shorter the range. Alpha particles are the strongest, and have the greatest mass and charge. Beta particles lie in the middle. Gamma rays have no charge or mass, because they are waves. They are the weakest, so they have the longest range.
