What is required for activated-charcoal adsorption (AC) devices to function?

Activated-charcoal adsorption devices rely on the principle of passive sampling, meaning they do not require any external power source to function effectively. These devices operate by allowing radon gas and its decay products to diffuse into a charcoal medium, where they are adsorbed onto the surface of the activated charcoal. The process is entirely based on the physical properties of the charcoal and the inherent diffusion of gases, rather than on electrical or mechanical systems.

As a result, these devices are particularly advantageous for measuring radon levels over an extended period, such as in residential or office settings, since they can be left to sample without the need for continuous monitoring or manual intervention. This passive absorption allows for localized monitoring without the complications of equipment needing electricity or intensive setup and management.

The other choices do not apply to the fundamental working principle of activated-charcoal adsorption devices. Power is unnecessary because the operation is passive, while manual operation and continuous monitoring are features more associated with active measurement systems like electronic detectors, which require power and regular checks.