Radioactivity

• Inside atoms, atoms have a central nucleus made of protons and neutrons which is surrounded by electrons.
• Nucleon number - number of protons + neutrons (top number)
• Proton number - number of protons (bottom number)
• Isotopes are atoms of the same element which have the same number of protons but a different number of neutrons.
• Atoms are radioactive due to an imbalance of protons and neutrons which makes it unstable
• The nucleus tries to become more stable by emitting radiation by radioactive decay
• Alpha, beta or gamma can be emitted
• Alpha : 4/2 He
• Beta : 0/-1 e
• Gamma : y
• Alpha is a helium nucleus (2 protons and 2 neutrons)
• Beta is a fast moving/ high energy electron
• Gamma is a high energy electromagnetic wave
• Alpha can be stopped by a thin sheet of paper, skin or few cm of air
• Beta can be stopped by a few mm of aluminium or up to a metre of air
• Gamma can be stopped by several cm of lead or very thick concrete
• Alpha's ionising power is very high - most damaging inside the body
• Beta's ionising power is medium
• Gamma's ionising power is low (compared with alpha and beta). Easily passes through the body.
• Radioactive decay occurs when an unstable nucleus emits radiation until it becomes stable
• The rate at which radioactive material decays is measured using half-life
• Half life is the time taken for half of the original number of atoms to decay
• Radioactive decay is random, we don't know what atom will decay next and spontaneous, we don't know when it will decay
• Ionising means that it interacts with cells in the body and damages DNA which causes cancer.
• Ionisation - when an atom gains or loses an electron
• Background radiation - naturally occurring radiation
• Alpha radiation - fast moving particles consisting of 2 protons and 2 neutrons, emitted by an unstable nucleus, (++) charge
• Beta radiation - very fast moving electrons emitted by an unstable nucleus, (-) charge
• Gamma radiation - waves similar to X-rays emitted by an unstable nucleus - no charge
• Electron - very small, negatively charged particle which orbits the nucleus
• Geiger-Muller tube - a piece of equipment which can detect and measure radioactivity
• Neutron - uncharged particle found in the nucleus
• Radioactive decay - The emission of radiation by an unstable nucleus
• Decay equations always need to be balanced. The top of the LHS must equal top of RHS. The bottom of LHS must equal bottom of RHS
• Background radiation is all around as radioactive atoms emit alpha beta and gamma
• Most background radiation comes from natural sources:

  ! Radon

  ! Cosmic Radiation

  ! Rocks

  ! Food and Buildings
• Some background radiation comes from artificial sources

  ! Medical Industry

  ! Nuclear Industry
• We need to correct for background radiation in our results. To do this we need to subtract the background radiation to find out how much radiation is coming from the source we are measuring
• Nuclear Waste is produced by nuclear power stations and in nuclear medicine.
• Its very difficult to get rid of as only time can make it safe. It can take thousands of year before waste stops being radioactive.