Energy Spectrum of the Soft Component near Sea Level

An analysis of the transition curves of Carmichael and Steljes has been carried out to yield the transition curves in lead of ion-chamber bursts produced by cascades initiated by the electrons and photons of the soft component incident from the atmosphere. From the rates at the maxima of these transition curves, the absolute omnidirectional integral energy spectrum of the electrons and photons of the soft component at sea level, in the energy range from about 100 Mev to 100 Bev, is deduced. Incident electrons and photons associated with extensive air showers, as identified by coincidences with a nearby larger ion chamber, are excluded. An additional single experimental point on the integral spectrum (8.4×${10}^{-3\mathrm{}}$ per sphere of unit area per sec) is obtained from the observed rate of electrons of all energies greater than 1 Mev which intersect the unshielded ion chamber. Since a quantitative relation from electromagnetic cascade theory is made use of in the derivation of the energy spectrum, and since this relation is at present uncertain for lead in the energy range involved, the possible error of the flux in the energy spectrum (±100%) is much larger than that of the observed rates of occurrence of bursts (±5%). In this respect the spectrum is preliminary only. In the energy range below 400 Mev the integral spectrum is in agreement with previous absolute measurements; below 2 Bev it is in conformity with a previous relative measurement; from 1.6 Bev to 100 Bev, where there are no previous determinations, it obeys a power law of exponent -2.00 and the rate for 1.6 Bev is 2.4×${10}^{-5\mathrm{}}$ per sphere of unit area per sec.