Abstract
The neutron monitor in Barentsburg is equipped with a modernized data acquisition system which allows registering time intervals between pulses with 1 μs accuracy. This high resolution makes it possible to study such fast and transient phenomenon like multiplicity. A multiplicity event is an isolated sequence of pulses with short time intervals between them. The Barentsburg neutron monitor consists of three sections, which are spaced at 5 m. In the present work a two-section multiplicity was studied, i.e. multiplicity events which are formed by pulses of two sections. We have assigned that each section must input no less than 4 pulses into an event to have a two-section multiplicity. The probability of a random coincidence of single pulses in this case is around 10–8 (one event per ~10 days). But the real number of such events is ~10 per day. The other characteristics of two-section multiplicity events (total time duration, time profile etc.) are similar to the values of one section multiplicity. So this is undoubtedly real multiplicity. We consider it to be an effect of atmospheric hadronic shower on the NM. The cross-section size of such shower is estimated about 10 m according to the distance between sections.
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