Ground gamma radiation associated with lightning and rain precipitation

Abstract

Gamma-rays with energies of 20 MeV associated with lightning phenomena by satellite and ground instruments in recent times has triggered interest in this natural phenomena. The inability of satellites to monitor the Brazilian Geomagnetic Anomaly (BGA) region and the extensive multi-parameter observational efforts of lightning phenomena in Brazil has provided incentive for this GGR experiment. A monitor system with a large area NaI(Tl)detector was set up near two rocket launchers for induced lightning. In few months of operation in 2005, increases in gamma-rays with intensity proportional to rain precipitation and an increase due to lightning induced by a rocket launch is monitored. The decay period of ~ 30 min, definitely identified the radon progeny in rain but we have not identified the source in the case of lightning. The spectral information indicates a power law index for both the phenomena. Although not conclusive, we report here an indication of a gamma-ray line at 1240 keV. Interestingly, proton interactions with Ar (an atmospheric constituent) produces an isotope 39Cl which has emission at this energy.