Decrease of Atmospheric Neutron Counts Observed during Thunderstorms

We report here, in brief, some results of the observation and analysis of sporadic variations of atmospheric thermal neutron flux during thunderstorms. The results obtained with unshielded scintillation neutron detectors show a prominent flux decrease correlated with meteorological precipitations after a long dry period. No observations of neutron production during thunderstorms were reported during the three-year period of data recording.

Figure 1

Schematic layout of an EN detector. Item 1, 6 in. photomultiplier tube (PMT); item 2, scintillator layer; item 3, light proof boxes; item 4, white light reflector.

Figure 2

Pulse induced by neutron capture (“neutrons,” top panel) and background “sharp” pulse (bottom panel).

Figure 3

Noise pulse shape produced by lightning.

Figure 4

Normalized neutron counting rate as a function of the time recorded by the A1 detectors installed at MEPhI-Moscow. The two vertical dashed lines define the duration of the thunderstorm that occurred on 20 July 2012. Pressure corrected data.

Figure 5

Neutron counting rate as a function of the time for two different rainfalls [panels (a) and (b)]. Pressure corrected data.

Figure 6

Neutron counting rate as a function of time registered by the EN-14 detector at Gran Sasso National Laboratory (LNGS) after a rainfall on 20 August 2013. Pressure corrected data.

Figure 7

Example of false neutron flux enhancement during a thunderstorm on 11 August 2012. (a) Outdoor EN-4 detector counting rate vs time; (b) roof EN-5 detector counting rate vs time; (c) electromagnetic noise vs time; (d) very slow pulses vs time from EN-5.

Figure 8

An example of a 35% possible false increase in the neutron counting rate during the 20 July 2012 thunderstorm measured through ${}^3\mathrm{He}$ counters without a pulse shape selection technique. (a) neutron counting rate vs time; (b) pulses with time intervals between the neighbors less than 0.1 ms vs time; (c) overall counting rate ($\text{neutrons}+\text{noise}$) vs time.