Altitude survey of the galactic cosmic ray flux with a Mini Neutron Monitor

We present the results of a survey of the galactic cosmic ray (GCR) flux measured at different altitudes, from the sea level, up to ∼4600 m a.s.l. This altitude survey was carried out with a “Mini” Neutron Monitor (MNM), and performed inside a small area of the central part of Mexico (centered around the 19° N and 97° W position) where the geomagnetic cutoff rigidity is ∼7.8 GV. In particular, the latitudinal variation of the survey was less than 1°. making negligible the associated changes in the geomagnetic cutoff rigidity (∼0.4 GV). This is the first time that an altitude survey has been performed using a MNM. This survey allowed us to compute the barometric coefficient β=0.00732±0.00054mbar-1 and β=0.00729±0.00055mbar-1 when we correct our data by the differences in the cutoff rigidity. This coefficient may be used to calibrate and correct the data of other cosmic ray detectors. We show that from the sea level up to ∼4600 m the barometric coefficient is constant and does not depend on the altitude as found in previous surveys. For comparison, we also present the counting rates measured by the NM64 located at Mexico City, as well as other observations carried out to determine the stability of the MNM.