How is radon concentration determined using an electret ion chamber?

Radon concentration is determined using an electret ion chamber by observing differences in voltage before and after testing. The electret ion chamber works by exploiting the ionization produced by radon decay products inside the chamber. When radon gas enters the chamber, it causes ionization as it decays, generating charged particles. This ionization results in a reduction of the electric charge on an electret — a device that stores electric charge.

Before testing, the electret has a certain voltage level, reflecting its initial charge. After the radon test is conducted over a specified time period, the voltage is measured again. The difference in voltage corresponds to the amount of radon gas that has entered the chamber and has caused ionization. This change is then used to calculate the radon concentration in the environment being tested.

The other options, such as measuring temperature changes, visual inspection, or counting particle emissions, do not pertain to how the electret ion chamber specifically measures radon levels. Instead, the unique mechanism of voltage change in response to ionization makes it a reliable method for determining radon concentration.