Final answer:
The commonly used measure of activity in a master file for radioactive substances is the curie (Ci), defined by the activity of 1 gram of radium-226, related to Marie Curie's research. In business contexts, activity measurement could also refer to tracking data changes in a file.
Step-by-step explanation:
A commonly used measure of the activity in a master file during a specified time period is known as the curie (Ci). The curie is defined as the activity of 1 gram of radium-226. This measure was named in honor of Marie Curie's work with radium, a substance that exhibits radioactive decay.
In a business or technological context, measuring activity might also refer to tracking changes or transactions within a master file. For example, if the master file holds customer data, the activity could be the number of records accessed, modified, added, or deleted over a certain period.