The Basic Design Data of a Guarded-Field Thimble Ionization Chamber: A Precision Ionometric Investigation

Abstract

A new type of cavity ionization chamber is described, which eliminates the need for the conventional collecting "peg" with associated electrode asymmetry and non-uniform electrostatic field distribution. The new chamber provides a true cylindrical cavity in which the collecting electrode is a disk coplanar with one end of the cavity, the disk being surrounded by a guard surface of appropriate width. Parallelism of the collecting field terminating on the collecting electrode is ensured by subdividing the cylindrical cavity wall into equal-width annuli evenly graded in potential between earth and the full polarizing voltage, the latter being applied to the end surface of the cavity opposite the collecting electrode. Some advantages of the new type of chamber in cavity ionization research and high energy radiation dosimetry are discussed, and the basic design data (derived from a series of precision ionometric investigations) are given.