Alpha, beta and gamma
Alpha is a helium nucleus (2 protons, 2 neutrons), stopped by paper. Beta is a fast electron, stopped by thin aluminium. Gamma is an electromagnetic wave, reduced by thick lead or concrete.
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Analogy
Alpha is a bowling ball: heavy but stopped easily. Gamma is a ghost that walks through walls.
Example
Alpha: stopped by paperBeta: stopped by aluminiumGamma: only reduced bythick lead
In practice
Smoke alarms use alpha because it is stopped by a few centimetres of air. Gamma is used in medical sterilising.
Practice
Flashcards
- Which radiation can be stopped by paper?Alpha.
Interview questions
- Compare alpha, beta and gamma radiation in terms of what they are and how far they penetrate.
- Alpha is a helium nucleus, stopped by paper
- Beta is a fast electron, stopped by thin aluminium
- Gamma is an electromagnetic wave, reduced by thick lead
- Alpha is most ionising and gamma least
Questions people ask
Which type of radiation is most ionising?
Alpha is the most ionising, because it is large and strongly charged, so it knocks electrons off atoms easily. Gamma is the least ionising. This also means alpha is the most harmful inside the body, but the least harmful outside, where paper or skin stops it.
How does the nucleus change in alpha and beta decay?
In alpha decay the nucleus loses 2 protons and 2 neutrons, so its mass number drops by 4 and its atomic number by 2. In beta decay a neutron turns into a proton, so the atomic number goes up by 1 and the mass number stays the same.