1. Radioactivity and Nuclear energy

2. We will discuss three basic types of nuclear change Fusion Fission Decay

3. Think about nuclear processes and what parts of our lives are they involved in… Nuclear weapons, power plants, radioactive dating, nuclear medicine

4. Radioactive elements (radioisotopes) found in rock, soil, water, air, and in food from the earth make there way in our bodies when we drink water, breath air or eat foods which contain them. These naturally occurring radioisotopes expose us to radiation from within our bodies.

5. Medical procedures account for nearly all (96%) human exposure to man-made radiation. Among these medical procedures, x-rays, mammography, and CT use radiation or perform functions similar to those of radioisotopes.

8. The nucleus is small and dense Consider a ton… A ton is 2,000 pounds If you were to build a nucleus the size of a ping pong ball it would weigh 2.5 billion tons The energies involved in nuclear processes are millions of times greater than those associated with chemical processes.

10. 19.1 radioactive decay
Think… What are the constituents of the nucleus? What are the charges on those particles? Are those charges attractive or repulsive? If so, what is holding the nucleus together? The larger the nucleus, the greater the repulsion Nuclei with more than 83 protons are all unstable, and will eventually break up into smaller pieces

11. Protons (p) and neutrons (n) atomic number (Z)
mini-review
A nucleus is made of nucleons:
Protons (p) and neutrons (n)
The number of protons is equal to the
atomic number (Z)
When you add the number of protons to the number of neutrons, you get the
mass number (A)
nuclei that have the same number of protons but a different number of neutrons are called…
isotopes

12. C 14 6 (A) mass number (Z) atomic number How many neutrons?
the nuclide can be represented this way C 14
(A) mass number 6
(Z) atomic number
How many neutrons?

16. Radioactive Decay: The spontaneous disintegration of a nucleus into a less massive and/or more stable nucleus, accompanied with particle or electromagnetic emission! initial nucleus = parent nuclide new nucleus = daughter nuclides can be written w/ equations, as long as...

17. Atomic #left = Atomic #right Mass #left = Mass #right
Parent Daughter
Atomic #left = Atomic #right
and
Mass #left = Mass #right

22. Alpha emission: parent  daughter + 

23. Th He Ra  + Write an equation for the alpha decay of Th-230. 230 90 4
226 88 Ra  +
parent
alpha
daughter

24. Write an equation for the decay of radium-226 by  emission.88 Ra 4 2 He Rn
222  + 86
parent
alpha
daughter

25. Write an equation for the decay of plutonium-240 by  emission.94 Pu 4 2 He U 
236 + 92
parent
alpha
daughter

26. The decay products for a nuclear reaction are an alpha particle and polonium-218. What was the parent nuclide? Rn 4 2 He
218 84 Po
222  + 86
parent
alpha
daughter

27. Questions? 27

28. Beta emission: parent  daughter + –
A beta particle is often an electron, but can also be a positron
If it is an electron, the number of neutrons decreases by 1 and the number of protons increases by 1
If it is a positron, the number of neutrons increases by 1 and the number of protons decreases by 1

29. Beta emission 14 6 C  -1 e + N 14 7
parent
beta
daughter

30. Potassium-40 undergoes beta emission
Potassium-40 undergoes beta emission. Write the equation for this reaction. -1 e 40 19 K  Ca 40 + 20
parent
beta
daughter

31. positron emission: parent  + + daughterNa e 1 Ne 22  22 + 11 10

32. w/ – emission a n  p
w/  + emission a p  n
after decay, the daughter has less E than parent

33. e Hg Au  + 201 80 201 -1 79 electron capture means…
An electron is captured by the…
Nucleus e
201 80 Hg Au 
201 + -1 79

36. Many nuclei are radioactive.
This means they are unstable, and will eventually decay by emitting a particle, transforming the nucleus into another nucleus, or into a lower energy state.
A chain of decays may take place until a stable nucleus is reached.

38. What is Radioactivity?

39. Questions? 39

40. 19.3 Detection of Radioactivity and the Concept of Half-Life
The most familiar instrument for measuring radioactivity levels is the Geiger counter The probe contains argon gas. The gas can be ionized by the rapidly moving particles released during radioactive decay Think: What are the 3 types of particles we have been discussing? Discuss with the person next to you: What could be useful applications for a Geiger counter?

41. Half-life (t1/2) is the period of time, for a substance undergoing decay, to decrease by half.
It is the time when the expected value of the number of entities that have decayed is equal to half the original number.
if there is just one radioactive atom with a half-life of 1 second, there will not be "half of an atom" left after 1 second. There will be either zero atoms left or one atom left, depending on whether or not the atom happens to decay.
time for half the parent nuclei to decay =
half-life (t1/2)

42. Example:
if 100,000 at beginning
then 50,000 after one half life
and 25,000 after 2nd half life
and 12,500 after 3rd half life; etc...
A half life can be long or short, depending on the isotope involved
There are many natural radioactive materials, some are man-made

45. example F-21 has a half-life of approximately 5 seconds.
If there were 20 grams to begin with, how much is there after 5 seconds?
10g
After 10 seconds? 5g
After 15 seconds?
2.5g
After 20 seconds?
1.25g

46. example
I-131 has a half-life of 8 days. How much is left after 24 days?
24 days is how many half-lives?
24/8 = 3
Three half-lives would leave how much material?
1/2 x 1/2 x 1/2 = 1/8 =
.125

47. Number of half-lives elapsed Fraction remaining Percentage remaining
1/1
100 1
1/2 50 2
1/4 25 3
1/8
12.5 4
1/16
6.25 5
1/32
3.125 6
1/64
1.563 7
1/128
0.781
... n
1/2n
100/2n

48. example
Cr-51 has a half-life of 28 days. How much of a 510-g sample is left after 1 year?
365 days / 28days per ½ life = 13 half lives
The fraction remaining is
1/2^n
1/2^13 = 1/8192
1/8192 x 510 g =
0.062 g

49. 19.4 Dating by Radioactivity
C-14 is made in upper atmosphere (from N-14) C-14 decays (t1/2 = 5730 y) C-14 gets absorbed & given off by living critters When critter dies, C-14 trapped! but still decays! lets us radiocarbon date something!

50. If you know rate of decay (t1/2 = 5730 y), then you can estimate how long it has been dead for example:
A living organism = 15.3 g C-14
If a dead organism is found to have 7.65 g then the fraction remaining is
.5 or ½
And that many half lives is how many years?
5700 y ago

51. 19.4
must be a pure sample not accurate past y For inorganic matter (fossils, rocks), different nuclides are used (e.g. U-238 or K-40)

52. radiochemical dating is often used to determine the age of bones discovered at archaeological sites. these bones were estimated to be from about 3000 BC. NT manuscripts dated this way could C-14 dating be used to determine the age of a stone disk on leather strands found near the skeleton in the glacier?

54. medical applications of radioactivity
we can use some radioisotopes in the body as tracers they act chemically just like non-radioactive atoms watching where they go we can deduce the health of certain organs e.g. C-14 can trace nutrient pathways in living systems

55. C e N  + 14 14 -1 6 7 Carbon-14 decays into Nitrogen-14
Write down the appropriate formula for that process 14 6 C  -1 e + N 14 7

56. pick an element that goes to a specific organ (like iodine)
Select (create) a radioactive isotope
send in as a tracer
Then pick up an image on a scanner

57. Why might medical professionals use isotopes with such a short half-life?

59. PET scan above
radioactive tracer in plant to the left

62. Questions ?

63. Trinity

64. 19.5 EOC questions What are tracers?
Why do they have a short half-life?
How else can radioactive materials be used in medicine?

65. 19.6 nuclear energy Fusion Fission
The energy that holds the nucleus together is over a million times greater than the energy in chemical reactions
Master that and you have an amazing energy source
Combining two nuclei to make a bigger one is…
Fusion
Splitting a big nucleus to make smaller ones is…
Fission

67. 19.7 nuclear fission
The fission of U-235 yields about 26 million times more E than burning the equivalent amount of methane

68. The process can be self-sustaining Each fission event releases neutrons which can cause the fission of more nuclei, a process called… a chain reaction…

69. The chain reaction must give off neutrons to keep it going. if (on avg
The chain reaction must give off neutrons to keep it going! if (on avg.) less than 1 neutron causes another fission event, it dies out if (on avg.) 1 neutron from each fission causes another, it sustains itself: critical if (on avg.) greater than 1 neutron from each event causes another fission, the process rapidly escalates and the heat build-up causes a violent explosion

71. to achieve the critical state, a certain mass of fissionable matter is needed= critical mass If the sample is too small, too many neutrons escape before they have a chance to cause a fission event

72. Questions?

73. 19.7 EOC questions
What is a chain reaction? What is critical mass? Which particle is the key to nuclear fission? What does it do?

74. 19.8 nuclear reactors
The heat from nuclear fission can be used to heat water and make steam The steam is used to turn turbines that are connected to generators

75. the fuel cylinders (rods) in the reactor core contain enriched uranium (3%) U-235
control rods are made of substances that absorb neutrons and are used to regulate the reactor
Reactors are designed so that the control rods are inserted automatically, in case of a reactor malfunction

77. Although the concentration of U-235 in the fuel rods is not great enough to allow an explosion (like in a fission bomb), the failure of the cooling system can lead to dangerously high temperatures (meltdown, excessive steam production)
1979 Three Mile Island, radioactive steam release and partial core melt-down
1986 Chernobyl, steam explosion & core meltdown, the resulting radioactive release was equivalent to ten times that at Hiroshima

78. Questions?

79. 19.8 EOC questions
China Syndrome Why are atoms split in a nuclear power plant? What is a fuel rod? What is a control rod? What are the dangers of excessive heat in a nuclear power plant?

80. 19.9 nuclear fusion The process of combining two light nuclei
Our sun gives off vast quantities of energy from the fusion of protons to form…
helium

82. Fusion reactors
Intense efforts are underway to develop a feasible fusion reactor
light nuclides are readily available

83. Fusion reactors
Unfortunately, initiating the fusion reaction is much more difficult than initiating fission
The forces that bind nucleons together to form a nucleus become effective only at very small distances
Large amounts of energy are
required to get the protons
close enough together

84. 19.9 EOC questions
What is a fusion reaction? Where do we see nuclear fusion taking place?

85. 19.10 effects of radiation
What is the definition of energy? What is the definition of work? The delivery of large amounts of energy to your body does work that can be catastrophic Radiation damage can be somatic or genetic Somatic damage: radiation damages destroys enough molecules to damage bodily functions. Symptoms include: Fatigue, Nausea, Loss of body hair, Death

86. For large doses, the damage may appear almost immediately For smaller doses, the damage may appear years later, usually in the form of cancer

87. genetic damage is the other thing to worry about Damage to your body cells’ DNA can cause cancer if your reproductive cells’ DNA are damaged that damage can be carried to the next generation

88. The biological effects depend upon several factors
1. The energy of the radiation higher energy radiation means more damage

89. The biological effects depend upon several factors
2. Penetrating ability of radiation
see that the big three can
penetrate to different levels
in the body
gamma is the most penetrating

90. The biological effects depend upon several factors
Penetrating ability of radiation
Alpha particles may be completely stopped by a sheet of paper,
beta particles by aluminum shielding.
Gamma rays can only be reduced by much more substantial barriers, such as a very thick layer of lead.

92. The biological effects depend upon several factors
Penetrating ability of radiation

93. The biological effects depend upon several factors
3. Ionizing ability of radiation Radiation that removes electrons from molecules in living tissues seriously disturbs their functions Gamma only occasionally causes ionization Alpha are very effective at causing ionization Therefore, the ingestion of alpha producing substances is particularly damaging

94. The biological effects depend upon several factors
4. Chemical properties of the radiation source If ingested, the capacity to cause damage depends upon how long it remains in the body radioactive Sr-90 is chemically similar to Ca and may collect in bones potentially causing bone cancer or leukemia

95. the rem is a unit to help us determine the potential damage to us

98. summary

100. 19.2 nuclear transformations
Yes, we can change one element into another = nuclear transformation How? By bombarding nuclei with neutrons or positive ions we can change the ID of a little critter It is relatively easier to throw a n at a nuclei, but we can throw a positive ion fast enough with a particle accelerator this is how the transuranium elements are formed (those >U on the Periodic Table)