Gaseous mixtures-detection media studies for the NEXT experiment: a contribution

Abstract

The purpose of this Master thesis is to contribute to the NEXT experiment (Neutrino Experiment with a Xenon Time Projection Chamber) by studying xenon based gaseous mixture properties. The work developed to study gaseous mixtures properties was based on three experimental setups: Ion Drift Chamber (IDC), Gas Proportional Scintillation Counter (GPSC) and Proportional Counter (PC). With the IDC, measurements of Ne and N2 ion mobilities in their parent gases were performed and the mobility of xenon ion in the Xe-N2 mixture was also measured. These measurements were performed at low pressures (4 to 16 Torr) and reduced electric elds between 6 and 35 Td. For the Xe-N2 mixture, the amount of dopant (N2) ranged from 0 to 10%. The results attained for Ne and N2 were in good agreement with other authors results. It could be concluded that adding nitrogen to xenon increases the xenon ion mobility. The results show that adding 10% of N2 increases xenon ion mobilities by almost 6%. The part of the work developed with the GPSC was the optimization of the rst NEXT prototype - NEXT-0. The task proposed was to optimize the setup to overcome its major limitation: not being able to operate at high electric elds. Although not fully accomplished, the limitation was minimized, thus allowing for normal operation up to at least 1.5 bar. Another limitation that prevented normal operation was caused by non-desired radiation being detected, impairing the detection of the radioactive source. This limitation was fully overcome. Furthermore, data was acquired and it was possible to observe that pressure interferes with the resolution behaviour of the detector. The drift and electroluminescence elds applied are also correlated with the detector's resolution behaviour. In this way, the results obtained seem to show that more pressure improves resolution and that also diminishes the electroluminescence eld requirements (it does not need to be as intense). In the last part of the experimental work, a cylindrical proportional counter was projected, assembled and tested, and is working simultaneously and in parallel with a GPSC, in a specially designed Ultra-High-Vacuum system. Although the GPSC is not fully working yet, preliminary data has already been successfully obtained with the PC.