Unit 5 Atomic physics
Section 5.2 Radioactivity
Detection of radioactivity
- Many nuclei of elements in the periodic table are stable but some are unstable. Unstable nuclei undergo radioactive decay.
- When a radioactive nucleus decays it may emit one or more of the following: alpha particles, beta particles or gamma rays.
- The radiations alpha, beta and gamma have their own individual characteristics, as shown in the
Nature 2 protons and 2 neutrons (helium nucleus) Symbol α or 24 He Charge positive Affected by magnetic and electric fields yes Penetrating power weak – stopped by thin paper Relative ionising effect strongest Dangerous yes Nature electron Symbol β or –10 e Charge negative Affected by magnetic and electric fields yes Penetrating power moderate – stopped by a few mm of aluminium Relative ionising effect medium Dangerous yes Nature electromagnetic radiation Symbol γ Charge uncharged Affected by magnetic and electric fields no Penetrating power strong – only stopped by many cm of lead or many m of concrete Relative ionising effect weakest Dangerous yes
- There is always radiation present all around us. This is known as background radiation. Background radiation comes from cosmic rays, rocks and atmospheric gases. A small amount (about 3%) of background radiation comes from human-made sources such as medical equipment, nuclear power stations and nuclear weapons testing.