Energy spectra from ionising radiation in the troposphere and stratosphere measured with a super-miniaturised scintillator detector

Motivated by the need to measure and understand the role of energetic particles in atmospheric processes, a super-miniaturised (40 g) CsI(Tl) scintillator (“microscintillator”) coupled to a PiN photodiode has been developed and tested in the atmosphere up to an altitude of 32 km. Specifically, a microscintillator and Geiger counters were flown with a meteorological radiosonde in July 2024. Separately, a hand-held microscintillator was carried on transatlantic passenger flights in March 2025. These deployments all occurred during calm space weather conditions, meaning that particles created by the galactic cosmic ray (GCR) background could be measured within the energy range of the instrument, 0.02–10 MeV. Geiger and microscintillator count rates from the balloon were well-correlated, with maximum count rates at ∼21 km, consistent with previous work. The spectral peak was centred on 1–2 MeV with an exponential decay coefficient of ∼0.5 MeV, consistent with the background GCR gamma spectrum. Energy spectra from the balloon and passenger flight at 10–12 km were consistent, with minor differences explained by lower-energy gammas and electrons not penetrating the plane's fuselage. Spectral lines from gammas created by GCR-neutron interactions with the atmosphere were detected in airborne data and were absent from ground-based data. These technology demonstrator flights provide background reference GCR ionising radiation spectra for comparison with more disturbed space weather conditions, where additional particles would be expected. Detection of gamma rays from GCR neutrons offers a way to directly calibrate neutrons measured at Earth's surface to ionising radiation in the atmosphere.