A balloon‐borne submicron aerosol counter was successfully flown on three stratospheric balloon experiments over Holloman Air Force Base, New Mexico, in May 1973. The results indicate that particulate matter at altitudes above 23km has markedly different scattering parameters from particles at lower levels. This effect is manifested in the form of increasingly steeper size distributions and a lack of particles larger than 0.4µm diameter. The extent to which these features are attributable either to nonspherical particles or to particle index of refraction uncertainties rather than to the actual size distribution, is a matter of conjecture at this time.
Measurements of the ionization due to beta radiation from the air, employing two thin‐walled ionization chambers in a differential arrangement, are described. Corrections for geometry, absorption of beta and gamma radiation in the shield, formation of secondary betas in the shield, and back‐scattering of betas within the chamber are discussed.
The results of 73 measurements, taken throughout the summers of 1955 and 1956, are reported. Two‐thirds of all the measurements fall within a range extending over one order of magnitude. The weighted mean of all the measurements is 0.67I. This is roughly ten times the expected value, computed from random and thoron concentrations measured at this locality. Wide (and rapid) fluctuations in ionization current were also noted.
All the mechanisms coming to mind which might account for the excess ionization observed over that expected are discussed, and rejected on various grounds. By process of elimination, the possibility of the existence of a “very soft” cosmic‐ray component is suggested.
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