Ionizing smoke detectors are designed so that gaining access to their radioactive sections would require the complete destruction of the device. Very low 1 kilometre km one example of a use of alpha radiation is in smoke detectors. A household smoke alarm measures the movement of alpha particles across a small gap. Alpha particles are subatomic fragments consisting of two neutrons and two protons. How does a smoke detector work how is radioactivity used in a smoke detector the radioactive source in a smoke detector is americium241. Radioactive isotopes which emit alpha particles can be used in smoke detectors. Radioactive elements that undergo alpha decay are used in smoke detectors see figure 3. The alpha particles ionise the molecules of the air forming ions and electrons which are attracted to a pair of charged plates as shown in the picture below.
Friendly reminder that your smoke detector is totally. Alpha particles are used for the ionizing smoke detector as they have high ionizing potential. Also there are live demonstrations using an americium 241 pellet from an ionizing smoke detector and a spark gap powered by a homemade. They contain an ionisation chamber which consists of a positive and negative electrode along with a very small amount of the radioisotope americium241. The ionization type typically uses americium 241 as the ionization source. Smoke alarms contain a small amount of the radioactive element, americium241.
Americium is a relatively save alpha emitter if handled properly. Inside the smoke detertor alpha particles are released. Two charged plates inside of the ionization smoke detector create a flow of positively and negatively charged ions. Ionization chamber smoke detectors contain very small amounts of nuclear material. Ni63 emits beta particles, which can travel a few feet but cannot penetrate a smoke detectors plastic housing. Speaking of alarms, whenever the words nuclear radiation are used an alarm goes off in many peoples minds.
Thickness monitoring radiation is absorbed as it passes through materials. They are so weak that they can be stopped by a single sheet of paper. The animation below shows a smoke detector with the radioisotope americium 241 as the alpha source. Americium in smoke detectors radiation protection us epa. The types of radiation from these sources cannot make anything else radioactive. What is detection of alpha radiation alpha particle detector definition december 14, 2019 by nick connor detection of alpha radiation is very specific, because alpha particles travel only a few centimeters in air but deposit all their energies along their short paths. In fact, the alpha particles emitted by the americium 241 in smoke detectors have a short range. A source of alpha radiation is used because the range is very low and alpha radiation has a very high. I will also analyse a variety of data based on smoke alarms, and finally, i will discuss the advantages and disadvantages of smoke alarms. Smoke from the fire is detected by the device, which then gives off an alarm. Jun 11, 20 maureen conleypublic affairs officer we sometimes get calls from people worried about radiation from smoke detectors in their homes. Do ionisation smoke detectors pose radiation danger.
Do not fear your smoke detector it could save your life u. Moreover, the ionizing smoke detectors outright failed to function 20 percent of the time, according to studies. Geiger counter gammascout rechargeable version hand held radiation detector. Alpha decay can provide a safe power source for radioisotope thermoelectric generators used for space probes and. The radiation dose to the occupants of a house from these smoke alarms is very small and does not pose a health risk. A smoke detector uses either a photoelectric cell or an ionization to detect smoke. Fires kill people but smoke detectors dont even irradiate them. Uses of radioactivity halflife wjec gcse physics single. Ionization smoke detectors expose people to a tiny amount of radiation about 1100 of a millirem per year. The alpha particles ionize air in an open ion chamber and a small current flows through the ionized air. Alpha radiation is actually a helium4 nucleus two protons and two neutrons.
It has very limited penetrating power because it is a big. Why do they use alpha in smoke alarms not beta or gamma answers. There are two types of smoke detector commonly available in many countries. How radiation works using americium 241, alpha particles.
Dec, 2008 how radiation works using americium 241, alpha particles and gamma rays duration. Ionization smoke detectors use americium as a source of alpha particles. This makes some particles positively charged and some negatively charged. What are the values of a and z in the following nuclear equation for the alpha decay of an americium241 nucleus. How they should be positioned in a home by bernard gladstone. Uses of radioactivity, alpha particles in smoke detectors pass my. Ionizing or ion chamber smoke detectors contain a very small amount of radioactive material, americium241 am241. May 12, 2020 some early models used radium226, and commercial smoke detectors and some residential units used nickel63. Why do they use alpha in smoke alarms not beta or gamma. The alpha particles from the smoke detector do not themselves pose a health hazard, as they are absorbed in a few centimetres of air or by the structure of the. They give off alpha particles and low energy gamma rays which escape harmlessly.
What does the alpha radiation do to the air in between the two metal plates in a smoke detector. The vital ingredient of household smoke detectors is a very small quantity of am241 as americium dioxide amo2. The ability of domestic smoke alarms to save life and property in house fires is well established. Do not fear your smoke detector it could save your life. Alpha radiation is completely shielded by a sheet of paper, by 2. Alpha radiation cannot penetrate a sheet of paper, and it is blocked by several centimeters of air. The americium is present in oxide form in the detector. What are some radioactive elements used in smoke detectors. One type uses the radiation from a small amount of radioactive material to assist in the detection or presence of smoke particles. For example, in some kind of smoke detectors, you can meet manmade radionuclides such as americium241, which is a source of alpha particles. Smoke that enters the detector reduces the amount of alpha particles that are detected and triggers the alarm.
Americium241 is the most common material used as the alpha emitter in a domestic smoke alarm. Ionizing radiation can be found in smoke detectors and sometimes emitted from color televisions. Alpha radiation is not dangerous under most circumstances, so as long as you dont disassemble the smoke detector, it is perfectly safe. Americium241 is a radioactive isotope used in domestic smoke detectors. Although there are concerns that this type of smoke detector emits radiation, the alpha particles used have low penetrative potential and so will not pass through plastic material. The radiation released by this element ionizes particles that are then detected by a chargedparticle collector.
Alpha particles from the americium source ionize air molecules. Is my household smoke detector emitting radioactive rays. This radiation strips off electrons and gives some of the air molecules a charge, which completes a circuit that smoke is really good at breaking. Alpha decay occurs in elements with high atomic numbers, such as uranium, radium, and thorium. The smoke detector has two ionization chambers, one open to the air, and a reference chamber which does not allow the entry of particles. The radioactive source in a smoke detector is americium 241. What is detection of alpha radiation alpha particle. Smoke that enters the detector reduces the amount of alpha particles that are detected and triggers the alarm static eliminators typically use alpha particles from polonium210 to remove static charges from equipment. Amercium241 has a half life of 432 years and is a good source of alpha particles. Inside the smoke detector, the alpha particles pass through an ionisation chamber, creating a small current between two electrodes. I came across my old smoke detectors and saw that they contain some americium 241 dioxide, so i wanted to try and extract it. Alpha particles are made of 2 protons and 2 neutrons. This is well below the background radiation level of about 360 millirems a year. Because the distance alpha particles travel in air is so short, there is no risk of being exposed to radiation by having a smoke detector in the house.
The ionizationtype smoke detectors use a tiny americium source to generate alpha particles. Americium in ionization smoke detectors radtown us epa. Alpha particles from the americium source ionize air molecules, allowing positive and negative ions to flow between charged plates in the smoke. Americium241 emits alpha radiation, which can cause the molecules in the air near it to gain a chargethis is key. The four areas below contain fact sheets that explain different types, sources, and uses of radioactive material or radiation. The amount of radiation in a smoke detector is extremely small. Mar 11, 2020 meanwhile, the radioactive material, americium241, is emitting alpha radiation. Some of the radiation could leave the smoke detector.
There are many reasons why the public need not fear these products. Americium241, an alpha emitter, is used in smoke detectors. The source of ionizing radiation is a minute quantity of americium241 perhaps 15000th of a gram, which is a source of alpha particles helium nuclei. Uses of radioactivity, alpha particles in smoke detectors. One type of smoke detector uses americium241, a source of alpha radiation, to detect smoke. Ionization smoke detectors have a small americium source encased in a layer of foil and ceramic, which stops the alpha particles from traveling outside of the smoke detector. Americium is one frequently used element as it is a major alpha particle source. Americium241 has a halflife of 432 years and decays by emitting alpha particles to produce neptunium. Detection of alpha radiation alpha particle detector. Maureen conleypublic affairs officer we sometimes get calls from people worried about radiation from smoke detectors in their homes. The alpha particles emitted by the am241 collide with the oxygen and nitrogen in air in the detector s ionization chamber to produce charged particles ions. The ionization smoke detector has two ionization chambers, one open to the air, and a reference chamber which does not allow the entry of particles. The smoke detector senses the drop in current between the plates and sets off the horn. Radioactive americium releases alpha radiation, which ionises the air inside the detector.
Most detectors make use of about two microcuries of americium241, which is used to make the air in the detector s. Jun 09, 2016 a smoke detector uses either a photoelectric cell or an ionization to detect smoke. Radioactive smoke detectors the health wyze report. Ionization smoke detectors use an ionization chamber and a source of ionizing radiation to detect smoke. There is some radioactive material inside the smoke detector.
Despite the shoddy results for the ionizing radioactive smoke detectors, which illustrate the prudence of exclusively using photoelectric smoke alarms, 95% of american homes with smoke detectors use the inferior, radioactive type. Ionization smoke detectors expose people to a tiny amount of radiationabout 1100 of a millirem per year. The alpha particles from americium241 bombard air molecules, knocking electrons free. A new smoke alarm can distinguish between safe household smells burned toast and a dangerous fire. A smoke detector is a device that senses smoke, typically as an indicator of fire.
The facts about smoke detector radiation from americium 241. Alpha short range, used in smoke alarms beta longer range, but less penetrating, used in the manufacture of aluminium gamma used in xrays. Alpha is weakly penetrating so smoke stops it, the current drops and the alarm goes off. Radioactivity in ionisation smoke alarms environmental. This changes atoms or molecules into charged particles. How radiation work using americium 241 as an example as it radiates alpha particles and gamma rays, slowly undergoing radioactive decay to become. Ionization chamber smoke detectors, the most common type, use radiation to detect smoke. Americium 241 is used in smoke detectors because it is a strong alpha particle emitter. How many alpha particles are emitted in each second by a 5. Alpha short range, used in smoke alarms beta longer range, but less penetrating, used in the manufacture of aluminium gamma used in xrays asked in. Ionization detectors have an ionization chamber and a source of ionizing radiation. The radioactive source emits alpha particles into both chambers, which ionizes some air molecules. Smoke detectors or smoke alarms are important safety devices, because of their obvious potential to save lives and property. Mar 30, 2018 i came across my old smoke detectors and saw that they contain some americium 241 dioxide, so i wanted to try and extract it.
Smoke from a fire absorbs alpha radiation, altering the ionisation and triggering the alarm. Smoke detectors top a poll of favorite everyday gadgets and technologies. The primary radiation from a smoke detector is atomic particle called an alpha particle, which can travel only a short distance but has the ability to charge the air molecules in the ionization chamber inside the smoke detector thereby creating the current necessary to operate the detector. Ionizing smoke detectors contain up to five microcuries 185,000 becquerels of americium 241. Inside an ionization detector is a small amount perhaps 15000th of a gram of americium241. This type of smoke detector is more common because it is inexpensive and better at detecting the smaller amounts of smoke produced by flaming fires. Am241 produces alpha particles which generate a lot of ions when they pass through the a. Why does a smoke detector use alpha radiation answers. They contain an ionisation chamber which consists of a positive and negative electrode. Smoke particles disrupt this current, triggering an alarm.
Alpha particles are absorbed and collide with the oxygen and nitrogen in the air and create charged particles called ions. Ionization detectors ionization detectors have an ionization chamber and a source of ionizing radiation. In fact, most common radiation detectors cannot detect the 241 am source while it remains in the steel chamber that it is sealed in. As a result, the level of radioactivity present in americium 241 smoke detectors is virtually undetectable. Commercial security devices issue a signal to a fire alarm control panel as part of a fire alarm system, while household smoke detectors, also known as smoke alarms, generally issue a local audible or visual alarm from the detector itself or several detectors if there are multiple smoke detectors interlinked. When smoke particles enter the detector, they scatter the light beam, and the photocell detects the reflected light. Some domestic smoke alarms use the radiation from a small amount of radioactive material to detect smoke or heat sources. Smoke in the detector absorbs this alpha radiation, so if smoke is. An isotope of americium which emits alpha particles. Am241 has a halflife of 458 years and emits alpha particles. Mazur instruments prmacintl international ac adapter with 58 cable and ltype dc plug, for prm80009000 geiger counter and nuclear radiation monitors. Ionization smoke detectors how do ionization smoke detectors work. How radiation works using americium 241, alpha particles and.
Alpha radiation cannot even penetrate a piece of paper, so it does not take much to shield against alpha. It is very easily stopped, no radiation leaves the smoke detector. Smoke detectors make use of the ionising properties of alpha particles. Smoke particles disrupt the low, steady electrical current produced by radioactive particles and trigger the detectors alarm. The radioactive source in a smoke detector is americium241. The alpha particles are absorbed within the detector, while most of the gamma rays escape harmlessly. Smoke particles from the fire that enter the chamber reduce the current, triggering the smoke detector s alarm. Alpha, beta and gamma radiation flashcards quizlet. They might use americium241, radium226 or nickel63. The alpha radiation ionises the air particles inside the smoke detector. Alpha particles are the weakest kind of radioactive decay, and can be stopped by a sheet of paper. Ionizing radiation alpha and beta particles, neutrons, and x and gamma rays causes damage by ionizing, i.
These electrons are then used to create an electrical current. The ionization chamber consists of two plates separated by about a centimeter. The americium in the smoke detector could only pose a danger if you were to inhale it. The additional exposure you receive from a smoke detector is considerably less than the normal background radiation in most parts of the country. Operation of smoke detectors americium241 emits alpha particles and low energy gamma rays. If a smoke detector contains radioactive materials, a printed notice on the packaging will say so. Why dont we use beta or gamma radiation in a smoke alarm. Because of this shielding, the smoke detector poses no radiation health risk when they are properly handled. When the ions and electrons hit the plates they provide a small amount of electricity a. Each of the locationbased categories below will lead you to indepth fact sheets, like our nonionizing radiation used in microwave ovens fact sheet.
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