A NEW METHOD FOR THE REDUCTION OF ALPHA-RAY BACKGROUND IN A GRIDDED IONIZATION CHAMBER

Abstract

By making use of grid pulses in a double-gridded ionization chamber, it was attempted to eliminate the background pulses caused by the alpha particles emitted from electrodes other than the cathode. Operating conditions for the reductions of the background in this method were investigated analytically. Using the double-gridded chamber of a parallel-plate type with a maximum sample area of 80 cm2 for alpha particles of 9 Mev, a background counting rate of one count per hour was achieved in the energy region from 3.5 to 9 Mev. It was found that an insulator like polyethylene could be used as a sample base with a good resolution for very weak activity. Spectra of weak alpha activities were measured by the present method. For the purpose of practical applications, the construction of a cylindrical double-gridded chamber is proposed.