Measuring ionizing radiation in the atmosphere with a new balloon-borne detector

Increasing interest in energetic particle effects on weather and climate has motivated development of a miniature scintillator-based detector intended for deployment on meteorological radiosondes or unmanned airborne vehicles. The detector was calibrated with laboratory gamma sources up to 1.3 MeV and known gamma peaks from natural radioactivity of up to 2.6 MeV. The specifications of our device in combination with the performance of similar devices suggest that it will respond to up to 17 MeV gamma rays. Laboratory tests show that the detector can measure muons at the surface, and it is also expected to respond to other ionizing radiation including, for example, protons, electrons (>100 keV), and energetic helium nuclei from cosmic rays or during space weather events. Its estimated counting error is ±10%. Recent tests, when the detector was integrated with a meteorological radiosonde system and carried on a balloon to ~25 km altitude, identified the transition region between energetic particles near the surface, which are dominated by terrestrial gamma emissions, to higher-energy particles in the free troposphere. Plain Language Summary High-energy subatomic particles from space, known as cosmic rays, constantly enter, and ionize, the atmosphere. Space weather events, such as storms on the Sun, can also episodically inject extra energetic particles into the atmosphere. The ions created by these particles have a small effect on the weather through cloud microphysics, infrared radiation, and lightning. Measurements of atmospheric ionization with the existing technology are patchy and infrequent, and models cannot yet represent the known variability. This motivated development of a small and low-cost sensor that can be piggy backed on routine meteorological radiosonde flights. Our sensor offers improved functionality since it can measure the energy, and therefore the type, of ionizing particles. Here we describe sensor development and testing, demonstrating that it can respond to a range of energies and particle types. We present results from two flights over the UK in August and October 2016 where we show that the ionization near the surface is mainly from natural radioactivity, but at higher altitudes, the ionization is dominated by higher-energy particles, as expected. The sensor can respond to many different types of energetic particles and is versatile enough to interface with a wide range of instruments.