Cesium (chemical symbol Cs) is a metal that may be stable (nonradioactive)
or unstable (radioactive). The most common radioactive form of
cesium is cesium-137. Another fairly common radioisotope is cesium-134.
Cesium-137 is much more significant as an environmental contaminant
than cesium-134. It is also very useful in industry for its strong
radioactivity.
Who discovered cesium and cesium-137?
In 1860, Gustav Kirchhoff and Robert Bunsen discovered nonradioactive
cesium in mineral water in Germany. Radioactive cesium-137, and
many other radionuclides that are used in nuclear medicine, was
discovered in the late 1930s by Glenn T. Seaborg and his coworker,
Margaret Melhase.
Where does cesium-137 come from?
Nonradioactive cesium occurs naturally in various minerals. Radioactive
cesium-137 is produced when uranium and plutonium absorb neutrons
and undergo fission. Examples of the uses of this process are
nuclear reactors and nuclear weapons. The splitting of uranium
and plutonium in fission creates numerous fission products. Cesium-137
is one of the more well-known fission products.
What are the properties of cesium-137?
Cesium, as well as cesium-137, is a soft, malleable, silvery
white metal. Cesium is one of only three metals that is a liquid
near room temperature (83 °F). The half-life of cesium-137
is 30 years. It decays by emission of a beta
particle and gamma rays
to barium-137m.
What is cesium-137 used for?
Cesium-137 is one of the most common radioisotopes used in industry.
Thousands of devices use cesium-137:
moisture-density gauges, widely used in the construction industry
leveling gauges, used in industries to detect liquid flow
in pipes and tanks
thickness gauges, for measuring thickness of sheet metal,
paper, film and many other products
well-logging devices in the drilling industry to help characterize
rock strata
Cesium-137 is also used in medical therapy to treat cancer.
Cesium-137 in the environment came from a variety of sources.
The largest single source was fallout from atmospheric nuclear
weapons tests in the 1950s and 1960s, which dispersed and deposited
cesium-137 world-wide. However much of the cesium-137 from testing
has now decayed.
Nuclear reactor waste and accidental releases such as the Chernobyl
accident in the Ukraine release some cesium-137 to the environment.
Spent nuclear fuel reprocessing plant wastes may introduce small
amounts to the environment. However, the U.S. does not currently
reprocess spent nuclear fuel.
Although hospitals and research laboratories generate wastes
containing cesium-137, they usually do not enter the environment.
Occasionally, industrial instruments containing cesium-137 are
lost or stolen. Anyone who unwittingly handles them may be exposed.
These devices are typically metal, and may be considered scrap
metal and sold for recycling. If they find their way into a steel
mill and are melted, they can cause significant environmental
contamination. They may also be discarded and sent to a municipal
landfill, or sold for other reasons. These devices should be considered
dangerous.
Cesium-137 undergoes radioactive decay with the emission of beta
particles and relatively strong gamma radiation. Cesium-137 decays
to barium-137m, a short-lived decay product, which in turn decays
to a nonradioactive form of barium. The half-life of cesium-137
is 30.17 years. Because of the chemical nature of cesium, it moves
easily through the environment. This makes the cleanup of cesium-137
difficult.
How do people come in contact with cesium-137?
Everyone is exposed to very small amounts of cesium-137 in soil
and water as a result of atmospheric fallout. In the Northern
Hemisphere, the average annual dose from exposure to cesium-137
associated with atmospheric fallout is less than 1 mrem; this
dose continues to diminish every year as cesium-137 decays.
People may also be externally exposed to gamma radiation emitted
by cesium-137 by walking on contaminated sites, coming in contact
with waste materials at contaminated sites, breathing the air
around these sites, and drinking contaminated water. Also, people
may unknowingly handle a strong industrial source of cesium-137.
How do I know if I'm near cesium-137?
You need special equipment to detect the presence of any radionuclide.
You cannot feel exposure to cesium-137, or taste or smell it.
How does cesium-137 get into the body?
People may ingest cesium-137 with food and water, or may inhale
it as dust. If cesium-137 enters the body, it is distributed fairly
uniformly throughout the body's soft tissues, resulting in exposure
of those tissues. Slightly higher concentrations of the metal
are found in muscle, while slightly lower concentrations are found
in bone and fat. Compared to some other radionuclides, cesium-137
remains in the body for a relatively short time. It is eliminated
through the urine. Exposure to cesium-137 may also be external
(that is, exposure to its gamma radiation from outside the body).
Like all radionuclides, exposure to radiation from cesium-137
results in increased risk of cancer. Everyone is exposed to very
small amounts of cesium-137 in soil and water as a result of atmospheric
fallout. Exposure to waste materials, from contaminated sites,
or from nuclear accidents can result in cancer risks much higher
than typical environmental exposures. Great Britain's National
Radiological Protection Board predicts that there will be up to
1,000 additional cancers over the next 70 years among the population
of Western Europe exposed to fallout from the nuclear accident
at Chernobyl, in part due to cesium-137.
If exposures are very high, serious burns, and even death, can
result. Instances of such exposure are very rare. One example
of a high-exposure situation would be the mishandling a strong
industrial cesium-137 source. The magnitude of the health risk
depends on exposure conditions. These include such factors as
strength of the source, length of exposure, distance from the
source, and whether there was shielding between you and the source
(such as metal plating).
Is there a medical test to determine exposure to cesium-137?
Yes, there are several. However, they are not routinely available
in a doctor's office, because they require special laboratory
equipment. Some tests can measure the amount of radionuclides
in urine, or in fecal samples, even at very low levels. A technique
called "whole-body counting" can detect gamma radiation
emitted by cesium-137 in the body. A variety of portable instruments
can directly measure cesium-137 on the skin or hair. Other techniques
include directly measuring the level of cesium-137 in soft tissues
samples from organs or from blood, bones, and milk.
What can I do to protect myself and my family from cesium-137?
Cesium-137 that is dispersed in the environment, like that from
atmospheric testing, is almost impossible to avoid. However the
exposure from cesium-137 in the environment is very small.
Serious exposure is unlikely. People most likely to accidentally
encounter a cesium-137 source typically work in scrap metal sorting,
sales and brokerage, metal melting and casting, and in municipal
landfill operations. They may unwittingly encounter an industrial
instrument containing a sealed cesium-137 radiation source.
Both EPA and the Nuclear Regulatory Commission regulate Cesium-137.
The Nuclear Regulatory Commission licenses the its use. EPA has
several regulations that protect you from cesium-137 in the environment.
These include standards for the maximum amount of cesium-137 that
nuclear facilities may release to the air, and maximum levels
for cesium-137 in drinking water. EPA also sets risk-based
criteria for clean up of soil and groundwater at sites contaminated
with cesium-137 that must be met before the site can be approved
for public use.
