Download Chemistry Lecture No.4______By : Asst. Lect. Tariq-H-AL

Chemistry Lecture No.4______By : Asst. Lect. Tariq-H-AL-mgheer
RADIOACTIVITY AND WCLEM CHEMISTRY
Previously we learned that there are isotopes of almost all the elements. Most
of these isotopes are stable, but some are unstable. The nuclei of unstable isotopes
undergo spontaneous nuclear reactions that cause particles and energy, called
nuclear radiation, to be given off. The emission of these particles and energy by an
isotope is called radioactivity. Only a few isotopes found in nature are radioactive.
The first example of a naturally occurring radioactive substance was discovered by
Henri Becquerel in 1896. He found that uranium ore gave off penetrating radiation
that darkened photographic film without exposing the film to light. Since then, other
scientists have found many other radioactive elements. More than 50 naturally
occurring radioactive isotopes are now known. In addition, scientists have been able
to make many radioactive isotopes not found in nature.
The discovery of radioactive isotopes has greatly affected our lives. The
awesome power of nuclear weapons, the promise of abundant energy, radiation
therapy, and contamination of the environment by nuclear waste products are all
results of the properties of the tiny nuclei of these radioactive isotopes. TYPIES OF
RADIATION
Early in the twentieth century, it was discovered that naturally occurring
isotopes emit three kinds of radiation. At that time, scientists did not understand
them, so their discoverers named them simply alpha (a) beta (p) and gamma (y).
Since then, scientists have discovered the identities and properties of these types of
radiation. Each has characteristic properties that determine how it affects living
systems
Alpha radiation is a stream of particles moving at about one-tenth the speed of
light. Each particles is the nucleus of helium atom that contains two protons and two
neutrons and has a charge of +2. Alpha particles are relatively large and heavy, so
they cannot travel very far without colliding with other particles. As a result these
particles do little damage to internal organs because they cannot penetrate the skin.
However, if a substance that emits alpha particles gets inside the body by being
inhaled or swallowed, the alpha particles can then damage internal organ.
Beta radiation is also a stream of particles, but the particles are electrons. The
electrons are produced within the nucleus by the transformation of a neutron into a
proton and an electron. The proton stays in the nucleus and the electron is emitted.
An electron is smaller than a helium nucleus (alpha particle), travels much faster, and
can penetrate the skin to a depth of a few centimeters. Exposure to beta radiation
causes the skin to appear burned. Damage to internal organs occurs when a
substance that emits beta particles gets into the body.
Gamma radiation is not a particle, but a form of energy similar to light waves,
radio waves, or x-rays. This radiation has high energy and can penetrate deep within
the body and cause serious damage. Gamma radiation usually occurs along with
alpha and beta radiation.
Two less common but still important types of nuclear radiation are neutrons
and positrons. A positron has about the same mass as an electron but has a
positive charge. The properties and symbols of these various forms of radiation are
summarized in Tablel. The emission of radiation from radioactive isotopes is also
called ionizing radiation.
Table 1. Properties of Various Forms of Nuclear Radiation
Type of
Radiation
Composition
Alpha
Helium nucleus
Beta
Electron
Gamma
Energy
Neutron
Neutron
Positron
Positron
Symbol
Mass
(amu)
Electrical
Charge
Approximate
penetration of skin
(cm)
4
+2
0.01
,-°e 1/1837
-1
1
0
0
100
1
0
10
, 1e0 1/1846
+1
1
4
2He
Y
n , 0n1
IONIZING RADIATION
The radiation from radioactive isotopes and x-rays can form ions in matter by
knocking electrons off the atoms and molecules in its path. For this reason, it is
called ionizing radiation. The chief effects of radiation on living systems are due to
these ionization reactions. Repeated exposure to low levels of radiation seems to
have a number of major effects on health. Among them are cancer (carcinogenic
effects), damage to the fetus, and genetic damage.
It has been known for many years that radiation causes cancer. Skin cancer,
bone cancer, leukemia, and other cancers are products of exposure to radiation.
Even at very low levels of exposure, there is danger from radiation. For example, x
rays used in diagnosis are not completely free of potential harm to a patient. Persons
who administer x-rays must take precautions to avoid exposure, because the effect is
cumulative. Exposure to high levels of radiation kills cells. Use is made of this fact tc
treat cancer. Cancer cells are exposed to high-energy x-rays or gamma radiation to
destroy these cells or to retard the spread of cancer.
Fetuses and small children are particularly sensitive to radiation. Ionizing
radiation affects them more strongly than adults. The effects of radiation are
widespread. Damage occurs to the brain, eyes, bones, and other organs.
The genetic risk of exposure to radiation is more difficult to determine because
the genetic damage may not be seen for several generations. Genetic damage is
caused by damage to the genes in the nuclei of cells. The damage to the structure of
the gene may cause death or a variety of physical defects in following generations.
Clearly, exposure to radiation is dangerous. But is there any level of exposure
below which radiation has no effect? According to one theory, called the threshold
theory, no damage occurs below a certain level of radiation, called the threshold
value. Opposed to this is the linear theory. According to the linear theory, the risk
ofdamage is proportional to exposure, even down to very low levels of radiation. The
current view is a compromise of these two theories: There is a risk of damage even
at low levels of radiation, but the risk is extremely small.
The dangers of ionizing radiation are compounded by the fact that this
radiation cannot be detected by the human body. We cannot see, feel, or smell
ionizing radiation. Therefore, a person can be exposed to lethal levels of radiation
without knowing it until it is too late. But we do have methods of detecting ionization
radiation. DETECTING IONIZING RADIATION
The methods of detecting ionizing radiation all make use of the fact that
radiation disturbs the electronic environment of the atoms and molecules that it
encounters; The three methods of detecting ionizing radiation most frequently used
are the photographic method, use of scintillation counters, and use of the Geiger
counter,
Becquerel discovered that uranium ore was radioactive because of its effect
on photographic film. Photographic film and paper shielded from light are exposed by
ionizing radiation. This exposure is detected by developing the film or paper in the
usual way. This fact is used to provide an individual detector for persons working
near sources of radioactivity. Each person wears a badge containing a piece of film.
The film is changed at regular intervals and developed. A certain level of radiation will
cause the film to be exposed, warning the wearer of potential danger.
Scintillation counters are instruments that contain a surface coated with a
special substance that gives off flashes of light when hit by ionizing radiation. The
invisible ionizing radiation strikes the surface and some of its energy is transformed
into visible light. Electronic devices magnify and record these flashes.
most common instrument used to detect and measure ionizing radiation is the
Geiger
counter,
shown
schematically in Figure 1.
The detecting part of the
instrument is a metal tube. It contains a gas, a wire down the center, and a window at
one end. The window is made of a thin material to allow alpha and beta particles to
enter. A large potential difference is maintained between the metal walls of the tube
and the central wire. When ionizing radiation enters the tube, it forms ions. This
causes a pulse of electricity to flow from the wire to the metal walls of the tube. This
pulse is counted by an electronic device that produces either a meter reading or an
audible clicking sound. Small, portable Geiger counters are in common use to detect
sources of radioactivity in the environment. When we detect ionizing radiation, it
usually means that a nuclear reaction has taken place. NUCLEAR REACTIONS
Alchemists in the Middle Ages dreamed of turning one chemical element into
another. The atomic theory seemed to shatter this dream because the atom assumed
the role of the stable and indivisible unit of matter. However, with the discovery of
radioactivity, scientists soon. realized that atoms do change from one kind to another
when they emit nuclear radiation. This change occurs during a nuclear reaction
whenever the nucleus of an isotope emits alpha or beta particles. When this happens,
the nucleus gains or loses positive charges and its atomic number is changed. A
change in atomic number means that one element has changed to another.
An example of a change of one element into another is the nuclear reaction of
one isotope of carbon, 6C14 (carbon-14). When 6C14 emits a beta particle, it is
changed into an isotope of nitrogen, 7 N14. We can represent this nuclear reaction by
means of the following nuclear equation.
14
6C
——
14
7N
(1)
Nuclear equations must be balanced. This means that the sum of all the protons
and neutrons is the same in the products as in the starting materials. No protons or
neutrons are lost during a nuclear reaction. Consequently, the sum of the superscripts
(mass numbers) and the subscripts (atomic numbers) of the particles on the left side
of the equation must equal the same sum on the right side. We can check this for
equation (1)
We can understand why one element is changed into another by examining a
balanced nuclear equation. When an alpha or a beta particle is emitted by an isotope,
the atomic number must change to compensate for this loss or gain of one or more
protons. The result of this change is the formation of an isotope of -a different
element. The atomic number determines the element, and the mass number
determines the particular isotope of that element.
Note: Answers the exercises in the page 64 in the book
HALF-LI FE
The breakup or decay of the nuclei of a particular radioactive isotope requires a
certain amount of time to occur. Not all nuclei decay at the same time rather; they
decay over a period of time. The time needed for one-half of the original nuclei of an
isotope to decay to other substances is called the half-life of the isotope. The symbol
(t1/ 2) is used to indicate hall-life,
Each radioactive isotope has a characteristic half-life. Values of the half-lives of
naturally occurring isotopes range from milliseconds to several billion years. The
values of the half-lives of several naturally occurring radioactive isotopes are given in
Table 2.
The importance of the half-life of a radioactive isotope is that it tells us how long
a
sample of the isotope will exist. For example, 90Th243 (thorium-234) has a relatively
short half-life of 24.1 days. If we have a 1.00 g sample of thorium-234, 0.50 g of it will
be left after 24.1 days because the other half will be turned into protactinium (Pa),
according to the following equation:
234
90Th
91Pa234 + -1β0
In another 24.1 days there would be only 25 percent of the original thorium-234
(0.25 g), and after three half-lives (3 X24.1 days, or 72.3 days) only 12.5 percent
(0.125 g) would remain. Theoretically, the amount of thorium-234 present never
reaches zero. But in practice, after 10 half-lives, or 241 days, the amount left is so
small (9.8 X 10-4 g) that its presence cannot be detected by any of the methods . For
all practical purposes, after 241 days, our sample of thorium-234 is all gone. It has
been converted into another element.
The value of the half-life of a radioactive isotope is independent of sample size.
Thus, whether the size of the sample of thorium-234 is 10 kg, 1 kg, or or 10 g half of it
will decay in 24.1 days.
_____
Table 2. HaIt-Lives of Some Naturally Occurring Radioactive Isotopes
Element
Isotope
Hydrogen
1H
3
12.3yr
Carbon
6C
12
5700 yr
Potassium
Half-Life
(Tritium)
19K
40
200 million yr
element. The atomic number determines the element, and the mass number
determines the particular isotope of that element.
Note: Answers the exercises in the page 64 in the book
HALF-LI FE
The breakup or decay of the nuclei of a particular radioactive isotope requires a certain
amount of time to occur. Not all nuclei decay at the same time rather; they decay over a period
of time. The time needed for one-half of the original nuclei of an isotope to decay to other
substances is called the half-life of the isotope. The symbol (t1/ 2) is used to indicate hall-life,
Each radioactive isotope has a characteristic half-life. Values of the half-lives of
naturally occurring isotopes range from milliseconds to several billion years. The values of the
half-lives of several naturally occurring radioactive isotopes are given in Table 2.
The importance of the half-life of a radioactive isotope is that it tells us how long a
sample of the isotope will exist. For example, 90Th243 (thorium-234) has a relatively
short half-life of 24.1 days. If we have a 1.00 g sample of thorium-234, 0.50 g of it will be left
after 24.1 days because the other half will be turned into protactinium (Pa), according to the
following equation:
90Th
91Pa234 + -1β0
234
In another 24.1 days there would be only 25 percent of the original thorium-234 (0.25
g), and after three half-lives (3 X24.1 days, or 72.3 days) only 12.5 percent (0.125 g) would
remain. Theoretically, the amount of thorium-234 present never reaches zero. But in practice,
after 10 half-lives, or 241 days, the amount left is so small (9.8 X 10-4 g) that its presence
cannot be detected by any of the methods . For all practical purposes, after 241 days, our
sample of thorium-234 is all gone. It has been converted into another element.
The value of the half-life of a radioactive isotope is independent of sample size. Thus,
whether the size of the sample of thorium-234 is 10 kg, 1 kg, or or 10 g half of it will decay in
24.1 days.
_____
Table 2. HaIt-Lives of Some Naturally Occurring Radioactive Isotopes
Element
Isotope
Hydrogen
1H
3
(Tritium)
Half-Life
12.3yr
Carbon
Potassium
6C
12
19K
5700 yr
40
200 million yr
Radon
3.8 days
86
Rn222
Radium
Thorium
Thorium
1600yr
88Ra
90Th
4
24.1 days
23
80,000 yr
235
90Th
Uranium
700 million yr
23
Uranium
U
92
238
92U
Polonium
Lead
4.5 billion yr
0.15 millisecond
84Po21
26.8 min
Pb214
82
Note: Answers the exercises in the page 66 in the book
RADIATION DOSAGES
Radiation causes damage to all living systems. The amount of damage is directly
related to the dose of radiation received. In this section, we will define several units of radiation
damage. Let us start with the basic unit of radioactivity. Curie and Becquerel
The curie, represented by the symbol Ci, is the level of radioactivity caused by 3.7X
10
10 radioactive disintegrations per second. This unit is a measure of the number of nuclei that
decay per second. It is Independent of the size of the radioactive sample.One curie represents
a large amount of radioactivity. As a result, more moderate units such as picocurie (10 -12 Ci),
microcurie (10-6 Ci), and millicurie(10-3 Ci) are generally used. The Sl unit of radioactivity is the
becquerel, whose symbol is Bq. One curie is equal to 3.7 X 1010 becquerel. The curie and ttie
becquerel are basic units of radioactivity. Unfortunately, equal numbers of curits of radiation
given off by different isotopes do not always produce the same biological effect. RAD
The rad, whose symbol is D, stands for radiation absorbed dose. It is a unit that
expresses the amount of energy from the radiation actually absorbed by tissue or other
material. One rad is equal to 2.4 X 10-3 cal of energy absorbed by 1 kg of tissue. This is a very
small unit. Converted U heat, this energy would raise the temperature of tissue only a few
thousandths of a degree. Because it is concentrated in a small particle, however, it causes
great damage to tissuThe Sl unit of absorbed dose is the gray, whose symbol is Gy. A gray is
defined as 1 J of energy absorbed per 1 kg of tissue. One hundred rads are equivalent to one
gray
The energy absorbed by living tissue is not the only factor that contributes to the biological
hazards of radiation. For this reason, a dose of 1 rad from one source is not necessarily equal
to a dose of 1 rad from another. The rem is the unit that takes all these differences into
account. REM
One rem is 1 rad multiplied by a factor called the relative biological equivalent (RBE).
Thus, Number of rem = RBE X number of rad
The factor RBE takes into account the differences in biological damage caused by
different kinds of ionizing radiation of the same energy. For example, the RBE of an alpha
particle is 10 times that of a beta particle. This means that alpha particles released in tissue
cause 10 times more damage than beta particles of the same energy. The rem is a more
accurate and comparable measure of biological damage caused by different ionizing radiation.
For this reason, it is commonly used to describe allowable doses of radioactivity. LDso
VALUES
The ionizing radiation dosage at which injury to humans begins is unknown. The best
we can do is to express the short-term exposure to ionizing radiation that is fatal to various
forms of life, This is expressed as the 30-day LD5o value, defined as the dose, in rem, that is
fatal to 50 percent of the population within 30 days.
The LD5o value for humans is estimated to be 500 rem. Thus, a person suddenly
exposed to 500 rem of ionizing radiation would have a 50 percent chance of remaining alive
after 30 days. Even after 30 days, the possibility of illness and death would still be great. The
LD5o values of most mammals are in the range 250 to 1000 rem. Simpler forms of life such as
insects can tolerate much more radiation. For example, some insects can tolerate more than
50,000 rem, and some microorganisms can tolerate even more.
We cannot escape ionizing ndiation. There are small amounts of naturally occurring
radioactive substances in the 3"il, in the food we eat, and in the water we drink. Streams of
particles called cosmic rays enter our atmosphere from the sun and bombard us These are all
part of natural background radiation. The exposure we receive from these natural sources is
very small. Each person receives about 100 millirem annually from natural background
radiation.
The use of radioactive substances in medicine, industry, and nuclear power plants has
increased our risk of exposure to radiation. Many of these radioactive substances are not
found naturally but are made for a specific use. TRANSMUTATION
Changing one element into another, either in nature or in the laboratory, is called
transmutation. Scientists do this by means of bombardment reactions.
A bombardment reaction occurs when particles of atomic or subatomic size strike atoms of
an element and change them into another element. For example, the reaction between an
alpha particle and a beryllium atom forms a carbon atom and a neutron according to the
following equation:
4Be
9
-
2He
4——> C12
6
+
For a bombardment reaction to occur, the bombarding particles must have enough
energy to overcome the highly charged nucleus of the target atom, especially when the target
atom has a high atomic mass. Most particles emitted by natural radioactive isotopes do not
have enough energy to do this, so their energies must be increased. This can be done by an
accelerator, a device that increases the speed of a charged atomic or subatomic particle.
Increasing the speed of a particle increases its energy and therefore increases its effect on the
atom it hits. MEDICAL USES OF RADIOACTIVE ISOTOPES
Radiation from radioactive isotopes is used extensively in medicine to treat cancer. The
radiation is directed at the cancer cetis from either outside or inside the body, depending on
the type of cancer. The most widely used external source of radiation is cobalt-60. This isotope
of cobalt has a half-life of 5.5 years and is .3 powerful beta and gamma emitter. The sample of
cobalt-60 is placed in a lead container with an opening that allows its radiation to be directed to
the site of the cancer.
The use of radioactive isotopes internally to treat cancer is based on the fact that all
isotopes of an element, radioactive or not, have identical electron arrangements and
consequently identical chemical properties .For example, when taken internally, the iodide ion
from sodium iodide is eventually concentrated in the thyroid gland. Use is made of this fact to
treat thyroid cancer. Iodine-131, a radioactive isotope of iodine is used. A patient is given a
drink of water containing sodium iodide. Some of the iodide ions are radioactive. When these,
ions are absorbed by the thyroid gland, radiation from their decay destroys the cancer cell.
Other radioactive isotopes used to treat cancer are given in Table3
Table 3. Selecte
'd Radio.
active Isot opes and
Their Medical Uses
Loiopc
Symbol
Half-Life
Use ,
Cobalc-60
60
27Co
5.3 yr
Iodine-., 31
5.31
Iodine-123
123
53I
Phosphorus-32
131
15p
32
13.3 hr
143 davs
cancer
Treatment of Icukcrnia
24
11Na
15,0 hr
lfon-^9
59
26Fc
45.6 days
99
43Tc
Source of radiation
for cancer therapy
Treatment of thyroid
cancer, diagnosis of
thyroid gland mal
function
Treatment of thyroid
8 days
Sodium-24
Techncriuro-99
Emission
6,1 hr
Check of proper function
of circulatory system
Determination of red
blood cell formation
and lifetime
Brain, kidney, and
lung scans
Radioactive isotopes are also used in medicine as tracers to diagnose illnesses. The
movement of these isotopes in the body can be followed or traced by means of the radiation
given off. For example, sodium-24 in the form of sodium chloride (salt) is given to a patient in a
water solution to locate blockages in the circulatory system. Several radioactive isotopes used
as tracers are given in Table 3.
Radioactive isotopes used in humans must be chosen carefully. First, the half-life must
be long enough for the isotope to do its job yet short enough that the isotope will disappear
from the body without subjecting the person to unnecessary radiation. Second, no isotopes
that emit alpha particles are used. The reason is that alpha particles are relatively large, and
they cause a great deal of damage to all tissue and organs if an isotope emits them eternally.
ENERGY AND NUCLEAR REACTIONS
The experiment that heralded the dawn of the nuclear age was carried out by a group of
physicists in Italy in 1933. They bombarded uranium atoms with low-energy neutrons (called
slow or thermal neutrons) and found that a number of elements of atomic masses lighter than
uranium were formed. Scientists soon realized that these products were formed by splitting the
nucleus of the uranium atom. The nuclear reaction that causes an atom to split into several
smaller parts is called a fission
reaction.
Further experiments provided additional facts about fission reactions. First, only a
few isotopes are known to undergo fission reactions when bombarded by neutrons. Uranium235 (U-235) is the only naturally occurring isotope that undergoes this reaction. Two other
isotopes formed by nuclear bombardment, plutonium-239 and uranium-233, also undergo
fission reactions. Second, a large amount of energy is released when a fission reaction occurs.
Finally, fission reactions form neutrons and gamma radiation as well as other elements.
This last fact is particularly important because it allows a chain reaction to occur
whenever enough uranium-235 atoms are present. A chain reaction is a series of repeated
reactions in which one reaction produces a product that allows the series of reactions to
continue. A chain reaction is shown in Figure 2. A slow neutron strikes an atom of uranium-235
and causes it to split into two nuclei of lighter mass with the emission of gamma radiation and
two, three, or four neutrons. These neutrons can strike other nearby uranium-235 atoms and
cause them to undergo fission reactions. Each fission reaction produces more neutrons, which
cause more fission reactions, which produce more neutrons, and so forth. For a chain reaction
to occur, enough fissionable nuclei must be present so that most of the neutrons will hit other
fissionable nuclei. It is the emission of neutrons by a fission reaction that keeps the chain
reaction going. The amount of material needed for a chain reaction to continue (to be selfsustaining) is called the critical mass.
The fission of uranium-235 can occur in more than 30 ways to produce about 200
different radioactive isotopes. These isotopes usually have atomic numbers between 30 and
64 and masses between 72 and 161. The following three equations are representative of the
fission reactions of uranium-235:
Notice that more neutrons are formed than are consumed in each of these fission
reactions.
Figuro2 chain reaction involving the fiss'on of uranium-235. Each act of fission,
produces more than one neutron, which keeps the chain reaction going.
An atomic explosion is an uncontrolled chain reaction. An atom bomb contains two
separate quantities of fissionable material, each less than the critical mass. The atomic
explosion is triggered by suddenly bringing together these subcritical masses. When this
occurs, fission occurs so rapidly that the whole mass explodes, producing temperatures
greater than 10,000,000° C.
Controlling the chain reaction allows the tremendous heat of the fission reaction to be
released over a long period of time. Fission reactions are controlled by placing material that
absorbs neutrons in the midst of, the fissionable material. Carbon, boron, and cadmium absorb
neutrons readily. These elements are made into rods that can be
inserted into the fissionable material. The amount of fission and the amount of energy released
can be controlled by the position of the rods in the fissionable material, called the core. The
number of nuclear fission reactrons is decreased by pushing the rods in and increased by
pulling them out. All nuclear reactions are stopped by putting all the rods into the core. In this
case, the rods absorb so many neutrons that not enough are present to cause fission reactions
to occur.
The heat given off in a controlled nuclear reaction can be used to generate electricity.
The method of generating electricity is the same in nuclear power plants and plants that burn
fossil fuels. The heat is used to turn water into steam. The steam drives turbines that generate
electricity. The difference is that the source of heat in a nuclear power plant is controlled
nuclear fission rather than burning of fossil fuel
Less than 1 percent of uranium ore is uranium-235. The more abundant isotope,
uranium-238, does not undergo fission reactions. To obtain enough uranium-235 for a chain
reaction, this isotope must be separated from uranium-238. This cannot be done chemically,
because both isotopes have identical chemical properties. Separation was originally
accomplished in 1943 by converting uranium ore to the gas uranium hexafluoride. Uranium
hexafluoride containing uranium-235 moves slightly more rapidly through air than does
uranium hexafluoride containing uranium-238. Therefore, when passed through a long tube
containing thousands of tiny consecutive pinholes, the uranium hexafluoride containing
uranium-235 travels faster and reaches the end of the tube first. In this way, scientists were
able to separate the two isotopes of uranium.
This method of separating uranium-235 from uranium-238 is long and tedious. Another souro
of fissionable material was made available by the discovery that bombarding uranium-238 wit
neutrons forms one isotope of plutonium, plutonium-239, that undergoes fission, becaus
uranium and plutonium are different elements, they can be separated chemically. This is a
muc easier way to obtain fissionable material. Today, plutonium-239 is the fissionable material
i most nuclear power plants.
Although nuclear power plants promise unlimited energy, they have several disadvantages.
The major one is that the products of fission are highly radioactive. As a result, their disposal is
a serious problem. Several of these radioactive isotopes are particularly dangerous because
they have long half-lives and they are absorbed and become part of plants and animals.
Several of these isotopes are listed in Table 4.
Table 4 Some dangerous radioactive elements
Stronrium-90 is particularly dangerous to people because it belongs to the same
Radioactivity and Nuclear Chemistry
Table 4-4. Some Dangerous Radioactive Elements Produced by Nuclear Fission
Isotope
Half-Life
Radiation Danger
Iodine-131
8 days
AY
Concentrates in thyroid and causes
thyroid cancer
Krypton-85
Xenon-133
10.8 yr 5.3
days
AY AY
Inhalation exposes lungs to radiation
Strontium-90
27.7 yr
A
Cesium-137
30 yr
AY
Concentrates in bone and causes bone
cancer
Acts like sodium and potassium because
it is in the same group; travels
throughout the body, thereby exposing it
to radiation
Radium-226
1,602 yr
a, y
Similar to strontium-90
The following is one example of a fusion reaction:
2
1H
+1H2 ——> 2H4
In this reaction, two nuclei of deuterium, a stable isotope of hydrogen (sec Section
3.6), arc forced together to form a helium nucleus, which is also stable. To
accomplish this reaction, a temperature of at least 10,000,000° C is needed to
provide the energy to force the two positive nuclei dose enough to fuse.
Such fusion reactions occur in two places in the world. The first is the sun,
whose heat and light are produced by fusion reactions. The other is in a hydrogen
bomb. The high temperature needed to carry out the fusion reaction is furnished by
the explosion of an atomic bomb (fission bomb). The atomic bomb is set off first and
provides the energy to trigger the hydrogen bomb.
The control of fusion reactions to produce energy in a power plant involves
such great technical difficulties that it will be many decades before this goal is
realized.