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 Smoke
Detectors and Americium-241
Ionization smoke detectors
use an ionization chamber and a source of ionizing radiation to
detect smoke. 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. Inside an ionization detector
is a small amount (perhaps 1/5000th of a gram) of americium-241.
The radioactive element americium has a half-life of 432 years,
and is a good source of alpha particles.
Another way to talk about the amount of
americium in the detector is to say that a typical detector
contains 0.9 microcurie of americium-241. 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. Generally, that means that 37 billion atoms in the
sample are decaying and emitting a particle of nuclear radiation
(such as an alpha particle) per second. One gram of of the
element radium generates approximately 1 curie of activity
(Marie Curie, the woman after whom the curie is named, did much
of her research using radium).
Food Irradiation
 Food
irradiation is a method of treating food in order to make it
safer to eat and have a longer shelf life. This process is not
very different from other treatments such as pesticide
application, canning, freezing and drying. The end result is
that the growth of disease-causing microorganismns or those that
cause spoilage are slowed or are eliminated altogether. This
makes food safer and also keeps it fresh longer.
Archaeological
Dating
Significant progress has
been made in this field of study since the discovery of
radioactivity and its properties. One application is carbon-14
dating. Recalling that all biologic organisms contain a given
concentration of carbon-14, we can use this information to help
solve questions about when the organism died. It works like
this..when an organism dies it has a specific ratio by mass of
carbon-14 to carbon-12 incorporated in the cells of it's body.
(The same ratio as in the atmosphere.) At the moment of death,
no new carbon-14 containing molecules are metabolized, therefore
the ratio is at a maximum. After death, the carbon-14 to
carbon-12 ratio begins to decrease because carbon-14 is decaying
away at a constant and predictable rate. Remembering that the
half-life of carbon-14 is 5700 years, then after 5700 years half
as much carbon-14 remains within the organism.
Geological Dating
U-238
is used for dating rocks. U-238 (half-life of 4.5 billion years)
decays to lead-206. The ratio of U-238 to Pb-206, present in a
rock, can be used to determine the age of a rock.
Tracing Chemical
Vitamin
B 12 can be tagged with a radioisotope of cobalt to study the
absorption of the vitamin from the gastrointestinal tract.
Compounds
tagged with Fe-59 and Fe-55 are used to study the absorption of
iron.
Glucose
tagged with carbon-11 (half-life, 20.3 minutes and positron
decay mode) circulates through the body, and the positrons
emitted in the heart, brain or some other organ are monitored by
a PET detector. A computer uses this information to construct an
image (called a PET scan) of the organ that is being examined.
PET scans have been used to study the effects of drugs on
cancers, to measure damage in victims of stroke or heart attack,
and to study chemical changes that occur during epileptic
seizures.
Melvin Calvin, a
biochemist, labeled CO2 with C-14 and worked out the process by
which plants photosynthesize carbohydrate from CO2 and
H2O
from-http://www.chemcool.com/regents/nuclearchemistry/aim5.htm
Detection of Disease
Iodine-131, a beta emitter, is taken as
sodium iodide in drinking water. Almost all of it will find its
way to the thyroid. The rate of iodine-131 uptake, determined
with a Geiger counter or other scanning device, indicates
whether the thyroid glands are functioning properly.
Sodium chloride containing sodium-24,
can be injected into the bloodstream to study blood circulation.
The beta particles emitted by the sodium-24 are followed and an
impaired circulation is immediately detected.
A thallium-201 compound injected into
the bloodstream will concentrate in normal heart muscle but will
not remain in damaged tissue. A photograph with a nuclear
scintillation camera allows the physician to locate the damaged
areas.
Technetium-99m is used for locating
brain tumors and damaged heart cells.Technetium-99m is probably
the most widely used radioisotope in medicine today; it is a
decay product, of molybdenum-99.
from-http://www.chemcool.com/regents/nuclearchemistry/aim5.htm
Treatment
of Disease
Radium-226
and cobalt-60 are used in cancer therapy.
from-http://www.chemcool.com/regents/nuclearchemistry/aim5.htm
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