Smoke detector is a very important safety device because it is use in every building and house to prevent serious damage and life threatening consequence that is cause by fire. This device is used by everyone in the world to keep property safe and save people life. There are two types of smoke detectors the first type is a Photoelectric smoke detector which is smoke detector device that use an optical sensor, the second type is an Ionization smoke detectors which is a smoke detector device that uses a small amount of radioactive material to detect smoke. People commonly use the Ionization smoke detectors because it is more reliable since it can detect fire in a wider range of condition. The last reason why Ionization smoke detector is more popular than Photoelectric smoke detector is because it is cheaper to purchase and install. Due to this reason, this discussion post is based on Ionization smoke detector.
The radioactive material that is use by the Ionization smoke detector is Americium-241. The amount of Americium-241 require for each detector is only around 1.0 microcurie. This radioactive material doesn’t exist naturally on its own instead it is the byproduct from the fission of Plutonium-239 when they irradiated with neutrons. Fission is when atom splits into smaller part to become more stable and this will decrease the mass of that element. During this reaction, beside just splitting some fraction of the atoms start to absorb two neutrons to form plutonium-241. The plutonium-241 will be taken out of the reaction so that it will undergo beta decay and form Americium-241. Beta decay is a radioactive decay where electron will be emitted from the nucleus. The last process will last the longest because plutonium have a half-life of 14 years. Half-life is the time that will take an radioactive atom to decay. A newly bought Ionization smoke detector contain 100% Americium but after 30 years 4.7% of the Americium will decayed into neptunium. This show that Ionization smoke detector is a very reliable smoke detector because Americium have a half-life of 432.2, which is way longer than the time the smoke detector will be in use. This also means that people doesn’t have to change the Americium-241 inside the smoking chamber because the radioactive atom will last the whole lifetime of the user.
This smoke detector work by having a positive and negative electrode inside the detecting chamber. The negative electrode is located on top, while the positive electrode is located right at the bottom of the negative one. In order for the smoke detector to work a low and steady electric current is apply to the two electrode so that the electrode will have a charge. There is an open in the chamber that allow air inside the room to flow inside the chamber, while this occur the Americium-241 inside the chamber continuously decay into Neptunium-241. Alpha decay is when two protons and two neutrons that are bound together is emitted from the nucleus. When Americium-241 decay it emit alpha particle, this particle will collide with oxygen and nitrogen molecules in the air. When it collide with the air molecule it will cause the molecule to ionise, which means that the emit alpha will knock the electron from the atom. As a result, negatively charge electron and positively charged atoms will be left in the chamber. These charge particle will be attracted to the electrode that have an opposite charge, for instance the positively charged atom will be attracted to the negatively charged electrode. This process produce a small amount of current that is detected by the electrical circuit in the smoke detector. The smoke detector will be able to detect that there is a fire because when smoke enter the chamber the electric current will drops and this signal will triggers the alarm to release the beeping sound. The reason why the electric current drops when smoke enter the chamber is because the emit alpha particles will collide with the smoke particle instead of the air particle. Due to this reason, there will be no negatively charge electron or positively charged atom because the alpha particle cannot ionise the smoke particle. This will cause a drop in the electric current and cause the smoke detector to release a beeping noise. To have a look at the animation of the particle movement inside the chamber, follow this link: http://www.passmyexams.co.uk/GCSE/physics/alpha-particles-in-smoke-detectors.html
In conclusion, Ionization smoke detector is very important and should be install in every houses, buildings and public infrastructures because it can protect these place from serious damage that is caused by fire and save people life.
Work Cited
Modern Chemistry by Holt McDougal
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