1. Radioactivity
Ch 10

2. Radioactivity
is the process in which an unstable atomic nucleus emits charged particles & energy
Any atom containing an unstable nucleus is called a radioactive isotope or radioisotope

3. How is the Atom Unstable?
The nuclear “glue” that holds the nucleus together sometimes isn’t strong enough.
Over time the atom “drops” some of it’s subatomic particles …called radioactive decay! 3

4. New Way of Writing Nuclides & Isotopes
3919 K ; K
Superscript is the mass number
Subscript is the atomic number
146C ; 126 C

5. Isotopes
have the same number of p+, different number of no
Another way to show an isotope is to have the mass number follow the name of the element (Carbon-14 or C-14)

6. Types of Nuclear Radiation
Alpha 2.Beta 3. Gamma

7. Alpha Decay
Alpha particle—a positively charged particle made up of two p+ & two no
the least penetrating
can be stopped by a sheet of paper

8. Alpha Decay An alpha particle looks like a helium atom (42He)
mass reduces by 4
atomic # reduces by 2

9. Examples:
U 
Po 

10. A beta particle is an e- emitted by an unstable nucleus
Beta Decay
A beta particle is an e- emitted by an unstable nucleus
can be stopped by a thin sheet of metal such as aluminum

11. Beta Decay A beta particle is written 0-1 e
mass remains the same & the atomic # increases by one

12. Examples:
Pb
Po

13. Gamma decay
A gamma ray is a penetrating ray of energy emitted by an unstable nucleus
Gamma rays are energy waves that travel through space at the speed of light

14. Gamma decay
atomic # and mass remain the same, but the energy of nucleus decreases
Gamma rays can be stopped by several centimeters of lead or by several meters of concrete

15. Thanks Cambridge Physics Outlet for amazing graphics!

16. STAR Questions
U-238 loses 4 total subatomic particles, 2 being protons.
What elements are formed?
Thorium and Helium
What type of decay has it undergone?
Alpha decay
What is the most penetrating decay?
Gamma rays 16

17. Background radiation
is nuclear radiation that occurs naturally in the environment (levels are low enough to be safe)
Radioisotopes in the air, water, rocks, plants, & animals all contribute

18. Background Radiation
Cosmic rays (streams of charged particles) from outer space that collide with the Earth’s atmosphere also contribute
When nuclear radiation exceeds background levels, cells in your body can mutate

20. Detecting Radiation
Devices used to detect radiation include Geiger counters & film badges

21. RATES OF NUCLEAR DECAY
A half-life is the time required for one half of a sample of radioactive sample of a radioisotope to decay
Unlike chemical reactions, nuclear decay rates are constant regardless of temperature, pressure or surface area

22. C-14 has a half life of 5730 years.
What fraction of a sample will be remaining after 1 half life?
After 2 half lives? 22

23. C-14 has a half life of 5730 years.
If you have a sample of 50 grams. How much of the sample will be remaining after 1 half life?
After 2 half lives? 23

24. RATES OF NUCLEAR DECAY
Transmutation is the conversion of atoms of one element to atoms of another
Transuranium elements are elements with atomic numbers higher than 92 (Uranium)
A quark is a subatomic particle theorized to be among the basic units of matter

25. FISSION AND FUSION
Fission is the splitting of an atomic nucleus into two smaller parts
Fusion is a process in which the nuclei of two atoms combine to form a larger nucleus 25

26. Fission
A chain reaction is a chain of fission reactions triggered by neutrons released during the fission of a nucleus
About 20% of the electricity in the US comes from fission reactions

27. Fission
A tremendous amount of energy is produced during a fission reaction

28. Fission Advantages: is the lack of air pollution.
Harris plant, near Raleigh
Advantages: is the lack of air pollution.
Disadvantages: include the risk of exposure & radioactive waste
Lake Harris

31. Not in my backyard…

32. Then sealed and transported by way of trucks and trains for more permanent storage. Low-level wastes will stay above ground until they become “stable”. 32

33. If high-level, the wastes are stored deep underground, where they wait for hundreds to thousands of years to become “stable”. 33

34. Fusion release huge amounts of energy
occur in the sun and stars (plasma)

35. Fusion
We do not use fusion reactions for energy b/c of the extremely high temperatures needed to start the reaction & because the plasma would need to be contained.

36. THREE MILE ISLAND
Three Mile Island power station is near Harrisburg, Pennsylvania
In 1979 at Three Mile Island nuclear power plant a cooling malfunction caused part of the core to melt in the # 2 reactor. The TMI-2 reactor was destroyed. 
Some radioactive gas was released a couple of days after the accident, but not enough to cause any dose above background levels to local residents. 
There were no injuries or adverse health effects from the Three Mile Island accident. 

37. CHERNOBYL
The Chernobyl accident in 1986 was the result of a flawed reactor design that was operated with inadequately trained personnel & without proper regard for safety.
The resulting steam explosion & fire released at least five percent of the radioactive reactor core into the atmosphere and downwind.
28 people died within four months from radiation or thermal burns, 19 have subsequently died, & there have been around nine deaths from thyroid cancer apparently due to the accident: total 56 fatalities as of 2004.
An authoritative UN report in 2000 concluded that there is no scientific evidence of any significant radiation-related health effects to most people exposed. This was confirmed in a very thorough study.

38. Examples
Iodine-131 has a half-life of 8.07 days. What fraction of a sample of iodine-131 is left unchanged after days?

39. Examples
The radioactive isotope Ni-63 has a half-life of 100 yrs. How much of a 10g sample remains after 300 yrs?

40. Examples
How long will it take a sample of Po-194 to decay to 1/8 of its original amount, if Po-194 has a half life of 0.7 seconds?

41. Examples
A sample of Cl-38 is observed to decay to 25% of its original amount in 74.4 min. What is the half-life of Cl-38?
sorry…no time for Star cards this time :o)