How is the specific activity of an isotopic source commonly measured?

The specific activity of an isotopic source is most commonly measured in curies per gram. Specific activity represents the radioactivity of a material per unit mass and indicates how much radioactive decay can occur in a given amount of the substance.

Curie is a unit of radioactivity that quantifies the decay of radioactive material. Specifically, one curie is defined as 37 billion disintegrations per second. By expressing specific activity in curies per gram, it allows for a straightforward understanding of how much radioactivity is contained in a sample relative to its mass. This is essential for applications in radiographic testing, where the intensity of radiation from an isotopic source can significantly influence the quality of imaging results.

The other measurement options do not relate directly to how radioactivity is quantified in the context of specific activity. Milligrams per gram would be used for concentration measures of substances, rad is a unit of absorbed radiation dose, and sievert is a unit of biological effect of radiation, not a direct measure of activity in terms of decay. Thus, for quantifying radioactivity relative to mass, curie per gram is the appropriate and widely accepted unit.