Abstract
Being able to be determined by subtracting the gamma-ray ionization intensity from that obtained with ionization chamber, cosmic-ray ionization intensity in free air was estimated by using with 15l air-filled ionization chamber and 3″φ spherical NaI (Tl) scintillation spectrometer.
Optimum applied voltage to 15l air-filled ionization chamber was determined in accordance with Scott and Greening's formula to obtain the ionization intensity caused by gamma-rays and cosmic-rays. Pulse-height distribution of cosmic-rays created in 3″φ spherical NaI (Tl) scintillation spectrometer was investigated for the precise determination of gamma-ray ionization intensity.
Field measurements were carried out by using with these two instruments at about 1.5 meter above the ground in the several locations around Research Reactor Institute of Kyoto University. Cosmic-ray ionization intensity in free air was estimated from the results obtained with air-filled ionization chamber and was 3.33±0.15μR/hr equivalent in natural environment near Research Reactor Institute of Kyoto University.
