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Introductory Chemistry, 2nd Edition Nivaldo Tro

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Introductory Chemistry, 3rd Edition
Nivaldo Tro
Chapter 17
Radioactivity
and Nuclear
Chemistry
Roy Kennedy
Massachusetts Bay Community College
Wellesley Hills, MA
2009, Prentice Hall
The Discovery of Radioactivity
• Antoine-Henri Becquerel designed an
experiment to determine if phosphorescent
minerals also gave off x-rays.
Tro's Introductory Chemistry, Chapter
17
2
The Discovery of Radioactivity,
Continued
• Bequerel discovered that certain minerals were
constantly producing penetrating energy rays he called
uranic rays.
пѓј Like x-rays.
пѓј But not related to fluorescence.
• Bequerel determined that:
пѓј All the minerals that produced these rays contained uranium.
пѓј The rays were produced even though the mineral was not
exposed to outside energy.
• Energy apparently being produced from
nothing?
Tro's Introductory Chemistry, Chapter
17
3
The Curies
• Marie Curie used an electroscope to detect the
radiation of uranic rays in samples.
• By carefully separating minerals into their
components, she discovered new elements by
detecting the radiation they emitted.
пѓјRadium named for its green phosphorescence.
пѓјPolonium named for her homeland.
• Since the radiation was no longer just emitted
from of uranium, she renamed it radioactivity.
Tro's Introductory Chemistry, Chapter
17
4
Electroscope
When charged, the metal
foils spread apart due to
like-charge repulsion.
When exposed to
ionizing radiation, the
radiation knocks
electrons off the
air molecules, which
jump onto the foils
and discharge them,
causing them to
drop down.
Tro's Introductory Chemistry, Chapter
17
5
Properties of Radioactivity
• Radioactive rays can ionize matter.
пѓјCause uncharged matter to become charged.
пѓјBasis of Geiger counter and electroscope.
• Radioactive rays have high energy.
• Radioactive rays can penetrate matter.
• Radioactive rays cause phosphorescent
chemicals to glow.
пѓјBasis of scintillation counter.
Tro's Introductory Chemistry, Chapter
17
6
What Is Radioactivity?
• Release of tiny, high-energy particles from
an atom.
• Particles are ejected from the nucleus.
Tro's Introductory Chemistry, Chapter
17
7
Types of Radioactive Rays
• Rutherford discovered there were three
types of radioactivity:
1. Alpha rays (a):
пѓјHave a charge of +2 c.u. and a mass of 4 amu.
пѓјWhat we now know to be helium nucleus.
2. Beta rays (b):
пѓјHave a charge of -1 c.u. and negligible mass.
пѓјElectron-like.
3. Gamma rays (g):
пѓјForm of light energy (not particle like a and b).
Tro's Introductory Chemistry, Chapter
17
8
Rutherford’s Experiment
++++++++++++
g
b
a
--------------
Tro's Introductory Chemistry, Chapter
17
9
Penetrating Ability of
Radioactive Rays
a
g
b
0.01 mm
1 mm
100 mm
Pieces of lead
Tro's Introductory Chemistry, Chapter
17
10
Order of Strength of Ionizing and
Penetrating Ability
• Ionizing ability = a > b > g.
• Penetrating ability = a < b < g.
Tro's Introductory Chemistry, Chapter
17
11
Facts About the Nucleus
• Very small volume compared to volume
of the atom.
• Essentially entire mass of atom.
• Very dense.
• Composed of protons and neutrons that
are tightly held together.
пѓјNucleons.
Tro's Introductory Chemistry, Chapter
17
12
Facts About the Nucleus,
Continued
• Every atom of an element has the same number of
protons; equal to the atomic number (Z).
• Atoms of the same elements can have different
numbers of neutrons.
пѓјIsotopes.
пѓјDifferent atomic masses.
• Isotopes are identified by their mass number (A).
пѓјMass number = number of protons + neutrons.
Tro's Introductory Chemistry, Chapter
17
13
Facts About the Nucleus,
Continued
• The number of neutrons is calculated by
subtracting the atomic number from the mass
number.
• The nucleus of an isotope is called a nuclide.
пѓјLess than 10% of the known nuclides are nonradioactive, most are radionuclides.
• Each nuclide is identified by a symbol.
пѓјElement в€’ mass number = X в€’ A.
mass number
at omicnumber
Element пЂЅ
Tro's Introductory Chemistry, Chapter
17
A
Z
X
14
Important Atomic Symbols
Particle
Symbol
Nuclear
symbol
Proton
p+
Neutron
n0
1
0
Electron
e-
0
-1
Alpha
a
Beta
b, b-
Positron
b, b+
1
1
4
2
1
1
H p
О±
0
-1
0
+1
ОІ
ОІ
n
e
4
2
He
0
-1
0
+1
e
e
15
Radioactivity
• Radioactive nuclei spontaneously decompose into
smaller nuclei.
пѓј Radioactive decay.
пѓј We say that radioactive nuclei are unstable.
• The parent nuclide is the nucleus that is undergoing
radioactive decay; the daughter nuclide are the new
nuclei that are made.
• Decomposing involves the nuclide emitting a particle
and/or energy.
• All nuclides with 84 or more protons are radioactive.
Tro's Introductory Chemistry, Chapter
17
16
Transmutation
• Rutherford discovered that during the radioactive
process, atoms of one element are changed into
atoms of a different element—transmutation.
Dalton’s atomic theory Statement 3.
• In order for one element to change into
another, the number of protons in the nucleus
must change.
17
Chemical Processes vs.
Nuclear Processes
• Chemical reactions involve changes in the
electronic structure of the atom.
пѓјAtoms gain, lose, or share electrons.
пѓјNo change in the nuclei occurs.
• Nuclear reactions involve changes in the
structure of the nucleus.
пѓјWhen the number of protons in the nucleus
changes, the atom becomes a different element.
Tro's Introductory Chemistry, Chapter
17
18
Nuclear Equations
• We describe nuclear processes using nuclear
equations.
• Use the symbol of the nuclide to represent the
nucleus.
• Atomic numbers and mass numbers are conserved.
пѓј Use this fact to predict the daughter nuclide if you
know parent and emitted particle.
Tro's Introductory Chemistry, Chapter
17
19
Alpha Emission
• An a particle contains 2 protons and 2 neutrons.
пѓјHelium nucleus.
4
2
О±
4
2
He
• Loss of an alpha particle means:
пѓјAtomic number decreases by 2.
пѓјMass number decreases by 4.
222
88
Ra п‚® He +
4
218
2
86
Tro's Introductory Chemistry, Chapter
17
Rn
20
a Decay
Tro's Introductory Chemistry, Chapter
17
21
Beta Emission
• A b particle is like an electron.
0
-1
пѓјMoving much faster.
пѓјProduced from the nucleus.
ОІ
0
-1
e
• When an atom loses a b particle, its:
пѓјAtomic number increases by 1.
пѓјMass number remains the same.
• In beta decay, a neutron changes into a proton.
Th п‚®
234
90
0
-1
e+
234
91
Tro's Introductory Chemistry, Chapter
17
Pa
22
b Decay
Tro's Introductory Chemistry, Chapter
17
23
Gamma Emission
0
0
Оі
• Gamma (g) rays are high-energy photons
of light.
• No loss of particles from the nucleus.
• No change in the composition of the
nucleus, however, the arrangement of the
nucleons changes.
пѓјSame atomic number and mass number.
• Generally occurs after the nucleus
undergoes some other type of decay and
the remaining particles rearrange.
Tro's Introductory Chemistry, Chapter
17
24
Positron Emission
• Positron has a charge of 1+ c.u. and
negligible mass.
0
ОІ
+1
пѓјAnti-electron.
0
+1
e
• When an atom loses a positron from the
nucleus, its:
пѓјMass number remains the same.
пѓјAtomic number decreases by 1.
• Positrons appear to result from a proton
changing into a neutron.
22
11
Na п‚®
0
+1
e+
22
10
Tro's Introductory Chemistry, Chapter
17
Ne
25
b+ Decay
Tro's Introductory Chemistry, Chapter
17
26
Particle Changes
• Beta emission: Neutron changing into a proton.
1
n
0
п‚®
1
p
1
+
0
b
-1
• Positron emission: Proton changing into a neutron.
1
p
1
п‚®
1
0
n
+
b
0
+1
Tro's Introductory Chemistry, Chapter
17
27
What Kind of Decay and How Many Protons
and Neutrons Are in the Daughter?
11 p+
9 n0
Alpha emission giving a daughter nuclide with
9 protons and 7 neutrons.
Tro's Introductory Chemistry, Chapter
17
28
What Kind of Decay and How Many Protons
and Neutrons Are in the Daughter?,
Continued
9 p+
12 n0
Beta emission giving a daughter nuclide with
10 protons and 11 neutrons.
Tro's Introductory Chemistry, Chapter
17
29
What Kind of Decay and How Many Protons
and Neutrons Are in the Daughter?,
Continued
5 p+
4 n0
Positron emission giving a daughter nuclide with
4 protons and 5 neutrons.
Tro's Introductory Chemistry, Chapter
17
30
Nuclear Equations
• In the nuclear equation, mass numbers and
atomic numbers are conserved.
• We can use this fact to determine the
identity of a daughter nuclide if we know
the parent and mode of decay.
Tro's Introductory Chemistry, Chapter
17
31
Example—Write the Nuclear Equation
for Positron Emission from C-11.
1. Write the nuclide symbols for both the
starting radionuclide and the particle.
C - 11 пЂЅ
11
6
positron пЂЅ
C
0
+1
Tro's Introductory Chemistry, Chapter
17
e
32
Example—Write the Nuclear Equation
for Positron Emission from C-11,
Continued.
2. Set up the equation.
•
•
Emitted particles are products.
Captured particles are reactants.
Cп‚®
e+
11
0
6
+1
A
Z
Tro's Introductory Chemistry, Chapter
17
X
33
Example—Write the Nuclear Equation
for Positron Emission from C-11,
Continued.
3. Determine the mass number and atomic
number of the missing nuclide.
•
Mass and atomic numbers are conserved.
Cп‚®
e+
A
e+
11
5
11
0
6
+1
11
6
Cп‚®
0
+1
Z
Tro's Introductory Chemistry, Chapter
17
X
X
34
Example—Write the Nuclear Equation
for Positron Emission from C-11,
Continued.
4. Determine the element from the atomic
number.
11
6
Cп‚®
0
+1
e+
11
5
Tro's Introductory Chemistry, Chapter
17
B
35
Practice—Write a Nuclear Equation for
Each of the Following:
• Alpha emission from Th-238.
• Beta emission from Ne-24.
• Positron emission from N-13.
Tro's Introductory Chemistry, Chapter
17
36
Practice—Write a Nuclear Equation for
Each of the Following, Continued:
• Alpha emission from Th-238.
238
4
234
92 U п‚® 2 He + 90Th
• Beta emission from Ne-24.
24
0
24
Ne
п‚®
ОІ
+
Na
10
-1
11
• Positron emission from N-13.
13
0
13
7 N п‚® +1ОІ + 6 C
Tro's Introductory Chemistry, Chapter
17
37
Detecting Radioactivity
•
To detect when a phenomenon is present, you need
to identify what it does:
1. Radioactive rays can expose light-protected
photographic film.
пѓј Use photographic film to detect the presence of
radioactive rays—film badges.
Tro's Introductory Chemistry, Chapter
17
38
Detecting Radioactivity, Continued
2. Radioactive rays cause air to become ionized.
пѓј An electroscope detects radiation by its ability to
penetrate the flask and ionize the air inside.
пѓј Geiger-MГјller counter works by counting electrons
generated when Ar gas atoms are ionized by radioactive
rays.
Tro's Introductory Chemistry, Chapter
17
39
Detecting Radioactivity, Continued
3. Radioactive rays cause certain chemicals to give off
a flash of light when they strike the chemical.
пѓј A scintillation counter is able to count the number of
flashes per minute.
Tro's Introductory Chemistry, Chapter
17
40
Natural Radioactivity
• There are small amounts of radioactive
minerals in the air, ground, and water.
• It’s even in the food you eat!
• The radiation you are exposed to from
natural sources is called background
radiation.
Tro's Introductory Chemistry, Chapter
17
41
Half-Life
• Each radioactive isotope decays at a unique rate.
пѓјSome fast, some slow.
пѓјNot all the atoms of an isotope change simultaneously.
пѓјRate is a measure of how many of them change in a
given period of time.
пѓјMeasured in counts per minute, or grams per time.
• The length of time it takes for half of the parent
nuclides in a sample to undergo radioactive decay
is called the half-life.
Tro's Introductory Chemistry, Chapter
17
42
Half-Lives of Various Nuclides
Nuclide
Half-life
Type of decay
Th-232
1.4 x 1010 yr
Alpha
U-238
4.5 x 109 yr
Alpha
C-14
5730 yr
Beta
Rn-220
55.6 sec
Alpha
Th-219
1.05 x 10–6 sec
Alpha
Tro's Introductory Chemistry, Chapter
17
43
How “Hot” Is It?
• When we speak of a sample being hot, we
are referring to the number of decays we get
per minute.
• For samples with equal numbers of
radioactive atoms, the sample with the
shorter half-life will be hotter.
пѓјThat is, more atoms will change in a given
period of time.
Tro's Introductory Chemistry, Chapter
17
44
Half-Life
• Half of the radioactive atoms decay each half-life.
Radioactive decay
Percentage of original sample
100
90
80
70
60
50
40
30
20
10
0
0
1
2
3
4
5
6
Time (half-lives)
7
8
9
10
45
Decay of Au-198
half-life = 2.7 days
Radioactivity (cpm.)
60000
50000
40000
30000
20000
10000
0
0
2
4
6
8
10
12
14
Time (days)
16
18
20
22
46
How Long Is the Half-Life of this
Radionuclide?
Tro's Introductory Chemistry, Chapter
17
47
Example 17.4—How Long Does It Take for a
1.80 mol Sample of Th-228 to Decay to
0.225 mol? (Half-Life Is 1.9 Years.)
• It is easiest to draw a table showing the amount of
Th-228 as a function of the number of half-lives.
To get
next line
in
Amount
of Th-238
column,
п‚ё 2.
Amount of
Th-238
Number of
Half-lives
1.80 mol
0
0.900 mol
1
0.450 mol
2
0.225 mol
3
Time
(yrs)
It takes
To
get next
three
half0
line
in
lives,
Time
5.7(yrs)
years,
1.9 or
column,
half3.8 +to1 reach
0.225
life.mol.
5.7
48
Practice—Radon-222 Is a Gas that Is Suspected of Causing
Lung Cancer as It Leaks into Houses. It Is Produced by
Uranium Decay. Assuming No Loss or Gain from Leakage,
if There Is 1024 g of Rn-222 in the House Today, How Much
Will There be in 5.4 Weeks? ( Rn-222 Half-Life Is 3.8 Days.)
Tro's Introductory Chemistry, Chapter
17
49
Practice—Radon-222 Is a Gas that Is Suspected of Causing
Lung Cancer as It Leaks into Houses. It Is Produced by
Uranium Decay. Assuming No Loss or Gain from Leakage, if
There Is 1024 g of Rn-222 in the House Today, How Much
Will There be in 5.4 Weeks? ( Rn-222 Half-Life Is 3.8 Days.),
Continued
5.4 weeks x 7 days/wk = 37.8 п‚» 38 days
Amount of
Rn-222
Number of
Half-lives
Time
(days)
Amount of
Rn-222
1024 g
0
0
512 g
1
256 g
Number of
Half-lives
Time
(days)
16 g
6
22.8
3.8
8g
7
26.6
2
7.6
4g
8
30.4
128 g
3
11.4
2g
9
34.2
64 g
4
15.2
1g
10
38
32 g
5
19.0
50
Practice—How Long Is the Half-Life of an Isotope if a
Sample of the Isotope that Registers 60,000 cpm on the
Geiger Counter Decays to 15,000 cpm After 150 Minutes?
Tro's Introductory Chemistry, Chapter
17
51
Practice—How Long Is the Half-Life of an Isotope if a
Sample of the Isotope that Registers 60,000 cpm on the
Geiger Counter Decays to 15,000 cpm After 150 Minutes?,
Continued
Fill in the “Amount…” and “Number of half-lives” columns
first, then divide the final time by the number of half-lives.
Amount of
isotope
60,000 cpm
Number of
half-lives
0
30,000 cpm
15,000 cpm
1
2
Time
(min)
0
75
150
Since it takes 2 half-lives, divide 150 by 2.
Tro's Introductory Chemistry, Chapter
17
52
Decay Series
•
In nature, often one radioactive nuclide changes
in another radioactive nuclide.
пѓј Daughter nuclide is also radioactive.
•
•
All of the radioactive nuclides that are produced
one after the other until a stable nuclide is made
is called a decay series.
To determine the stable nuclide at the end of the
series without writing it all out:
1.
2.
3.
Count the number of a and b decays.
From the mass nunmber, subtract 4 for each a decay.
From the atomic number, subtract 2 for each a decay and
add 1 for each b.
Tro's Introductory Chemistry, Chapter
17
55
U-238 Decay Series
Tro's Introductory Chemistry, Chapter
17
56
Practice—Write All the Steps in the U-238
Decay Series and Identify the Stable Isotope
at the End of the Series.
• a, b, b, a, a, a, a, b, a, b, a, b, b, a
Tro's Introductory Chemistry, Chapter
17
57
Practice—Write All the Steps in the U-238
Decay Series and Identify the Stable Isotope
at the End of the Series, Continued.
• a, b, b, a, a, a, a, b, a, b, a, b, b, a
a
U-238
b
Daughter
Th-234
Granddaughter
b
Pa-234
Great
Great great
granddaughtera granddaughter
U-234
Th-230
a
a
a
b
a
Ra-226
Rn-222
Po-218
At-218
Bi-214
b
Po-214
a
b
b
Pb-210
Bi-210
a
Po-210
Tro's Introductory Chemistry, Chapter
17
Pb-206
58
Practice—Determine the Stable Isotope at the
End of the U-238 Decay Series.
• a, b, b, a, a, a, a, b, a, b, a, b, b, a
Tro's Introductory Chemistry, Chapter
17
59
Practice—Determine the Stable Isotope at the
End of the U-238 Decay Series, Continued.
• a, b, b, a, a, a, a, b, a, b, a, b, b, a
238
U
92
8a
238 - 32
92 - 16
6b
?
206 - 0
76 + 6
Tro's Introductory Chemistry, Chapter
17
?
206
=
Pb
82
60
Object Dating
• Mineral (geological).
пѓј Compare the amount of U-238 to Pb-206.
пѓј Compare amount of K-40 to Ar-40.
• Archeological (once living materials).
пѓј Compare the amount of C-14 to C-12.
пѓј C-14 radioactive with half-life = 5730 years.
пѓј While substance is living, C-14/C-12 is fairly constant.
пѓ� CO2 in air is ultimate source of all C in body.
пѓ� Atmospheric chemistry keeps producing C-14 at the same rate it decays.
пѓј Once dies, C-14/C-12 ratio decreases.
пѓј Limit up to 50,000 years.
Tro's Introductory Chemistry, Chapter
17
61
Radiocarbon Dating
C-14 Half-Life = 5730 Years
% C-14
(relative to
living
organism)
Number of
half-lives
Time
(yrs)
100.0
0
0
50.0
25.00
12.50
1
2
3
5,730
11,460
17,190
6.250
3.125
4
5
22,920
28,650
1.563
6
34,380
62
Radiocarbon Dating
% C-14 (compared to
living organism)
Object’s age (in years)
100%
0
90%
870
80%
1850
60%
4220
50%
5730
40%
7580
25%
11,500
10%
19,000
5%
24,800
1%
38,100
63
Example 17.5—A Skull Believed to Belong to
an Early Human Being Is Found to Have a C14 Content 3.125% of that Found in Living
Organisms. How Old Is the Skull?
• From Table 17.2, when the concentration of
C-14 is 3.125% of that found in living
organisms, the age of the object is 28,560
years.
Tro's Introductory Chemistry, Chapter
17
64
Nonradioactive Nuclear Changes
• A few nuclei are so unstable, that if their nuclei are
hit just right by a neutron, the large nucleus splits
into two smaller nuclei. This is called fission.
• Small nuclei can be accelerated to such a degree
that they overcome their charge repulsion and
smash together to make a larger nucleus. This is
called fusion.
• Both fission and fusion release enormous
amounts of energy.
пѓј Fusion releases more energy per gram than fission.
Tro's Introductory Chemistry, Chapter
17
65
Fission
+ energy!!
Tro's Introductory Chemistry, Chapter
17
66
Fission Chain Reaction
• A chain reaction occurs when a reactant in the
process is also a product of the process.
пѓјIn the fission process it is the neutrons.
пѓјSo you only need a small amount of neutrons to
start the chain.
• Many of the neutrons produced in the fission
are either ejected from the uranium before they
hit another U-235 or are absorbed by the
surrounding U-238.
• Minimum amount of fissionable isotope needed
to sustain the chain reaction is called the
critical mass.
Tro's Introductory Chemistry, Chapter
17
67
Fission Chain Reaction, Continued
Tro's Introductory Chemistry, Chapter
17
68
Fissionable Material
• Fissionable isotopes include U-235, Pu-239,
and Pu-240.
• Natural uranium is less than 1% U-235.
пѓјThe rest is mostly U-238.
пѓјNot enough U-235 to sustain chain reaction.
• To produce fissionable uranium the natural
uranium must be enriched in U-235:
To about 7% for “weapons grade.”
To about 3% for “reactor grade.”
Tro's Introductory Chemistry, Chapter
17
69
Nuclear Power
• Nuclear reactors use fission to generate
electricity.
пѓјAbout 20% of U.S. electricity.
пѓјThe fission of U-235 produces heat.
• The heat boils water, turning it to steam.
• The steam turns a turbine, generating
electricity.
Tro's Introductory Chemistry, Chapter
17
70
Nuclear Power Plants vs.
Coal-Burning Power Plants
• Use about 50 kg of
fuel to generate
enough electricity for
1 million people.
• No air pollution.
• Use about 2 million kg
of fuel to generate
enough electricity for 1
million people.
• Produces NO2 and SOx
that add to acid rain.
• Produces CO2 that adds
to the greenhouse effect.
Tro's Introductory Chemistry, Chapter
17
71
Nuclear Power Plants—Core
• The fissionable material is stored in long tubes,
called fuel rods, arranged in a matrix.
пѓјSubcritical.
• Between the fuel rods are control rods made
of neutron absorbing material.
пѓјB and/or Cd.
пѓјNeutrons needed to sustain the chain reaction.
• The rods are placed in a material to slow down
the ejected neutrons, called a moderator.
пѓјAllows chain reaction to occur below critical mass.
Tro's Introductory Chemistry, Chapter
17
72
Pressurized Light Water Reactor
(PLWR)
• Design used in U.S. (GE, Westinghouse).
• Water is both the coolant and moderator.
• Water in core kept under pressure to keep it
from boiling.
• Fuel is enriched uranium.
пѓјSubcritical.
• Containment dome of concrete.
Tro's Introductory Chemistry, Chapter
17
73
Nuclear Power Plant
74
Containment
building
PLWR
Turbine
Condenser
Boiler
Core
Cold
water
75
PLWR—Core
Hot
water
Control
rods
Fuel
rods
Cold
water
76
Concerns About Nuclear Power
• Core melt-down.
пѓј Water loss from core, heat melts core.
пѓј China syndrome.
пѓј Chernobyl.
• Waste disposal.
пѓј Waste highly radioactive.
пѓј Reprocessing, underground storage?
пѓј Federal High Level Radioactive Waste Storage Facility at Yucca
Mountain, Nevada.
пѓ� Delay in opening, 2017?
• Transporting waste.
• How do we deal with nuclear power plants that are no
longer safe to operate?
Tro's Introductory Chemistry, Chapter
17
77
Nuclear Fusion
• Fusion is the combining of light nuclei to make a
heavier one.
• The sun uses the fusion of hydrogen isotopes to
make helium as a power source.
• Requires high input of energy to initiate the
process.
пѓј Because need to overcome repulsion of positive nuclei.
• Produces 10x the energy per gram as fission.
• No radioactive byproducts.
• Unfortunately, the only currently working
application is the H-bomb.
Tro's Introductory Chemistry, Chapter
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78
Fusion
+
2
1H
+
3
1H
4
2He
deuterium + tritium
1
0n
helium-4 + neutron
Tro's Introductory Chemistry, Chapter
17
79
Biological Effects of Radiation
• Radiation is high energy, energy enough to
knock electrons from molecules and break
bonds.
пѓјIonizing radiation.
• Energy transferred to cells can damage
biological molecules and cause malfunction
of the cell.
Tro's Introductory Chemistry, Chapter
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80
Acute Effects of Radiation
• High levels of radiation over a short period
of time kill large numbers of cells.
пѓјFrom a nuclear blast or exposed reactor core.
• Causes weakened immune system and
lower ability to absorb nutrients from food.
пѓјMay result in death, usually from infection.
Tro's Introductory Chemistry, Chapter
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81
Chronic Effects
• Low doses of radiation over a period of time show
an increased risk for the development of cancer.
пѓј Radiation damages DNA that may not get repaired
properly.
• Low doses over time may damage reproductive
organs, which may lead to sterilization.
• Damage to reproductive cells may lead to a
genetic defect in offspring.
Tro's Introductory Chemistry, Chapter
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82
Factors that Determine
Biological Effects of Radiation
1. The more energy the radiation has, the larger its effect.
2. The better the radiation penetrates human tissue, the
deeper the potential effect.
пѓј Gamma >> beta > alpha.
3. The more ionizing the radiation, the greater the effect
of the radiation.
пѓј Alpha > beta > gamma.
4. The radioactive half-life of the radionuclide.
5. The biological half-life of the element.
6. The physical state of the radioactive material.
Tro's Introductory Chemistry, Chapter
17
83
Biological Effects of Radiation
• The amount of danger to humans of radiation
is measured in the unit rems.
Dose (rems) Probable outcome
20–100
100–400
500+
Decreased white blood cell count;
possible increased cancer risk
Radiation sickness;
increased cancer risk
Death
Tro's Introductory Chemistry, Chapter
17
84
Radiation Exposure
Tro's Introductory Chemistry, Chapter
17
85
Medical Uses of Radioisotopes,
Diagnosis
• Isotope scanners.
пѓј Certain organs absorb most or all of a
particular element.
пѓј Can measure the amount absorbed by
using tagged isotopes of the element and
a Geiger counter, film, or a scintillation
counter.
пѓј Use radioisotope with short half-life.
пѓј Use radioisotope low ionizing.
пѓ� Beta or gamma.
Tro's Introductory Chemistry, Chapter
17
86
Radioisotopes Used for Diagnosis
Nuclide
Iodine-131
Iron-59
Molybdenum-99
Phosphorus-32
Strontium-87
Technetium-99
Half-life
8.1 days
45.1 days
67 hours
14.3 days
2.8 hours
6 hours
Organ/system
Thyroid
Red blood cells
Metabolism
Eyes, liver
Bones
Heart, bones, liver,
lungs
Tro's Introductory Chemistry, Chapter
17
87
Medical Uses of Radioisotopes:
Treatment—Radiotherapy
•
Cancer treatment.
пѓј Cancer cells are more sensitive to radiation than
healthy cells.
1. Brachytherapy.
пѓ� Place radioisotope directly at site of cancer.
2. Teletherapy.
пѓ� Use gamma radiation from Co-60 outside to
penetrate inside.
3. Radiopharmaceutical therapy.
пѓ� Use radioisotopes that concentrate in one area of the
body.
Tro's Introductory Chemistry, Chapter
17
89
Gamma Ray Treatment
Tro's Introductory Chemistry, Chapter
17
90
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