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Ch10 nuclear chem
1. Nuclear Chemistry
Chapter 10
by
Prof. Geronimo J. Fiedalan Jr., MAT
1
2. OBJECTIVES
• Define nuclear Chemistry
• Describe stable, unstable, and very
unstable isotopes
• Describe the characteristics of the types
of radiation
• Define half-life
• Give uses of radioisotopes
• Differentiate nuclear fission from
nuclear fusion
2
3. Nuclear Chemistry
• Nuclear Chemistry
deals with radioactivity,
its origin, nature,
properties and
characteristics as well as
its implication to nature
and the physical world.
3
4. Nuclear Chemistry
• Radioactivity is the spontaneous
emission of the particles alpha, and beta,
or gamma rays through the disintegration
of atomic nuclei of radioisotopes.
• Radioisotopes are radioactive isotopes.
4
5. Nuclear Chemistry
• Radioactive decay is the disintegration of
an unstable atomic nucleus by
spontaneous emission of radiation.
5
6. Nuclear Chemistry
• Radiation is the energy emitted by the
nucleus (of atom) of an infinitesimal size
which travel through space.
– Ionizing radiation
– Non-ionizing radiation
6
7. Nuclear Chemistry
• Ionizing Radiation
– have sufficient energy to ionize an atom
– α, β, γ
• Non-ionizing Radiation
– The energy radiates (i.e., travels outward in
straight lines in all directions) from its
source.
7
10. Discovery of Radioactivity
• Henri Becquerel (1852 – 1908) found that
uranium crystals had the property of “fogging” a
photographic plate that had been placed near
crystals, which took place even though the
photographic plate was wrapped in black paper.
10
11. Discovery of Radioactivity
• Marie Curie and Pierre Curie discovered other
radioactive elements (Th, Po, Ra) . They also
found that radioactivity of substances was
associated with their elements, not with
compounds.
Marie Curie called the
radiation discovered
by Becquerel as
radioactivity.
11
14. • Radioactivity was
discovered by Becquerel in
1896.
• Radioactive elements
spontaneously emit alpha
particles (α), beta particles (β)
and gamma (γ) rays from their
nuclei.
• By 1907 Rutherford found that
alpha particles emitted by
certain radioactive elements
4
were helium nuclei ( 2 He 2 ). 14
15. Rutherford’s alpha particle scattering experiment.
Rutherford in 1911 performed experiments that
shot a stream of alpha particles at a gold foil.
15
5.5
16. Rutherford’s alpha particle scattering experiment.
Most of the alpha particles passed through the foil
with little or no deflection.
16
5.5
17. Rutherford’s alpha particle scattering experiment.
He found that a few were deflected at large angles
and some alpha particles even bounced back.
17
5.5
18. Rutherford’s alpha particle scattering experiment.
An electron with a mass of 1/1837 amu could not
have deflected an alpha particle with a mass of 4
amu. 18
5.5
20. Rutherford’s alpha particle scattering experiment.
Rutherford concluded that each gold atom
contained a positively charged mass that occupied
a tiny volume. He called this mass the nucleus.
20
5.5
21. Rutherford’s alpha particle scattering experiment.
If a positive alpha particle approached close
enough to the positive mass it was deflected.
21
5.5
22. Rutherford’s alpha particle scattering experiment.
Most of the alpha particles passed through the gold
foil. This led Rutherford to conclude that a gold
atom was mostly empty space. 22
5.5
23. Deflection
Scattering
Deflection and scattering of alpha particles by positive gold nuclei.
23
5.5
27. Stable and Unstable Nuclides
• Stable
12
6 X n=6 p=6
70
32 X n = 38 p = 32
27
28. Stable and Unstable Nuclides
• Unstable
3
1 X n=2 p=1
59
28 X n = 31 p = 28
28
29. Stable and Unstable Nuclides
• Very Unstable
8 n=3 p=5
5 X
58 n = 29 p = 29
29 X
29
30. Stable and Unstable Nuclides
1) Atomic nuclei with even number of
protons and neutrons are stable.
(Of the 264 stable isotopes, 157 have
even numbers of both protons and
neutrons. Only 4 have odd numbers of
protons and neutrons.)
12
6 C
30
31. Stable and Unstable Nuclides
2) Atomic nuclei with even number of
neutron and odd number of proton, odd
number of neutrons and even number of
proton, or odd numbers of both neutrons
and protons are unstable.
17
8 O
31
32. Stable and Unstable Nuclides
3) “Magic” numbers of either protons
or neutrons.
(Magic numbers are 2, 8, 20, 50, 82,
and 126).
4) An atomic number of 83 or less.
(All isotopes with atomic numbers
greater than 83 are radioactive).
32
33. Stable and Unstable Nuclides
5) There should be no more protons than
neutrons in the nucleus, and the ratio of
neutrons to protons should be close to 1
if the atomic number is 20 or below.
33
35. Types of Radiation
1) Background Radiation is the ever-present
radiation from cosmic rays and from natural
radioactive isotopes in air, water, soil, and
rocks. It causes minimal harm.
2) Ionizing Radiation is a radiation that
produces ions at it passes through matter. It
arises from interaction of radiation by
knocking electrons from atoms and
molecules, converting them into ions.
35
36. Types of Radiation
• Ionizing radiation devastate living cells by
interfering with their normal chemical
processes
– Transformation of water to highly reactive
hydrogen peroxide (H2O2).
– Affects the bone marrow resulting to low
production of RBC leading to anemia, leukemia
and cancer.
– Change in the molecules of heredity (DNA) in
the reproductive cells producing mutations.
36
37. Types of Radiation
3) Medical Irradiation is obtained from
exposure to X-rays and LASERS for
medical purposes.
- Light Amplification by Stimulated Emission of
Radiation (LASER)
4) Natural Radiation is the type of decay
exhibited by radioactive isotopes.
37
38. Types of Radiation
5) Artificial Radiation is the type of decay
exhibited by normally non-radioactive
light elements through bombardment.
-nuclear reactions
38
40. Alpha (α) Particles
• positively charged.
• He nuclei has two
protons and two
neutrons, thus having
a charge of +2.
4
2 He 2
• result from radioactive
decay of heavy
elements such as
radium and uranium.
40
41. Alpha (α) Particles
A A 4 4 A A 4 4
Z X Z 2 Y 2 He Z X Z 2 Y 2
238 4
92 U 2 __ 234
Th
90
212 4 208
84 Po 2 __ 82 Pb
41
42. Alpha (α) Particles
• When an atom emits an alpha particle,
its mass number decreases by 4 and its
atomic number decreases by 2.
• Reason for instability:
– Nucleus is too large
42
43. Beta (β-) Particles
• Beta particles are negatively
charged.
• Beta particles have a charge
of negative one (1-)
• Beta particles have a very
small mass.
43
44. Beta (β-) Particles
• Beta particles are high-speed electrons
produced in the nucleus by the
transformation of a neutron into a proton and
an electron.
1 1 0 1 1 0
0 n 1 p -1 e 0 n 1 H -1
retained emitted
in nucleus
– The electron is emitted as a beta particle
and the proton remains in the nucleus.
44
45. Beta (β) Particles
A A 0
Z X Z 1 Y -1 e
234 234 0
90 Th 91 Pa -1
32 0 32
15 P 1- __ 16 S
14 0 14
6 C 1- __ 7 N
97 0
40 Zr 1- __ 97
41 Nb
45
46. Beta (β-) Particles
• When an atom emits a beta particle, its
mass number remains the same, but its
atomic number increases by 1.
• Reason for instability:
– Nucleus has too many neutrons
relative to the number of protons.
46
47. Gamma (γ) Rays
• Gamma rays have no charge
– not affected by an electrostatic
field.
• are not particles, so
– they have no mass.
• are electromagnetic radiation
similar to X-rays.
47
48. Gamma (γ) Rays
• often emitted along with alpha or beta
particles.
• Originate from unstable atoms releasing
energy to gain stability.
238 238 *
92 U 92 U
• (*) indicates a slightly lower energy
48
49. Gamma (γ) Rays
99 m 99
Tc
43 43Tc
m = indicates metastable (unstable)
49
50. Gamma (γ) Rays
• When an atom emits a gamma ray,
there is no change in the atomic number
or mass number.
• Reason for instability:
– Nucleus has excess energy.
50
52. Positron (β+) Emission
• Positron (β+) is a particle equal in mass
but opposite in charge to the electron. It is
represented by 0 e.
1
1
p n1 0
e
1 0 1
Neutrino - an elementary
particle that usually travels
close to the speed of light,
is electrically neutral, and is
able to pass through
ordinary matter almost
unaffected
52
53. • After the positron is 0 0 0
emitted, the original 1 e 1 e 2 0
radioactive nucleus β+ β-
has one fewer proton
and one more
neutron than it has When the emitted
before. positron encounters
– Therefore, the mass an electron, both
number of the particles are
product nucleus is annihilated quickly
the same, but its resulting to the
atomic number has production of two
been reduced by 1. gamma photons.
53
54. Positron (β +) Emission
18 0 18
9 F 1 e __ 8 O
38
38
K 0
__ 18 Ar
19 1
• Reason for instability:
– Nucleus has too many protons
relative to the number of neutrons
54
55. Electron Capture (EC)
• Electron capture (EC) – is a process in
which a nucleus absorbs an electron from
an inner electron shell, usually the first or
the second. Once inside the nucleus, the
captured electron combines with a proton
to form a neutron. 1 0 1
1 p 1 e 0 n
55
56. Electron Capture (EC)
• When an electron from a higher shell
drops to the level vacated by the captured
electron, an X-ray is released.
125 0 125
53 I 1 e 52Te
• Iodine – 125 is used as medicine to
diagnose pancreatic function and intestinal
fat absorption, decays by EC.
56
57. Electron Capture (EC)
37 0 37
18 Ar 1 e __ 17 Cl
55 0 55
26 Fe 1 e __ 25 Mn
• Reason for instability:
– Nucleus has too many protons
relative to the number of neutrons.
57
58. Radioactive Decay and Nuclear Change
Type of Decay Particle Particle Change in Change in
Decay Particle Mass Charge Nucleon Atomic
Number Number
Alpha α 4 2+ Decrease by 4 Decrease by
decay 2
Beta β 0 1- No change Increase by
decay 1
Gamma γ 0 0 No change No change
ray
Positron β+ 0 1+ No change Decrease by
emission 1
Electron e- 0 1- No change Decrease by
capture (absorbed) 1
58
61. Penetrating and Ionizing Power
– Alpha particles have very low
penetrating power and cannot pass
through skin.
• Can be stopped by skin, Al foil, or paper
– have very high ionizing power
• Cause more damage than X-rays or
gamma radiation
• Not harmful to humans or animals as
long as they do not get into the body.
62. Penetrating and Ionizing Power
– Beta particles are less damaging to
tissue than alpha particles but
penetrate farther and so are generally
more harmful.
• Have slight penetrating power but can
be stopped by heavy clothing
62
63. Penetrating and Ionizing Power
– Gamma rays, which can easily
penetrate skin, are by far the most
dangerous and harmful form of
radiation.
– causing cellular damage as they travel
through the body.
63
65. Terms and Units of Measurement of
Nuclear Radiation
The physical unit of radiation is a measure
of the number of nuclear disintegrations
occurring per second in a radioactive source.
• Curie (Ci) - the number of nuclear
disintegrations occurring per second in 1 g of
Ra.
– one Ci = 3.7 x 1010 dps
• Becquerel (Bq): equal to one disintegration or
nuclear transformation per second.
66. Terms and Unit of Measurement of
Nuclear Radiation
• Roentgen (R): a measure of the energy
delivered by a radiation source.
– A unit of radiation applied to X-rays and
gamma rays only
– the amount of radiation that produces
ions having 2.58 x 10-4 coulomb/kg;
66
67. Terms and Units of Measurement of
Nuclear Radiation
• Radiation absorbed dose (Rad) - total amount
of ionizing radiation absorbed by tissue that
has been radiated; the SI unit is the gray (Gy)
– 1 rad = 100 ergs of energy absorbed/gram of
tissue
– Gray (Gy): one Gy = 1 joule/kilogram (1 J/kg)
• Roentgen-equivalent-man (Rem): a measure of
the effect of the radiation when one roentgen is
absorbed by a person; the SI unit is the sievert
(Sv) where one Sv = 1 J/kg 67
69. Chemical Reactions Nuclear Reactions
Atoms retain their identity Atoms change from one element
to another
Reactions involve only Reactions mainly involve protons
electrons and usually only and neutrons.
outermost electrons.
Reactions rates can be Reactions rates are unaffected by
speeded up by raising the changes in temperature.
temperature.
Energy absorbed or given Reactions sometimes involve
off in reactions is enormous changes in energy.
comparatively small.
Mass is conserved. Huge changes in energy are
accompanied by measurable 69
changes in mass (E=mc2).
71. Half - life
• Half-life – is the amount of time required for
one-half the radioactive nuclei in a sample to
decay.
– The fraction of the original isotope that
remains after a given number of half-lives
passed is calculated from the relationship
1
fraction remaining =
2n
where
–n is the number of half - lives
71
72. Half – life
• The amount left after a radioactive atom
underwent decay can be calculated by
t
1
A A orig
2
– where
• t is the number of half-lives that
passed
72
73. Problem 1: Cobalt – 60 has a half-life of 5.25
years. If you have a 400-mg sample of Co-60,
how much remains after 15.75 years?
• Solution:
1 1 1
Fraction remaining
2n 23 8
1
A 400 mg 8
A 50 mg
73
74. Problem 1: Cobalt – 60 has a half-life of 5.25
years. If you have a 400-mg sample of Co-60,
how much remains after 15.75 years?
• Solution:
no. of years 15.75 yrs
t
half - life 5.25 yrs 1 t
A A orig 2
t 3
1 3
400 mg 2
A 50 mg
74
75. 234
Problem 2: Starting with a 2-gram sample of Th 90
, how much remains at the end of 48 days? The
half-life of Th-234 is 24 days?
Problem 3. Krypton-81 m is used for lung
ventilation studies. Its half-life is 13 seconds.
How long does it take the activity of this isotope
to reach one-quarter of its original value?
a) 0.5 g b) 26 s
75
76. N ame Half-life Radiation
Hydrogen-3 (tritium) 12.26 y Beta
Carb on -14 5730 y Beta
Ph os phoru s-28 0.28 s Positron
Ph os phoru s-32 14.3 d Beta
Potass iu m-40 1.28 x 109 y Beta + gamma
Scandium-42 0.68 s Positron
Cob alt-60 5.2 y Gamma
Strontium-90 28.1 y Beta
Tech netium-99m 6.0 h Gamma
Indiu m-116 14 s Beta
Iod ine-131 8d Beta + gamma
Mercury-197 65 h Gamma
Polonium-210 138 d Alp ha
Radon-205 2.8 m Alp ha
Radon-222 3.8 d Alp ha
Uraniu m-235 4 x 109 y Alp ha
77. Half-life of Some Common Radioisotopes
Radioisotopes Half-life Uses
Tc-99m 6 hr Imaging of brain, liver, lung, bone
marrow, kidney
Fe-59 45 days Detection of anemia
Ra-226 1600 yr Radiation therapy for cancer
I-131 8 days Thyroid therapy
P-32 14.3 days Detection of skin cancer
Co-60 5.3 yr Radiation cancer therapy
C-11 20.3 min Brain scans
H-3 12.3 yr Determining total body water
Ga-67 78 hr Scan for lung tumors
Cr-51 27.8 days Blood volume determination
Na-24 15 hr Locating obstruction in blood flow
77
Ir-192 74 days Breast cancer therapy
79. Uses of Radioisotopes
1. Tracers
2. Nuclear Medicine
3. Food Irradiation
4. Radioisotopic Dating
5. Warfare
6. Power Generation
79
80. Tracers
• Tracers are radioactive isotopes used to
trace movement or locate the sites of
radioactivity in physical, chemical, and
biological systems.
80
81. Nuclear Medicine
• Nuclear Medicine involves two distinct
uses of radioisotopes – therapeutic and
diagnostics.
– Therapeutic involves the use of
radiation therapy to treat or cure
diseases.
– Diagnostic involves the use of
radioisotopes to obtain information
about the state of a patient’s health.
81
82. Nuclear Medicine
• Therapeutic
– Iodine-131and Iodine-123 – treatment of
thyroid conditions
– Cobalt-60 and Cobalt-57 – for treatment of
many different types of cancer
– Gold-198 – treatment of pleural and
peritoneal metastases (spreading disease
from original sites).
– X-ray therapy – uses Ra or Co-60. X-rays
can be used for treatment of superficial skin
conditions, deep-seated malignancies and
many different types of cancer.
82
83. Nuclear Medicine
• Diagnostic
– Technetium–99m – used for many
types of scans and measuring blood
volume
– Krypton-79 – for evaluation of
cardiovascular system
– Selenium-75 – for determination and
size of the pancreas
– Mercury-197 – for evaluation of spleen
function and for brain scans.
83
84. Nuclear Medicine
• Diagnostic
– PET (Positron Emission tomography) Scan
– is a technique that uses radioisotopes
to get three dimensional pictures showing
function processes occurring in the
human body.
This technique is used
to trace gamma rays
sent forth by positron
producing
radionuclide.
84
85. Nuclear Medicine
• Diagnostic
– MRI (Magnetic Resonance Imaging) – is
a noninvasive (nonsurgical) method of
following biochemical reactions in both
cells and entire organs under normal
physical conditions.
85
86. Nuclear Medicine
• MRI (Magnetic Resonance Imaging)
MRI doesn’t
involve
ionizing
radiation, as
do X-rays and
CT scans.
MRI takes
advantage of
something you
have plenty of
in your body:
86
water.
87. Nuclear Medicine
• Diagnostic
– X-ray - radiation similar to visible light but
of much higher energy and much more
penetrating.
87
89. Food Irradiation
• Food Irradiation consists of exposing food
to some of ionizing radiation, such as gamma
rays or X-rays to kills insects and
microorganisms and also to halt the ripening
of fruits.
Co-60 is used for this
purpose. Irradiation
lengthens the shelf life of
food and reduces the need
for preservatives, some of
which have toxic effects.
89
90. Radioisotopic Dating
• Radioisotopic Dating is used in determining
the age of objects.
– Carbon-14 dating – a technique for
determining the age of artifacts based on the
half-life of C-14. Ex. Shroud of Turin
90
91. Radioisotopic Dating
• Radioisotopic Dating is used in determining
the age of objects.
– Tritium dating (H-3) – is useful for dating items up
to about 100 years old, i.e. beverages, wine.
– Tritium has a half-life of 12.43 years.
91
92. Radioisotopic Dating
• Radioisotopic Dating is used in determining
the age of objects.
– Uranium dating – uses U-238 to determine
the age of the earth and other heavenly
bodies.
92
93. Warfare
• Warfare – involves construction of nuclear
bombs and nuclear weapons.
93
94. Warfare and Power Generation
• Power Generation – involves production of
electricity using nuclear energy from nuclear
fission of radioactive material, i.e., U-235 in
nuclear reactors.
94
96. Artificial Transmutation
• Artificial Transmutation is the changing of
one element into another.
• In order to accomplish transmutation, one
must alter the stable nucleus by bombarding
it with
– Alpha particle - Electrons
– Neutrons -Deuterons (Hydrogen-2)
– Protons
– Other particles
96
97. Artificial Transmutation
14 4 17 1
7 N 2 He 8 O 1 H
• The hydrogen nucleus is simply a proton,
1
hence the alternative symbol 1 H for the
proton.
39 1 36
19 K 0 n 17 Cl ?
• Answer: 4
He
2
97
98. Artificial Transmutation
7 1
3 Li 1 H 2 4 He
2
40 1 1 40
18 Ar 1 H __ 0 n 19 K
114 2 1 115
48 Cd 1 H __ 1 H 48 Cd
238 12 1
92 U 6 C __ 60 n 244
Cf
98
14 1 1
6 C 0 n __ 1 H 14
C
6
27 4 1
13 Al 2 __ 0 n 30
P
15
98
99. Artificial Transmutation
• When chlorine–37 is bombarded with a
neutron, a proton is ejected. What new
element is formed?
37 1 37 1
17 Cl 0 n 16 S 1 p
37 1 37 1
17 Cl 0 n 16 S 1 H
99
101. Nuclear Reaction
Nuclear Reaction is the process by which
one type of nucleus changes into another.
Types of Nuclear Reaction
1. Nuclear Fission
2. Nuclear Fusion
101
102. Nuclear Fission
• Nuclear Fission – is a process by which
certain heavy nuclei split into lighter nuclei
when they absorb slow moving neutrons.
102
103. Nuclear Fission
1 235 145 88 1
0 n 92 U 56 Ba 36 Kr 3 n
0 energy
• When uranium-
235 is
bombarded with
neutron, it is
broken into two
smaller
elements.
103
104. Nuclear Fission
1 235 145 88 1
0 n 92 U 56 Ba 36 Kr 3 n
0 energy
– The products have less mass than the
starting materials.
– The mass decrease in fission is
converted into energy.
– This form of energy is called atomic
energy.
105. Nuclear Fission
• Nuclear fission is a chain reaction
Chain Reaction is a
self-sustaining
reaction which once
started, steadily
provides energy and
matter needed to
continue the reaction.
106. Nuclear Fission
• Nuclear reactions do not obey the law of
conservation of mass. They obey the
combined Law of Conservation of Mass and
Energy which states that the amount of
mass that disappears is converted into an
equivalent amount of energy.
• This can be calculated by using Einstein’s
equation E = mc2.
106
107. Nuclear Fission
1 235 145 88 1
0 n 92 U 56 Ba 36 Kr 30 n energy
(kg) 1.0087 234.9934 93.9154 138.9179 3(1.0087)
Total mass of reactants = 236.0021 kg
Total mass of products = 235.8594 kg
Loss in mass = 0.1427 kg
• Using Einstein’s equation, E=mc2, we find
E mc 2
8 2
0.1427 kg 3 x 10 m/s
16
E 1.28 x 10 J 107
108. Nuclear Fission
• Nuclear reactors use U3O8 (a compound
enriched with scarce fissionable U-235).
• Because the supply of U-235 is limited
breeder reactor has been developed.
• Breeder reactors use neutrons to convert
non-fissionable isotopes such as U-238 or
Th-232 to fissionable isotopes , Pu-239 or
U-233.
108
109. Nuclear Fission
• Breeder reactors
1 238 239 239 239
0 n 92 U 92 U 93 Np 94 Pu
1 232 233 233 233
0 n 90 Th 90 Th 91 Pa 92 U
• Atomic bomb uses Pu-239
1 238 239 239 239
0 n 92 U 92 U 93 Np 94 Pu
109
110. Nuclear Fusion
• Nuclear Fusion is the process whereby nuclei
of light atoms combine to form a heavier
nucleus with the release of energy.
The sun
provides us
with energy
through
nuclear fusion.
110
111. Nuclear Fusion in the Sun
1 1 2 0
Step 1 : H
1 1 H 1 H 1 e energy
2 1 3
Step 2 : H
1 1 H 2 He energy (occurstwice)
3 3 4 1
Step 3 : He
2 2 He 2 He 2 H energy
1
• The reaction that takes place in the Sun is
called thermonuclear reactions because
very high temperatures (million of degrees)
are required in order to initiate them. The
fusion of only 1 g of H releases an amount of
energy equivalent to the burning of nearly 20
tons of coal. 111
113. Protection from Radiation
• Shielding, distance, and limiting exposure
are the only effective preventive methods
against radiation exposure.
• Exposure to external radiation can be
controlled by increasing distance between the
body and the source of the radiation. The
amount of radiation received varies inversely
as the square of the distance.
113
114. Problem: A nurse receives an exposure of 20
mrem when standing 3 ft from a radioactive
source. What will be the exposure at a distance
of (a) 6 ft?
1 rem = 1 R
2 rem = amount of
exposure at distance1 d2
ionizing radiation,
exposure at distance 2 2
d1 that when absorbed
by human, has an
2
20 mrem 6 ft effect equal to the
x 2 absorption of 1 R.
3 ft
mrem is a smaller
x 5 mrem unit.
114
