Download Nuclear Fusion

Ms. Sipe
Nuclear Chemistry
Reactions in the nuclei of atoms
 Nuclear reactions
 Changes in the nuclei
 Involve the emission of energy- rays or
particles
 Not affected by temperature, pressure , or
catalysts like regular chemical reactions
 In chemical rxns bonds break and rearrange to
form new substance (reactivity based on what
subatomic particle?)
Nuclear Chemistry
Types of nuclear reactions
 Fusion- combining of nuclei, releases a lot of energy
 Stars and the sun
 Fission- splitting of nuclei into smaller nuclei
 Radioactive Decay or radioactivity
 Reactions begin with unstable isotopes called radioisotopes
that undergo change to become stable
Nuclear Fusion
The energy emitted by the sun results from
nuclear fusion.
• Fusion occurs when nuclei combine to produce a nucleus of
greater mass.
• In solar fusion, hydrogen nuclei (protons) fuse to make helium
nuclei. A LOT OF ENERGY PRODUCED!
The reaction also produces
two positrons.
Nuclear Fission
The figure below shows how uranium-235 breaks into two smaller fragments
of roughly the same size when struck by a slow-moving neutron.
Neutron
91
36
Kr
Krypton-91
3
235
U 92
Uranium-235
(fissionable)
1
0
n
236
U 92
Uranium-236
(very unstable)
142
56
Ba
Barium-142
More neutrons are released by the fission.
These neutrons strike the nuclei of other uranium-235 atoms,
which cause chain reactions.
Recap: Fusion vs Fission
 Combining 2 light nuclei to
 Splitting a heavy nucleus
form a heavier nucleus
 Requires high T & P
 Powers stars & sun
into 2 nuclei with smaller
mass #
 Radioactive decay (w/o
neutron)
Types of Nuclear
Emissions/Radiation
Characteristics of Some Types of Radiation
Type
Consists of
Alpha
Alpha particles
radiation (helium nuclei)
Symbol
or
Beta
Beta particles
radiation (electrons)
or
a
Charge
Mass
(amu)
Common Penetrating
source
power
2+
4
Radium226
Low (0.05 mm body
tissue)
1/1837
~0
Carbon14
Moderate
0
Cobalt-60
b 1–
High-energy
Gamma
electromagnetic
radiation radiation
g
0
(4 mm body tissue)
Very high (penetrates
body easily)
Alpha Radiation
238
92
Radioactive
decay
U
Uranium-238
234
90
Th
Thorium-234
+
4
2
He (a emission)
Alpha particle
Mass # decreases by 4 & Atomic # decreases by 2
Beta Radiation
14
6
C →
Carbon-14
(radioactive)
1
0
n →
Neutron
14
7
N
+
0
–1
e (b emission)
Nitrogen-14
(stable)
1
1
p
Proton
+
Beta particle
0
–1
e
Electron
(beta
particle)
An electron resulting from the breaking apart of neutrons in
an atom
# of protons increases while #of neutrons decreases.
Same Mass #; Atomic # increases by one
Gamma Radiation
230
90
Th →
Thorium-230
234
90
Th →
Thorium-234
226
88
Ra +
Radium-226
234
91
Pa +
Protactinium
-234
4
2
He + g
Alpha
particle
0
–1
Gamma
ray
e + g
Beta Gamma
particle
ray
 Nuclei often emit gamma rays along with alpha or beta
particles during radioactive decay.
 Gramma ray – no mass/no electric charge - Does not alter
the atomic number or mass number of an atom.
Balancing Nuclear Equations
U-238 alpha decay- Helium particle emitted
238 U
92
Na -24
 ? + 23490Th
beta decay- electron emitted
24 Na
11
 ? + 2412Mg
Balancing Nuclear Equations
U-238 alpha decay- Helium particle emitted
238 U
92
Na -24
 42He + 23490Th
beta decay- electron emitted
24 Na
11
 0-1e + 2412Mg
Nuclear Chemistry
Application of Radioisotopes
 Smoke Detectors
 Food Irradiation
 Archaeological Dating
 Medical Uses
 Nuclear Power
 Nuclear Weapons
Applications of Nuclear Reactions
Nuclear power and Nuclear weapons
Most common nuclear fuel: Uranium-235, Plutonium-239
Difference btw power & weapon
Power – can control E release & convert to heat
Weapon – uncontrolled release of E
Power
 Nuclear energy – Fr ~80%, US 20%, Japan 35%, Germany –
30%
Weapon
 Fission weapons – Atomic bombs (A-bomb)
 Fusion weapons – Hydrogen bombs (H-bomb)
 Manhattan Project WWII
 Submarines – that use nuclear energy stay longer
underwater
A Few Pros and Cons
 No more need for oil
 Hard to control
 Not using fossil fuel
 Nuclear waste
 Fission > energy compared to
gasoline
 Will have unlimited amounts
of energy (esp if fusion works;
sun)
 No need for us to depend on
other countries
 Pollution
 Radiation
 Nuclear reactor – away from large
population, waterways, earthquake
zones
 Japan reactor explosion – then
cooling system fails so further
explosion or leak of radioactive
material can occur
 Nuclear reactor overheating –
explode like a nuclear weapon
 Nuclear weapon – destructive
potential
A half-life (t½) is the time required for one-half of
the nuclei in a radioisotope sample to decay to
products.
After each half-life,
half of the original
radioactive atoms
have decayed into
atoms of a new
element.
Half-Life
Comparing Half-Lives
Half-lives can be as short as a second or as long as billions of years.
Half-Lives of Some Naturally Occurring Radioisotopes
Isotope
Half-life
Radiation emitted
Carbon-14
5.73 × 103 years
b
Potassium-40
1.25 × 109 years
b, g
Radon-222
3.8 days
a
Radium-226
1.6 × 103 years
a, g
Thorium-234
24.1 days
b, g
Uranium-235
7.0 × 108 years
a, g
Uranium-238
4.5 × 109 years
a
Half-Life
Comparing Half-Lives
Uranium-238 decays through a complex series of unstable isotopes to the
stable isotope lead-206.
• The age of uranium-containing
minerals can be estimated by
measuring the ratio of
uranium-238 to lead-206.
• Because the half-life of
uranium-238 is 4.5 × 109 years,
it is possible to use its half-life
to date rocks as old as the
solar system.
Half Life Calculations
The half-life of beryllium-11 is 13.81 seconds.
Let's say you start with 16 grams of 11Be. After 13.81s, you have 8
grams of that isotope left (the rest will have decayed to something
else). After another 13.81s, you have 4 grams left; 13.81 seconds
more, and you have 2 grams left……so after 3 half lives berllium-11
decayed from 16g to 2 g. In chemistry, you set up tables like this:
Time
Amount remaining
0s
16 grams
13.81 s
8 grams
27.62 s
4 grams
41.43 s
2 grams
Practice Problem…
In a particular bone sample, you have 80g of a parent and
560g of a daughter isotope. The half life of the sample is
100 years. How old is the bone?
560g + 80g = 640 g for the original parent
640  320  160  80 equals 3 half lives
(3)(100 yrs) = 300 years old
Now, you try some…
Closure:
Germany said it would close all of its 17 nuclear reactors
by 2022, a sharp policy reversal that will make it the first
major economy to quit atomic power in the wake of the
nuclear crisis in Japan. Do you think USA should do the
same?
 Provide 3 reasons to support your answer