New types of spark-chambers for imaging γ or x emitters, and their medical applications

In order to adapt spark-chambers to low-energy particles, a first attempt was made using a two-electrode device operating as a proportional counter. The signal obtained triggers a high-voltage pulse which is applied to the same device and a spark occurs near the track of the particle. A three-electrode device including a detection space associated to the sparks space was then used. It was noticed that the spark was formed spontaneously at the point where the particle passed, when suitable direct-current voltages were applied to the electrodes; the high voltage is slightly lower than on the other types of chamber. This phenomenon makes the three-electrode device very easy to use for X or γ rays. The characteristics of the first device filled with argon and methane are given and the first results obtained in the medical field with a device filled with xenon methylal are presented. (author)