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Nuclear Chemistry
Unit 15
I. Nuclear Reactions
A. Involve a change in the nucleus of the
atom
1. made of protons and neutrons (called
nucleons together)
2. atoms referred to as nuclides, identified
by number of protons and neutrons
carbon – 14 or nuclear symbol (board)
B. Stability
1. For low atomic numbers the ratio of
protons:neutrons should be 1:1, for high
atomic numbers, the ratio should be 1:1.5
(neutrons help hold it together)
2. Even number of nucleons usually
stable.
3. Others unstable - can undergo
transmutations - change in nucleus
identity because protons change
(converts one element to another)
C. Radiation produced in
nuclear change
Capture: taken in, Emission: given off)
1. alpha particle – helium nucleus, , 42He
2. beta particle – electron, β (on right), 0–1e
3. positron – like electron but positive, 0+1e
4. electron capture (K capture) – electron,
on left, 0–1e
5. neutron - 10n
6. gamma rays – energy, 00γ
D. Writing and Balancing
Nuclear Equations
Mass must be equal on both sides
Therefore, the top numbers must be add to the
same number on both sides
Charge must be equal on both sides
Therefore, the bottom numbers must add to the
same number on both sides
Find the missing numbers
Identify the particle or element (look on the
periodic table for the bottom number)
Nuclear Equations Examples:
Q. Write the nuclear 14
equation for C-14(β) 6 C
0
14
→ -1 e + 7 N
Q. Write the nuclear 209
4
205
+
→
Po
He
209
84
2
82 Pb
equation for Po(α)
Q. Complete this fission reaction:
235
1
1
139
94
+
0 n → 3 0 n + 56 Ba + 36 Kr
92 U
HalfHalf-Life
Half-life is the time is takes a sample to
decay to half its original amount.
Half-Life Demonstration from GCSE
Examples: (on board)
1. What fraction will remain after 15 days if
the half life is 36 hours?
2. How many g of a 100 g sample will
remain after 4 half-lives?
Radioactive Dating
N-14 converts to C-14 in the upper
atmosphere. There has been a constant rate
of production in the past 75 years.
C-14 is part of the CO2 ingested by plants and
animals. When something dies, it stops
ingesting and the C-14 starts to decay. The
half-life is 5715 years.
Organic materials can be dated back to
50,000 years. Carbon dating agrees with tree
ring data within 10%.
Minerals and rocks can be dated
back to as many as 4 billion years.
Other Applications
2. Radioactive tracers: help doctors
follow the transport of materials through
the body. Help diagnose cancer and
other diseases.
3. Agriculture: determine how much
fertilizer is absorbed by plants, increase
shelf-life of food (irradiation kills bacteria
and insects)
4. Cancer treatment
III. Biological Effects of
Radiation
A. Everyone is subject to background radiation.
About .1 rem per year. Other sources include
cosmic rays, medical/dental x-rays/other tests.
B. Damage to nucleic acids (DNA/RNA) is
worst type.
C. Radiation affects cells that are undergoing
cell division the most. Most at risk:
1. Children (especially developing fetuses)
2. Cancer cells (cancer is just uncontrolled cell
division)
D. Penetrating abilities
1. Alpha: least penetrating - only travels a
few cm, stopped by paper or skin , most
damaging - can cause damage if ingested
or inhaled
2. Beta: medium penetration and damage travel close to speed of light, 100 times
more penetrating than alpha, stopped by
thin sheet of metal (like aluminum)
3. Gamma: most penetrating, least
damaging - stopped by thick sheet of lead
&/or concrete
Damage can be affected
by:
Time – how long you are exposed
Shielding – radiation absorbing
material
Distance – how far away from source
Amount of radiation (usually can’t control
this, except with medical imaging like xrays)
Nuclear Fission
Chemical reactions involve
outer electrons
Nuclear reactions involve changes in nuclei
Nuclear Fission – breaking apart of heavy
nuclei into two parts
A. Some happens spontaneously - radioactive decay
series like uranium-235
B. Others need bombardment by neutrons
1. Can start a chain reaction - produces neutrons which
can also start reactions
2. Must reach critical mass before it can be sustained
a. uncontrolled - explosion
b. controlled - nuclear reactor to create energy or
radioactive nuclides for medical or agricultural use
Nuclear Reactors
(Fission only)
All are fission reactors - fusion reactors require more
energy than they give back (future??)
Shielding: radiation-absorbing material
Fuel rods contain enriched uranium pellets
Control Rods (boron, cadmium, gadolinium) – absorbs
neutrons to slow or shut down reaction (alternate with fuel
rods )
Moderators – slow down neutrons to sustain reaction
Coolant – water is most common, energy gained
can power generator
Small amount of waste produced
Compare nuclear vs. coal power plants
Nuclear Fusion
Joining of two light nuclei into a heavier,
more stable nucleus
A. Powers the sun and stars - hydrogen
joins to form helium
B. Hydrogen Bomb
1. Uncontrolled fusion
2. Fission gives heat and pressure to cause
fusion
Fusion Reactors
(Don’t exist yet)
FUTURE?? – none now
1. Advantages:
a. fuel is cheap and available (use
seawater)
b. little or no radioactive waste
2. Major Problem: very high activation
energy (high temps needed) not energy
efficient yet