Atomic Structure

• Atoms have a radius of 0.1 nanometres, which is 1x10^-10m
• The radius of a nucleus is less than 1/10,000 of the atom, about 1x10^-14
• Electrons have a relative mass of 1/2000
• When the atom absorbs electromagnetic radiation, electrons gain energy and may move to a higher energy level
• If the atom emits electromagnetic radiation, the electrons may move to a lower energy level
• An isotope has the same number of protons but a different number of neutrons
• The atomic number is the number of protons in the nucleus
• John Dalton - Atoms are solid spheres that cannot be divided into smaller particles.
• JJ Thomson - plum pudding model
• Ernest Rutherford - nuclear model, disproved plum pudding model. Alpha scattering experiment, most of the atom made up of empty space with a positive nucleus
• Neils Bohr - electron shell model
• The proton was discovered before the neutron
• James Chadwick - neutron
• An alpha particle is a helium nucleus, made of 2 protons and 2 neutrons
• A beta particle is a fast moving electron ejected from a nucleus
• Gamma is electromagnetic radiation emitted from the nucleus
• Activity is the rate that an unstable nucleus decays, and it's measured in becquerel (Bq)
• Count rate is the number of decays recorded per second by a detector such as a Geiger-Muller tube
• Alpha radiation has a small penetrating power, and can be stopped by skin or a sheet of paper.
• Alpha particles can travel less than 5 cm
• Alpha particles have a high ionising power
• Beta radiation is stopped by 3 mm of aluminium foil
• Beta radiation can travel 1 metre
• Beta has a low ionising power
• Gamma radiation can be stopped by lead or concrete.
• Gamma radiation has a very low ionising power
• Gamma radiation can travel more than 1 km.
• Radioactive decay is a random process - it's impossible to predict which atom will decay next
• A half-life is the time it takes for the number of nuclei of an isotope in a sample to half, or for the count rate or activity of a radioactive source to halve.
• Net decline = reduction in activity / initial activity
• Radioactive contamination is the unwanted presence of radioactive atoms on other materials.
• Irradiation is the process of exposing an object to nuclear radiation.
• An object that is irradiated doesn't become radioactive
• It's very difficult to remove radioactive contamination
• To remove irradiation, the source simply need to be removed or shielding added.
• How can we protect against contamination and irradiation?

  • Keep a distance from the radiation, e.g. using tongs at arm's length
  • Limit the time of exposure to radioactive source
  • Use shielding, e.g. storing in a leaded lined box or by wearing protective clothing
• Why is it important to publish the findings of studies into the effects of radiation on humans?

  So scientists can peer review the work.
• Natural sources of background radiation:

  • Rocks
  • Cosmic rays from space
• Man-made sources of background radiation:

  • Nuclear accidents
  • Nuclear fallout from weapons testing
• Radiation dose is a measurement of the health risk of exposure to radiation