* The half-life of I-123 is 13 hours * We want to know how much is left after 39 hours * 39 hours is 3 half-lives (39/13 = 3) * Each half-life, the amount is reduced by half * Starting with 64 mg: ** After 1 half-life: 64/2 = 32 mg ** After 2 half-lives: 32/2 = 16 mg ** After 3 half-lives: 16/2 = 8 mg * Therefore, the amount left after 39 hours is 8 mg.

1. NUCLEAR CHEMISTRY

2. Radioactivity
Radioactivity was 1st
discovered by Antoine
Becquerel, when
a photographic plate
never exposed to
sunlight in his lab had become exposed.
The only possible culprit was a nearby
uranium salt sitting on the bench top.

3. History of Radioactivity
The term radioactivity
was 1st used by Marie
Curie in 1898. Curie
and her husband, Pierre,
found that radioactive
particles were emitted as
either electrically
negative which were
called beta particles (β)
or positive particles
called alpha particles (α).

4. Nuclear Chemistry
Nuclear
reactions are
reactions that
affect the
nucleus of the
atom.

5. Radioactivity is the
phenomenon of
radiation (particles
and/or energy) being
ejected
spontaneously by
an unstable nucleus
until it reaches a
more stable
arrangement.

6. Nuclear Stability
is determined by
the ratio of
protons to
neutrons in the
nucleus.

7. Composition & Structure of
Nucleus
A. Nucleons
1. Protons
2. Neutrons
B. Strong nuclear force
–The force that holds the
nucleons together

8. Characteristics of a nuclear
reaction
1. Isotopes of one elements are
changed into isotopes of another
element
2. Contents of the nucleus change
3. Large amounts of energy are
released

9. Radioactive decay is the process
by which the unstable nuclei lose
mass and/or energy by emitting
radiation.
Eventually unstable nuclei
achieve a more stable state
when they are transformed into
atoms of a different element.

10. This graph
shows the
stable
nuclei in
red. There
are several
things to
notice:

11. •There are no
stable nuclei
with an
atomic
number
higher than
83 or
a neutron
number
higher than
126.

12. •The more
protons in the
nuclei, the more
neutrons are
needed for
stability. Notice
how the stability
band pulls away
from the P=N
line.

13. •Stability is
favored by even
numbers of
protons and even
numbers of
neutrons. 168 of
the stable nuclei
are even-even
while only 4 of the
stable nuclei are
odd-odd.

14. Types of Radioactive Decay
When unstable nuclei decay, the
reactions generally involve the
emission of a particle and or energy.
For each type of decay, the equation is
balanced with regard to atomic number
and atomic mass. In other words, the
total atomic number before and after the
reaction are equal. And the total atomic
mass before and after the reaction are
also equal.

15. Transmutation
When particles
break down in the
nucleus in an atom
of an element
(radioactive decay),
the element
changes into
another element.
This is called
transmutation.

16. TYPES OF RADIATION
Gamma emission is the high energy
electromagnetic radiation given off in
most nuclear reactions. GAMMA
RAYS ARE NOT MATTER, THEY
ARE ENERGY. Therefore, they are
not involved in balancing the nuclear
equation. They are very damaging
and difficult to shield against.

17. Types of nuclear reactions
1. Radioactive decay - emission of the
following particles:
– Gamma
– Alpha
– Beta
– positron
2. Nuclear disintegration - emission of a
proton (p+) or a neutron (n0)
3. Fission - splitting of the nucleus
4. Fusion - combining of nuclei

18. Gamma Emission (γ)
Generally accompanies other radioactive
radiation because it is the energy lost from
settling within the nucleus after a change.

19. Happens when
the atomic
number is
greater than 83
The 2 p+ 2n
( ) loss
brings the atom
down and to the
left toward the
belt of stable
nuclei.
Alpha Particle Emission (α)
He4
2
4
2
He

20. Alpha Particle Emission (α)
Uranium - 238 Thorium - 238 Alpha Particle (α)

21. BETA EMISSION (β)
A beta particle (a high energy electron,
charge of -1) is emitted from the
nucleus as a neutron is converted into
a proton.
eNC 0
1
14
7
14
6 
Carbon - 14
Nitrogen - 14
Beta
Particle

22. Beta Particle Emission (β)
Happens to nuclei
with high
neutron:proton
ratio
A neutron
becomes a proton
causing a shift
down and to the
right on the
stability graph

23. Positron Emission
A positron is an antimatter particle that has the
same mass as an electron but has a positive
charge. A positron is emitted from the nucleus
as a proton is converted to a neutron.
eOF o
1
18
8
18
9 
Fluorine - 18 Oxygen - 18 Positron

24. Positron Emission
Happens to nuclei
with a low
neutron:proton
ratio
A proton becomes
a neutron causing
a shift up and to
the left

25. This graph
shows all
the trends of
decay and
the band of
stable nuclei

26. Penetrating Power of Radiation

27. Nuclear Chemistry
Name Symbol
Particle
Emitted
Mass
Atomic
Number
What is
Happening?
Blocked
By
Alpha
Helium
Nucleus
Decrease by
4
Decrease
by 2
Helium
nucleus is
given off
Paper
Beta
High Speed
Electron
No Change
Increase by
1
Neutron
changes to
Proton
Metal
Gamma
High Speed
Photon
No Change No Change
Accompanies
Alpha & Beta
Decay
Partially by
Lead &
Concrete
4He2
0β-1
0 γ0

28. Decay Series
• A series of radioactive nuclides produced
by successive radioactive decay until a
stable nuclide is reached.

29. Decay Series for Uranium - 238

30. Artificial Nuclear Reactions
New elements or new isotopes of known elements are
produced by bombarding an atom with a subatomic particle
such as a proton or neutron -- or even a much heavier
particle such as 4He and 11B.
Reactions using neutrons are called
g reactionsbecause a g ray is usually emitted.
Radioisotopes used in medicine are often made by g reactions.

31. Artificial Nuclear Reactions
Example of a g reaction is
production of radioactive 31P for use
in studies of P uptake in the body.
31
15P + 1
0n ---> 32
15P + g

32. Transuranium Elements
Elements beyond 92 (transuranium) made
starting with an g reaction
238
92U + 1
0n ---> 239
92U + g
239
92U ---> 239
93Np + 0
-1b
239
93Np ---> 239
94Pu + 0
-1b

33. Radiation Detection
Film badges
are used to
monitor the
amount of
radiation
exposure
people have
received.

34. Geiger Counter
Instrument that
detects radiation
by measuring
current
produced
by gas particles
ionized by
radioactivity

35. Uses for Nuclear Radiation
Since the physical and chemical
properties of radioisotopes of an
element are the same as stable ones,
many uses for radioactive nuclides are
possible.

36. In medicine radioactive nuclides are used to
destroy cancer cells and as tracers to tract
substances through the body or identify
cancer and other diseases.
Cobalt - 60 Radioactive Tracer

37. In agriculture,
radioactive
nuclides are
used as tracers
in fertilizer to
determine the
effectiveness or
to prolong shelf
life of food by
irradiating to
destroy
microorganisms.

38. In dating
radioactive
nuclides are
used to
determine
the age of
objects.
Example:
Carbon -14
is used to
date
organic
materials.

39. In energy production, currently nuclear
fission is used to create energy.
Example: Comanche Peak nuclear
power plant in Glen Rose produces
energy that is used by TXU Energy.

40. Nuclear Waste
Nuclear fission produces radioactive
wastes that must be contained and
stored on-site (temporary) or disposed
of (permanent).

41. Containment
• Radioactive waste from medical research
has half-lives of only a few months.
• Waste in nuclear reactors will take
hundreds to thousands of years to decay.

42. Storage
• Spent fuel rods from nuclear power plants
are stored in either water pools or dry
casks.
• This is temporary and at some point the
rods must be moved to underground
storage facilities

43. Disposal
• There are 77 disposal sites in the U.S.
• Disposal sites are created with the
intention of never going back for the spent
fuel rods.
• The current storage permanent disposal
site is WIPP near Carlsbad, NM.

44. Nuclear Fission

45. Nuclear Fission
Fission is the splitting of atoms
These are usually very large, so that they are not as stable
A chain reaction begins wherein the material that starts
the reaction is also one of the products of the reaction,
and can start another reaction.

46. Representation of a fission process.

47. Nuclear Fission & POWER
• Currently about 103
nuclear power plants
in the U.S. and about
435 worldwide.
• 17% of the world’s
energy comes from
nuclear.

48. World Nuclear Power

49. US Nuclear Power

50. Nuclear Power Plants
• Shielding (containment shell): radiation-
absorbing materials that prevent exposure
to gamma rays
• Control rods: neutron-absorbing rods that
control the reaction by limiting the number
of free neutrons
• Moderator: slows down the fast neutrons
by fission

51. Diagram of a nuclear power plant.

52. Nuclear Power Accidents
Three Mile Island, Pennsylvania
March 28, 1979
•a. No one is killed
•b. Very little radiation
released

53. Nuclear Power Accidents
Chernobyl, Ukraine
April 1986
•a. 30 people killed
initially
•b. Large area
uninhabitable
Chernobyl, Ukraine
Unit 4 Reactor
Destroyed
http://www.youtube.com/watch?v=-NlP2-Sbl9w

54. Chernobyl Disaster Documentary

55. Nuclear Power Accidents
Fukushima Daiichi
March 11, 2011
•a. No immediate deaths
•b. failure occurred because the plant was hit by
a tsunami caused by an earthquake

56. Nuclear Fusion
Fusion
small nuclei combine
2H + 3H 4He + 1n +
1 1 2 0
Occurs in the sun and other stars
Energy

57. Nuclear Fusion
Fusion
• Excessive heat can not be contained
• Uncontrolled fusion reactions of
hydrogen are the source of hydrogen
bombs.
• Attempts at “cold” fusion have FAILED.
• “Hot” fusion is difficult to contain

58. Half-Life
Half-Life (t1/2) is
the time
required for half
of the atoms of
a radioisotope
to emit radiation
and to decay to
products.

59. Half-Life
Decay of 20.0 mg of 15O. What remains after 3 half-lives?
After 5 half-lives?

60. Kinetics of Radioactive Decay
For each duration (half-life), one half of the substance
decomposes.
For example: Ra-234 has a half-life of 3.6 days
If you start with 50 grams of Ra-234
After 3.6 days > 25 grams
After 7.2 days > 12.5 grams
After 10.8 days > 6.25 grams

61. Learning Check!
The half life of I-123 is 13 hr. How much of
a 64 mg sample of I-123 is left after 39
hours?