Energetic radiation associated with lightning stepped-leaders

With the use of a NaI scintillation detector, bursts of radiation with energies in excess of 1 MeV were recorded at a mountain-top observatory immediately before three, nearby cloud-to-ground, negative lightning strikes. Coincident recordings of the electric field changes due to the discharges showed that, in each case, the bursts began between 1 and 2 milliseconds before and continued until the onset of the first return stroke. This radiation was associated with approaching stepped-leaders and may have influenced their development.