ABSTRACT
Terrestrial cosmic rays (i.e., atmospheric secondary radiation), which are related to primary cosmic rays (CRs) impacting the earth’s upper atmosphere, have been measured by a wide variety of techniques since the 1930s. In particular, systematic and uninterrupted monitoring of atmospheric radiation was initiated in 1932 using ionization chambers and has continued since 1951 using neutron monitors (NMs) (Shea and Smart 2000). From this date, the NM rapidly became the detector of choice to monitor cosmic radiation variations, due to some limitations of the ionization chambers in detecting primary CRs below ~4 GeV and to potential long-term drift and calibration problems (Shea and Smart 2000).
