### Cosmic-Ray Air Showers at Sea Level

#### Abstract

An investigation at sea level of cosmic-ray showers with sizes from 5×${10}^{5}$ to over ${10}^{9}$ particles is described. The core locations, arrival directions, and particle density distributions of several thousand showers whose cores landed within an area of ${10}^{5}$ ${\mathrm{m}}^{2}$ were determined by the techniques of fast-timing and density sampling. The most important results are as follows: (1) The existence of primary particles with energies greater than ${10}^{18}$ ev is established by the observation of one shower with more than ${10}^{9}$ particles. (2) The function $f\left(r\right)=0.45\left(\frac{N}{{{R}_{0}}^{2}}\right){r}^{-0.7}{\left(1+r\right)}^{-3.2}$, where $r=\frac{R}{{R}_{0}}$ and ${R}_{0}=79$ m, describes the lateral distribution of particles at distances in the range and for showers with sizes in the range $5×{10}^{5}. (3) At distances greater than 50 m from the core the density fluctuations in individual showers have a Poisson distribution. (4) The size and zenith angle distribution can be represented by the formula , where $x={x}_{0}sec\theta$, ${x}_{0}=1040$ g ${\mathrm{cm}}^{-2}$, ${s}_{0}=\left(6.6±1.0\right)×{10}^{-8}$ ${\mathrm{cm}}^{-2}$ ${\mathrm{sec}}^{-1}$ ${\mathrm{sterad}}^{-1}$, $\Gamma =1.9±0.1$, $\Lambda =\left(113±9\right)$ g ${\mathrm{cm}}^{-2}$, ${x}_{0}, and $7×{10}^{5}. (5) No evidence is found of anisotropy in the arrival directions or of a break in the energy spectrum of the primaries up to the largest energies observed. (6) Assuming a specific model for shower development and taking into account fluctuations in the depth of the first interaction, the integral energy spectrum of the primaries is $J\left(E\right)={J}_{0}{\left(\frac{{10}^{15}}{E}\right)}^{\gamma }$, where ${J}_{0}=\left(8.1±3.1\right)×{10}^{-11}$ ${\mathrm{cm}}^{-2}$ ${\mathrm{sec}}^{-1}$ ${\mathrm{sterad}}^{-1}$, $\gamma =2.17±0.1$, and .

DOI: http://dx.doi.org/10.1103/PhysRev.122.637

• Published in the issue dated April 1961

© 1961 The American Physical Society

#### Authors & Affiliations

• Laboratory for Nuclear Science, Massachusetts Institute of Technology, Cambridge, Massachusetts

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