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Positron annihilation inside thunderclouds creates a 511-keV photon flux enhancement. This finding, observed by the In-flight Lightning Damage Assessment System (ILDAS) on an aircraft, links atmospheric electricity to gamma ray emissions.

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Area of Science:

  • Atmospheric physics
  • Nuclear physics
  • Aerospace engineering

Background:

  • Thunderstorms are associated with complex electrical phenomena.
  • High-energy photons have been detected in atmospheric conditions.
  • Positron annihilation produces characteristic gamma ray signatures.

Purpose of the Study:

  • To investigate the source of 511-keV photon flux enhancements observed within a thundercloud.
  • To correlate gamma ray emissions with in-cloud electrical activity.
  • To determine the location of positron annihilation.

Main Methods:

  • In-flight measurements using the In-flight Lightning Damage Assessment System (ILDAS) on an A340 test aircraft.
  • Detection of gamma rays with two onboard detectors.
  • Measurement of electromagnetic field variations using an onboard antenna.
  • Geant4 Monte Carlo simulations to model the aircraft and estimate emission areas.

Main Results:

  • A significant increase in gamma ray count rate, specifically 511-keV photons and their Compton component, was detected.
  • Ten distinct gamma ray enhancements, each lasting approximately 1 second, were observed.
  • These enhancements were synchronous with fast electromagnetic field variations attributed to static discharges from the aircraft.
  • Simulations indicated positron annihilation occurred in the immediate vicinity or within the aircraft structure.

Conclusions:

  • Positron annihilation is a confirmed source of 511-keV photon flux within thunderclouds.
  • Atmospheric electrical discharges, particularly static discharges from aircraft, can trigger these events.
  • The study provides evidence for high-energy photon production linked to atmospheric electricity and aircraft interaction.