Recent Studies at High Elevations

Certain phases of counter technique are reviewed. The conditions necessary to make and operate reliable proportional counters are discussed. It is shown that certain mixtures of gases, notably argon-carbon tetrachloride and argon-boron trifluoride, when used in counters give these the property of producing large pulses over considerable voltage ranges below the threshold. The size of the pulse (in volts) will be roughly proportional to the amount of ionization produced in the counters by the passage of the ionizing particle being studied. Because of this proportionality, these counters can, for example, distinguish between alpha-and beta-rays over considerable voltage ranges without the necessity of much vacuum-tube amplification. Neutron counters are made using B${\mathrm{F}}_3$ gas, the ${\mathrm{B}}^{10}(n,\alpha ){\mathrm{Li}}^7$ reaction producing the alpha-particle which is detected by the proportional counting procedure described. Flights have been made with instruments carried by small balloons and using single Geiger counters. The data were transmitted from the balloon to the ground station by automatic short wave radio. Such flights show no diurnal effect in the cosmic radiation at great elevations (½ meter of water) as large as four percent of the total cosmic-ray intensity. Further, the flights show that no increase in the ionization as great as two percent of that due to the cosmic-ray intensity takes place at an altitude of 20 km, which can be correlated with a solar flare, although this same flare produced abundant ionization below 80 km and caused a radio fade-out. The absorption coefficients for the flare radiation are calculated. Flights were made with neutron counters and the radio-balloon method, which yielded measurements of the neutron intensity as a function of elevation. It is found that the neutrons increase rapidly with elevation, the rate of increase being faster than that of the total intensity of the cosmic radiation, and approximately equal to that of the big bursts. The production of neutrons in the atmosphere by the cosmic radiation is discussed, and a production cross section of ${10}^{-35\mathrm{}}$ sq. cm is computed.