A search for neutrons of solar origin using balloon borne detectors 1967–69

Abstract

A series of telescopes having approximately a 30° half opening angle and responding to neutrons in the energy range 50 MeV to 350 MeV has been flown to the top of the atmosphere on balloons released from an equatorial launching site at Kampala, Uganda, between 1967 and 1969. The aim of the experiment was to attempt to detect solar neutrons during periods of enhanced solar activity. No neutrons of solar origin were detected, but an upper limit of the order of 30 neutrons m⁻² s⁻¹ at the Earth has been placed on the continuous solar neutron flux in the above energy range, and a limit of four photons m⁻² s⁻¹ has also been placed on the corresponding γ-ray flux above 80 MeV. Limits have likewise been placed on the total emission from various flares. For a 1B flare the values were 23 × 10⁴ neutrons m⁻² and 6 × 10⁴ photons m⁻².