Cosmic Radiation Intensity-Time Variations and Their Origin. I. Neutron Intensity Variation Method and Meteorological Factors

Abstract

An experimental method has been developed for extending the study of primary cosmic radiation intensity variations vs time to the low energy portion of the primary particle spectrum by measuring the nucleonic component intensity within the atmosphere. It is pointed out that this extension of intensity variation observations to the low energies now makes it possible to determine the energy dependence of primary intensity variations as well as to determine the intensity variations with time. The possibility of determining acceleration, perturbation, or injection processes within the solar system as the origin of intensity-time variations is considered. A phenomenological outline of kinds of intensity variations with definitions is presented and their relation to the present studies are discussed. The detector system is a pile structure of lead and paraffin within which the rate of local neutron production is measured by ${\mathrm{B}}^{10}$${\mathrm{F}}_{3}$ proportional counters. Details on the large geomagnetic latitude effect of the nucleonic component or local neutron production are discussed.The quantitative problem of relating intensity-time variations outside the atmosphere to pile neutron production deep in the atmosphere has been treated for primary energies below \ensuremath{\sim}15 Bev for protons and \ensuremath{\sim}7 Bev per nucleon for nuclei of $Z>1$. In particular, the contributions of primary protons and alpha-particles to the neutron yield in a pile are considered. The general problem of variations (a) due to primary intensity changes, (b) due to geomagnetic field variations, and (c) due to changing meteorological conditions are considered for nucleonic component measurements. The atmospheric pressure coefficient $\ensuremath{\alpha}$ is essentially constant over the geomagnetic latitude range $\ensuremath{\lambda}=0\ifmmode^\circ\else\textdegree\fi{}$ to $\ensuremath{\lambda}>54\ifmmode^\circ\else\textdegree\fi{}$N and for atmospheric depths >600 g-${\mathrm{cm}}^{\ensuremath{-}2}$ (mountain altitudes or lower). $\ensuremath{\alpha}=\ensuremath{-}(0.94\ifmmode\pm\else\textpm\fi{}0.03)$ percent/mm Hg. The difficulties in determining $\ensuremath{\alpha}$ due to accidental correlations with primary intensity variations is discussed, and a modified method for computing $\ensuremath{\alpha}$ is illustrated. The effect of atmospheric temperature variations upon observed pile neutron intensity is evaluated by a study of the upper limit contributions which $\ensuremath{\pi}$ and $\ensuremath{\mu}$ mesons make as links in the nucleonic cascade. The evidence, including a two month temperature-cosmic-ray intensity correlation study, indicates a negligibly small local or atmospheric temperature coefficient for the nucleonic component.Pile designs are given both for a simple pile standard which may be constructed anywhere for inter-calibration of experiments and for a 12 counter pile which produces \ensuremath{\sim}7000 counts per minute at $\ensuremath{\lambda}=48\ifmmode^\circ\else\textdegree\fi{}$ and altitude 680 g-${\mathrm{cm}}^{\ensuremath{-}2}$. Details are presented on the associated instrumentation. At the present time continuously operating piles are located at geomagnetic latitudes $\ensuremath{\lambda}=0\ifmmode^\circ\else\textdegree\fi{}, 29\ifmmode^\circ\else\textdegree\fi{}\mathrm{N}, 42\ifmmode^\circ\else\textdegree\fi{}\mathrm{N}, 48\ifmmode^\circ\else\textdegree\fi{}\mathrm{N}, \mathrm{and} 52\ifmmode^\circ\else\textdegree\fi{}\mathrm{N}$ in the geographic longitude interval 75\ifmmode^\circ\else\textdegree\fi{}-106\ifmmode^\circ\else\textdegree\fi{}W.