Gas-filled avalanche or spark producing image intensifier detector for X and γ rays

The authors formerly described a high efficiency, gas filled device for the visualization of X and γ sources distributed in a Volume 1, 2, 3. Latest work in this connexion has revealed great further scope: in first approximation, there does not appear to be any limit to the particle rate that can be recorded. If the density of the particle flux is high, the grid-anode gap field permits the creation of electron avalanches only, and the light signal is amplified by a conventional image intensifier, whereas for a lower flux density, the higher field permits sparking. Spark energy is reduced and controlled by an original device: the anode is a conductive coating of several 103 to 105 ohms per square and limits instantaneous current, while an electronic circuit triggered by initiation of the spark discharges the grid-anode capacitance. We have obtained images from avalanches with exposures ranging from a fraction of a second to several seconds and from sparks with an exposure of up to 30 minutes or more, using radioactive collections of X-emitters with energies of 27 and 70 keV. Impact localization can be recorded with an accuracy of a few tenths of a millimeter, and the image size may be as much as thirty centimeters or more.