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
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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
7
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
9
 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
11
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.

15
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.
19
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
30
The decay of a radioactive nucleus over
time is shown in the following fig 11.4

31
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
38
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.
46
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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