  Air radon concentration measurement is useful for research on geophysical
effects, but it is strongly sensitive to site geology and many geophysical and
microclimatic processes such as wind, ventilation, air humidity and so on that
induce very big fluctuations on the concentration of radon in air. On the
contrary, monitoring the radon concentration in soil by measuring the thermal
neutron flux reduces environmental effects. In this paper we report some
experimental results on the natural thermal neutron flux as well as the
concentration of air radon and its variations at 4300 m a.s.l. These results
were obtained with unshielded thermal neutron scintillation detectors
(en-detectors) and radon monitors located inside the ARGO-YBJ experimental
hall. The correlation of these variations with the lunar month and 1-year
period is undoubtedly confirmed. A method for earthquakes prediction provided
by a global net of the en-detectors is currently under study.
