General Chemistry

1. Chapter 9
The Nucleus, Radioactivity, and
Nuclear Medicine
Denniston
Topping
Caret
7th
Edition
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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. 9.1NaturalRadioactivity
B11
5
atomic symbol
atomic number
number of protons
mass number
number of
protons and
neutrons
Nuclear Symbols

4. B11
5
9.1NaturalRadioactivity
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

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
9.1NaturalRadioactivity

6. 9.1NaturalRadioactivity
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

7. ααHeHe 4
2
4
2
24
2
+
9.1NaturalRadioactivity
Alpha Particles
• Alpha particle (α) - 2 protons, 2 neutrons
• Same as He nucleus (He2+
)
• Slow moving, and stopped by small
barriers
• Symbolized in the following ways:

8. ββe 0
1-
0
1−
9.1NaturalRadioactivity
Beta Particles
• Beta particles (β) - 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. γ
9.1NaturalRadioactivity
Gamma Rays
• Gamma rays (γ) - pure energy
(electromagnetic radiation)
• Highly energetic
• The most penetrating form of radiation
• Symbol is simply…

10. 9.1NaturalRadioactivity 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

11. 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

12. 9.3Propertiesof
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 1
H) with more protons than
neutrons are unstable
Stable Radioisotopes

13. 9.3Propertiesof
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

14. Half-Lives of Selected
Radioisotopes
9.3Propertiesof
Radioisotopes

15. 9.3Propertiesof
Radioisotopes
Decay Curve for the Medically
Useful Radioisotope Tc-99m

16. 9.3Propertiesof
Radioisotopes
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 5.0 ng 2.5 ng 1.3 ng 0.63 ng
1st
half-life 2nd
half-life 3rd
half-life 4th
half-life
• 0.63 ng remain after 4 half-lives

17. 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

18. 9.6MedicalApplicationsof
Radioactivity
• 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
Cancer Therapy Using Radiation

19. 9.6MedicalApplicationsof
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 131
I and 125
I will allow the study of
how the thyroid gland is taking in iodine

20. 9.6MedicalApplicationsof
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

21. 9.6MedicalApplicationsof
Radioactivity
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