Radioactive isotopes which emit alpha particles can be used in smoke detectors. The alpha particles emitted from the Americium-241 collide with the oxygen and nitrogen molecules in the air causing them to ionise. To ionise means to knock off electron/electrons from an atom.
Photoelectric alarms work using a photoelectric sensor and a light source. As smoke enters the chamber and crosses the path of the light beam, light is scattered by the smoke particles, aiming it toward the sensor, which in turn triggers the alarm.
Alpha particles have low penetrating power but this still provides a range of useful applications: smoke detectors – americium-241 is commonly used in ionising smoke detectors. Smoke that enters the detector reduces the amount of alpha particles that are detected and triggers the alarm.
An optical smoke alarm (also called photo-electric smoke alarm) works using the light scatter principle. The alarm contains a pulsed infrared LED which pulses a beam of light into the sensor chamber every 10 seconds to check for smoke particles.
Americium-241 is used as a neutron source in non-destructive testing of machinery and equipment, and as a thickness gauge in the glass industry. However, its most common application is as an ionization source in smoke detectors, and most of the several kilograms of americium made each year are used in this way.
How they work. Ionization chamber smoke detectors rely on radiation to "ionize" the air inside the chamber. A radioactive source "decays," or sheds particles and photons from unstable atoms. The particles interact with neutral air molecules flowing through the chamber.
How they work: Photoelectric-type alarms aim a light source into a sensing chamber at an angle away from the sensor.Smoke enters the chamber, reflecting light onto the light sensor; triggering the alarm. For each type of smoke alarm, the advantage it provides may be critical to life safety in some fire situations.
Beta particles can be used to treat health conditions such as eye and bone cancer and are also used as tracers. Strontium-90 is the material most commonly used to produce beta particles. Beta particles are also used in quality control to test the thickness of an item, such as paper, coming through a system of rollers.
An alpha particle is identical to a helium atom that has been stripped of its two electrons; thus, an alpha particle contains two protons and two neutrons. Because an alpha particle has no electrons to balance the positive charge of the two protons, it has a charge of +2 and can be represented as He2+.
EXIT signs: Some EXIT signs contain the radioactive gas called tritium, allowing them to glow in the dark without electricity or batteries. The tritium used in EXIT signs gives off low-level beta radiation, causing a light-emitting compound to glow.
Smoke detectors typically fall within two categories: photoelectric and ionization. When it comes to disposal, old photoelectric detectors can be safely put in the trash, so long as you remove the battery first.
So, to answer the question of whether or not carbon monoxide detectors also detect radon, the answer is no. CO detectors are made to do just what the name implies: detect carbon monoxide gas. Radon gas can only be detected by a radon test kit, which is a one-time use kit.
As a smoke alarm's battery nears the end of its life, the amount of power it produces causes an internal resistance. Most homes are the coolest between 2 a.m. and 6 a.m. That's why the alarm may sound a low-battery chirp in the middle of the night, and then stop when the home warms up a few degrees.
A smoke detector blinking red could mean: It's Working Properly: Some brands use an occasional red blinking light to indicate the unit is working properly. The Batteries are Low: Usually accompanied by a loud beep, a blinking red light could mean the batteries in the unit are low.
The passage of smoke into the chamber causes the light from the source to be scattered and fall on the photocell. The photocell output is being used to initiate an alarm. In the Light obscuring smoke detector, smoke interferes with a light beam between a light source and photocell.
When smoke detectors are activated by the by-products of combustion (smoke) they emit a loud screeching noise. If the detector is just emitting an intermittent “chirping†noise it means that the battery needs to be replaced.
Resetting the Alarm
- Turn off the power to the smoke alarm at the circuit breaker.
- Remove the smoke alarm from the mounting bracket and disconnect the power.
- Remove the battery.
- Press and hold the test button for at least 15 seconds.
- Reconnect the power and reinstall the battery.
Explanation: Ionization smoke detectors use the alpha particles from americium oxide, AmO2 , to detect smoke. One gram of AmO2 provides enough material for more than three million smoke detectors. The plutonium-241 in spent nuclear fuel decays to form americium-241.
The most likely reason smoke detectors go off unexpectedly is that people aren't changing the batteries in them often enough. That's because smoke in the air will reduce the current. If your battery is dying, the current that's flowing through your sensor also goes down.
The main reason that alpha particles are used is that they are strongly ionizing, because they are helium nuclei without any orbiting electrons; they will rip electrons off of any particles that they encounter, whereas gamma rays and beta particles will not.
