Why do variations between duplicate measurements increase with lower radon concentrations?

The correct answer emphasizes that bias and background interferences are more pronounced at lower radon concentrations, impacting measurement accuracy. At lower levels of radon, the signal detected by measurement devices may approach the noise level of those devices. As a result, small variations or fluctuations in the environment, such as changes in temperature, humidity, or other background radiation can significantly alter the readings. This is because the relative impact of these interferences is proportionally greater when the absolute level of radon is lower, making duplicate measurements appear more inconsistent.

Instruments measuring radon are calibrated for a specific range of concentrations. When radon levels drop, the precision of these instruments diminishes, leading to an increased variation between measurements. It's at these lower concentrations where the effect of background interference becomes more evident, causing discrepancies that would not be as impactful in higher concentration scenarios where the radon signal is strong and clear. Thus, understanding the limitations of measurement accuracy at varying radon levels is crucial in ensuring reliable data collection and assessment.