Quenched and non-quenched Ar-Xe Penning mixtures as detection media for a Gridded-Microstrip Gas Chamber X-ray detector

Abstract

N02·143for the PI 0 mixture) and gas gain as compared to those obtained with a standard microstrip plate [3].Abstract -The performance of quenched and non-quenched argon-xenon Penning mixtures in a Gridded-Microstrip Gas Chamber is studied for 5.9keV X-rays. The best energy resolution obtained was 12.7% for the 90 0 /oAr-l0 0 /oXe mixtures. Charge multiplication gains one order of magnitude higher than in pure xenon were obtained for 95 % Ar-5 % Xe. With the addition of the quenching agent (methane), although the gas gain at the same anode voltage decreases, a better energy resolution of 12.3% is achieved for the 85.5 % Ar-5 % Xe-9.5 % CH4 mixture. CathodeGrid Anode GridIndex Terms -microstrip plate, X-ray gaseous detector, Penning mixtures, argon-xenon and PI0-xenon gas mixtures. Fig. 1 Schematic view of the dual anode microstrip plate with the anode surrounded by close-lying grid and cathode further apart.Bearing in mind the optimization of the performance of the structure developed, in the present work further investigation is described namely in the field of detection media. In charge multiplication based detectors such as the G-MSGC the lower limit of the experimental energy resolution, Le. the intrinsic energy resolution R, is limited by the statistical fluctuations in the number of primary electrons (characterized by the so-called Fano factor, F), and also in the charge multiplication process (characterized by the parameter j), and is given by [6] where w is the mean energy required to form a primary electron in the gas and Ex is the energy of the incident x-rays.By virtue of their low w values, zero electron affinities and lack of vibrational and rotational energy loss mechanisms, the noble gases are common fillings of gas detectors for X-rays. It has also been demonstrated [7]- [9], that by adding a small amount of a heavier noble gas (less than approximately 5% for metastable Penning mixtures and 8-10% for non-metastable ones) with lowest ionization potential than some of the excited states of the lighter component, energy transfer between the two components can take place and extra electrons will be released. From this process, known as Penning effect, parameters wand F decrease [9] and as a result, the intrinsic limit of the energy resolution will improve and the ionization efficiency becomes higher than for pure components at relative low voltages. It has also been shown that by using a lighter noble gas as a Penning partner, these mixtures increase the absorption depth of X-rays, reducing the spectra distortion towards the low energy regions [10], [11] and consequently are