Last edited Sun Oct 27, 2024, 09:53 AM - Edit history (2)
X-rays are produced by electrons being bumped into high-energy orbitals from the very lowest-energy orbitals in an atom. As the electrons drop back down into the core orbitals, they emit EM radiation at very short wavelengths. Gamma rays, in contrast, are formed by similar excitations of nucleons with the nucleus, and since the energies involved are typically much larger, can reach much shorter wavelengths. The least energetic known gamma radiation is actually in the far UV, though.
The wavelengths involved in the two types of radiation overlap extensively, so there is, TBOMK, no way to distinguish between gamma and X-rays within the range of overlap, unless possibly there is some difference in polarization, which is (again TBOMK) not easy to measure.
The point being: gamma rays from lightning need not imply nuclear process are taking place; it could be, instead, that X-rays are being emitted by highly excited multiply charged ions, which will have larger energies as the charge increases. It's hard to know what atoms with high atomic numbers (which give shorter-wavelength X-rays) would be present at high altitudes, though it's plausible that very common ions like Ca, Fe, Zn might be present in miniscule quantities. It wouldn't necessarily take much.
The article mentions that gamma rays are due to collisions of high-energy electrons with air molecules, which I suppose could imply (it's not clear) that the electrical energy is being converted directly radiation on impact (Brehmsstrallung, or "braking radiation" ), just as in an X-ray tube, without necessarily any intermediate excited states involved. X-ray tubes typically operate at a few kilovolts; higher voltage in an electrical storm could generate much shorter wavelengths.
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