A Search for Cosmic-Ray Diurnal Effects at Balloon Altitudes

In two balloon flights in Minnesota a search was made for diurnal effects in the cosmic radiation at altitudes above 50,000 feet. Measurements were made simultaneously of the total ionizing radiation, $\gamma$-radiation in the energy range of approximately 0.75 to 5 Mev, and fast neutrons. The ionizing radiation and $\gamma$-radiation component was measured by means of a central horizontal counter tube surrounded by a closely packed ring of horizontal counters. Coincidences between the central counter and the outer ring determined the ionizing radiation, while anticoincidences gave the intensity of the $\gamma$-radiation. The neutron flux was measured by two B${\mathrm{F}}_3$ counters, one filled with enriched B${\mathrm{F}}_3$, mounted side by side in a vertical paraffin cylinder eight inches in diameter surrounded by Cd. One flight was launched at 12:30 A.M. LCT and remained aloft until 8:30 A.M. The other flight was launched at 6:00 P.M. and landed at 10:00 P.M. No diurnal effects were observed. The statistical accuracy of this measurement is on the order of 1 percent for the total ionizing radiation, 3 percent for the $\gamma$-radiation, and 2 percent for the neutron measurement.