Effect of the muon contribution on the barometric coefficient of neutron monitors

The barometric coefficient of a cosmic-ray neutron monitor is found to increase with atmospheric depth from ~ 150 mm Hg to 600 mm Hg and then to decrease slowly with depth down to 760 mm Hg (Bachelet et al. 1965; Carmichael and Bercovitch 1969). Bachelet et al. 1965) tentatively attributed this change in the slope of the barometric coefficient versus atmospheric depth curve at 600 mm Hg to the contribution made by muons to the neutron monitor counting rate. Carmichael and Bercovitch (1969) have shown that the contribution to the monitor counting rate made by obliquely incident nucleons may be the real cause. Singh et al. (1970) have derived an expression for the barometric coefficient for vertically incident particles in a neutron monitor which increases continuously with increasing atmospheric depth down to 760 mm Hg, demonstrating more definitely that the above explanation of Carmichael and Bercovitch is correct.