Which statement about specific activity is true?

• A. It is the energy emitted per decay.
• B. It is the activity per unit mass or volume used to compare materials and estimate dose from a given mass.
• C. It is the total activity of a source regardless of mass.
• D. It is the activity per unit time per unit area.

Answer: (B)

Specific activity tells you how radioactive a material is for a given amount. It equals the activity divided by mass (or by volume for liquids), so you get units like Bq/kg or Ci/kg. This normalization lets you compare different materials on a common basis and estimate the dose from a specific mass because the dose depends on how much material is present, not just the total activity. If you only know the total activity, two samples with different masses can have very different radiological impacts; normalizing to mass allows meaningful comparisons and dosimetry.

It’s not the energy emitted per decay—that’s the decay energy. It’s not the total activity of the source regardless of mass—that would be the activity itself, not per-mass. And it’s not activity per unit time per unit area—that would describe a flux or surface activity, not specific activity.