Radioactive decay is a wild ride in the atomic world. Alpha, beta, and gamma radiation each have their own unique properties and penetrating powers. Understanding these types of decay is key to grasping nuclear chemistry.
Nuclear equations help us predict decay products and follow radioactive decay series. These series, starting with unstable parent nuclei and ending with stable daughters, are crucial for radiometric dating and understanding nuclear processes in nature.
Radiation Types: Composition and Penetration
Alpha Radiation
- Consists of helium nuclei (2 protons and 2 neutrons)
- Has the least penetrating power
- Stopped by a sheet of paper or skin
- Emitted particles have a +2 charge and a mass of 4 atomic mass units (amu)
- Examples: Radon-222 (²²²Rn) and Uranium-238 (²³⁸U) decay by alpha emission
Beta Radiation
- Consists of high-energy electrons (β⁻) or positrons (β⁺)
- Has moderate penetrating power
- Stopped by a few millimeters of aluminum or plastic
- Beta minus (β⁻) particles are electrons emitted from the nucleus
- Beta plus (β⁺) particles are positrons (antiparticles of electrons) emitted from the nucleus
- Examples: Carbon-14 (¹⁴C) decays by beta minus emission, Sodium-22 (²²Na) decays by beta plus emission
Gamma Radiation
- Consists of high-energy electromagnetic waves
- Has the highest penetrating power
- Requires several centimeters of lead or concrete to be stopped
- Gamma rays have no charge and no mass
- Often accompanies alpha or beta decay
- Examples: Cobalt-60 (⁶⁰Co) and Cesium-137 (¹³⁷Cs) decay by beta emission followed by gamma emission
Nuclear Equations for Decay
Alpha Decay Equations
- General format: ᴀₓX → ᴀ₋₄ₓ₋₂Y + ₂⁴He
- X is the parent nucleus, Y is the daughter nucleus
- a and x represent the mass number and atomic number, respectively
- Example: ²³⁸U → ²³⁴Th + ₂⁴He
Beta Minus Decay Equations
- General format: ᴀₓX → ᴀₓ₊₁Y + e⁻ + ν̄ₑ
- X is the parent nucleus, Y is the daughter nucleus
- e⁻ represents an electron, ν̄ₑ represents an electron antineutrino
- Example: ¹⁴C → ¹⁴N + e⁻ + ν̄ₑ
Beta Plus Decay Equations
- General format: ᴀₓX → ᴀₓ₋₁Y + e⁺ + νₑ
- X is the parent nucleus, Y is the daughter nucleus
- e⁺ represents a positron, νₑ represents an electron neutrino
- Example: ²²Na → ²²Ne + e⁺ + νₑ
Predicting Decay Products
Alpha Decay Products
- Daughter nucleus has an atomic number decreased by 2 compared to the parent nucleus
- Daughter nucleus has a mass number decreased by 4 compared to the parent nucleus
- Example: ²¹⁰Po (parent) → ²⁰⁶Pb (daughter) + ₂⁴He
Beta Minus Decay Products
- Daughter nucleus has an atomic number increased by 1 compared to the parent nucleus
- Daughter nucleus has a mass number unchanged compared to the parent nucleus
- Example: ³H (parent) → ³He (daughter) + e⁻ + ν̄ₑ
Beta Plus Decay Products
- Daughter nucleus has an atomic number decreased by 1 compared to the parent nucleus
- Daughter nucleus has a mass number unchanged compared to the parent nucleus
- Example: ¹⁸F (parent) → ¹⁸O (daughter) + e⁺ + νₑ
Gamma Emission
- Often accompanies alpha or beta decay
- Does not change the atomic number or mass number of the nucleus
- Example: ⁶⁰Co undergoes beta minus decay to ⁶⁰Ni, followed by gamma emission
Radioactive Decay Series
Decay Series Concept
- A sequence of nuclear decays starting from an unstable parent nucleus and ending with a stable daughter nucleus
- Each step involves either alpha or beta decay
- The product of one decay becomes the parent for the next decay in the series
- Used in radiometric dating techniques to determine the age of rocks and minerals
Thorium Series
- Starts with ²³²Th and ends with stable ²⁰⁸Pb
- Includes several alpha and beta decays
- Example: ²³²Th (parent) → ²²⁸Ra (daughter) + ₂⁴He, followed by ²²⁸Ra (parent) → ²²⁸Ac (daughter) + e⁻ + ν̄ₑ
Uranium Series
- Starts with ²³⁸U and ends with stable ²⁰⁶Pb
- Includes several alpha and beta decays
- Example: ²³⁸U (parent) → ²³⁴Th (daughter) + ₂⁴He, followed by ²³⁴Th (parent) → ²³⁴Pa (daughter) + e⁻ + ν̄ₑ
Actinium Series
- Starts with ²³⁵U and ends with stable ²⁰⁷Pb
- Includes several alpha and beta decays
- Example: ²³⁵U (parent) → ²³¹Th (daughter) + ₂⁴He, followed by ²³¹Th (parent) → ²³¹Pa (daughter) + e⁻ + ν̄ₑ