Thesis

Optimization and applications of gas detectors for high energies

• Call:

  IDPASC Portugal - PHD Programme 2015

• Academic Year:

  2015 / 2016

• Domains:

  Experimental Particle Physics | Astrophysics

• Supervisor:

  Filomena Pinto dos Santos

• Co-Supervisor:

  Rui Curado da Silva

• Institution:

  Universidade de Coimbra

• Host Institution:

  Universidade de Coimbra

• Abstract:

  This proposal comes mostly within the scope of the international collaboration NEXT (Neutrino Experiment with Xenon TPC, http://next.ific.uv.es/next/ - a CERN experiment), that uses a TPC (Time Projection Chamber) with high pressure (20 atm.) gaseous xenon. High pressure noble gases are a very efficient detection medium for high energy, comparable to liquids, but with better energy resolution and with less purification problems. High energy experiments are very demanding in what concerns energy resolution requiring near intrinsic behavior in that field. Thus, the preferred amplification method in some of these experiments is electroluminescence, instead of charge multiplication whose fluctuations deteriorate the energy resolution. With electroluminescence production as amplification mechanism noble gases are a favored choice and, among them for several reasons in NEXT experiment, xenon has been the chosen. In spite of the continual intense investigation there is still margin for improvement in gaseous detectors for high energy. The perfection of these detectors, in several aspects where their performance can still be improved, is what is proposed in the present doctoral program. Explicitly in xenon diffusion coefficients are high and drift velocity is low, which is a concern in high dimension detectors as those used in these rare event experiments and event tracking and background rejection are of paramount importance; also, at high pressures the voltage applied seems to be lower than those practicable at lower pressures. There is no explanation to this fact. Moreover also at high pressure there may be the formation of negative ion clusters which, again, would endanger the energy resolution. The degree of polarization of a radiation source increases the number of parameters that characterize it, namely concerning physical processes involved, presence of magnetic fields, etc, a matter of increasing relevance in Astrophysics. The degree of polarization reflects on the anisotropy of the electron cloud produced. The study of this anisotropy is another use for gas detectors (possibly at high pressure, if detection of high energies is required), in this case with charge multiplication as amplification mechanism as it enhances spatial resolution most needed in this case.