“…Furthermore, since the collector is small weight and volume, a radon detector using activated charcoal can be conveniently transported even in large quantities. These features of radon collectors are being used in recent research on radon concentration in unique natural environments, such as radioactive spas (Koga et al, 1994), and underground areas (Pensko, 1983), in addition to surveys of general indoors (Murase et al, 1999). As mentioned above, we have several research reports on radon measurements using ACRC in special areas, where the relative humidity is approximately 100%.…”