An Empty planchet is for G-M detectors, internal proportional counters, low background beta counters, alpha spectrometers.
Scintillation vial containing scintillant and sample known to contain no radioactivity: for liquid scintillation counters.
Container filled with distilled water: for gamma spectrometers.
Background measurements: Measurements made with either active instruments exposed to a radon-free gas, such as aged air or nitrogen, or for passive detectors by analyzing unexposed detectors. Results are subtracted from the actual field measurements before calculating the reported concentration. Background levels may be due to electronic noise of the analysis system, leakage of radon into the detector, detector response to gamma radiation, or other causes.