Nuclear Decay Reactions & Equations

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NUCLEAR DECAY REACTIONS & EQUATIONS

Transcript of Nuclear Decay Reactions & Equations

Page 1: Nuclear Decay Reactions & Equations

NUCLEAR DECAY REACTIONS & EQUATIONS

Page 2: Nuclear Decay Reactions & Equations

NUCLEAR REACTIONS…

•Chemical reactions – gain/loss/share of electrons

•Nuclear reactions – change of nuclei

•Changes in protons and neutrons

Page 3: Nuclear Decay Reactions & Equations

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

Page 4: Nuclear Decay Reactions & Equations

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

Page 6: Nuclear Decay Reactions & Equations

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….

Page 8: Nuclear Decay Reactions & Equations

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.

Page 9: Nuclear Decay Reactions & Equations

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

Page 10: Nuclear Decay Reactions & Equations

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-= �

Page 11: Nuclear Decay Reactions & Equations

ALPHA DECAY

• Very heavy nuclei

• Too many neutrons and protons

• DECREASES PROTONS AND NEUTRONS!

• Alpha Particle = Helium Nuclei

• α = �

�He

Page 12: Nuclear Decay Reactions & Equations

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!)

Page 14: Nuclear Decay Reactions & Equations

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

Page 16: Nuclear Decay Reactions & Equations

SUMMARY OF DECAY PROCESSES

Page 17: Nuclear Decay Reactions & Equations

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

Page 20: Nuclear Decay Reactions & Equations

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