Rapid Review

Types of Radioactive Decay

Mode of decay

Effect on parent nucleus

Example

a emission Mass number decreases by 4
Atomic number decreases by 2 _{86Rn²¹⁰ �
₈₄Po²⁰⁶ + ₂He⁴}
b emission Neutron turns into a proton
Atomic number increases by 1
Mass number remains the same _{6C¹⁴ �
₇N¹⁴ + _-1e⁰}
Electron capture Proton turns into a neutron
Atomic number decreases by 1
Mass number remains the same _{53I¹²⁵ + _-1e⁰ �
₅₂Te¹²⁵ + X-ray photon

(The captured electron decelerates and its kinetic energy is converted into electromagnetic energy)}
Positron emission Proton turns into a neutron
Atomic number decreases by 1
Mass number remains the same _{5B⁸ �
₄Be⁸ + ₊₁e⁰}
g emission None except nucleus becomes less excited _{43Tc^99M �
₄₃Tc⁹⁹ + g

(The "M" stands for metastable)}
Spontaneous fission Becomes much smaller _{98Cf²⁵² �
₅₄Xe¹⁴⁰ + ₄₄Ru¹⁰⁸ + 4 ₀n¹}

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Mode of decay	Effect on parent nucleus	Example
a emission	Mass number decreases by 4 Atomic number decreases by 2	_{86Rn²¹⁰ � ₈₄Po²⁰⁶ + ₂He⁴}
b emission	Neutron turns into a proton Atomic number increases by 1 Mass number remains the same	_{6C¹⁴ � ₇N¹⁴ + _-1e⁰}
Electron capture	Proton turns into a neutron Atomic number decreases by 1 Mass number remains the same	_{53I¹²⁵ + _-1e⁰ � ₅₂Te¹²⁵ + X-ray photon (The captured electron decelerates and its kinetic energy is converted into electromagnetic energy)}
Positron emission	Proton turns into a neutron Atomic number decreases by 1 Mass number remains the same	_{5B⁸ � ₄Be⁸ + ₊₁e⁰}
g emission	None except nucleus becomes less excited	_{43Tc^99M � ₄₃Tc⁹⁹ + g (The "M" stands for metastable)}
Spontaneous fission	Becomes much smaller	_{98Cf²⁵² � ₅₄Xe¹⁴⁰ + ₄₄Ru¹⁰⁸ + 4 ₀n¹}