Calibration of a pencil ionization chamber with and without preamplifier

Abstract

The pencil ionization chamber is a cylindrical dosimeter developed for computed tomography beams. Many kinds of ionization chambers have a preamplifier connected to the chamber to make it electrically more stable, specially for field instruments. In this study, the performance of a Victoreen pencil ionization chamber with the original preamplifier and after its removal was compared. The objective of the preamplifier removal was to enable connecting the chamber to other kinds of electrometers available in the laboratory. To assure the proper performance of the chamber in its new condition, the main quality control tests were performed, as short and long term stability, leakage current and energy dependence in diagnostic and mammography calibration beams. The behavior of the pencil ionization chamber before and after the removal of the preamplifier was very similar, and the results obtained were always within the limits of international recommendations. The results obtained in both situations allow, if necessary, the preamplifier removal of the system without lack of precision in the measurements.