131_I_53 is an artificially made radioactive isotope of iodine, produced during the operation of nuclear power plants and the detonation of nuclear bombs. Exposure to high concentrations of 131 53I represents a serious risk for human health. However, small doses of this radioactive isotope are put to good use in medical studies. 131 53I is widely used in treating thyroid cancer and in diagnosis of abnormal liver and kidney function.

Required:
What is emitted when the radioactive nucleus of 131_I_53 decays to form the stable isotope of xenon 131_Xe_54?

Since the atomic number of 131_I_53 increases by one to 131_Xe_54, we have the release of a beta particle since only a beta particle can cause a change in atomic number without a change in mass number. Since a beta particle is one electron, ₋₁⁰e, our nuclear equation is

¹³¹I₅₃ → ¹³¹X₅₄ + ₋₁⁰e

The atomic and mass numbers on both sides are balanced

mass number 131 = 131 + 0 = 131

atomic number 53 = 54 - 1 = 53

Thus a beta particle is emitted