NUCLEAR DECAY REACTIONS & EQUATIONS

NUCLEAR REACTIONS…

•Chemical reactions – gain/loss/share of electrons

•Nuclear reactions – change of nuclei

•Changes in protons and neutrons

CHEMICAL, NUCLEAR OR PHYSICAL?

•2 HCl + CaCO3 � CaCl2 + H2O + CO2

•H2O (g) � H2O (l)

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•C (graphite) � C (diamond)

•HNO3 + Zn � ZnNO3 + H2

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N

Chemical

Physical

Nuclear

Physical

Chemical

Nuclear

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

TRANSMUTATION

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.

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.

WHY DECAY??

•The neutron to proton ratio determines the decay

that will occur.

•Too many neutrons to protons – beta emission

• Increases protons

•Too many neutrons and protons – alpha emission

• Decreases protons and neutrons

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

•

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.

SUMMARY OF DECAY PROCESSES

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

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!!

NUCLEAR EQUATIONS

• Plutonium-238 undergoes alpha decay and forms an unknown product.

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��Pu �

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X +

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�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

NUCLEAR EQUATIONS

• Write a balanced nuclear equation for the reaction in which oxygen-15

undergoes positron emission.

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�β +

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N

• What type of decay occurs when thorium-229 decays to form radium-225?

• Alpha Decay

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