Nuclear Equations (Cambridge International A-Level Physics)

Representing Simple Nuclear Reactions

• A nucleus can be described using $\mathrm{X} pre_{Z} pre^{A}$notation

${}_{Z}^{A}\mathrm{X}$notation is used to describe the constituents of a nucleus

• The top number A represents the nucleon number or the mass number

  • Nucleon number (A) = total number of protons and neutrons in the nucleus

• The lower number Z represents the proton or atomic number

  • Proton number (Z)= total number of protons in the nucleus

Worked Example When a neutron is captured by a uranium-235 nucleus, the outcome may be represented by the nuclear equation:

U _ 92 ^ 235 + n _ 0 ^ 1 -> Mo _ 42 ^ 95 + La _ 57 ^ 139 + x n _ 0 ^ 1 + 7 e _ - 1 ^ 0

Determine the value of x.

Answer:

Step 1: Balance the nucleon numbers (the top number)

235 + 1 = 95 + 139 + x(1) + 7(0)

Step 2: Rearrange to find the value of x

x = 235 + 1 − 95 − 139 = 2