nuclear decay reactions & equations
TRANSCRIPT
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NUCLEAR DECAY REACTIONS & EQUATIONS
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NUCLEAR REACTIONS…
•Chemical reactions – gain/loss/share of electrons
•Nuclear reactions – change of nuclei
•Changes in protons and neutrons
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CHEMICAL, NUCLEAR OR PHYSICAL?
•2 HCl + CaCO3 � CaCl2 + H2O + CO2
•H2O (g) � H2O (l)
•���
��U �
���
��Th +
�
�α
•C (graphite) � C (diamond)
•HNO3 + Zn � ZnNO3 + H2
•��
�C �
�
�β +
��
N
Chemical
Physical
Nuclear
Physical
Chemical
Nuclear
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TRANSMUTATION
•Transmutation – the conversion of an atom of one element
to the atom of another element
• Induced transmutation – striking nuclei with high velocity
particles
•Can occur from:
• Radioactive decay
• Particles bombarding the nucleus of an atom
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TRANSMUTATION
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TRANSURANIUM
•All elements above atomic number 82 are
radioactive
• Transuranium elements - The elements in the periodic table with atomic numbers above 92, the atomic number of uranium
• All transuranium elements undergo transmutation.
• None of the transuranium elements occur in nature, and all are radioactive.
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STRONG FORCE• Remember, in the nucleus of stable elements….
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NUCLEI AND DECAY
• More than 1,500 different nuclei are known.
• 264 are stable and do not decay or change with time.
• In a region called the band of stability.
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WHY DECAY??
•The neutron to proton ratio determines the decay
that will occur.
•Too many neutrons to protons – beta emission
• Increases protons
•Too few neutrons to protons – electron capture, positron
emission
• Decreases protons
•Too many neutrons and protons – alpha emission
• Decreases protons and neutrons
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BETA DECAY
• Above the band of stability
• Too many neutrons to protons
• INCREASES NUMBER OF PROTONS!!
• Beta particle = fast moving electron that is emitted when a neutron
converts into a proton
• n � p + β
• β or e-= �
�
•
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ALPHA DECAY
• Very heavy nuclei
• Too many neutrons and protons
• DECREASES PROTONS AND NEUTRONS!
• Alpha Particle = Helium Nuclei
• α = �
�He
•
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POSITRON EMISSION• Below the band of stability
• Low neutron to proton ratio
• DECREASES NUMBER OF PROTONS!
• Positron = particle that has the same mass as an
electron but an opposite charge
• Positron emission = proton in nucleus is converted
to a neutron and a positron and the positron is
emitted
• p � n + β+
• β+ or e+ = �
��
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ELECTRON CAPTURE
• Below the band of stability
• Low neutron to proton ratio
• DECREASES NUMBER OF PROTONS!
• Electron capture = nucleus draws in a surrounding electron and
combines with a proton to form a neutron
• p + e- � n
• e- = �
�(Also a β particle!)
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GAMMA EMISSION
• The emission of gamma radiation from a nucleus does not involve
any change in the atomic (proton) number or mass number.
• When a 'new' nucleus is formed it tends to have excess energy making it
potentially unstable.
• To become more 'nuclear stable' the nucleus loses some energy as a burst
of gamma radiation but the proton and neutron numbers do not change.
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DECAY PROCESSES
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SUMMARY OF DECAY PROCESSES
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RADIOACTIVE DECAY SERIES
• Radioactive decay series –
series of nuclear reactions
that begins with an
unstable nucleus and
results in the formation of
a stable nucleus
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NUCLEAR EQUATIONS
•Nuclear reactions (alpha decay, beta decay,
positron emission, and electron capture) are all
expressed by balanced nuclear equations.
•Mass numbers and charges are conserved!!
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NUCLEAR EQUATIONS
• Plutonium-238 undergoes alpha decay and forms an unknown product.
���
��Pu �
�X +
�
�He
• What is the unknown product? (X)
• Find the mass: 238 = A + 4
A = 234
• Find the atomic number: 94 = Z + 2
Z = 92
• Unknown product: ���
��U
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NUCLEAR EQUATIONS
• Write a balanced nuclear equation for the reaction in which oxygen-15
undergoes positron emission.
•��
�O �
�
�β +
��
N
• What type of decay occurs when thorium-229 decays to form radium-225?
• Alpha Decay
•���
�� Th�
���
��Ra +
�
�He