Edexcel A Level (IAL) Physics-5.15 Nuclear Decay Equations- Study Notes- New Syllabus

Writing and Interpreting Nuclear Equations Using Particle Symbols

Nuclear equations describe changes in atomic nuclei during radioactive decay or nuclear reactions. They must obey conservation of nucleon number and conservation of charge.

Nuclear Notation

An атом is written as:

• \( A \) = mass (nucleon) number = protons + neutrons
• \( Z \) = proton (atomic) number
• \( X \) = chemical symbol

 Relevant Particle Symbols

• Alpha particle: \( ^4_2\alpha \)
• Beta minus particle (electron): \( ^0_{-1}\beta \)
• Gamma ray: \( ^0_0\gamma \)
• Neutron: \( ^1_0 n \)
• Proton: \( ^1_1 p \)
• Antineutrino: \( \bar{\nu} \)

Note: Gamma rays carry energy but no mass or charge.

Conservation Rules

• Total mass number is conserved.
• Total charge (atomic number) is conserved.

These rules apply to all nuclear equations.

Alpha Decay

In alpha decay, the nucleus emits an alpha particle.

\( ^A_Z X \rightarrow ^{A-4}_{Z-2} Y + ^4_2\alpha \)

Example:

\( ^{238}_{92}\mathrm{U} \rightarrow ^{234}_{90}\mathrm{Th} + ^4_2\alpha \)

• Mass number decreases by 4
• Atomic number decreases by 2

 Beta Minus Decay

In beta minus decay, a neutron changes into a proton.

\( n \rightarrow p + \beta^- + \bar{\nu} \)

At the nuclear level:

\( ^A_Z X \rightarrow ^A_{Z+1} Y + ^0_{-1}\beta + \bar{\nu} \)

Example:

\( ^{14}_{6}\mathrm{C} \rightarrow ^{14}_{7}\mathrm{N} + ^0_{-1}\beta + \bar{\nu} \)

• Mass number unchanged
• Atomic number increases by 1

 Gamma Emission

Gamma emission occurs when a nucleus releases excess energy.

\( ^A_Z X^* \rightarrow ^A_Z X + ^0_0\gamma \)

• No change in mass number
• No change in atomic number

 Interpreting Nuclear Equations

To interpret a nuclear equation:

1. Identify the emitted particle.
2. Check conservation of mass number.
3. Check conservation of charge.
4. Determine the change in the nucleus.