Observation of 2.45 MeV neutrons correlated with natural atmospheric lightning discharges by Lead‐Free Gulmarg Neutron Monitor

Abstract

The first experimental evidence of detecting the neutrons correlated with the natural atmospheric lightning discharges (NALD) was obtained with Lead‐Free Gulmarg Neutron Monitor (LFGNM) operating at High Altitude Research Laboratory, Gulmarg, Kashmir, India, and was reported in the year 1985. The neutron observations still continue with LFGNM. However, the current configuration of LFGNM is the upgraded version of the system used earlier to record neutron bursts (in the recording period of 320 μs in four successive electronic gates of 80 μs each) supposedly originating from an NALD. In the current system the neutron recording time period/interval has been extended to 1260 μs with 63 successive gates of 20 μs each. The system also simultaneously records the differential times—maximum up to 14—between the consecutive strokes of a multistroke lightning flash. The distance between an NALD channel and LFGNM setup is determined empirically by making use of the time delay (td)/time of flight (TOF) measurement of the first detected neutron subsequent to the sensing of the electrostatic field variation caused by the initiation of an NALD in the ambient atmosphere of the LFGNM setup. Assuming a priori incident energy as 2.45 MeV of the detected neutrons supposedly generated due to the fusion of deuterium ions in the lightning discharge channel leads to quantifying the neutron emission flux if the NALD channel distance with respect to the LFGNM setup is established. In this paper we discuss the experiment and the time profiles of several of a large number of the major neutron burst events recorded with LFGNM in association with NALDs. Moreover, a rare and an extraordinary neutron burst event, in terms of its associated “td/TOF” of first detected neutron after triggering, recorded by this system is specifically discussed. In this event, the recorded TOF of 14 μs of the escaping neutron detected by the system immediately after getting triggered by the NALD that struck a nearby tree found located just around 300 m (physically measured) away from the detector position indicates the energy of the detected neutron ϵn ≈2.45 MeV. In the light of this only event, we, therefore, cautiously suggest deuteron‐deuteron fusion reaction, 2H(2H,n)3He, as one of the possible mechanisms of the neutron generation correlated with an NALD. Nonetheless, the observations so far have reconfirmed production of neutrons in an NALD.

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“…Since the late 1990s, many other studies have also claimed statistically significant detections of thunderstorm-produced neutrons from all over the world [7][8][9][10] . However, the detectors could not distinguish neutrons from other particles such as electrons and γ-ray photons -all three would produce similar electriccurrent pulses in the detectors 11 .…”

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“…The first, with null result, attempt (Fleisher, ) to detect thunderstorm‐related neutrons was followed by communications claiming neutron flux enhancements in thunderstorms (Bratolyubova‐Tsulukidze et al, ; Chilingarian et al, , , , , ; Gurevich et al, ; Ishtiaq et al, ; Kuroda et al, ; Kuzhewskiĭ, ; Martin & Alves, ; Shah et al, ; Shyam & Kaushik, ; Starodubtsev et al, ). Possibly, after Libby and Lukens the neutron generation in thunderstorms was related to reactions in lightning channels (Fleisher, ; Kuzhewskiĭ, ; Shah et al, ; Shyam & Kaushik, ).…”

“…In view of the shortcomings in Babich and Roussel‐Dupré () and given new experimental (Briggs et al, ; Chilingarian et al, , , , , ; Connaughton et al, ; Cummer et al, , ; Gurevich et al, ; Ishtiaq et al, ; Kelley et al, ; Kuroda et al, ; Marisaldi, Fuschino et al, ; Marisaldi, Tavani et al, ; Martin & Alves, ; Starodubtsev et al, ; Tavani et al, ; Tsuchiya et al, , , , ) and computational (Babich, ; Babich et al, , ; Babich, Bochkov, Kutsyk et al, ; Babich, Bochkov, Donskoĭ et al, ; Babich, Bochkov, Kutsyk et al, ; Babich, Bochkov, Dwyer et al, ; Babich et al, ; Carlson et al, ; Celestin, Xu, & Pasko, ; Dwyer, ; Dwyer, Grefenstette, & Smith, ; Kelley et al, ; Tsuchiya et al, ; Xu, Celestin, & Pasko, ) data on thunderstorm γ rays and neutrons, reanalyzing of the problem of the production by thunderstorms is expedient. The new analysis is based not on a limited number of detections of thunderstorm neutrons as in Babich and Roussel‐Dupré () but on a vast amount of new data obtained from detecting of thunderstorm ground enhancements, i.e., enhanced fluxes of high‐energy electrons, hard γ rays, and neutrons on the Earth's surface, which have been copiously collected on Mount Aragats, Armenia (3250 m above sea level) (Chilingarian et al, , , , , ) and at other sites worldwide: Japan (sea level and 2770 m above sea level) (Tsuchiya et al, , , ); Tibet, China (4300 m above sea level) (Tsuchiya et al, ); Himalayas, India (2743 m above sea level) (Ishtiaq et al, ; Shah et al, ); and Tien Shan, Kazakhstan (3340 m above sea level) (Gurevich et al,…”

“…An inclusion of two‐neutron events threefold increases the δ magnitude. On the other hand, during the observational period from year 2006 to 2009, Ishtiaq et al () recorded events with more than two neutrons correlated with each of sensored 150 EMPs; 19 and 13 of these events contained more than five and more than 10 neutrons, respectively. During May and June of the year 2006, when the thunderstorms occurred in the vicinity of the neutron monitor, 60 EMPs were sensored, with which 50 recorded events were correlated with ≥4 neutrons per event.…”

“…During May and June of the year 2006, when the thunderstorms occurred in the vicinity of the neutron monitor, 60 EMPs were sensored, with which 50 recorded events were correlated with ≥4 neutrons per event. In five of them more than 20 neutrons per event were recorded (Ishtiaq et al, ). Hence, according to these observations δ may vary from about 0.01 to 1 depending on the number of detected neutrons.…”