1. 4/22/14

2. Do Now (4/22/14) (7 minutes): What are some words and images that come to mind when you hear the word “radioactivity”? Define: Atomic Number Mass Number Isotope Half Life Pass in any Spring Break Bonuses

3. Atomic number Number of protons in the nucleus of the atom

4. Mass number Sum of protons and neutrons in the nucleus of the atom

5. Isotope Atomic nuclei having the same number of protons but different number of neutrons

6. Nuclear reaction A reaction in which the number of protons or neutrons in the nucleus of an atom changes.

7. Alpha decay Radioactive decay process in which the nucleus of an atom emits an alpha particle

8. Alpha Particle Nucleus of a helium atom

9. Alpha Particle What is the mass number of an alpha particle? 4

10. Beta decay Occurs when a neutron is changed to a proton and a beta particle and an antineutrino are emitted

11. Gamma decay Radioactive process of decay that takes place when the nucleus of an atom emits a gamma ray.

12. Half Life What is the Half-Life of an element?

13. Half Life: Half-life: time needed for half of remaining mass of element to decay

14. Which of the following would decay the slowest?

15. Example #1 (2 minutes): Fermium-253 has a half-life of 0.334 seconds. A radioactive sample is considered to be completely decayed after 10 half-lives. How much time will elapse for this sample to be considered gone?

16. Decay Rate T1/2=half life λ=decay rate

17. Example #2: (2 minutes) The half life of Zn-71 is 2.4 minutes. If a mass of Zn-71 had 100 g at the beginning, what is the decay rate of Zn-71?

18. Mass remaining m=mass remaining m 0 =Original mass

19. Example #3 (2 minutes): The half life of Zn-71 is 2.4 minutes. If a mass of Zn-71 had 100 g at the beginning, how many grams would be left after 7.2 minutes elapsed?

20. All Elements Have Radioactive Isotopes All elements have more than one isotope Some isotopes of all elements are radioactive Some half-lives are so short that the isotope is not found naturally

21. Which of the following would likely not be found in nature?

22. Practice: Use the rest of class to work on the paper: Radioactivity worksheet.

23. Do Now (4/24/14) (5 minutes): U-238 has a half-life of 4.46x10 9 years. What percentage of a sample of U-238 would remain after 25 x10 9 years old? 1. Find the decay rate. 2. Find the percentage left or

24. Fraction Left Over Convert from Fraction to Percentage

25. Using Logarithms Using the equation above, rearrange and solve the equation for time.

26. Using Logarithms

27. Solving for t:

28. Solve for Decay Rate (30 seconds) Rearrange this equation and solve for the decay rate, λ.

29. Using Logarithms Solving for λ:

30. Grades Three weeks of school left. Check your grades this weekend.

31. Practice Extension If you are working all of class, without having to be told to stay on task, you may turn in the practice tomorrow. You will not be given any warnings to stay on task.

32. Tough Problems If you get stuck, write down your givens and identify which equation you should use. Pay attention to the difference between a material decaying to 30% and a material decaying by 30%.

33. Practice: Worksheet is due at the end of class. Keys are on the board. If you finish early there are bonuses.

34. Do Now (4/28/14) (5 minutes): If Uranium-238 decays to Thorium-234, what is the resulting change in mass number? What is emitted from this decay?

35. Decay The change in mass number tells us what particle was emitted as a result of the decay. We look at the pre-decay mass number, then the post-decay mass number. The difference tells us what was emitted.

36. Conservation of ???? This is an example of what physics theory? Conservation of Mass

37. Two Day Lab We will be in the Lab on Monday and Tuesday. Two Labs and a Bonus You will be working in assigned groups, check the front of the Lab

38. End of Today You need to complete at least one of the labs by the end of class today. This will be worth 4 points towards your lab grade.

39. End of the Semester These may be the last two lab grades and one of the last quizzes is Wednesday. They are worth a large percentage of your fourth-quarter grade.

40. Lab Meet here tomorrow. To the lab ROOM 128!!!

41. Do Now (4/29/14) (5 minutes): Write down three things that you will put on your notecard. Pass in your Do Now!!!

42. Lab By the end of class today you should completed both labs. The last 10 minutes of class we will review a few concepts for the quiz.

43. Lab There is a bonus if you finish early. If you finish the bonus study for your quiz and make your notecard. Head over to Room 128.

44. The Uranium Decay Series The only radium that exists today is that which is created as a result of the decay of uranium. Decay series animation

45. Carbon-14 Production Neutron enters nucleus and kicks out a proton. 0 n 1 + 7 N 14 ---------> 6 C 14 + 1 p 1

46. Carbon-14 Enters the Ecosystem

47. Carbon Dating Since living organisms continually exchange carbon with the atmosphere in the form of carbon dioxide, the ratio of C-14 to C-12 approaches that of the atmosphere. From the known half-life of carbon-14 and the number of carbon atoms in a gram of carbon, you can calculate the number of radioactive decays to be about 15 decays per minute per gram of carbon in a living organism.

48. Measuring the Age of Organic Matter A German tourist in the Italian Alps discovered the remains of the "Iceman" in the ice of a glacier in 1991.

49. Calculating the Iceman's Age The current activity per gram of carbon half what it would be if the Iceman were alive. Since the half-life of carbon-14 is about 5700 years, the Iceman's remains are about 5700 years old.

50. Radioactivity Equations N(t) = population at time t N(0) = population at time zero N 0 = N(0) = decay constant N(t) = N 0 e - t Example: N 0 = 1000 = 2 x 10 -3 years -1 When will N = 200? N = N 0 e - t (1) e - t = N /N 0 (2) ln (e - t ) = ln (N /N 0 ) (3) - t = ln (N /N 0 ) (4) t = - [ln (N /N 0 )] / (5) = - [ln (200/1000)] /2 x10 -3 (6) = 805 years

51. Half-Life Problem The half-life of a radioactive substance is 10 hours. What is the decay constant, ? -------------------------------------------------------- N = N 0 e - t (1) 0.50 N 0 = N 0 e - 10 (2) e - 10 = 0.50 (3) ln(e - 10 ) = ln(0.50) (4) -10 = -0.693 (5) = 0.0693 hrs -1 (6)

52. Half-Life Problem From the previous problem, how much time will it take for the sample's activity to fall to only 20% of what it was originally? ---------------------------------------------- N = 0.20 N 0 (7) 0.20 N 0 = N 0 e -0.0693 t (8) -0.0693 t = ln (0.20) (9) t = 23 hours

53. Decay Constant and Half-Life N = N 0 e - t (1) 0.50 N 0 = N 0 e - T (2) (T = half-life) e - T = 0.50 (3) ln(e - T ) = ln(0.50) (4) - T = -0.693 (5) T = 0.693/ (6) = 0.693/T (7)

54. Half-Life Example 38 Sr 90 (strontium-90) has a half-life of 28.5 years. How long will it take for 98% of a sample of strontium-90 to disappear? ------------------------------------------------------------------ = 0.693/T 1/2 = 0.693 / 28.5 = 0.0243 years -1 0.02 = e -0.0243 t t = - ln(0.02) /0.0243 years -1 = 161 years

55. Radioactivity Units A = number of disintegrations per second, activity A = N One becquerel (Bq) is one disintegration per second. One curie is the number of disintegrations per second (the "activity") of one gram of radium, or about 3.7 x 10 10 Bq.

56. Units of Absorbed Radiation Rad: 10 milli-joules per kilogram 20 rads of X-rays doesn't do the same damage to humans as 20 rads of alpha particles. ---------------------------------------------- Rem: an absolute biological damage unit

57. Radiation Sickness Dose (rems) Effect 50-300Sickness 400-500Lethal 50% (LD 50 ) Above 600Lethal 100% (LD 100 )

58. Calculate Rems from Rads (Relative Biological Effectiveness) Radiation R (rems/rad)  -particles 20 Neutrons 10 Protons 10  -particles 1  -rays 1 X-rays 1 Example: How many rads of protons will kill a person? ------------------------------ 600 rems is fatal RBE for protons is 10 Number of rads = 600 / 10 = 60 Example: One joule of energy per kilogram is absorbed in the form of neutrons. Will this prove fatal? -------------------------------- 1 rad is ten milli-joules 1 rad = 0.010 J

59. Radon Poisoning Uranium in earth's crust decays to radium, which decays to radon. Radon is an odorless, tasteless, lighter- than-air gas which rises from the ground through cracks and fissures in the earth into homes. When breathed, the alpha- emitting radon can cause cancer of the lung. Radon is the single greatest source of radiations for humans, providing about 200 milli-rems per year per person.