Energetic radiation associated with lightning stepped-leaders

With the use of a NaI scintillation detector, bursts of radiation with ener gies in excess of 1 MeV were recorded at a mountain-top observatory immedia tely before three, nearby cloud-to-ground, negative lightning strikes. Coin cident recordings of the electric field changes due to the discharges showe d 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 wa s associated with approaching stepped-leaders and may have influenced their development.