The neutron 'thunder' accompanying large extensive air showers
  The bulk of neutrons which appear with long delays in neutron monitors nearby the EAS core (~'neutron thunder'~) are produced by high energy EAS hadrons hitting the monitors. This conclusion raises an important problem of the interaction of EAS with the ground, the stuff of the detectors and their environment. Such interaction can give an additional contribution to the signal in the EAS detectors at {\em km}-long distances from the large EAS core after a few $\mu s$ behind the EAS front. 
A. D. Erlykin