What is a dosimeter used for?

A dosimeter is specifically designed to measure an individual's exposure to ionizing radiation. This tool is essential for monitoring radiation levels that personnel may be exposed to in environments where radioactive materials are present. By collecting and quantifying the exposure over time, dosimeters help ensure that individuals do not surpass established safety limits, thereby protecting their health.

In contrast, options discussing filtering air particles or assessing temperature levels do not pertain to the purpose of a dosimeter. Similarly, while indicating radiation sources might seem relevant, the dosimeter's main function is focused on measuring exposure rather than identifying or locating sources of radiation. Therefore, the correct answer highlights the dosimeter's critical role in radiation safety by monitoring exposure levels effectively.