Which of the following is crucial for ensuring reliability in low concentration measurements?

Calibration of equipment is critical for ensuring reliability in low concentration measurements because it helps maintain the precision and accuracy of the measurement instruments used. Calibration involves comparing the measurement outputs of instruments against known standards or reference points. This process ensures that the readings produced accurately reflect the actual concentrations of radon in the environment, particularly when measuring low levels where variations can be significant.

When instruments are calibrated, any deviations or errors in the measurement can be identified and corrected, leading to more trustworthy data. In low concentration scenarios, where the differences can be subtle, proper calibration becomes even more essential, as small measurement errors can affect the reliability of the results and potentially lead to incorrect conclusions regarding radon levels and associated health risks.

Other methods like early detection techniques, high-grade filters, or standard measurement intervals play important roles in different contexts but do not directly ensure the reliability of low concentration measurements as effectively as calibration does.