Atomic structure

• An atom contains a nucleus with positive charge, which is orbited by a negative electron
• Observation of Rutherford's experiment

  • most Alpha particles went straight through, some were deflected at large angles and few were deflected at less than 90 degrees
• Conclusions of Rutherford's experiment

  • most of the atom is empty space
  • the nucleus is small and dense, and has a positive charge
• an isotope is a version of an atom with the same number of protons and a different number of neutrons
• Some isotopes have an unstable nuclei, they emit radiatin in a process known as nuclear decay
• radiation is energy emitted as waves or particles
• ionisation is when radiation collides with neutral atoms or molecules, it alters their structure by knocking off electrons. This leaves behind ions.
• Nuclear decay is a completely random process - you cannot speed it up by changing its environment
• What happens in Alpha Decay

  • mass number decreases by 4
  • atomic number decreases by 2
• What happens in Beta Decay

  • mass number stays the same
  • atomic number increases by 1
• during Gamma Decay, there is no change to the make up of the nucleus and so no new element is formed
• a Radioactive Isotope is a radioactive atom that has a nucleus that is unstable and therefore emits radiation
• Half Life is the average time it takes for the number of nuclei of an isotope to halve
• Radioactive Activity is the count rate measured by a Geiger Counter - measured in Bequerels (Bq)
• Irradiation is when objects are exposed to to ionising radiation from a radioactive source, the energy can be harmful to living things but the object doesn't become radioactive
• Contamination is the unwanted presence of materials containing radioactive atoms in an object or organism. The exposure will cause damage until the material is removed.