Flash tube chambers for electron and photon detection

Abstract

The construction and operation of a simple, inexpensive, electron-photon detector, of the sampled shower type, is described the sampling planes consisting of layers of high pressure, methane doped, neon flash tubes, with CAMAC compatible digitised outputs. The detector was tested in a positron beam at energies from 0.5 to 4,0 GeV, No adverse effects due to the high background radiation were experienced, and an energy resolution of 43% and spatial and angular resolutions of 5 mm and 4º (FWHM) were obtained. The maximum event rate at which the detector could operate was limited to ~1 sec(^-1), by the presence of internal fields which resulted in spuriousness or inefficiency. The use of modified H„T, pulsing systems has also been investigated as a means of reducing the internal field, A modified detector was constructed, utilising large diameter, low pressure flash tubes, in an attempt to improve the maximum event rate, yet maintain the same useful resolution. An energy resolution of 33% and spatial and angular resolutions of 11 mm and 2º (FWHM) were obtained, which compares favourably with more complex and expensive detectors. Unexpectedly, at event rates in excess of a few per second, the tubes behaved either spuriously or inefficiently, due to large internal fields. Investigations into the mechanisms of formation and decay of the internal fields have been made by observation of the digitisation output pulse. This novel approach may, with refinement, be of use in future studies of gas discharges since it is particularly sensitive to the gas breakdown mechanism. The significance of the outer surface resistance of the flash tube has also beer demonstrated to be of importance to the performance of the tube. A mechanism, which results in the flash tube igniting spuriously, is suggested and a threshold value of the internal field, at which spuriousness occurs, has been determined.