Natural thermal neutron flux long-term variations at 4300 m a.s.l

Long-term variations in the natural thermal neutron flux in Tibet at an altitude of 4300 m above sea level are studied using scintillation electron-neutron detectors (en-detectors) developed at the Institute for Nuclear Research, Russian Academy of Sciences. Substantial growth (on the level of several percent each year over the last 3.5 years) in the thermal neutron flux recorded by the en-detectors is observed. The effect is explained by an increase in the low-energy cosmic ray flux, due to decreasing solar activity in the current solar cycle. Seasonal variations in anti-correlation with the rain season were also established.