Nuclear physics

• Nuclear fusion

  The fusing of light nuclei to produce heavier nuclei releasing energy in the process
• Activity

  Activity is the rate of decay of unstable nucleus or the number of decays per second dN/dt or A, Units Bq
• Ionising radiation

  Radiation with sufficient energy to ionise atoms by removing electrons
• Two conditions for nuclear fusion

  • Very high density (large number of collisions)
  • Very high temperatures (large kinetic energy to overcome forces of repulsion between nuclei)
• Random meaning (nuclear physics)

  We cant identify when an individual nucleus will decay
• Decay constant

  The decay constant is the probability that a certain nucleus will decay in a certain second, a large value of this means that the sample will decay quickly
• Binding energy of a nucleus

  This is the energy required to separate all the nucleons in a nucleus
• Half-life

  The mean time taken for the number of nuclei in the sample to halve and the mean time taken for the activity of the sample to halve
• Spontaneous meaning (nuclear physics)

  The decay cannot be influenced by any external factors
• Why is activity always greater than count rate?

  The activity is the total number of emission per second in all directions from the source taken, however detectors do not usually surround the source and so only a small fraction of particles are detected
• Safety procedures to minimise the dose when handling radioactive sources

  • Use tongs and hold the source away from your body
  • Wash your hands after the experiment
  • Put the source away as soon as possible
• Why do stars stop fusing at iron-56

  The binding energy per nucleon is a maximum for iron-56 so isotopes larger than iron-56 would require energy to fuse rather than release energy