Pulse-Mode Readout Electronics for Ionization Chambers

Initial results of evaluation of a new highly sensitive readout system for use with ionization chamber environmental low level radiation detectors are presented. The designed readout provides low noise shaping and filtering of the signals from the individual ionization events in such detectors, and also provides interface to the external continuously running Data Acquisition system. A dedicated analog to digital converter operating at a sampling rate in the range of 50 to 200 kHz and the developed data processing algorithms allow extraction of the ionization event signals from the data flow and measurement of the ionization value for each event in the detector. Such measurement provides an opportunity to roughly characterize the energy spectrum of the observed environmental radiation field. The new readout was installed in a commercial Reuter-Stokes High Pressure Ionization Chamber. The Data Acquisition system was assembled using the M-Audio Audiophile 192 High-Definition 24-bit/192 kHz audio PCI card installed in a PC computer operating under LINUX OS. The ionization chamber with installed electronics was tested in operation in several locations around the site at the CEBAF accelerator for continuous monitoring of very small, less than 0.2 murem/h, dose variations correlated to the accelerator operations. The results indicate feasibility of using this technique in setups where a very high sensitivity and stability of environmental radiation dose measurements is required and there is a need for detecting small man-generated signals in the presence of larger and variable natural radiation background.