Derivation of a simple analytical expression of the gain of pure argon filled CAT proportional counters

In previous publications, we described the intrinsic properties of CAT dete ctors, formed as a unique or a collection of individual single holes (gas p roportional pixel detector). In our last paper, we have shown that the calc ulated gain of the avalanche along the electric field lines was dependent o n the distance of photon absorption with respect to the symmetry axis of a single hole. On the contrary, the measured gain did not follow this depende nce and it was suggested that the gain of the detector was similar to the o ne measured along the hole symmetry axis, irrespective of the shape of the off-axis electric field lines. We present here a simple calculation of the on-axis gain of such structures that corresponds to the measurements and ta kes into account the detector geometry. (C) 2000 Elsevier Science B.V. All rights reserved.