THE CLOUD CHAMBER
A unique device for detection and measurement is the Cloud Chamber, invented by the British physicist Charles Wilson in 1911. The Cloud chamber makes it possible to visually see the path of ionizing radiation thus making it possible to photograph it. The cloud chamber consists of a plastic or glass container, which sits on dry ice. A dark cloth is saturated with alcohol and placed around the inside of the container near the top. A small radioactive material may be suspended from the lid of the container. In the chamber, the alcohol evaporates from the cloth and condenses as it reaches the cold region created by the dry ice at the floor of the container. Just above the floor of the chamber there is a region where the alcohol vapor does not condense unless there are seeds around, so that drops of alcohol can form. This condition is similar to that of seeding clouds with a chemical to form rain. The idea is that only seeds available in the chamber are those of ions produced by the interaction with radiation. The resulting trail of alcohol droplets can be seen against the black background in the bottom of the chamber.
These are only a few of the devices commonly utilized for purposes of detection and measurement of radioactivity and radiation. It is important to understand that when working with radioactivity/radiation, due to our inability to sense radiation, we need them to assist us in detecting the presence of radiation and we also need them to help monitor the radiation.
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