9-1 Topic 6 Radioactivity 2

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Which of these is correct for half-life?

  • It is half the time for all the atoms to decay
  • It is the time it takes for an atom to half decay
  • It is the time it takes for half an atom to decay
  • It is the time it takes for half the atoms to decay

Radiographers are restricted to a smaller annual dose of radiation nowadays compared to 50 years ago. This is because nowadays:

  • the radioactive sources have decayed
  • we can measure radiation more accurately
  • we have a better understanding of the risks from radiation
  • we have more effective ways of shielding against radiation

The diagram shows light from a point source, S, spreading out as it gets further from S. The intensity of light passing through the surface which is 1 m from S is 2.5 W/m2. Complete the following: The intensity of light, in W/m2, passing through the surface which is 2 m from S is

  • 2.5 2
  • 2.5 4
  • 2.5 x 2
  • 2.5 x 4

The sign shows that this food has been deliberately exposed to gamma radiation. Gamma radiation is used because:


  • produce cancer cells in the food
  • kill cancer cells in the food
  • kill microbes in the food
  • make the food radioactive.