CHAPTER I
PRELIMINARY
1.1. Background
The alkali
metals are lithium (Li),sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr).This group lies in the s-block of the periodic table as
all alkali metals have their outermost electron in an s-orbital. The alkali metals provide
the best example of group trends in properties in the periodic
table, with elements exhibiting well-characterized homologous behavior.
The alkali
metals, found in group 1 of the periodic table (formerly known as group IA),
are very reactive metals that do not occur freely in nature. These metals have
only one electron in their outer shell. Therefore, they are ready to lose that
one electron in ionic bonding with other elements. As with all metals, the
alkali metals are malleable, ductile, and are good conductors of heat and
electricity. The alkali metals are softer than most other metals. Cesium and
francium are the most reactive elements in this group. Alkali metals can
explode if they are exposed to water
Small amounts of caesium-134 and
caesium-137 were released into the environment during nearly all nuclear weapon
tests and some nuclear accidents, most notably the Chernobyl disaster. As of
2005, caesium-137 is the principal source of radiation in the zone of
alienation around the Chernobyl nuclear power plant. Together with caesium-134,
iodine-131, and strontium-90, caesium-137 was among the isotopes with greatest
health impact distributed by the reactor explosion.
The mean contamination of
caesium-137 in Germany following the Chernobyl disaster was 2000 to 4000 Bq/m2.
This corresponds to a contamination of 1 mg/km2 of caesium-137, totaling about
500 grams deposited over all of Germany.Caesium-137 is unique in that it is
totally anthropogenic. Unlike most other radioisotopes, caesium-137 is not
produced from its non-radioactive isotope, but from uranium. It did not occur
in nature before nuclear weapons testing began. By observing the characteristic
gamma rays emitted by this isotope, it is possible to determine whether the
contents of a given sealed container were made before or after the advent of atomic
bomb explosions. This procedure has been used by researchers to check the
authenticity of certain rare wines, most notably the purported “Jefferson
bottles”.
1.2. Limitation Problem
The limitation problems of this
paper are:
1.
What is Cesium?
2.
What are the effects of Cesium in human life?
1.3. Purposes of Writing
The purposes of writing this paper
are:
1.
To know sources of Cesium in nature.
2.
To know the characteristic of Cesium
3.
To find out the benefits and dangers of Cesium in human
life.
1.4. The Benefits Of Writing
The benefits of writing this paper
are:
1.
Known the existence of cesium in
nature.
2.
Known the
characteristics of the cesium.
3.
Known the benefits and dangers
of cesium for
human life
DISCUSSION
3.1. Definition of
Cesium
Cesium is a soft, silvery
white-gray metal that occurs in nature as cesium-133. The natural source
yielding the greatest quantity of cesium is the rare mineral pollucite.
American ores of pollucite, found in Maine and South Dakota, contain about 13%
cesium oxide. Although it is a metal,cesium melts at the relatively low
temperature of 28o C (82o F), so like mercury it is
liquid at moderate temperatures. This most alkaline of metals reacts
explosively when it comes in contact with cold water.There are 11 major
radioactive isotopes of cesium. (Isotopes are different forms of an element
that have the same number of protons in the nucleus but a different number of
neutrons.) Only three have half-lives long enough to warrant concern:
cesium-134, cesium-135 and cesium-137. Each of these decays by emitting a beta
particle, and their half-life range from about 2 to 2 million years. The
half-lives of the other cesium isotopes are less than two weeks. Of these
three, the isotope of most concern for Department of Energy (DOE) environmental
management sites and other areas is cesium-137 which has a half-life of 30
years. Its decay product, barium-137m stabilizes itself b emitting an energetic
gamma ray with a half-life of about 2.6 minutes. It is this decay product that
makes cesium an external hazard (that is, a hazard without being taken into the
body). Cesium-135 and cesium-134 are typically of less concern because of their
radiological decay characteristics. The very long half-life of cesium-135 means
it has a very low specific activity, and the slow decay rate combined with its
low decay energy contribute to its low hazard. Cesium-134 has a half-life of
2.1 years and decays by emitting a beta particle. The relatively small amount
of cesium-134 produced more than 20 years ago would essentially all be gone
today due to radioactive decay.
3.1.1.
Isotopes Of Cesium
Only one
naturally occurring isotope of cesium is known, cesium-133. Isotopes are two or
more forms of an element. Isotopes differ from each other according to their
mass number. The number written to the right of the element's name is the mass
number. The mass number represents the number of protons plus neutrons in the
nucleus of an atom of the element. The number of protons determines the
element, but the number of neutrons in the atom of any one element can vary.
Each variation is an isotope.
A number of
artificial radioactive isotopes of cesium are known also. A radioactive isotope
is one that breaks apart and gives off some form of radiation. Radioactive
isotopes are produced when very small particles are fired at atoms. These
particles stick in the atoms and make them radioactive.
One radioactive
isotope of cesium is of special importance, cesium-137. It is produced in
nuclear fission reactions. Nuclear fission is the process in which large atoms
break apart. Large amounts of energy and smaller atoms are produced during
fission. The smaller atoms are called fission products. Cesium-137 is a very
common fission product.
Nuclear fission
is used in nuclear power plants. The heat produced by nuclear fission can be
converted into electricity. While this process is going on, cesium-137 is being
produced as a by-product. That cesium-137 can be collected and used for a
number of applications.
As an example,
cesium-137 can be used to monitor the flow of oil in a pipeline. In many cases,
more than one oil company may use the same pipeline. How does a receiving
station know whose oil is coming through the pipeline? One way to solve that
problem is to add a little cesium-137 when a new batch of oil is being sent.
The cesium-137 gives off radiation. That radiation can be detected easily by
holding a detector at the end of the pipeline. When the detector shows the
presence of radiation, a new batch of oil has arrived.
This isotope of
cesium can also be used to treat some kinds of cancer. One procedure is to fill
a hollow steel needle with cesium-137. The needle can then be implanted into a
person's body. The cesium-137 gives off radiation inside the body. That
radiation kills cancer cells and may help cure the disease.
When a hollow
steel needle filled with cesium-137 is implanted into a person's body, the
isotopes's radiation can kill cancer cells.
Cesium-137 is
often used in scientific research also. For example, cesium tends to stick to
particles of sand and gravel. This fact can be used to measure the speed of
erosion in an area. Cesium-137 is injected into the ground at some point. Some
time later, a detector is used to see how far the isotope has moved. The
distance moved tells a scientist how fast soil is being carried away. In other
words, it tells how fast erosion is taking place.
Cesium-137 has
also been approved for the irradiation of certain foods. The radiation given
off by the isotope kills bacteria and other organisms that cause disease. Foods
irradiated by this method last longer before beginning to spoil. Wheat, flour,
and potatoes are some of the foods that can be preserved by cesium-137
irradiation.
3.1.2.
Characteristics Of Cesium
−
The Physical
Properties
Caesium
is a very soft (it has the lowest Mohs hardness of all
elements, 0.2), very ductile, silvery-white metal,
which develops a silvery-gold hue in the presence of trace amounts of oxygen.It has a melting
point of 28.4 °C (83.1 °F), making it one of the
few elemental metals which are liquid near room temperature. Mercury is the only elemental metal with a known melting point
lower than caesium. In addition, the metal has a rather low boiling
point, 641
°C (1,186 °F), the lowest of all metals other than mercury. Its compounds burn with a
blue color.
Caesium
forms alloys with the
other alkali metals as well as with gold, and amalgams with mercury. At temperatures below 650 °C (1,202 °F), it alloys with cobalt, iron, molybdenum, nickel, platinum, tantalum or tungsten. It forms well-defined intermetallic
compounds with antimony, gallium, indium and thorium, which are photosensitive. It mixes with the other alkali metals (except with
lithium), and the alloy with a molar distribution
of 41% cesium, 47%potassium, and 12% sodium has the
lowest melting point of any known metal alloy, at −78 °C(−108 °F). A few amalgams have been
studied: CsHg2 is black with a purple metalliclustre, while CsHg is
golden-colored, also with a metallic luster
3.2. The Effects of
Cesium in Human Life
Cesium has a limited number of uses. One is as a getter in
bulbs and evacuated tubes. The bulb must be as free from gases as possible to
work properly. Small amounts of cesium react with any air left in the bulb. It
converts the gas into a solid cesium compound. Cesium is called a getter
because it gets gases out of the bulb.
Cesium is also used in photoelectric cells, devices for
changing sunlight into electrical energy. When sunlight shines on cesium, it
excites or energizes the electrons in cesium atoms. The excited electrons
easily flow away, producing an electric current.
An important use of cesium today is in an atomic clock. An
atomic clock is the most precise method now available for measuring time. Here
is how an atomic clock works. Cesium-137 is used in atomic clocks, the most
precise method for measuring time.
A beam of energy is shined on a very pure sample of
cesium-133. The atoms in the cesium are excited by the energy and give off
radiation. That radiation vibrates back and forth, the way a violin string
vibrates when plucked. Scientists measure the speed of that vibration. The
second is officially defined as that speed of vibration multiplied by 9,192,635,770.
Cesium
iodide (CsI), bromide (CsBr) and cesium fluoride (CsF)
crystals are employed for scintillators in scintillation
counters widely used in mineral
exploration and particle physics research as they are well suited for the
detection of gamma and x-ray radiation. Cesium, being a heavy
element, provides good stopping power contributing to better detectivity.
Caesium compounds may also provide a faster response (CsF) and be less
hygroscopic (CsI).
Because
of their high density, solutions of cesium
chloride (CsCl), sulfate (Cs2SO4),
and trifluoroacetate (Cs(O2CCF3))
are commonly used in molecular biology for density
gradientultracentrifugation.This technology is primarily applied to the
isolation of viral particles,
sub-cellular organelles and fractions, and nucleic acids from biological samples.
Relatively
few chemical applications exist for cesium. Doping
with cesium compounds is used to enhance the effectiveness of several metal-ion
catalysts used in the production of chemicals, such as acrylic acid, anthraquinone, ethylene oxide, methanol, phthalic anhydride,styrene, methyl methacrylate monomers, and various olefins. It is also used in the
catalytic conversion of sulfur
dioxide into sulfur trioxide in the production of sulfuric acid.
Cesium
fluoride enjoys niche use in organic chemistry as a base,
or as an anhydrous source of fluoride ion. Cesium salts sometimes
replace potassium or sodium salts in organic
synthesis, such as cyclization, esterification, and polymerization.
3.2.1.
Health Effects of Cesium
Humans may be exposed to cesium by breathing, drinking or
eating. In air the levels of cesium are generally low, but radioactive cesium
has been detected at some level in surface water and in many types of foods.
The amount of cesium in foods and drinks depends upon the
emission of radioactive cesium through nuclear power plants, mainly through
accidents. These accidents have not occurred since the Chernobyl disaster in
1986. People that work in the nuclear power industry may be exposed to higher
levels of cesium, but many precautionary measurements can be taken to prevent
this.
It is not very likely that people experience health effects
that can be related to cesium itself. When contact with radioactive cesium
occurs, which is highly unlikely, a person can experience cell damage due to
radiation of the cesium particles. Due to this, effects such as nausea,
vomiting, diarrhoea and bleeding may occur. When the exposure lasts a long time
people may even lose consciousness. Coma or even death may than follow. How
serious the effects are depends upon the resistance of individual persons and
the duration of exposure and the concentration a person is exposed to.
Cesium can be taken into the body by
eating food, drinking water, or breathing air. After being taken in, cesium
behaves in a manner similar to potassium and distributes uniformly throughout
the body. Gastrointestinal absorption from food or water is the principal
source of internally deposited cesium in the general population. Essentially
all cesium that is ingested is absorbed into the bloodstream through the
intestines. Cesium tends to concentrate in muscles because of their relatively
large mass. Like potassium, cesium is excreted from the body fairly quickly. In
an adult, 10% is excreted with a biological half-life of 2 days, and the rest
leaves the body with a biological half-life of 110 days. Clearance from the
body is somewhat quicker for children and adolescents. This means that if
someone is exposed to radioactive cesium and the source of exposure is removed,
much of the cesium will readily clear the body along the normal pathways for
potassium excretion within several months.
Cesium-137 presents an external as well
as internal health hazard. The strong external gamma radiation associated with
its short-lived decay product barium-137m makes external exposure a concern,
and shielding is often needed to handle materials containing large concentrations
of cesium. While in the body, cesium poses a health hazard from both beta and
gamma radiation, and the main health concern is associated with the increased
likelihood for inducing cancer.
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