The instrument performs a self-test and acquires a new Background count each time it is powered up.
It runs continuously, updating backgrounds whenever no weight is detected inside the chamber.
A new count is initiated every time a door open/door close sequence is detected.
Because of interference caused by other sources, a Geiger counter would be rendered ineffective within the walls of a nuclear containment building for screening individual articles (i.e., clothing, tools, etc.).
A SAM has thick lead walls, which shield the internal scintillation detectors from outside radiation, this allows it to accurately measure the amount of radiation and the type of radionuclides present.