Friday, June 17, 2011
The recent remarkable report that positrons are observed to originate from thunderstorms was nothing short of amazing, namely because subatomic anti-matter particles are not expected to be present in the terrestrial environment. Yet the energy signatures data shows that this is the case. When a positron is near rest and encounters an electron, the two annihilate each other, resulting in the formation of two gamma ray photons emitted in opposite directions.
As it turns out, the gamma rays produced by positron-electron annihilation are the key to proving the existence of positrons in T-storms. Because they're produced by particles of known masses, the gamma rays have energies of 0.511 MeV (mega-electron volts). This energy uniquely identifies them in the data (See. Fig. 1, from Eos Transactions, Vol. 92, No. 22, 'Positrons Observed to Originate from Thunderstorms')
The actual process under investigation (which was originally predicted as long ago as 1925 in a paper by Scottish physicist C.T.R. Wilson) is known as relativistic runaway electron avalanche, which can generate electrons of > 20 MeV in T-storms. Basically, in this process, high-energy electrons collide with the atmosphere originating x-rays and gamma rays. If the latter are sufficiently energetic they will produce electrons and poistrons in the pair production process. (The inverse process also occurs, that is, an energetic positron slows down by ionization in any material.
Unfortunately, physicists will have to settle for detecting positrons indirectly in T-storms since reproduction in the laboratory is not feasible, because of the very high electric field required (hundreds of kilovolts per meter).
One interesting facet is that satellites in orbit around the Earth, originally designed for detection of astrophysical phenomena (e.g. radiation from gamma ray bursters) have come into their own as terrestrial gamma ray detectors. Indeed, the terrestrial gamma rays (associated with -e production) have been found to be several orders of magnitude greater in intensity than solar or stellar sources.