Measurements of thoron in the atmosphere

A study has been made on a method for calibrating the ionization current to be determined when measuring thoron concentration with an ionization chamber. The ionization current generated by the thoron exhausted from RdTh solution would appear to be controlled mainly by the bubbling velocity in the bottle, and the reciprocal of the current is a linear function of the reciprocal of the velocity. The ionization current was calculated from thoron concentration by taking the following three conditions into consideration: (1) loss of ions by columnar recombination, (2) loss of range by the chamber wall, and (3) the condition of the air flow through the chamber. The calibrated and measured values coincided well with each other. Thoron concentrations in the atmosphere were measured on the university campus in Nov. 1968, and the concentration was found to be 0.3-0.6×10^-16Ci/cm³ at 1m above the ground surface. (author)