Radioactivity

• Nuclei with too many neutrons undergo beta minus decay (with anti-neutrino) and nuclei with too few nuclei undergo beta plus decay (with neutrino)
• The mass number remains constant during alpha, beta minus, or gamma emission but changes during fission or fusion.
• Random nature of radioactive decay:

  • we cannot tell when a particular nucleus will decay
  • we cannot tell which nuclei will decay in a set time
• Radioactive decay is spontaneous so it isn't affected by external forces (pressure) and other nuclei in the sample
• The activity of a source ,A, is the rate at which nuclei decay in a sample
• Radioactive decay is the process by which unstable nuclei split, or decay, emitting ionising radiation
• Alpha particles penetrate the least, being stopped by just a few centimeters of air or a single sheet of paper. Beta particles can pass through paper but are stopped by thin aluminium. Gamma rays are the most penetrative, passing easily through paper and aluminium, they are stopped by thick lead
• The half-life is how long it takes for the number of atoms to decrease by half. This is done by plotting the number of atoms remaining against time on a logarithmic scale
• Radioactive dating is a method of dating rocks and minerals using radioactive isotopes. By measuring the quantity of unstable atoms left in a rock and comparing it to the quantity of stable daughter atoms in the rock, scientists can estimate the amount of time that has passed since that rock formed