Transcript Ionization Smoke Detector - Physics @ CSU Stanislaus

Ionization Smoke Detector
By Shawna Miller & Crystal Thomas
Outline
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Define Terms
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Americum-241
Ionizing Radiation
Alpha Particles
Curie
What it is
How it works
Look inside an Ionization Chamber
Simplify
A look into the safety factor
Sources
What is americium-241?
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Americium (chemical symbol Am) is a man-made
radioactive metal, with Atomic Number 95.
A silvery metal; whose isotopes americium-237
through -246 are all radioactive. Americium-241 is
formed spontaneously by the beta decay of
plutonium-241.
A typical detector contains 0.9 micro-curie of
americum-241
What is Ionizing Radiation?
Ionizing radiation is a type of particle
radiation in which an individual particle, such
as an electron, carries enough energy to
ionize an atom or molecule, that is, to
completely remove an electron from its orbit.
 If the individual particles do not carry this
amount of energy, it is essentially impossible
for even a large flood of particles to cause
ionization.
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What are alpha particles?
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They are a highly ionizing form of particle
radiation which have low penetration. They
consist of two protons and two neutrons
bound together into a single particle.
What is curie?
A curie is a unit of measure for nuclear
material.
 If you are holding a curie of something in
your hand, you are holding an amount of
material that undergoes 37,000,000,000
nuclear transformations per second.
 That means 37,000,000,000 atoms are
decaying an emitting particles of nuclear
radiation per second.
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How does this pertain to the smoke
detector?
Ionization Smoke Detectors
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Ionization smoke detectors use an ionization chamber and
a source of ionizing radiation to detect smoke.
Ionization sensor smoke alarms contain a small amount of
radioactive material, americium embedded in a gold foil
matrix within an ionization chamber. This thin goldamericium foil is then sandwiched. This is thick enough to
completely retain the radioactive material, but thin enough to
allow the alpha particles to pass.
The ionization chamber is basically two metal plates a small
distance apart. One of the plates carries a positive charge,
the other a negative charge.
More on Ionization Detectors…
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The positively charged metal plate attracts the negatively
charged ions (electrons) and the negatively charged plate
attracts the positively charged ions (mostly oxygen and
nitrogen). The steady flow of ions creates a small but steady
current.
These atoms-are ionized when electrons are kicked out of
the molecules by alpha particles from the radioactive
material.
The current is disrupted when smoke enters the ionization
chamber. Smoke particles attach to the charged ions and
restore them to a neutral electrical state. This reduces the
flow of electricity between the two plates in the ionization
chamber, and when the electric current drops below a
certain threshold, the alarm is triggered
How an Ionization Detector Works
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The ionization chamber in an ionization detector is
an aluminum can containing the ionization source.
There's also an ionization radiation. The ionization
radiation uses an Americium-241 and it helps
power the detector.
The ionization chamber has two plates separated
by a centimeter. When smoke enters the ionization
chamber, the particles attach to ions and neutralize
them preventing the particles from reaching the
plates.
Inside an Ionization Smoke
Detector
Inside an Ionization Chamber
Break it Down…
The smoke that permeates smoke detectors
is made by carbon.
 Americium is what detects the smoke.
 Smoke particles float around and then reach
the inside of the smoke detector.
 The smoke gets near the sensor and then
the electric horn is activated.
 When the horn is activated it's an early
warning telling you to get out of the house
before the fire starts all the way.
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Other Facts
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Does it emit radiation?
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The very low-level radiation in ionization smoke
detectors is not harmful and when compared, in
all cases, is less than the maximum permitted
from other consumer products that emit
radiation, such as television sets.
Ionization detectors are the safest for flame
fires.
Sources
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http://en.wikipedia.org/
wiki/Main_Page
http://chemistry.about.c
om/cs/howthingswork
http://home.howstuffwo
rks.com/smoke2.htm
http://www.epa.gov/radi
ation/sources/smoke_i
on.htm
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Dr. Gary A Ruff, Glenn
Research Center
(GRC), NASA's lead
center for microgravity
combustion research.
Demonstration