What is not utilized by a rate of rise heat detector?

A rate of rise heat detector is designed to respond to quickly rising temperatures in an environment, typically indicating a fire. Such detectors primarily rely on specific mechanisms that react to heat rather than chemical or radioactive properties.

Mercury is commonly used in some types of heat detectors because it expands and contracts with temperature changes, allowing for detection of temperature increases. Carbon monoxide can be part of combination smoke and gas detection systems, but it is not a direct mechanism for rate of rise heat detection. Thermal imaging devices utilize infrared sensors to detect temperature changes in their field of view and can identify hot spots caused by fires.

Americium 241, however, is a radioactive isotope often used in ionization smoke detectors but is not relevant to the function of a rate of rise heat detector. This type of heat detector does not utilize radioactive materials in its detection process, which is why it is the correct answer in this context.