Radon has been recognized to be one of the major contributors to the natural radiation causing even lung cancer if it is present
at enhanced levels. Its monitoring at highly confined locations such as underground caves, mines and tube-wells is very essential
for finding the health related hazards among the workers. This paper reports the investigations of the levels of radon, thoron
and their progeny monitored in the tube-wells of the Halls of residence at A.M.U., Aligarh, which lies in the subtropical
region of Indo-Gangetic plains situated in North India. The twin cup dosimeters were fixed for exposure at a depth of 5–35 feet
with a difference of 5 feet from the ground surface. The values of radon and thoron concentrations were found to vary from
6.58 to 1218.57 and 7.41–3226.61 Bq m−3, respectively. The preliminary results of this study for ‘bare mode’ detectors have been separately published and compared
with the recent data.