CHAPTER 20 Nuclear Chemistry and Radioactivity 20.3 Rate of Radioactive Decay.
Unit 6 Radioactivity and Nuclear Decay
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Transcript of Unit 6 Radioactivity and Nuclear Decay
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Unit 6Radioactivity and Nuclear
Decay
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Nuclear ChangesChapter 10.1
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What is Radioactivity?
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Radioactivity
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Radioactivity• Radioactive decay is the disintegration of an
unstable atomic nucleus into one or more different nuclides.
• After radioactive decay, the element changes into a different isotope of the same element or into an entirely different element.
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Radioactivity• Nuclear radiation is the release of
particles from the nucleus during radioactive decay.
• These particles can either be alpha, beta, or gamma particles.
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Types of Radiation• Alpha particles can be stopped by paper.• Beta particles can be stopped by aluminum.• Gamma particles can be stopped by lead.
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Alpha Decay• Alpha particle (α) is a positively charged
particle that consists of two protons and two neutrons and that is emitted from a nucleus during radioactive decay.
• This is a helium nucleus.
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Alpha Decay
(Atomic Mass #)
(Atomic #)3. Since the atomic # = 82, then
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Beta Decay• Beta particle (β) is an electron or
positron that is emitted from a nucleus during radioactive decay.
• A positron is a positively charged electron, NOT a proton.
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Beta Decay
(Atomic Mass #)
(Atomic #)3. Since the atomic # = 84, then
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Gamma Decay• Gamma ray (γ) is a high-energy photon
emitted by a nucleus during fission and radioactive decay.
• A photon is a packet of electromagnetic radiation or energy.
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Gamma Decay
(Atomic Mass #)
(Atomic #)3. Since the atomic # = 84, then
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Neutron Emission• Neutron emission consists of matter
that is emitted from an unstable nucleus• Neutrons have no charge, and therefore do
not want to interact with other particles.
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How old are rocks?• If you were asked to determine the age of a
rock, you would probably not be able to do so easily.
• How, then, would you go about finding the rock’s age?
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Radioactive Decay Rates• One way to find the age involves radioactive
decay.• It is possible to predict the time required for half of
the nuclei in a given radioactive sample to decay.• Half-life is the time required for half of the sample
of a radioactive isotope to break down by radioactive decay to form a daughter isotope.
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Half-Life and Exponential Decay• The definition of half-life tells us that after the first half-life time of a
radioactive sample has passed, half of the sample remains unchanged.• After the next half-life, half of the remaining half decays, so only a
quarter of the original element remains.• Of that quarter, half will decay in the next half-life, so only one-
eighth will remain unchanged• This relationship is called exponential decay.
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Half-life Time Frames
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Half-Life Equations
Half- Life Fractions 1st = 1/2 # of 2nd = 1/4 HL’s 3rd = 1/8 4th = 1/16 5th = 1/32
1st = 1/2 2nd = 1/4 3rd = 1/8 4th = 1/16 5th = 1/32