Variations observed in environmental radiation at ground level.

To investigate and monitor environmental radiation at ground level, Physikalisch-Technische Bundesanstalt (PTB) has installed several dosemeters and particle detectors at the new Ambient Radiation Dosimetry Site. The separation of the total ambient dose equivalent rate H*10(env) of environmental radiation into the different contributions is achieved by comparing the data of different detectors: the muon detector MUDOS, a modified neutron dosemeter, proportional counters and ionisation chambers. The response of the latter two dosemeter systems to cosmic radiation was determined at the Cosmic Radiation Dosimetry Site on a lake near PTB. Besides the increase of the ambient dose equivalent rate during rainfall, variations owing to air pressure, solar activity and temperature changes in the upper atmosphere are observed. Without rain and solar effects, smooth variations of the cosmic component at ground level of +/-6.9 nSv h(-1) should be treated as naturally occurring variations during an entire year.