What is the primary reason measurement devices should not be placed on natural stone surfaces?

Placement of measurement devices on natural stone surfaces can lead to inaccuracies primarily due to gamma interference. Natural stones, such as granite, can contain varying levels of radioactive minerals, including uranium, thorium, and potassium-40. These elements may emit gamma rays, which can interfere with the readings of radiation measurement devices. If a measurement device is placed in proximity to these radioactive materials, the detected levels may reflect not just the radon being measured but also the background radiation from the stone itself, leading to misleading results.

Moisture absorption is a factor when considering the integrity of certain devices, but it does not directly impact the accuracy of the radon measurements in the same way that gamma interference does. Structural instability may affect the placement of the device in a physical sense, but it is not as directly related to the measurement of radon levels as gamma interference. Therefore, the central issue with placing measurement devices on natural stone surfaces revolves around the potential for gamma rays emitted by the stones to skew the data collected.