Smoke Detector


  The ionisation smoke detector makes use of the [alpha]
  radiation emitted by Americium-241, which has a half-
  life of 432 years. It consists of two components:

• a sensor to sense the smoke
• an electronic alarm

  The sensor is composed of an ionisation chamber and
  an Americium source. An electrical potential is applied 
  across the chamber with the radioactive source 
  alongside. The alpha particles emitted will ionise the 
   oxygen and nitrogen particles in the air, the ions are 
   attracted to the opposite electrodes and will produce a 
   small current flow between the electrodes. This current is 
   sensed by the electronics in the smoke detector. When smoke enters the ionisation
   chamber, ions are attracted to the smoke particles and are thus neutralized. The smoke 
   detector will sense the drop of current and initiate the alarm.


   Thickness gauge   
    This makes use of the penetrating property of beta radiation and helps to control the
    thickness of papers or tyres in factories. The piece of paper (or tyre) is put between a 
    beta source and a detector. If excessive radiation is detected, the paper (or tyre) is 
    made too thin and vice versa.

   Sterilisation
    Radiation can be used for food irradiation and surgical sterility because it can kill the 
    microorganisms living on food and on the surface of surgical equipment.

    Food Irradiation-Certain types of food are exposed to beta radiation or [gamma rays]to 
    kill the microbes and bacteria on them. Potatoes, onions and garlic are irradiated to 
    prevent sprouting; the shelf life of strawberries, mangoes and papayas can be increased 
    by irradiation; Salmonella and Listeria, which are infectious bacteria, can be reduced to 
    harmless level in meat, fish and poultry by food irradiation. However, irradiated food has 
    led to a lot of controversies and therefore is not yet generally accepted and available to the 
    public.


   Surgical sterilisation
    Delicate surgical instruments such as cardiac pacemakers cannot be sterilized by heat. They 
    are either treated by ethylene oxide or by radiation. Disposable items such as scalpels, gloves
    and syringes are also treated in bulk by radiation.


    Radioactive lightning conductor
    A lightning conductor is installed on the top of a building to prevent the building from being 
    struck by lightning during a thunderstorm. When clouds are blown around by wind, they 
    become charged. If a negatively charged thundercloud gathers over a building, a positive 
    charge will be induced on the roof. Sometimes the force of attraction between two oppositely 
    charged objects may become so large that the electrons will jump from the cloud to the roof, 
    resulting in a flash of lightning and causing damages to the building. With the help of a 
    radioactive lightning conductor, alpha particles (positive ions) are released into the air to 
    reduce the induced charge on the roof and neutralize some of the charge on the cloud. As 
    the force of attraction is reduced, the building will remain saved.


   Detection of leakage
    Leakages of underground pipes can be detected by putting certain radioactive material into
    the pipe and detecting the radiation with a detector. Area in which excess radiation is detected 
    corresponds to area of pipe leakage.


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