1. 7.3 Nuclear Reactions (text p 312-325)
You will learn:
Fission is a nuclear reaction in which a large nucleus breaks apart, producing two or more smaller nuclei, subatomic particles, and energy.
Fission is the source of energy for all nuclear power generation used today. The daughter products are often radioactive and are a significant waste disposal problem.
Fusion is a nuclear reaction in which small nuclei combine to produce a larger nucleus. Other subatomic particles as well as energy are released in this process.
Fusion is the source of energy in the Sun.
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2. How are Nuclear Reactions different from Chemical Reactions?
no changes to the nuclei
mass is conserved
energy changes are relatively small
nucleus of atoms changes by gaining or releasing particles or energy
protons, neutrons, electrons, and/or gamma rays can be lost or gained
Small changes of mass = huge changes in energy
Eg nuclear fission of 1 g of uranium -235 releases the same amount of energy as obtained from burning about 2 tonnes of coal.
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3. Crash Course Video https://www.youtube.com/watch?v=FU6y1XIADdg
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4. What is Nuclear Fission?
Nuclear fission is the splitting of one heavy nucleus into:
two or more smaller nuclei,
some sub-atomic particles,
and energy.
Heavy nuclei tend to be unstable due to repulsive forces between the many protons. In order to increase their stability, atoms with heavy nuclei may split into atoms with lighter nuclei.
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5. Why would an atom split apart?
Nuclear Fission
Why would an atom split apart?
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6. Why would an atom split apart?
Nuclear Fission
Why would an atom split apart?
Heavy nuclei tend to be unstable due to repulsive forces between the many protons. In order to increase their stability, atoms with heavy nuclei may split into atoms with lighter nuclei.
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7. What good is Nuclear Fission?
Nuclear Fission generates a lot of power
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8. Nuclear Fission recap
A heavy nucleus is usually unstable, due to many positive protons pushing apart.
When fission occurs:
Energy is produced.
Neutrons are released.
Albert Einstein’s famous equation E = mc2 illustrates the energy found in even small amounts of matter
See pages
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9. Induced Nuclear Reactions
Natural radioactive decay consists of the release of three types of radiation: alpha, beta and gamma radiation.
Induced Nuclear Reactions: Scientists create nuclear reactions by smashing nuclei with alpha, beta and gamma radiation.
Scientist make nuc unstable by smashing it with a, B or gamma
The difference is that the alpha particle is now a reactant, nt a product. The diagram can be written as a nuclear reaction
See pages
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10. Induced Nuclear Reactions
The rules for writing these equations are the same as earlier nuclear equations:
Mass numbers must equal on both sides of the equation
Charges must equal on both sides of the equation
Scientist make nuc unstable by smashing it with a, B or gamma
The difference is that the alpha particle is now a reactant, nt a product. The diagram can be written as a nuclear reaction
See pages
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11. Subatomic Particle Symbols
A hydrogen-1 nucleus can be written as 11H or as a proton, 11p because a proton and an hydrogen-1 nucleus are the same thing.
Proton notationshows that a proton has an satomic number of 1 (1 proton)and a mass number of 1 (1proton + O neutrons)
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12. Induced Nuclear Reactions
The main reaction in fission nuclear weapon and in Canadian nuclear power plants:
The uranium-235 nucleus absorbs a neutron briefly becoming uranium-236 which is unstable so it decays into two smaller nuclei releasing 3 neutrons and energy.
Scientist make nuc unstable by smashing it with a, B or gamma
The difference is that the alpha particle is now a reactant, nt a product. The diagram can be written as a nuclear reaction
See pages
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13. Nuclear Fission of Uranium-235
It is much easier to crash a neutral neutron than a positive proton into a nucleus to release energy.
When a nucleus of Uranium-235 is struck by a neutron, the nucleus absorbs the neutron. As a result, the mass number of the nucleaus increase by one. Because the number of protons has not changed, this is still an atom of uranium, just a different isotope.
But the new Uranium-236 is very unstable andimmdediatey splits apart into two smaller nucl, relaseing serveral neutrons and a lot of energy. The released neutrons trigger more fission reacions. 369….chain reaction
The induced nuclear fission of uranium-235. This nuclear reaction is the origin of nuclear power and nuclear bombs.
See pages
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14. Nuclear Fission of Uranium-235
When a stable nucleus of Uranium-235 is struck by a neutron , the nucleus absorbs the neutron.
As a result, the mass number of the nucleus increases by one, creating unstable uranium-236, which then undergoes radioactive decay.
Because the number of protons has not changed, this is still an atom of uranium, just a different isotope.
When a nucleus of Uranium-235 is struckby a neutron, the nucleus absorbs the neutron. As a result, the mass number of the nucleaus increase by one. Because the number of protons has not changed, this is still an atomof uranium, just a different isotope.
But the new Uranium-236 is very unstable andimmdediatey splits apart into two smaller nucl, relaseing serveral neutrons and a lot of energy. The released neutrons trigger more fission reacions. 369….chain reaction
See pages
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15. Nuclear Fission of Uranium-235
But the new Uranium-236 is very unstable and immediately splits apart into two smaller nuclei, releasing several neutrons and a lot of energy.
After several steps, atoms of krypton and barium are formed, along with the release of three neutrons and huge quantities of energy.
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16. Chain Reaction
The neutrons released in the induced reaction can then trigger more reactions on other uranium-235 atoms. 369 causing a chain reaction
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17. Once the nuclear fission reaction has started, it can keep going.
Chain Reactions
Once the nuclear fission reaction has started, it can keep going.
The neutrons released can then trigger more reactions on other uranium-235 atoms. This process where one reaction starts the next is called a chain reaction.
This chain reaction can quickly get out of control.
This danger is managed using materials that
absorb neutrons.
Nuclear reactors have
complex systems to ensure the
chain reaction stays at safe levels.
An uncontrolled chain reaction can result
in a violent nuclear explosion.
Nuclear bombs are created using this concept.
Nuclear Chain Reaction.
Once a nuclear fission reaction begins, it can initiate the next reaction, creating a chain reaction. The number of fissions and energy being released can increase rapidly and lead to a violent nuclear explosion..
How to keep the chain reaction from getting out of hand?
Enrico Fermi received Nobel Prize I physics in 1938 for his work on induced radioactivity. He realized that materials that absorb neurtons could be used to control the chain reaction.
See page 318
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18. Chain Reactions
Enrico Fermi used cadmium rods to absorb neutrons in the first reactor and control the chain reaction
Need image
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19. Nuclear Energy used to produce power comes from fission.
See page 312
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20. Nuclear Power Plants generate large amounts of electricity
Ontario, Quebec and New Brunswick currently generate nuclear power.
Eg CANDU (CANada Deuterium Uranium)
Deuterium is an isotope of hydrogen with a proton and neutron in its nucleus.
deuterium oxide (heavy water) moderator and its use of (originally, natural) uranium fuel.
CANDU reactors are considered
safe and effective and are sold
throughout the world.
Deuterium is an isotope of Hydrogen-1 that is twice as heavy asit has both a proton and a neutron.
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21. The Bruce Nuclear Generating Station on the shore of Lake Huron, in Ontario
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22. CANDU reactors fuel is bundles of rods with uranium pellets
How does it work?
CANDU reactors fuel is bundles of rods with uranium pellets
Each used for 15 months
Used ones are very radioactive
They must be stored in water pools for 10years
Then transferred to shielded storage containers
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23. Nuclear Energy: Advantages
Advantages of using Nuclear Energy:
Nuclear Energy produces fewer greenhouse gas emissions during the production of electricity compared to traditional sources like coal power plants.
Used in medical imaging.
Produce a lot of heat. Heat used to make steam used to power turbines that drive generators that produce electricity.
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24. CANDU Reactors and Hazardous Wastes
5. The CANDU reactors are known to be safe and easy to shut down in an emergency.
Inside a CANDU reactor.
Canada, South Korea, China, India, Argentina, Romania and Pakistan
Produce a lot of heat. Heat used to make steam used to power turbines that drive generators that produce electricity
See pages
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25. Nuclear Power: Disadvantages
Disadvantages of Nuclear Energy:
Like fossil fuels, nuclear fuels are non-renewable energy resources.
And if there is an accident, large amounts of radioactive material could be released into the environment.
Waste products of fission are radioactive and remains radioactive and is hazardous to health for thousands of years.
Sun uses fusion. Nuc Reaction use fission.
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26. Hazardous wastes produced by nuclear reactions are problematic.
Radioactive Waste
Hazardous wastes produced by nuclear reactions are problematic.
Used U-235 rods can be hazardous to get rid of as they continue to be radioactive for twenty half-lives (thousands of years). Some rods can be re-used, but others must be stored sealed inside concrete or metal containers underground.
Canada, South Korea, China, India, Argentina, Romania and Pakistan
Produce a lot of heat. Heat used to make steam used to power turbines that drive generators that produce electricity
Used U-235 rods can be hazardous to get rid of as they continue to be radioactive for twenty half-lives (thousands of years). Some rods can be re-used, but others must be stored sealed inside concrete or metal containers underground.
See pages
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27. Nuclear Fusion
Nuclear fusion is the joining of two light nuclei into one heavier nucleus.
Occurs in the sun
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28. The fusion of hydrogen nuclei
Nuclear Fusion
In the core of the Sun, two hydrogen nuclei join
under tremendous heat and pressure to form a
helium nucleus.
When the helium atom is formed, huge amounts
of energy are released.
Scientists cannot yet find a safe, manageable
method to harness the energy of nuclear fusion.
Need high pressure and temperature.
So-called “cold fusion” would occur at
temperatures and pressures that could be
controlled.
The fusion of hydrogen nuclei
In the sun, fusion occurs between Hydo=rogen-2 and hydrogen-3  huge energyradiation to us as light and heat.
High Temperature and pressure needed.
Container would melt.
See pages
Take the Section 7.3 Quiz
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29. Check your understanding
What is the standard atomic notation for a proton?
What is the majory difference between a chemical and nuclear reaction?
What do you call a nuclear reaction caused by bombarding nucleus with subatomic articles?
What is a chain reaction?
What do CANDU reactors use as fuel?
What happens to used CANDU reactor fuel bundles?
Fission or Fusion:
Used for electrical power generation
Joining of two lighter nuclei
Occurs in our sun\often creates radioactive products
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30. 7.3 Nuclear Reactions
Nuclear fission and fusion are processes that involve extremely large amounts of energy.
Fission = the splitting of nuclei
Fusion = the joining of nuclei
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