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After reading the title, some of you may be wondering “What is a Neutron Dosimeter?” Neutrons are particles found in the nucleus (center) of an atom which do not carry an electric charge. A dosimeter is a device used to measure a person’s exposure to radiation. So, a Bubble Detector is a type of neutron dosimeter that measures a person's exposure to neutron radiation. Even though there are always some harmless neutrons around us in the natural environment, a high exposure to neutron radiation can be harmful to the human body, so measuring neutron exposure is important.
The Bubble Detector was invented in the early 1980s by Dr. Harry Ing (President of Bubble Technology Industries) and his colleagues. It became Bubble Technology Industries' first product in 1988 when the company opened. It is a unique device because it provides a very accurate measurement of neutron exposure, without being affected by other types of radiation. Also, it does not require a power source and it gives the user real-time results—the moment you see a bubble form is the moment the detector has come in contact with a neutron.
A Bubble Detector consists of a clear plastic tube, filled with a special polymer gel, enclosed by a black screw-top cap. Tiny droplets of a superheated detector liquid are dispersed throughout the gel. "Superheated" simply means the droplets of detector liquid are being held by the gel above their normal boiling point, but without changing into a gas. When the detector cap is opened, the detector is ready to measure. If a neutron comes in contact with a superheated droplet, it provides a ‘kick’ of energy that vaporizes the liquid droplet and turns it into a gas bubble. The gas bubble is then trapped inside the polymer gel and can be easily seen with the human eye. The number of droplets in the detector provides a direct measurement of the neutron exposure. This means that when a person wears a bubble detector, the bubble detector can be used to measure how much neutron radiation the person's body has received. Once the user has counted the bubbles in the detector, they can then close the detector cap. This will squeeze (or ‘recompress’) the bubbles back into their liquid state in order to be ready for the next set of measurements. The sensitivity of the Bubble Detector can be controlled by changing the number of tiny droplets inside the detector when it is being manufactured.
Since its invention, the Bubble Detector has been used all around the world, including places like Canada, USA, France, Belgium, Russia, and Japan. It has been used to measure neutron radiation on Earth, in space, and under the sea. Besides astronauts, common users of the Bubble Detector include military personnel, nuclear power station workers, and hospital staff.
Special thanks to Bubble Technology Industries for this Backgrounder.