Attenuation of neutron monitor radiation in the atmosphere

Abstract

An NM-64 neutron monitor latitude survey made by road transport in the summer of 1965 in Canada, the United States, and Mexico was extended, in the summer of 1966, to the western seaboard of the United States and Hawaii. In 1966 in the vicinity of Mt. Hood (2.43 GV), Palomar Mt. (5.71 GV), and Mt. Haleakela (13.3 GV) advantage was taken of the possibility of changing altitude without significant change of geomagnetic cutoff. At each of these places also a smaller lead polyethylene neutron monitor was flown at seven different pressure altitudes between 530 mm Hg and 140 mm Hg. The airborne monitor was calibrated in terms of the NM-64 when the transport van was at 10 000 ft on the summit of Haleakela. It was found that graphical smoothing of vertical trajectory cutoffs in latitude and longitude eliminated an unnatural kink in the latitude curve near Mexico City. The 1965 and 1966 rates were adjusted to May 12–13, 1965, the date of the IQSY maximum, using data from a fixed monitor and allowing for the dependence of the secular fluctuations on cutoff and altitude. The attenuation coefficient throughout the atmosphere was determined from the data and also a new specific attenuation coefficient which is a function only of rigidity of the primary flux and depth in the atmosphere. The specific attenuation coefficient has a comparatively high value consistent with that observed for solar proton events.

Terrestrial cosmic ray intensities

“…This figure is from the most comprehensive study ever made of the attenuation of cosmic rays on earth [33]. Data from most of the locations described in Figure 10 were combined with data from other mobile nucleon detectors on ships and airplanes to map out most of the earth.…”

“…This beautiful study is like the last apple of the season: It is rich with flavoi and detail, but it also contains a worm (see Figure 12). From [33], leproduced with permission.…”

Online application for the barometric coefficient calculation of the NMDB stations

“…The affection of the atmospheric pressure to the measured cosmic ray intensity on the Earth's surface is a well known phenomenon (Carmichael et al, 1968;Dorman, 1972Dorman, , 1974. In the case the cosmic ray incoming flux is constant, the measured intensity N depends only on the local atmospheric pressure and this dependence can be described via the expression:…”

An online application for the barometric coefficient calculation of NMDB stations

“…The method of defining the barometric coefficient of the different components of secondary cosmic rays has been studied to a large extent [2], [3] and [4]. Specifically, the affection of the barometric pressure on the counting rate of neutron monitors can be represented by: …”

“…This effect induces considerable variation in the counting rate of a cosmic ray detector that is not related to the primary variation of the cosmic rays flux but only to the local atmospheric pressure of the station. For this reason, the correction of the counting rate for the barometric pressure is one of the main tasks of the primary data processing [1], [2].…”