Tracer
/trˈeɪsər/
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Definition
(noun) A compound, element, or isotope used to track the progress or history of a natural process.
Sentence Examples
Positron Emission Tomography uses a radioactive tracer to visualize metabolic activity within the human body.
CEFR Practice Quiz
The doctor used a radioactive ____ to track the flow of blood through the patient's heart during the scan today.