I.
What is radioactivity?
A. Nuclear radiation – charged particles or
energy emitted by an unstable nucleus.
1. Radioactivity – unstable nucleus emits
one or more particles or energy in the
form of electromagnetic pulse.
2. 4 types of radiation:
a) Alpha particle: α
1) Has +2 charge.
2) Consists of 2 protons and 2
neutrons.
3) Resembles a helium nuclei.42He
(top # = mass #, bottom # =
atomic #)
4) Does not travel far through
matter b/c it is so massive.
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b)Beta particle: β
1)Has –1 charge.
2)Fast moving electrons.
3)Symbol: 0-1e
4)Travel farther and faster through
matter b/c not as massive as α.
5)Most stopped by 3 mm of Aluminum
or 10 mm or wood.
c)Gamma particle: γ
1)Not matter and has no charge =>
electromagnetic energy.
2)High energy radiation.
3)Penetrates up to 60 cm of Al or 7
cm of lead.
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d)Neutron emission:
1)Has no charge.
2)Symbol: 10n.
3)Can travel farther than α or β
particles.
4)Need 15 cm thick block of lead to
stop neutrons.
5)Very dangerous to organisms.
B. Nuclear decay:
1. Alpha decay:
a)An alpha particle is released from an
atom.
b) 22688Ra -> 22286Rn + 42He
c)226 = 222 + 4
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88 = 86 + 2
2. Beta decay:
a)A nucleus gains a proton and loses a
neutron.
b) 146C -> 147N + 0-1e
c)14 = 14 + 0
6 = 7 + -1
d)Mass number does not change.
C. Radioactive Decay Rates
1. Half-life – time required for half a
sample of radioactive nuclei to decay.
a) Varies with each radioactive isotope.
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2. Problems:
1.Radium-226 has ½-life = 1599 years
 How long did it take for 7/8 to
disappear?
1)How much is remaining?
1 – 7/8 = 1/8 remaining
2)How many ½-lives did it take?
½ x ½ x ½ = 1/8, so 3 ½-lives
3)Total time:
3 ½-lives x 1599 yrs. = 4797 yrs
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½-life
• Practice p. 228 (1-5)
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II. Nuclear Fission and Fusion
A. Nuclear Fission – nucleus SPLITS into
two or more smaller fragments,
releasing neutrons and energy.
1. Release of energy is expressed as:
E = mc2
E = energy
(Einstein) m = mass
c = speed of light
2. Nuclear chain reaction – series of
fission reactions in which the
neutrons emitted by a dividing
nucleus cause the division of other
nuclei. (Figure 7-8)
a) Critical mass – minimum mass needed
to sustain a chain reaction.
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B.
Fusion – light nuclei combine at high
temperatures, forming heavier nuclei
and releasing energy.
1. Occurs in stars.
2. 4 H -> 42He + γ (gamma ray)
III. Dangers and Benefits of Nuclear Radiation
A. Dangers:
1. Health concerns:
a) Change hemoglobin
b) Lung cancer (radon in buildings)
c) Radiation sickness (cancer, sterility, hair
loss, etc.)
d) Genetic mutations
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B. Benefits:
1. Used to treat cancers (brain, etc.)
2. Radioactive tracer
3. Nuclear power:
a)Advantages:
1)No gaseous pollutants
2)More known energy reserves than
fossil fuels.
b)Disadvantages:
1)Radioactive products => nuclear
waste
2)Public safety => nuclear meltdown
(Chernobyl and Three-mile island).
3)Very expensive
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