1. 7.3 Nuclear Reactions

2. Radioactivity &
Radioactive Decay

3. S CAESAR..B.E Mays H.S Standards-SP2 a & b Grade: 9,10,11,12
Description: SP2 Students will evaluate the significance of energy in understanding the structure of matter and the universe.
Elements: a. Relate the energy produced through fission and fusion by stars as a driving force in the universe. b. Explain how the instability of radioactive isotopes results in spontaneous nuclear reactions.

4. Describe the cause and types of radioactivity.
Chapter 30 Objectives
Describe the cause and types of radioactivity.
Explain why radioactivity occurs in terms of energy.
Use the concept of half-life to predict the decay of a radioactive isotope.
Write the equation for a simple nuclear reaction.
Describe the processes of fission and fusion.

5. Chapter 30 Vocabulary Terms
radioactive
alpha decay
beta decay
gamma decay
radiation
isotope
radioactive decay
shielding
fission reaction
CAT scan
ionizing
nonionizing
ultraviolet
fusion reaction
nuclear waste
neutron
half-life

6. 30.1 Radioactivity
The word radioactivity was first used by Marie Curie in
She used the word radioactivity to describe the property of certain substances to give off invisible “radiations” that could be detected by films.

7. 30.1 Radioactivity
Scientists quickly learned that there were three different kinds of radiation given off by radioactive materials.
Alpha rays
Beta rays
Gamma rays
The scientists called them “rays” because the radiation carried energy and moved in straight lines, like light rays.

8. 30.1 Radioactivity
We now know that radioactivity comes from the nucleus of the atom.
If the nucleus has too many neutrons, or is unstable for any other reason, the atom undergoes radioactive decay.
The word decay means to "break down."

9. 30.1 Radioactivity
In alpha decay, the nucleus ejects two protons and two neutrons.
Beta decay occurs when a neutron in the nucleus splits into a proton and an electron.
Gamma decay is not truly a decay reaction in the sense that the nucleus becomes something different.

10. Vocabulary Chain reaction Fission Fusion Nuclear equation
Nuclear reaction

11. 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
See page 312

12. 7.3 Nuclear Reactions
Nuclear power plants can generate large amounts of electricity.
Ontario, Quebec and New Brunswick currently generate nuclear power.
Canadian-made nuclear reactors are called CANDU reactors.
CANDU reactors are considered safe and effective and are sold
throughout the world.
The Bruce Nuclear Generating Station on the shore of Lake Huron, in Ontario
See page 312

13. Nuclear Fission
Nuclear energy used to produce power comes from fission.
Nuclear fission is the splitting of one heavy nucleus into two or more smaller nuclei, some sub-atomic particles, and energy.
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

14. Nuclear Fission
Nuclear reactions are different than chemical reactions.
In chemical reactions, mass is conserved, and energy changes are relatively small.
There are no changes to the nuclei in chemical reactions.
In nuclear reactions, the actual nucleus of atoms changes.
Protons, neutrons, electrons, and/or gamma rays can be lost or gained.
Small changes of mass = huge changes in energy
See pages

15. Nuclear Equations for Induced Nuclear Reactions
Natural radioactive decay consists of the release of
alpha, beta and gamma radiation.
Scientists can also create nuclear reactions by smashing nuclei with alpha, beta and gamma radiation.
See pages

16. Nuclear Equations for 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
See pages

17. Nuclear Chemistry
In this chapter we will look at two types of nuclear reactions.
Radioactive decay is the process in which a nucleus spontaneously disintegrates, giving off radiation.
Nuclear bombardment reactions are those in which a nucleus is bombarded, or struck, by another nucleus or by a nuclear particle.
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18. Radioactivity
The phenomena of radioactivity was discovered by Antoine Henri Becquerel in 1896.
Alpha rays bend away from a positive plate indicating they are positively charged.
They are known to consist of helium-4 nuclei (nuclei with two protons and two neutrons).
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19. Radioactivity
The phenomena of radioactivity was discovered by Antoine Henri Becquerel in 1896.
Beta rays bend in the opposite direction indicating they have a negative charge.
They are known to consist of high speed electrons.
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20. Radioactivity
The phenomena of radioactivity was discovered by Antoine Henri Becquerel in 1896.
Gamma rays are unaffected by electric and magnetic fields.
They have been shown to be a form of electromagnetic radiation similar to x rays, but higher in energy and shorter in wavelength.
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21. Nuclear Equations For example, the nuclide symbol for uranium-238 is
A nuclear equation is a symbolic representation of a nuclear reaction using nuclide symbols.
For example, the nuclide symbol for uranium-238 is
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22. Nuclear Equations
A nuclear equation is a symbolic representation of a nuclear reaction using nuclide symbols.
The radioactive decay of by alpha-particle emission (loss of a nucleus) is written
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23. Nuclear Equations Other particles are given the following symbols.
A nuclear equation is a symbolic representation of a nuclear reaction using nuclide symbols.
Other particles are given the following symbols.
Proton or
Neutron
Electron or
Positron or
Gamma photon
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24. Nuclear Equations
A nuclear equation is a symbolic representation of a nuclear reaction using nuclide symbols.
The total charge is conserved during a nuclear reaction.
This means that the sum of the subscripts for the products must equal the sum of the subscripts for the reactants.
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25. A Problem To Consider The nuclear equation is
Technetium-99 is a long-lived radioactive isotope of technetium. Each nucleus decays by emitting one beta particle. What is the product nucleus?
The nuclear equation is
From the superscripts, you can write
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26. A Problem To Consider The nuclear equation is
Technetium-99 is a long-lived radioactive isotope of technetium. Each nucleus decays by emitting one beta particle. What is the product nucleus?
The nuclear equation is
Similarly, from the subscripts, you get
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27. A Problem To Consider The nuclear equation is
Technetium-99 is a long-lived radioactive isotope of technetium. Each nucleus decays by emitting one beta particle. What is the product nucleus?
The nuclear equation is
Similarly, from the subscripts, you get
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28. Nuclear Stability
The existence of stable nuclei with more than one proton is due to the nuclear force.
The nuclear force is a strong force of attraction between nucleons that acts only at very short distances (about m).
This force can more than compensate for the repulsion of electrical charges and thereby give a stable nucleus.
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29. Nuclear Stability
Several factors appear to contribute the stability of a nucleus.
No stable nuclides are known with atomic numbers greater than 83.
-On the other hand, all elements with
Z equal to 83 or less have one or more
stable nuclides.
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30. Types of Radioactive Decay
There are six common types of radioactive decay.
Alpha emission (abbreviated a): emission of a nucleus, or alpha particle, from an unstable nucleus.
An example is the radioactive decay
of radium-226.
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31. Types of Radioactive Decay
There are six common types of radioactive decay. (see Table 21.2)
Beta emission (abbreviated b or b-): emission of a high speed electron from a stable nucleus.
An example is the radioactive decay of carbon-14.
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32. Types of Radioactive Decay
There are six common types of radioactive decay.
Positron emission (abbreviated b+): emission of a positron from an unstable nucleus.
The radioactive decay of techencium-95 is an example of positron emission.
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33. Types of Radioactive Decay
There are six common types of radioactive decay.
Gamma emission (abbreviated g): emission from an excited nucleus of a gamma photon, corresponding to radiation with a wavelength of about m.
In many cases, radioactive decay produces a product nuclide in a metastable excited state.
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34. Types of Radioactive Decay
There are six common types of radioactive decay.
Gamma emission (abbreviated g): emission from an excited nucleus of a gamma photon, corresponding to radiation with a wavelength of about m.
An example is metastable technetium-99.
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35. Types of Radioactive Decay
There are six common types of radioactive decay.
Spontaneous fission: the spontaneous decay of an unstable nucleus in which a heavy nucleus of mass number greater than 89 splits into lighter nuclei and energy is realeased.
For example, uranium-236 undergoes spontaneous fission.
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36. Nuclear Bombardment Reactions
In 1919, Ernest Rutherford discovered that it is possible to change the nucleus of one element into the nucleus of another element.
Transmutation is the change of one element to another by bombarding the nucleus of the element with nuclear particles or nuclei.
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37. Nuclear Fission of Uranium-235
It is much easier to crash a neutral a neutron than a positive proton into a nucleus to release energy.
Most nuclear fission reactors and weapons use this principle.
A neutron, , crashes into an atom of stable uranium-235 to create unstable uranium-236, which then undergoes radioactive decay.
Caused by Uranium
See pages

38. Nuclear Fission of Uranium-235
After several steps, atoms of krypton and barium are formed, along with the release of three neutrons and huge quantities of energy.
The induced nuclear fission of uranium-235. This nuclear reaction is the origin of nuclear power and nuclear bombs.
See pages

39. Chain Reactions
Once the nuclear fission reaction has started, it can keep going.
The neutrons released in the induced reaction can then trigger more reactions on other uranium-235 atoms.
This chain reaction can quickly get out of control.
Fermi realized that materials that could
absorb some neutrons could help
to control the chain reaction.
Nuclear reactors have
complex systems to ensure the
chain reaction stays at safe levels.
See page 318

40. Chain Reactions An uncontrolled chain reaction can result
in a violent nuclear explosion.
Nuclear bombs are created using this concept.
Nuclear Chain Reaction.
See page 318

41. CANDU Reactors and Hazardous Wastes
Canada’s nuclear research into the safe use of nuclear reactions has resulted in the creation of CANDU reactors.
CANDU reactors are found in various countries around the world.
Canada, South Korea, China, India, Argentina, Romania and Pakistan
The reactors are known to be safe and easy to shut down in an emergency.
Heat energy produced turns electricity-generating turbines.
Inside a CANDU reactor.
See pages

42. CANDU Reactors and Hazardous Wastes
Hazardous wastes produced by nuclear reactions are problematic.
Some waste products, like fuel rods, can be re-used.
Some products are very radioactive, however,
and must be stored away from living things.
Most of this waste is buried underground
or stored in concrete.
It will take 20 half-lives (thousands of years)
before the material is safe.
See pages

43. Nuclear Fusion
Nuclear fusion = joining of two light nuclei into one heavier nucleus.
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.
See pages

44. The fusion of hydrogen nuclei
Nuclear Fusion
Scientists cannot yet find a safe, manageable
method to harness the energy of nuclear fusion.
So-called “cold fusion” would occur at
temperatures and pressures that could be
controlled.
The fusion of hydrogen nuclei
See pages

45. Summary
Nuclear reactions involve the splitting of heavy nuclei (fission) or the joining together of lightweight nuclei (fusion), both of which can release large amounts of energy.
Radioactive decay, fission, and fusion reactions can be symbolized using nuclear equations.

46. 30.1 Half-life The half-life of carbon- 14 is about 5,700 years.
If you start out with 200 grams of C-14, 5,700 years later only 100 grams will still be C-14.
The rest will have decayed to nitrogen-14.

47. 30.1 Half-life
Most radioactive materials decay in a series of reactions.
Radon gas comes from the decay of uranium in the soil.
Uranium (U-238) decays to radon-222 (Ra-222).

48. 30.1 Applications of radioactivity
Many satellites use radioactive decay from isotopes with long half-lives for power because energy can be produced for a long time without refueling.
Isotopes with a short half-life give off lots of energy in a short time and are useful in medical imaging, but can be extremely dangerous.
The isotope carbon-14 is used by archeologists to determine age.

49. 30.1 Carbon dating Living things contain a large amount of carbon.
When a living organism dies it stops exchanging carbon with the environment.
As the fixed amount of carbon-14 decays, the ratio of C- 14 to C-12 slowly gets smaller with age.