7.3 Nuclear Reactions:7.3 Nuclear Reactions:

• Nuclear reactions are different than chemical reactionsNuclear reactions are different than chemical reactions

Chemical Chemical ReactionsReactions

Mass is Mass is conserved conserved (doesn’t (doesn’t change)change)

Small Small energy energy changeschanges

No changes in the No changes in the nucleinuclei

Nuclear Nuclear ReactionsReactions

Small Small changes in changes in massmass

Huge Huge energy energy changeschanges

protons, neutrons, protons, neutrons, electrons and electrons and gamma rays can be gamma rays can be lost or gainedlost or gained

Induced Nuclear ReactionsInduced Nuclear Reactions

• Scientists can also force ( = induce) nuclear reactions by Scientists can also force ( = induce) nuclear reactions by smashing nuclei with alpha, beta and gamma radiation to smashing nuclei with alpha, beta and gamma radiation to make the nuclei unstablemake the nuclei unstable

4 14 17 12 7 8 1 + N O + p

4 14 17 12 7 8 1He + N O + H

or

Symbols to Remember:Symbols to Remember:

Nuclear ReactionsNuclear Reactions

• Two typesTwo types::

• FissionFission = the splitting of nuclei = the splitting of nuclei

• FusionFusion = the joining of nuclei (they = the joining of nuclei (they fusefuse together)together)

• Both reactions involve extremely large Both reactions involve extremely large amounts of energyamounts of energy

Albert Einstein’s equation E = mc2 illustrates the energy found in even small amounts of matter

1. Nuclear Fission:1. Nuclear Fission:

• Nuclear fissionNuclear fission is the splitting of one heavy is the splitting of one heavy nucleus into two or more smaller nuclei, as well nucleus into two or more smaller nuclei, as well as some sub-atomic particles and energy.as some sub-atomic particles and energy.

• A heavy nucleus is usually unstable, due to A heavy nucleus is usually unstable, due to many positive protons pushing apart.many positive protons pushing apart.

• When fission occursWhen fission occurs::

1.1.Energy is produced.Energy is produced.

2.2.More neutrons are given off.More neutrons are given off.

Induced Nuclear FissionInduced Nuclear Fission

• Neutrons are used to make nuclei unstableNeutrons are used to make nuclei unstable• It is much easier to crash a neutral neutron than a positive proton It is much easier to crash a neutral neutron than a positive proton

into a nucleus to release energy.into a nucleus to release energy.

Induced Nuclear Fission of Uranium-235Induced Nuclear Fission of Uranium-235

• is the origin of nuclear power and nuclear bombs.

• A neutron, , crashes into an atom of stable uranium-235 to create A neutron, , crashes into an atom of stable uranium-235 to create unstable uranium-236, which then decays.unstable uranium-236, which then decays.

• After several steps, atoms of krypton and barium are formed, along After several steps, atoms of krypton and barium are formed, along with the release of 3 neutrons and huge quantities of energy.with the release of 3 neutrons and huge quantities of energy.

10n

Chain Reactions:Chain Reactions:

• The neutrons released in the induced reaction can The neutrons released in the induced reaction can then trigger more reactions on other uranium-235 then trigger more reactions on other uranium-235 atoms…causing a atoms…causing a CHAIN REACTIONCHAIN REACTION

• A chain reaction can quickly get out of controlA chain reaction can quickly get out of control• materials that absorb some neutrons can help to control the chain materials that absorb some neutrons can help to control the chain

reaction.reaction.

• Nuclear reactors have complex systems to ensure the chain Nuclear reactors have complex systems to ensure the chain reaction stays at safe levels.reaction stays at safe levels.

• An uncontrolled chain reaction can result in the release of An uncontrolled chain reaction can result in the release of excess energy as harmful radiationexcess energy as harmful radiation

• It is on this concept that nuclear bombs are created.It is on this concept that nuclear bombs are created.

• Nuclear “meltdown” occurs if the chain reactions cannot be Nuclear “meltdown” occurs if the chain reactions cannot be controlledcontrolled

Nuclear energy used to produce Nuclear energy used to produce power comes from fissionpower comes from fission

• Nuclear power plants can generate large amounts of Nuclear power plants can generate large amounts of electricity.electricity.• In Canada, Ontario, Quebec and New Brunswick In Canada, Ontario, Quebec and New Brunswick

currently use nuclear power.currently use nuclear power.• Canadian-made nuclear reactors are called CANDU reactors.Canadian-made nuclear reactors are called CANDU reactors.

• CANDU reactors are considered safe and effective, and are CANDU reactors are considered safe and effective, and are soldsold

throughout the world.throughout the world.

The Bruce Nuclear Generating Station on the shores of Lake

Huron, in Ontario

CANDU ReactorsCANDU Reactors

• CANDU reactors are found in various countries CANDU reactors are found in various countries around the world.around the world.

• Canada, South Korea, China, India, Argentina, Romania Canada, South Korea, China, India, Argentina, Romania and Pakistanand Pakistan

• The reactors are known to beThe reactors are known to be safe and easy to shut down insafe and easy to shut down in an emergency.an emergency.

• Heat energy produced turnsHeat energy produced turns electricity-generating turbines.electricity-generating turbines.

Hazardous WastesHazardous Wastes

• Hazardous wastes produced by nuclear reactions Hazardous wastes produced by nuclear reactions are problematic.are problematic.• Some waste products, like fuel rods, can be re-usedSome waste products, like fuel rods, can be re-used• Some products are very radioactive, and must be Some products are very radioactive, and must be

stored away from living things.stored away from living things.• Most of this waste is buried underground, or stored in Most of this waste is buried underground, or stored in

concreteconcrete

• It takes 20 half-lives (thousands of years) before the It takes 20 half-lives (thousands of years) before the material is safe.material is safe.

Provincial Exam QuestionProvincial Exam Question

2. Nuclear Fusion2. Nuclear Fusion

• joining of two light nuclei into joining of two light nuclei into one heavier nucleus.one heavier nucleus.• In the core of the Sun, two In the core of the Sun, two

hydrogen nuclei join under hydrogen nuclei join under tremendous heat and pressure to tremendous heat and pressure to form a helium nucleus.form a helium nucleus.

• When the helium atom is formed, When the helium atom is formed, huge amounts of energy are huge amounts of energy are released. released.

The fusion of hydrogen

nuclei

Provincial Exam QuestionProvincial Exam Question

Provincial Exam QuestionProvincial Exam Question

Provincial Exam QuestionProvincial Exam Question

Which isotope correctly completes the following nuclear reaction?

A. Helium-4B. Barium-141C. Strontium-90D. Cesium 143

• Scientists cannot yet find a safe, and manageable Scientists cannot yet find a safe, and manageable method to harness the energy of nuclear fusion.method to harness the energy of nuclear fusion.• ““cold fusion” would occur at temperatures and cold fusion” would occur at temperatures and

pressures that could be controlled (but we haven’t pressures that could be controlled (but we haven’t figured out how to get it to happen)figured out how to get it to happen)

Take the Section 7.3 Quiz