Effective measuring point of ion chambers for photon dosimetry in phantoms

Publisher Website
Google Scholar
Abstract
The effective point of measurement for spherical ionization chambers was determined for 60Co and 137Cs .gamma.-rays and for 300 kV X-rays inside a human water phantom. Measurements with a thimble-type Baldwin-Farmer ion chamber were used for comparison. For spherical ion chambers the displacement correction factors were 1 - (0.37 .+-. 0.04)r .cntdot. 10-2 for 60Co .gamma.-rays and 1 - (0.22 .+-. 0.05) r .cntdot. 10-2 for 137Cs .gamma.-rays, where r is expressed in mm. No displacement was observed for X-rays. The differences in displacement obtained for the various types of radiation are attributed to differences in attenuation and scatter characteristics of the various radiation qualities.