practical 12 - radiation

• equipment

  • gamma source
  • geiger counter
  • meter ruler
  • stopwatch
• method

  • place source far from geiger counter and start stopwatch recording total count reading after 20 minutes
  • background count
  • set source at 0.6m from geiger counter and start stopwatch recording after 5 minutes
  • reduce distance by 0.1m and repeat reducing by 0.1m each time to 0.1m
  • repeat experiment twice more and record mean count rate for each distance
• graphs and calculations

  • calculate and tabulate count rate for each distance and find background count rate
  • $C=$$\frac{N}{t}$
  • plot graph of $\frac{1}{\sqrt{C}}$ against distance
  • gives straight line verifying inverse square law
  • $Cx^2=$$k\ \ \rightarrow\ \frac{1}{\sqrt{C}}=$$\frac{x}{\sqrt{k}}$
• safety

  • exposure to radiation can damage cells

  precautions

  • keep as far away as possible
  • keep radioactive source in lead-lined container when not being used
  • handle source with tongs and don't touch source
• improvements

  • graph might not pass through origin as exact position of gamma material inside sealed source is unknown
  • systematic error
  • plotting graph of $\frac{1}{\sqrt{C}}$ against x instead of C against $\frac{1}{x^2}$ obtains a straight line anyway