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Chapter 11
Nuclear Chemistry
Use of 131I in detecting Hyper- or hypo- thyroidism
1
Brain images with 123I-labeled compound
2
Nuclear Reactions
3
© 2003 John Wiley and Sons Publishers
4
11.2 The Discovery of Nature of
Radioactivity
Radioactivity: The spontaneous emission of
radiation from a nucleus.
Henry Becquerel, a French physicist, discovered
radioactivity in 1896. Henry Becquerel placed a
sample of uranium-containing mineral on top of a
photographic plate wrapped in black paper. On
developing the plate, Becquerel found a silhouette
of the mineral on the plate. He concluded some
kind of radiation emitted by the mineral passed
through the paper and exposed the photographic
plate.
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11.3 Stable and Unstable Isotopes
A radioactive
isotope has an
unstable nucleus
and emits
radiation to
become more
stable.
Isotopes of
elements may be
stable or unstable.
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11.4 Nuclear Decay
Alpha Decay
When a radioactive
nucleus emits an
alpha particle, a new
nucleus results.
The mass number of
the new nucleus is 4
less than that of the
initial nucleus.
The atomic number
is decreased by 2.
Animation
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Equation for Alpha Decay
Write an equation for the alpha decay of Rn-222.
222Rn
new nucleus + 4He
86
2
Determine the mass and atomic numbers of the
new nucleus.
Mass number:
222 – 4 = 218
Atomic number: 86 – 2 = 84
Symbol of element 84
= Po
Complete the equation with the new symbol:
222Rn
218Po
4He
+
86
84
2
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Beta Decay
A beta particle
Is an electron
emitted from the
nucleus.
Forms when a
neutron in the
nucleus breaks
down.
1n
0e + 1H
0
-1
1
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Potassium - 42 is a beta emitter.
42K
new nucleus + 0e
19
-1
The atomic number of the new nucleus
increases by 1.
Mass number :
(same) = 42
Atomic number:
19 + 1 = 20
Symbol of element 20
= Ca
The nuclear equation is
42K
42Ca
0e
+
19
20
-1
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Learning Check
Write the nuclear equation for the beta
decay of Co-60.
60Co
27
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Solution
Write the nuclear equation for the beta
decay of Co-60.
60Co
60Ni
27
28
+ 0e
1
beta particle
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Gamma Radiation
Gamma radiation is energy emitted from
an unstable nucleus indicated by m.
In a nuclear equation for gamma emission,
the mass number and the atomic number
are the same.
99mTc
99Tc
43
43
+
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Summary of Radiation
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11.6 Radioactive Decay Series
Decay series: A sequential series of nuclear disintigrations
(decay) leading from a heavy radioisotope to a nonradioactive
product, Fig 11.5.
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Producing Radioactive Isotopes
A nucleus is converted to a radioactive
nucleus by bombarding it with a small
particle.
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Learning Check
What radioactive isotope is produced when a
neutron bombards cobalt-59?
59Co
27
+
1n
0
???? +
4He
2
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Solution
What radioactive isotope is produced
when a neutron bombards cobalt-59?
mass numbers
= 60
59Co + 1n
27
0
= 27
= 60
56Mn +
4H e
25
2
= 27
atomic numbers
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11.8 Detecting Radiation
A Geiger counter
detects radioactive
radiations.
Ions produced by
radiation create an
electrical current.
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Geiger counter
20
A Geiger counter determines the amount of
ionization by detecting an electric current.
A thin window is penetrated by the radiation
and causes the ionization of Ar gas.
The ionized gas carried a charge and so
current is produced.
The current pulse generated when the
radiation enters is amplified and counted.
Chapter 22
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Slide 21
Biological Effects of Radiation
The penetrating power of radiation is a function of
its mass: -rays > -particles >> -particles.
When ionizing radiation passes through tissue it
removes an electron from water to form H2O+ ions.
The H2O+ ions react with another water molecule to
produce H3O+ and a highly reactive •OH radical.
Free radicals generally undergo chain reactions,
producing many radicals in the biomolecules.
Chapter 22
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Slide 22
Radiation Measurement
The Curie measures the number of atoms that
decay in one second. Curie: 1 Ci = 3.7 x 1010
disintegrations
The rad (radiation absorbed dose) measures
the radiation absorbed by the tissues of the
body.
The rem (Roentgen equivalent for man (rem) )
measures the biological damage.
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Calibration of film dosimeters
In calibrating film badges the object is to obtain a
series of curves relating radiation exposure to the
blackening of the film.
Different typesof film and holder require different
conditions of calibration.
Exposure-absorbance curves should be produced
for each new batch of films manufactured, and in
addition, for each set of films processed, a few
badges should be exposed to known doses to
check that there has been no change in the
exposure-absorbance curve
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Biological Effects of Radiation
Radiation absorbed dose (rad)
1 rad = 1 x 10-5 J/g of material
Roentgen equivalent for man (rem)
1 rem = 1 rad x Q
Quality Factor
-ray = 1
=1
= 20
Curie: 1 Ci = 3.7 x 1010
disintegrations/s
SI unit is the becquerel:
Bq = 1 disintegrations/s
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Units of Radiation Measurement
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Background Radiation
A person is exposed to
radiation from
naturally occurring
radioisotopes and
medical X rays.
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Effects of Radiation
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Radioactive Decay Rates
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11.5 Radioactive Half-Life
Half-life is
the time for
the radiation
level to
decrease
(decay) to
one-half of
the original
value.
decay curve
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The decay of a radioactive nucleus over
time is shown in the following fig 11.4
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Half-Lives of Some Radioisotopes
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Half-Life Calculations
After one half-life, 40 mg of a radioisotope will
decay to 20 mg. After two half-lives, 10 mg of
radioisotope remain.
40 mg x 1 x 1 = 10 mg
2
2
Initial
40 mg
1 half-life
20 mg
2 half-lives
10 mg
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Learning Check
The half life of I-123 is 13 hr. How much
of a 64 mg sample of I-123 is left after 26
hours?
1) 32 mg
2) 16 mg
3) 8 mg
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Solution
2) 16 mg
Half life
= 13 hrs
Number of half lives = 2
Amount remaining
= 64 mg x 1 x 1 = 16 mg
2
2
13 hrs
64 mg
13 hrs
32 mg
16 mg
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Medical Applications
Radioisotopes with short half-lives
Are used in nuclear medicine.
Have the same chemistry in the body as the
nonradioactive atoms.
In the body give off radiation that exposes a
photographic plate (scan), which gives an
image of an organ.
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Radioisotopes in Medicine
•
1 out of every 3 hospital patients will undergo a nuclear
medicine procedure
•
24Na,
•
131I,
t½ = 14.8 hr, emitter, thyroid gland activity
•
123I,
t½ = 13.3 hr, ray emitter, brain imaging
•
18F,
t½ = 1.8 hr, + emitter, positron emission tomography
•
99mTc,
t½ = 14.8 hr, emitter, blood-flow tracer
t½ = 6 hr, ray emitter, imaging agent
Brain images
with 123I-labeled
compound
23.6
37
Some Radioisotopes Used in
Nuclear Medicine
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Nuclear Medicine: Imaging
Thyroid imaging using Tc-99m
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Food Irradiation
•Food can be irradiated with rays from
60Co or 137Cs.
•Irradiated milk has a shelf life of 3 mo.
without refrigeration.
•USDA has approved irradiation of meats
and eggs.
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Learning Check
Which of the following radioisotopes are
most likely to be used in nuclear medicine?
1) 40K half-life 1.3 x 109 years
2) 42K half-life 12 hours
3) 131I half-life 8 days
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Solution
Which of the following radioisotopes are
most likely to be used in nuclear medicine?
Radioisotopes with short half-lives are used
in nuclear medicine.
2) 42K half-life 12 hours
3) 131I half-life 8 days
42
11.11 Nuclear Fission and Nuclear
Fusion
In nuclear fission, a large nucleus is
bombarded with a small particle.
The nucleus splits into smaller nuclei,
several neutrons and a great amount of
energy.
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Nuclear Fission
When a neutron bombards U-235, an
unstable nucleus of U-236 undergoes fission
(splits) to form smaller nuclei such as Kr-91
and Ba-142.
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Chain Reaction
A chain reaction
occurs when a
critical mass of
uranium undergoes
fission so rapidly
that the release of a
large amount of
heat and energy
results in an atomic
explosion.
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Nuclear Fusion
Fusion involves the combination of small
nuclei to form a larger nucleus.
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Learning Check
Indicate if each of the following is
1) nuclear fission or 2) nuclear fusion
___ A. A nucleus splits.
___ B. Large amounts of energy are released.
___ C. Small nuclei form larger nuclei.
___ D. Hydrogen nuclei react.
___ E. Several neutrons are released.
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Solution
Indicate if each of the following is
1) nuclear fission or 2) nuclear fusion
1 A. A nucleus splits.
1, 2 B. Large amounts of energy are released.
2 C. Small nuclei form larger nuclei.
2 D. Hydrogen nuclei react.
1 E. Several neutrons are released.
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Chapter Summary
Nuclear reaction: reaction that changes an atomic
nucleus, causing the change of one element into
another.
Radioactivity: Spontaneous emission of radiation
from nucleus of unstable atom.
radiation, radiation, and radiation are the three
major types of radiation.
The rate of nuclear reaction is expressed in units of
half life (t1/2).
High energy radiation of all type is known as
ionizing radiation.
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Chapter Summary Contd.
Radiation intensity is expressed in various ways
depending on the radiation properties measured.
- The curie (Ci) measures the number of
radioactive
disintigrations per second in a
sample.
- The Roentgen (R) measures the ionizing ability
of radiation;
- The rad measures the amount of radiation
energy absorbed per gram of tissue;
- The rem measures the amount of tissue damage
caused by radiation.
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Chapter Summary Contd.
Nuclear fission: Splitting of nucleus apart by the
bombardment of neutrons to give smaller
fragments. Enormous amount of energy is
released in the fission process.
Nuclear fusion: Combination of two lighter
nuclei to produce a heavier one. Like fusion,
fission also releases enormous amount of energy.
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End of Chapter 11
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