Mexico City Cosmic Ray Observatory detects
high energy particles coming from outer space and continuosly impinging
on the earth´s atmosphere from all directions. It is part of the
World Network of Neutron Monitors. In 1912, Victor Hess , an intrepid
austrian phycisist, made flights in aerostatic balloons beyond 5000
meters of altitude. His results led him to establish the existence of
what he called “a penetrating radiation from outer space”.
Years later, Millikan called them “cosmic rays”; cosmic
due to the clearly origin in the outer space and rays because he thought
they were of the same nature as the recently discovered gamma rays.
In 1930 started the works to explain if they were particles or electromagnetic
radiation. Compton´s results gave the answer, it was established
they were particles, but nothing was known about the nature of these
particles. In 1932, the Belgian George Lemaitre and the Mexican Manuel
Sandoval Vallarta and at the same time, the Italian Bruno Rossi, predicted
that there was a difference in the number of particles arriving from
East or from the West. Luis Alvarez and Arthur Compton , on the roof
of the Geneva Hotel in Mexico City using a Geiger Counter, detected
more particles coming from the West and since then it was established
that cosmic rays were particles with a positive charge presumably
In 1948. with the aim of monitoring the intensity of cosmic radiation,
the Carnegy Institution in Mexico City, installed an Ionisation Chamber.
Eight years later, with the development of new technologies and with
the aim to participate in the International Geophysical Year, The Chicago
University installed a Neutron Monitor in the Campus of the Universidad
National Autónoma de Mexico (UNAM), a Simpson Monitor. After
a while, the Instituto de Geofisica, acquired a Neutron Supermonitor
NM64 and took charge of the Simpson Monitor. Nowadays, the Simpson Monitor
is out of work.
The Cosmic Ray Observatory installed in the Campus of the UNAM, consists
of two types of detectors: a Neutron Supermonitor 6NM64 and a Muon Telescope,
detecting the nucleonic and the hard components of secondary cosmic
radiation , respectively. The detection range of these instruments ranges
from 8.5 to 200 GeV of energy (1 GeV= 10 9 eV).
The Mexico City Neutron Monitor, is located at 2274 m asl has a cutoff
rigidity of 8.2 GV it is in continous operation since 1990. The Muon
Telescope is in process of upgrading.
The 6NM64 consists of six proportional counters of Boron Triflouride
(BF3). The intensity of cosmic radiation is affected by pressure
changes, so it is necessary to make some corrections to the intensity
detected by the instruments to eliminate the variations due to the atmosphere.
To do that, the atmospheric pressure is registered concomitant to the
cosmic ray intensity and a digital barometer Meteolabor-ag GB1 is used
to obtain the five-minute readings of the height of the barometer.
Data obtained from all the system are collected by a data acquisition
system, designed and built up by the technicians in charge of the Observatory.
All this information is emptied out into a personal computer. Recently,
a modernization of all the system was carried out and we have all data
in real time available to the community and public in general.