40 Years of Solar Neutron Observations from Ground

E.O. Flückiger and R. Bütikofer, University of Bern, Physikalisches Institut / HFSJG - Bern, Switzerland

In association with the X8 /2B solar flare on 3 June 1982, the neutron monitors at Jungfraujoch, Lomnický štít, and Rome were the only ones in the worldwide neutron monitor network to record simultaneously a short, small increase in the counting rate. The analysis of these records and of observations of solar electromagnetic emissions implied that these count rate increases were due to the impact of high energy solar neutrons into the Earth’s atmosphere. This first observation of terrestrial effects by neutrons of solar origin not only provided supporting evidence for a theory pointed out by [Biermann et al. in 1951][bierman1951], but it triggered an intense activity in the theoretical study of particle acceleration and emissions in high-energy processes at the Sun, as well as in the development of dedicated solar neutron detectors. The establishment of global networks of such detectors enables the detection of an eventual solar neutron event around the clock. In addition, the identified need for real-time data with high time resolution initiated the Neutron Monitor Data Base, NMDB. The presentation gives a historical overview of the 3 June 1982 event and summarizes its main scientific impact over the last 40 years.