INITIAL NEUTRON AND GAMMA AIR-EARTH INTERFACE MEASUREMENTS

Abstract : Measurements of total gamma dose, gamma dose rate, neutron flux, and neutron dose were made at the surface and at heights up to 950 feet to determine the effect of the air-ground interface on initial nuclear radiation. Measurements of total gamma dose and neutron flux were made with dosimeters fastened to towers 500 feet high and to the mooring cables of captive balloons 950 ft high. Total gamma measurements were made with three types of film badges, two types of phosphate glass dosimeters, quartz-fiber dosimeters, and chemical dosimeters. Neutron-flux measurements were made with sulfur pellets and with nuclear track emulsions. Neutron-dose measurements were made with chemical dosimeters. Measurements of gamma dose rate were made with air-filled, saturated, ion-chamber detectors carried by captive balloons with signals carried by miniature coaxial cable to ground stations and recorded on magnetic tape. It was found that total gamma dose increased with height to a value, at 400 ft, 30% greater than ground measurements. There was no further increase up to 950 ft. The effect was the same at all stations from 1,500 to 3,500 yards horizontal distance from burst point. There was no change in the ratio of gamma dose rates at the balloon stations compared to dose rates at ground stations over the first 5-second interval for which records were obtained.