1. The Nucleus, Radioactivity, and Nuclear Medicine
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Chapter 9
The Nucleus, Radioactivity, and Nuclear Medicine
Denniston Topping Caret
5th Edition

2. 9.1 Natural Radioactivity
Radioactivity - process by which atoms emit energetic particles or rays
Radiation - the particles or rays emitted
comes from the nucleus
Nuclear symbols - what we use to designate the nucleus
Atomic symbol
Atomic number
Mass number

3. 9.1 Natural Radioactivity
Nuclear Symbols
mass number number of protons and neutrons
9.1 Natural Radioactivity
atomic symbol
atomic number number of protons

4. Writing Nuclear Symbols
This defines an isotope of boron
In nuclear chemistry, often called a nuclide
This is not the only isotope of boron
boron-10 also exists
How many protons and neutrons does boron-10 have?
5 protons, 5 neutrons
9.1 Natural Radioactivity

5. Three Isotopes of Carbon
Each nucleus contains the same number of protons
Only the number of neutrons is different
With different numbers of neutrons the mass of each isotope is different
9.1 Natural Radioactivity

6. 9.1 Natural Radioactivity
Unstable Isotopes
Some isotopes are stable
The unstable isotopes are the ones that produce radioactivity
To write nuclear equations we need to be able to write the symbols for the isotopes and the following:
alpha particles
beta particles
gamma rays
9.1 Natural Radioactivity

7. 9.1 Natural Radioactivity
Alpha Particles
Alpha particle (a) - 2 protons, 2 neutrons
Same as He nucleus (He2+)
Slow moving, and stopped by small barriers
Symbolized in the following ways:
9.1 Natural Radioactivity

8. 9.1 Natural Radioactivity
Beta Particles
Beta particles (b) - fast-moving electron
Emitted from the nucleus as a neutron, is converted to a proton
Higher speed particles, more penetrating than alpha particles
Symbolized in the following ways:
9.1 Natural Radioactivity

9. 9.1 Natural Radioactivity
Gamma Rays
Gamma rays (g) - pure energy (electromagnetic radiation)
Highly energetic
The most penetrating form of radiation
Symbol is simply…
9.1 Natural Radioactivity g

10. Properties of Alpha, Beta, and Gamma Radiation
Ionizing radiation - produces a trail of ions throughout the material that it penetrates
The penetrating power of the radiation determines the ionizing damage that can be caused
Alpha particle < beta particle < gamma rays
9.1 Natural Radioactivity

11. 9.2 Writing a Balanced Nuclear Equation
Nuclear equation - used to represent
nuclear change
In a nuclear equation, you do not balance the elements, instead...
the total mass on each side of the reaction arrow must be identical
the sum of the atomic numbers on each side of the reaction arrow must be identical

12. 9.2 Writing a Balanced Nuclear Equations
Alpha Decay =
9.2 Writing a Balanced Nuclear Equations
mass number =
atomic number

13. 9.2 Writing a Balanced Nuclear Equations
Beta Decay
Upon decomposition, nitrogen-16 produces oxygen-16 and a beta particle
In beta decay, one neutron in nitrogen-16 is converted to a proton and the electron, the beta particle is released
9.2 Writing a Balanced Nuclear Equations

14. 9.2 Writing a Balanced Nuclear Equations
Gamma Production
Gamma radiation occurs to increase the stability of an isotope
The energetically unstable isotope is called a metastable isotope
The atomic mass and number do not change
Usually gamma rays are emitted along with alpha or beta particles
9.2 Writing a Balanced Nuclear Equations

15. Predicting Products of Nuclear Decay
To predict the product, simply remember that the mass number and atomic number are conserved
What is the identity of X?
9.2 Writing a Balanced Nuclear Equations
239 Np 93

16. 9.3 Properties of Radioisotopes
Nuclear Structure and Stability
Binding energy - the energy that holds the protons, neutrons, and other particles together in the nucleus
Binding energy is very large
When isotopes decay (forming more stable isotopes) binding energy is released

17. 9.3 Properties of Radioisotopes
Stable Radioisotopes
Important factors for stable isotopes
Ratio of neutrons to protons
Nuclei with large number of protons (84 or more) tend to be unstable
The “magic numbers” of 2, 8, 20, 50, 82, or 126 help determine stability – these numbers of protons or neutrons are stable
Even numbers of protons or neutrons are generally more stable than those with odd numbers
All isotopes (except 1H) with more protons than neutrons are unstable
9.3 Properties of Radioisotopes

18. 9.3 Properties of Radioisotopes
Half-Life
Half-life (t1/2) - the time required for one-half of a given quantity of a substance to undergo change
Each radioactive isotope has its own half-life
Ranges from a fraction of a second to a billion years
The shorter the half-life, the more unstable the isotope
9.3 Properties of Radioisotopes

19. Half-Lives of Selected Radioisotopes
9.3 Properties of Radioisotopes

20. Decay Curve for the Medically Useful Radioisotope Tc-99m
9.3 Properties of Radioisotopes

21. Predicting the Extent of Radioactive Decay
A patient receives 10.0 ng of a radioisotope with a half-life of 12 hours. How much will remain in the body after 2.0 days, assuming radioactive decay is the only path for removal of the isotope from the body?
Calculate n, the number of half-lives elapsed using the half-life as the conversion factor
n = 2.0 days x 1 half-life / 0.5 days = 4 half lives
Calculate the amount remaining
10.0 ng ng ng ng ng
1st half-life nd half-life 3rd half-life 4th half-life
0.63 ng remain after 4 half-lives
9.3 Properties of Radioisotopes

22. 9.4 Nuclear Power Energy Production E = mc2
Equation by Albert Einstein shows the connection between energy (E) and mass (m)
c is the speed of light
The equation shows that a very large amount of kinetic energy can be formed from a small amount of matter
Release this kinetic energy to convert liquid water into steam
The steam drives an electrical generator producing electricity

23. Nuclear Fission 9.4 Nuclear Power
Fission (splitting) - occurs when a heavy nuclear particle is split into smaller nuclei by a smaller nuclear particle
9.4 Nuclear Power
Accompanied by a large amount of energy
Is self-perpetuating
Can be used to generate steam

24. Fission of Uranium-235 9.4 Nuclear Power
Chain reaction - the reaction sustains itself by producing more neutrons
9.4 Nuclear Power

25. Representation of the “Energy Zones” of a Nuclear Reactor
A nuclear power plant uses a fissionable material as fuel
Energy released by the fission heats water
Produces steam
Drives a generator or turbine
Converts heat to electrical energy
9.4 Nuclear Power

26. Nuclear Fusion 9.4 Nuclear Power
Fusion (to join together) - combination of two small nuclei to form a larger nucleus
Large amounts of energy is released
Best example is the sun
An Example:
No commercially successful plant exists in U.S.
9.4 Nuclear Power

27. Breeder Reactors 9.4 Nuclear Power
Breeder reactor - fission reactor that manufactures its own fuel
Uranium-238 (non-fissionable) is converted to plutonium-239 (fissionable)
Plutonium-239 undergoes fission to produce energy
9.4 Nuclear Power

28. 9.5 Radiocarbon Dating
Radiocarbon dating - the estimation of the age of objects through measurement of isotopic ratios of carbon
Ratio of carbon-14 and carbon-12
Basis for dating:
Carbon-14 (a radioactive isotope) is constantly being produced by neutrons from the sun

29. Radiocarbon Dating 9.5 Radiocarbon Dating
Living systems are continually taking in carbon
The ratio of carbon-14 to carbon-12 stays constant during its lifetime
Once the living system dies, it quits taking in the carbon-14
The amount of carbon-14 decreases according to the reaction:
9.5 Radiocarbon Dating
The half-life of carbon-14 is 5730 years
This information is used to calculate the age

30. 9.6 Medical Applications of Radioactivity
Modern medical care uses the following:
Radiation in the treatment of cancer
Nuclear medicine - the use of radioisotopes in the diagnosis of medical conditions

31. 9.6 Medical Applications of Radioactivity
Cancer Therapy Using Radiation
Based on the fact that high-energy gamma rays cause damage to biological molecules
Tumor cells are more susceptible than normal cells
Example: cobalt-60
Gamma radiation can cure cancer, but can also cause cancer
9.6 Medical Applications of Radioactivity

32. 9.6 Medical Applications of Radioactivity
Nuclear Medicine
The use of isotopes in diagnosis
Tracers - small amounts of radioactive substances used as probes to study internal organs
Nuclear imaging - medical techniques involving tracers
Example:
Iodine concentrates in the thyroid gland
Using radioactive 131I and 125I will allow the study of how the thyroid gland is taking in iodine
9.6 Medical Applications of Radioactivity

33. 9.6 Medical Applications of Radioactivity
Tracer Studies
Isotopes with short half-lives are preferred for tracer studies. Why?
They give a more concentrated burst
They are removed more quickly from the body
Examples of imaging procedures:
Bone disease and injury using technetium-99m
Cardiovascular disease using thallium-201
Pulmonary disease using xenon-133
9.6 Medical Applications of Radioactivity

34. Making Isotopes for Medical Applications
Artificial radioactivity - a normally stable, nonradioactive nucleus is made radioactive
Made in two ways:
In core of a nuclear reactor
In particle accelerators – small nuclear particles are accelerated to speeds approaching the speed of light and slammed into another nucleus
9.6 Medical Applications of Radioactivity

35. Examples of Artificial Radioactivity
Tracer in the liver
Used in the diagnosis of Hodgkin’s disease
9.6 Medical Applications of Radioactivity

36. Preparation of Technetium-99m
Some isotopes used in nuclear medicine have such a short half-life that they need to be generated on site
99mTc has a half-life of only 6 hours
9.6 Medical Applications of Radioactivity

37. 9.7 Biological Effects of Radiation
Radiation Exposure and Safety
The Magnitude of the Half-Life
Isotopes with short half-lives have one major disadvantage and one major advantage
Disadvantage: larger amount of radioactivity per unit time
Advantage: if accident occurs, reaches background radiation levels more rapidly

38. 9.7 Biological Effects of Radiation
Radiation Exposure and Safety
Shielding
Alpha and beta particles need a low level of shielding: lab coat and gloves
Lead, concrete or both are required for gamma rays
Distance from the Radioactive Source
Doubling the distance from the source decreases the intensity by a factor of 4
9.7 Biological Effects of Radiation

39. Radiation Exposure and Safety
Time of Exposure
Effects are cumulative
Types of Radiation Emitted
Alpha and beta emitters are generally less hazardous then gamma emitters
Waste Disposal
Disposal sites are considered temporary
9.7 Biological Effects of Radiation

40. 9.8 Measurement of Radiation
Nuclear Imaging
Isotope is administered
Isotope begins to concentrate in the organ
Photographs (nuclear images) are taken at periodic intervals
Emission of radioactive isotope creates the image

41. 9.8 Measurement of Radiation
Computer Imaging
Computers and television are coupled
Gives a continuous and instantaneous record of the voyage of the isotope throughout the body
Gives increased sensitivity
CT scanner is an example
9.8 Measurement of Radiation

42. 9.8 Measurement of Radiation
The Geiger Counter
Detects ionizing radiation
Has largely been replaced by more sophisticated devices
9.8 Measurement of Radiation

43. 9.8 Measurement of Radiation
Film Badges
A piece of photographic film that is sensitive to energies corresponding to radioactive emissions
The darker the film, when developed, the longer the worker has been exposed
9.8 Measurement of Radiation

44. Units of Radiation Measurement
The Curie
The amount of radioactive material that produces 3.7 x 1010 atomic disintegrations per second
Independent of the nature of the radiation
9.8 Measurement of Radiation

45. 9.8 Measurement of Radiation
Units of Radiation Measurement
The Roentgen
The amount of radiation needed to produce 2 x 109 ion pairs when passing through one cm3 of air at 0oC
Used for very high energy ionizing radiation only
9.8 Measurement of Radiation

46. Units of Radiation Measurement
Rad - Radiation absorbed dosage
The dosage of radiation able to transfer 2.4 x 10-3 cal of energy to one kg of matter
This takes into account the nature of the absorbing material
9.8 Measurement of Radiation

47. Units of Radiation Measurement
The Rem
Roentgen Equivalent for Man
Obtained by multiplication of the rad by a factor called the relative biological effect (RBE)
RBE = 10 for alpha particles
RBE = 1 for beta particles
Lethal dose (LD50) - the acute dosage of radiation that would be fatal for 50% of the exposed population
LD50 = 500 rems
9.8 Measurement of Radiation