Ionization and Geiger-Muller counter measurements of Co 60 gamma-rays were made in effectively spherical geometry up to a distance of 252.8 cm (16 mean free paths of the primary radiation) corresponding to an exponential attenuation of the primary radiation by a factor of 8.8 X10 6 . The "build-up factor" was observed to climb up to 33.8 and approached closely the theoretically predicted trend of asymptotic variation r lA . Preliminary information on the spectral distribution of the radiation is included.
The true heights of electron density for Washington were computed using the parabolic method for winter, summer, and equinox of 1945 at noon and at midnight. Representative curves were formed by combining the data from a large number of days.
The distributions obtained show a lower height of the maximum electrondensity of the F2 region at midday as compared with midnight. The curves are compared with similar curves for Huancayo, in which the height of maximum ion‐density is greater at midday than at midnight.
Predicted values of F2 critical frequencies for all hours of the day for Watheroo, Western Australia, and for Baton Rouge, Louisiana, were compared with observed values. It was found that predicted values for Baton Rouge, based on data from Watheroo, agreed with observe values almost as well as those predicted from Baton Rouge values. The two stations in questions are located at almost antipodal points. Similar tests conducted for other stations in corresponding geographical latitudes, north or south, but not antipodally located showed poorer agreement. It is concluded from this that data observed at any given station may be applied with consideration assurance to antipodal points for which no data are available.
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