Thermal neutrons’ response to the GLEs Original Research Article

Thermal neutrons’ flux near the Earth’s crust is very sensitive regarding different processes and phenomena both in the near-Earth space and in the Earth’s crust by reason of the dual nature of the thermal neutron flux. Its first source is associated with high-energy particles of cosmic rays penetrating into the Earth’s atmosphere and interacting with its elements. The second source originates from the radioactive gases contained in the Earth’s crust. So the contributions of these two sources are specified by the Earth’s crust conditions and its movements, on one hand and variations of high-energy particles flux near the Earth. The paper presents the observations of the thermal neutrons flux during the Ground level enhancements (GLEs) recorded on January 20, 2005 and December 13, 2006. January 20, 2005 event became the first clear response to GLE in thermal neutrons’ data during the whole period of observations (from 1994). The biggest response observed at Antarctic experimental unit, was in good time correspondence with the response at Neutron Monitors (NMs). The difference of the amplitudes of the response at these units must be explained by different energy ranges of the registered particles. GLE on December 13, 2006 registered by one of Moscow thermal neutrons’ units, corresponded to NM data both in amplitude and time of the observed effect. The absence of the response at another Moscow unit must be linked to energy spectra of this event different from the previous and higher sensitivity of the first unit to the relative low energy neutrons coming from above due to “thin roof”