Activity 3.1 - α, β, and γ

Learning Aims:
  • To identify three kinds of radiation and their properties
  • To measure the absorption properties by matter for alpha, beta, and gamma radiation
Materials:
  • A computer with internet connection
  • Radiation sources: Alpha source (e.g. Po-210), Beta source (e.g. Sr-90) and Gamma source (e.g. Co-60)
  • A detection device: a Geiger-Müller counter or radiation sensor with a data-logger and software (Coach 6)
  • A set of absorbers e.g. paper, aluminium and lead of varying thicknesses
    Suggestions for use:

    Here students get familiar with different types of natural radiation.

    In activity 1 they recall their knowledge about gamma radiation.

    In activity 2 they explore alpha, beta, and gamma radiation properties, their behaviour in an electric and magnetic field and penetration properties. Instead of analysing images included in the worksheet students can use animation available at: http://www.passmyexams.co.uk/GCSE/physics/properties-of-radiation-electr....

    Alpha particles are attracted to the negatively charged plate and are deflected by a magnetic field. This confirms that they must be positively charged. Alpha particles are helium nuclei; they contain 2 protons, which gives them their positive charge.

    Beta particles are attracted to the positively charged plate and are deflected by a magnetic field in the opposite direction of alpha particles. This confirms that they are negatively charged. Beta particles are fast moving electrons. They are deflected much more than the heavier alpha particles.

    Gamma rays are unaffected by an electric field and are also unaffected by a magnetic field. Gamma rays are highly energetic waves with no charge associated with them.

    In the investigation of penetrating properties students use sources of different radiation. They measure the effect of absorbers placed between the source and the detecting device.
    Alpha particles should be stopped by anything except the very thinnest piece of paper or foil. If you do not have a pure alpha source, you need to be careful about trying to show the properties of alpha using a Geiger-Müller tube. The radiation from a mixed source like 241Am can penetrate aluminium and has a long range. This is because it gives out gamma as well as alpha radiation. Beta radiation can be stopped by a sheet of Perspex, an exercise book, or thin aluminium. Gamma radiation is very penetrating and needs thick layer of lead to reduce it to a low level.
    It can be easily demonstrated that alpha radiation has a very short range (between 3-10 cm), beta has a range of about 10 cm, and gamma gets weaker with distance but doesn’t come to a stop at any particular distance.

    If there is no equipment for student investigations then a teacher demonstration should be performed in which students should be actively involved.

    Also students can perform these experiments in a virtual lab, for example in a virtual radiation lab at http://visualsimulations.co.uk/software.php?program=radiationlab

    In activity 4 students evaluate why radioactive materials emitting alpha and beta radiation are not suitable for nuclear medicine.
    Possible questions:
    • What are alpha, beta and gamma radiations?
    • What are properties of alpha, beta and gamma radiation?
    • Which material stops alpha radiation? Beta radiation? Gamma radiation?
    • Which radiation, alpha, beta or gamma has the longest range? How do you know?
    • Why alpha and beta radioactive materials are not suitable for nuclear medicine?