1. “Nuclear Changes”

2. Radioactive Decay
Radioactivity occurs when the nucleus of an unstable atom breaks down in a process called radioactive decay.
After decaying, radioactive atoms change into other more stable atoms.

3. Radioactive Decay The 3 main types of radioactive decay are: alpha
beta
gamma

4. Radioactive Decay
Alpha particles are positively charged, more massive than any other type of nuclear radiation, and made of 2 protons and 2 neutrons (like He).
Symbol: α

5. Radioactive Decay
Alpha decay results in a new element with an atomic number less than 2 and a mass number less than 4 from the original element.
Example: Po → Pb

7. Chapter 10 Section 1: “What is Radioactivity?”
Beta particles are fast moving negative electrons or positive positrons (with the same mass as electrons [ e] ).
Symbol: β

8. Chapter 10 Section 1: “What is Radioactivity?”
Beta decay will result in the atomic number increasing by 1 from the original value and the mass number staying the same.
Example: I → Xe

10. Radioactive Decay Gamma rays are a form of electromagnetic energy.
Symbol: γ

11. Radioactive Decay
Gamma decay does not change the mass number or atomic number of an atom.

13. Radioactive Decay
Transmutations are the changing of one element into another by radioactive decay, nuclear bombardment, or similar processes.

14. U→ Th → Pa → → ? α ? β α β Ac ? Th ? Radioactive Decay
LET’S PRACTICE 
Remember:
alpha decay (α) makes an element’s mass # decrease by 4 and the atomic # decrease by 2.
beta decay (β) makes an element’s atomic # increase by 1.
gamma decay (γ) creates no change in mass or atomic #.
U→ Th
→ Pa → → ? α ? β α β Ac ? Th ?

15. Decay Curves
The time it takes for one-half of a sample of radioactive material to decay is called a half-life.
A decay curve is a graph of the number of radioactive parent nuclei remaining in a sample as a function of time.
Decay curves show exponential decay.

16. Decay Curves

17. Radiometric Dating
Scientists use the knowledge of half-lives to date very old specimens. This is called radiometric dating.
Carbon-14 is a common isotope that is used to date specimens that were once living.

18. Decay Curves LET’S PRACTICE 
If we start with 200 g of iodine-131, how much will be left after 1 half life?
1 half life = 50%
.50 x 200 = 100 g
2 half lives?
2 half lives = 25%
.25 x 200 = 50 g
3 half lives?
3 half lives = 12.5%
.125 x 200 = 25 g

19. Decay Curves
Potassium-42 has a half-life of 12.4 hours. How much of an 848 g sample of potassium-42 will be left after 62.0 hours?
62.0 hr / 12.4 hr = 5 half lives
5 half lives = 3.125%
848 g x = 26.5 g

20. Decay Curves
The half-life of hafnium-156 is seconds. How long will it take a 560 g sample to decay to one-fourth of its original mass?
¼ = 2 half lives
2 half lives x 1.25 s = 2.50 s

21. Decay Curves
What is the half-life of a g sample of nitrogen-16 that decays to 12.5 grams in 21.6 seconds?
12.5 g / 100 g = .125 or 12.5%
12.5% = 3 half lives
21.6 s / 3 half lives = 7.2 s
1 Half Life = 7.2 s

22. Nuclear Fission and Fusion
Strong nuclear force is the force that causes protons and neutrons in the nucleus to attract one another.

23. Nuclear Fission and Fusion
Neutrons contribute to nuclear stability. Since protons and neutrons both attract and repel one another, the most stable nuclei have stronger attractive forces than repulsive forces.
Too many neutrons or protons can cause a nucleus to become unstable and decay.
Any nuclei with over 83 protons are going to be unstable.

24. Nuclear Fission and Fusion
Mass-energy equation:
E = mc2
This is Albert Einstein’s mass energy equation explaining the equivalence of mass and energy.
It means that matter can be converted into energy, and energy into matter.

25. Nuclear Fission and Fusion
Fission is the process by which a nucleus splits into two or more fragments and releases neutrons and energy.

26. Nuclear Fission and Fusion
A nuclear chain reaction is a continuous series of nuclear fission reactions.

27. Nuclear Fission and Fusion
Fusion is the process in which light nuclei combine at extremely high temperatures, forming heavier nuclei and releasing energy.
Fusion is the power source of stars.

28. Dangers and Benefits of Nuclear Radiation
Background radiation: nuclear radiation that arises naturally from cosmic rays and from radioactive isotopes in the soil, water, and plants.
Most living organisms have adapted to survive.

29. Dangers and Benefits of Nuclear Radiation
Exposure varies from one location to another depending upon the elevation of the city and the amount of rocks in the area.
Participation in high risk activities can also increase the amount of radiation you absorb.
Activity
Radiation Exposure (millirems/year)
Smoking 1 ½ packs of cigarettes per day
8000
Flying for 720 hours (airline crew)
267
Inhaling radon from the environment
360
Giving or receiving medical X-Rays
100
Location
Radiation Exposure (millirems/year)
Tampa, Fl
63.7
Richmond, VA
64.1
Las Vegas, NV
69.5
Los Angeles, CA
73.6
Portland, OR
86.7
Rochester, NY
88.1
Wheeling, WV
111.9
Denver, CO
164.6

30. Dangers and Benefits of Nuclear Radiation
The risk of damage from nuclear radiation depends on what 2 factors:
type of radiation
amount of exposure

31. Dangers and Benefits of Nuclear Radiation
The human body has evolved to withstand basic background radiation but there is a limit to how much it can block. Each of the types of radiation require a different level of protection:
Alpha (paper, clothes, skin)
Beta (sheet of metal)
Gamma (wall of lead or concrete)

32. Dangers and Benefits of Nuclear Radiation
If human are exposed to high levels of radiation without proper protective clothing, they can experience the following:
burns
radiation sickness
mutation

33. Dangers and Benefits of Nuclear Radiation
4 ways nuclear radiation can be used to benefit humans.
smoke detectors
used to detect diseases (radioactive tracer)
treat cancer
tracers and radioisotopes in agriculture
nuclear power

34. Nuclear Energy
Nuclear energy uses a fission reaction to create electricity. It is a benefit to humans because it is a viable long term solution that produces more power and less green house gases than fossil fuels.

35. Nuclear Energy
Nuclear energy does have its down falls. The used fuel rods are highly radioactive. Currently there is no way to recycle them so they must be buried for thousands of years. Nuclear power plants are also very expensive to build.