The properties of alpha, beta and gamma radiation

• Alpha particles consist of:

  • 2 neutrons, 2 protons
• Beta particles are:

  • 1 electron
• Gamma radiation is:

  • High energy photons
• Why are a and B deflected in opposite directions in a magnetic field?

  a is positively charged and B is negatively charged
• Why is the B deflected more than a?

  B has a smaller mass (1/2000)
• Why is y-radiation unaffected by the magnetic field?

  It is uncharged
• Explain how the ionisation chamber works

  • The chamber contains air at atmospheric pressure
  • Ions created in the chamber are attracted to the oppositely charged electrode where they are discharged
  • Electrons pass through the picoammter as a result of ionisation in the chamber
  • Current is proportional to the number of ions per second created
• The cloud chamber is used for detecting particles of ionising radiation. In its most basic form, a cloud chamber is a sealed environment containing a supercooled, supersaturated water or alcohol vapour
• When an alpha particle or beta particle interacts with the mixture in the cloud chamber, it ionises it. The resulting ions act as condensation nuclei, around which a mist will form (because the mixture is on the point of condensation)
• The high energies of alpha and beta particles mean that a trail is left, due to many ions being produced along the path of the charged particle
• Alpha particles produce straight tracks that radiate from the source and are easily visible. The tracks from a given isotope are all of the same length, indicating that the a particles have the same range
• Beta particles produce wispy tracks that are easily deflected as a result of collisions with air molecules. The tracks are not as easy to see as a particles tracks because B particles are less ionising than a particles
• What should be done before a source is tested?

  The count rate due to background radioactivity should be measured
• Explain how we would investigate how an absorber may be tested

  • The count rate is then measured with the source at a fixed distance from the tube without any absorber present
  • The background count rate is then subtracted from the count rate with the source present to give the corrected count rate from the source