Iodine-131 decays through both beta and gamma emission - HSC - SSCE Chemistry - Question 27 - 2012 - Paper 1

Iodine-131 is utilized for both diagnosis and therapy primarily due to its dual decay mode, which is both beta and gamma emissions. The beta particles emitted, being negatively charged electrons, have low penetration potential and can be aimed at tumor tissues to provide localized treatment. In contrast, the gamma rays have higher penetration ability, allowing them to pass through biological tissues, which is useful for imaging during diagnosis.

On the other hand, Iodine-123, which solely emits gamma rays, is favored for diagnostic purposes only, owing to its high penetration ability which results in clearer imaging but lacks therapeutic impact since it doesn’t provide targeted treatment through beta emission. Thus, the distinct properties of ionizing radiation from each isotope determine their specific applications in medical practices.