1. How is atomic mass calculated?
• Relative atomic mass of an element is the
weighted average of the masses of the
isotopes of the naturally occurring element;
found on periodic table
• Relative abundance is a ratio of the naturally
occurring isotopes of an element on Earth
2. Example 1: Average Atomic Mass of C
Isotope Percent abundance Atomic mass (amu)
• Data: 12C 98.9% 12
13C 1.1% 13
• Atomic mass =
(relative abundance of isotope 1)(mass of isotope 1) +
(relative abundance of isotope 2)(mass of isotope 2) +
(relative abundance of isotope 3)(mass of isotope 3) + ...
3. Example 2: Average Atomic Mass of Cl
Isotope Percent abundance Atomic mass (amu)
• Data: Chlorine-35 75.76%
Chlorine-37 24.24%
• Atomic mass =
(relative abundance of isotope 1)(mass of isotope 1) +
(relative abundance of isotope 2)(mass of isotope 2) +
(relative abundance of isotope 3)(mass of isotope 3) + ...
4. Example 2: Relative abundance of Cu
Isotope Rel. abundance Atomic mass (amu)
• Data: Copper-63
Copper-65
• n = relative abundance of one isotope
• (n)(mass of isotope 1) + (1 – n)(mass of isotope 2) = average mass
5. Review: Nuclear Symbols
• What is the mass number of 14 C ?
6
(“carbon-14”)
• How many protons are in 141 I -1 ?
53
• What is the symbol for uranium-238? 238
U
92
6. Write these nuclear symbols!
• P = 47 n = 50 e = 48
• P = 82 n = 80 e = 82
• P = 11 n = 15 e = 17
7. Nuclear Chemistry
• Radioactive decay occurs when an unstable
nucleus releases energy by emitting radiation
• Radiation refers to the penetrating rays and
particles emitted by a radioactive source
• Types of radiation:
– Alpha (α)
– Beta (β)
– Gamma (γ)
8. Alpha (α) Radiation
• Nucleus decays by emitting an alpha particle
4
– Symbols: α or He
2
– Contains two protons and two neutrons
– Charge: +2
• Example:
230 226 4
90 Th 88 Ra 2 He
(Alpha
• Blocked by: _____________ particle)
9. Beta (β) Radiation
• Nucleus decays by emitting a beta particle
• General forms:
1 0
0
1
n 1H 1 e
(neutron) (proton) (β- particle)
1 1 0
1H 0 n 1e
(proton) (neutron) (β +particle)
27 27 0
• Example: 12 Mg 13 Al 1 e
(electron, or β- particle)
• Blocked by: _____________
10. Gamma (γ) Radiation
• High-energy radiation (photons) emitted from
decaying nuclei
• Often accompanies alpha or beta radiation
• Blocked by: _____________
11. Electron Capture
• Nucleus decays by capturing an electron and
emitting a neutron
• General forms:
1 0 1
1 H e
1 0n
(proton) (electron) (neutron)
26 0 26
• Example: 13 Al 1e 12 Mg ve
(electron) (neutrino)
• Neutrinos blocked by: _____________
13. Review: Types of Radiation
• Alpha Radiation
238 234 4
92 U 90 Th 2 He
• Beta Radiation
137 137 0
55 Cs 56 Ba 1 e
• _________Radiation (with _______ ray)
Alpha gamma
241 237 4
95 Am 93 Np 2 He
14. Why do atoms emit radiation?
• Unstable atoms emit one
of the three types of
radiation to become
stable
• Atoms with a number of
neutrons that is equal to
or greater than the
number of protons tend
to be stable
• This is graphed and
known as the band of
stability
15. Nuclear Binding Energy
• The energy liberated when a nucleus is
created from other nuclei
• Derived from the strong nuclear force, the
force holding protons and neutrons together
in the nucleus AND the force holding quarks
and gluons together to make protons and
neutrons
16. Review
• Radioactive atoms have unstable nuclei
because of the ratio of protons to neutrons.
• Unstable nuclei eventually break down,
forming a completely different type of atom
– This is radioactive decay
• Although radioactive isotopes decay at a
constant rate, we cannot predict exactly when
an individual atom will decay
18. Definition of Half-Life (t ½)
• The time it takes to reduce the number of
nuclei of an isotope in a sample by ½
• After each half-life, we expect half of the
existing radioactive atoms to have decayed
into atoms of a new element.
21. Half-Life is Exponential Decay
100%
Amount of
sample (g)
1/2
t ½ = 2 days
1/4
1/8
1/16
1/32
Days
22. After 24 days, 10.0 grams of thorium-
234 have decayed to 5.0 grams. What
is the half-life of Th-234?
A. 5 days
B. 10 days
C. 12 days
D. 24 days
23. True or false: After 48 days, all of the
initial 10.0 grams of Th-234 will have
undergone radioactive decay.
A. True
B. False
24. Fluorine-18 has a half-life of 110
minutes. If you begin with 110 atoms
of 18F, how many atoms of 18F will
remain after 110 minutes?
A. Exactly 110 atoms
B. Approximately 110 atoms
C. Exactly 55 atoms
D. Approximately 55 atoms
E. Impossible to predict
25. Half-Life Calculations
• Manganese-56 has a half-life of 2.6 hours.
What is the mass of manganese-56 in a 16
gram sample of the isotope after 10.4 hours?
10.4 h / 2.6 h = 4 half-lives have passed
(16 g)(½)(½)(½)(½) = 1.0 g
or (16 g)(½)4 = 1.0 g
26. Half-Life Calculations
• What is the half-life of a 100.0 g sample of
nitrogen-16 that decays to 12.5 g of nitrogen-
16 in 21.6 seconds?
• How many half-lives have elapsed?
100.0 g 50.0 g 25.0 g 12.5 g
3 half-lives have elapsed
• 21.6 seconds / 3 half-lives = 7.20 seconds
27. Half-Life Calculations
• The mass of cobalt-60 in a sample is found to
have decreased from 0.800 g to 0.200 g in a
period of 10.5 years. From this information,
calculate the half-life of cobalt-60.
28. Fractional # of Half-Lives
• If we start with 20.0 g of nitrogen-14, how
much would remain after 30.0 seconds? The
half-life of nitrogen-14 is 21.3 seconds.
• 30.0 s / 21.3 s = 1.41 half-lives
• (20.0 g)(½)1.41 = 7.53 g
29. Test Your Understanding
• For each of the following radiation sources or
processes, would a long or a short half-life
desirable?
– Smoke detectors
– Carbon dating
– Medical diagnostic imaging
– Nuclear fuel rods
31. Fission vs. Fusion
• Fission: A nuclear reaction in which a heavy
isotope splits into smaller fragments, often in a
chain reaction
– Ex: Nuclear Reactors, Atomic Bomb
• Fusion: The combining of two small nuclei to
form a larger, more stable nucleus with the
release of energy
– Produces the most energy and is difficult to contain.
– Ex: Sun, Hydrogen Bomb, Fusion Reactors
– Both fission and fusion release large amounts
of energy (though fusion releases more)
35. Nuclear Fission Nuclear Fusion
Fission is the splitting of a large atom Fusion is the fusing of two or more
Definition:
into two or more smaller ones. lighter atoms into a larger one.
Fission reaction does not normally
Natural occurrence of the process: Fusion occurs in stars, such as the sun.
occur in nature.
Fission produces many highly
Byproducts of the reaction: Few radioactive particles are produced.
radioactive particles.
A million times greater than that
The energy released by fusion is three
released in chemical reactions; but
Energy Released: to four times greater than the energy
lower than the energy released by
released by fission.
nuclear fusion.
One class of nuclear weapon is a fission One class of nuclear weapon is the
Nuclear weapon: bomb, also known as an atomic bomb hydrogen bomb, which uses a fission
or atom bomb. reaction to "trigger" a fusion reaction.
Critical mass of the substance and High density, high temperature
Conditions:
high-speed neutrons are required. environment is required.
Takes little energy to split two atoms in
Energy requirement: Extremely high energy is required.
a fission reaction.
http://www.diffen.com/difference/Nuclear_Fission_vs_Nuclear_Fusion
36. Nuclear Power Plant
• Nuclear reactors use controlled fission to
produce useful energy.
• How does this work?
– Fission produces lots of heat energy.
– Coolant fluid removes heat from reactor core.
– Heat generates steam.
– Steam drives a turbine, creating electricity.
38. Controlling the Nuclear Reaction
• Control rods: Keep
reaction from going too
fast by absorbing some of
the neutrons; often
made of cadmium
• Moderator: slows down
neutrons so that the
reactor fuel (235U or 239Pu)
can capture them; water
and graphite are good
moderators
39. Meltdown!
• If the chain reaction
goes too fast, it gets too
hot and the coolant
fluid cannot take the
heat away fast enough,
possibly leading to a
meltdown.
40. Three Mile Island
• 1979
• Middletown,
Pennsylvania
• Partial
meltdown
due to
stuck-open
valve which
allowed lots
of coolant to
escape
41. Three Mile Island generator moving to Shearon Harris
Posted: Jan. 22, 2010
MIDDLETOWN, Pa. — A generator in storage for more than three decades following
the accident at Three Mile Island nuclear power plant is heading to North Carolina.
Officials at the Nuclear Regulatory Commission say the electrical generator from the
damaged Unit 2 reactor at TMI will be used at Progress Energy Inc.'s Shearon
Harris nuclear plant in southwest Wake County.
NRC spokesman Neil Sheehan said Thursday that preliminary work is under way to
move the generator. It will be transported in two parts, weighing a combined 670
tons.
Progress Energy spokeswoman Julia Milstead said the generator is coming from the
non-nuclear side of TMI. The generator has been refurbished, and the parts were
extensively tested to ensure they weren't contaminated.
The Raleigh-based utility will save money by using the older generator instead of
buying a new one, meaning the cost savings can be passed on to its customers,
Milstead said.
The generator will be shipped to Shearon Harris by rail and will not impact traffic on
any area roads, she said.
TMI's Unit 2 reactor has been shut down since a partial meltdown in 1979.
43. What do you do with spent fuel?
• Nuclear waste (leftover
fuel and fission
products) must be
stored in “holding
tanks” filled with water
for a few years.
• Eventually, they are
taken to a more
permanent storage
facility.
44.
45. Chernobyl
• 1986
• Ukraine (formerly USSR)
• Full meltdown due to a
safety test gone awry
• Soviet-designed RBMK
reactor had serious
design flaws
• No containment dome
• Last Chernobyl reactor
taken offline in 2000
• Other RMBK reactors still
in use in Eastern Europe
