Recently a radon sensor using a glass scintillator in a fiber bundle structure was developed at Rutgers University. This instrument employs a flow of atmospheric air carrying the radon gas and its progeny in trace amounts through the bundle at room temperature. A central problem of interpretation is to distinguish whether the radioactive Rn-222 atoms whose a decay is detected in the sensor are in the gas phase in the narrow spaces between the fibers or are adsorbed on the surfaces of the fibers. At the 43rd National Symposium of the American Vacuum Society (1996), calculated physical adsorption isotherms of radon were reported over a wide range of pressures, coverages, and temperatures. The latter explicitly included room temperature (300 K). The question arises as to whether this calculated isotherm is applicable to the Rutgers sensor. From radioactive considerations alone, in one experiment, it is estimated that there is either an upper bound of 5.5 X 10(-10) Torr on the partial pressure of Rn or an upper bound of 3.9 X 10(-11) monolayers on the coverage. Application of the theoretical isotherms to this experiment yields a unique value of 4.8 X 10(-10) Torr at a coverage of 5 X 10(-12) monolayers (i.e., 13% of all atoms adsorbed). A careful record of counting rates during temperature variations around room temperature was kept. These variations were between 292 and 308 K, and counting rates varied by 26% being highest when the temperature was lower. application of the theoretical isotherms at these two temperatures gave good agreement with the counting rates.