Which of the following describes a measure of exposure related to both the number of people exposed and the radiation dose received?

The term that best describes a measure of exposure related to both the number of people exposed and the radiation dose received is "person-rem." This unit quantifies the total exposure to a population and accounts for both the dose of radiation each individual receives and the number of individuals exposed. It is particularly useful in assessing the impact of radiation on health within a population, making it an essential measure in radiation epidemiology and public health assessments.

Person-rem is calculated by multiplying the dose (in rem) by the number of people exposed. This way, it gives a comprehensive picture of the potential health risk from radiation exposure within a group. As such, it's a critical concept for environmental health specialists who evaluate the implications of radiation exposure and work to mitigate risks to public health.

Other options, while related to radiation, do not encapsulate the combination of both the number of individuals and the dose in the same way. Decay rate pertains to how quickly a radioactive substance loses its radioactivity, dose equivalent quantifies the biological effect of radiation but does not directly involve the number of people, and radiation dose reflects exposure to an individual without considering the population aspect.