Sviluppo di nuove tecniche per lo studio di atomi di Francio in una Trappola Magneto-Ottica

Abstract

The cooling and trapping of atoms , meaning the reduction of their average speed through the use of \nlaser techniques and their confinement in a region of a few mm3 space represents a new frontier for \nthe physics at low energies. The use of Magneto ‐ Optical Trap (MOT) for radioactive atoms allows \nthe realization of unique experiments for the study of fundamental interactions, in particular the \nstudies of Atomic Parity Non‐Conservation (APNC). This thesis presents the experimental apparatus \nused at the National Laboratories of Legnaro (LNL) of the INFN for the production and the on‐line \ntrapping of francium atoms (Fr) in a MOT. The Fr has no stable isotopes and is produced by a nuclear \nreaction, which is obtained by using Electrostatic Tandem‐XTU accelerator at LNL. The purpose of this \nline of research is the development of new techniques for trapping and detection of atoms of \nfrancium, specifically aimed at increasing the number of trapped atoms, in order to be able to make \nfuture relevant APNC measurements as a test of the Standard Model of elementary particles. The \nexperimental results achieved in the last three years (2011‐2013) will be described throughout the \nthesis, with a focus on the development of a new technique for detection of weak atomic transitions. \nThis is a direct method of investigation, based on the excitation of atoms in the MOT through a probe \nlaser beam, resonant with the transition being studied, and the detection of the transition through \nthe variations of the atomic population of the trap. Several hyperfine levels of the isotope of \nrubidium 85 have been excited by the probe beam, showing progressively lines of weaker intensity. \nThe application of this technique to radioactive atoms will allow to detect very weak transitions, such \nas those that indicate a transfer of the atoms trapped at energy levels that have not been \ninvestigated yet. The first evidence of Light‐Induced Atomic Desorption (LIAD effect) on a foil of \nyttrium, used as a neutralizer for the ionic beam of rubidium, will be presented in the thesis. It has \nbeen observed, both in the pulsed and in the continuous regimes, an increase of the MOT atomic \npopulation as a result of the desorption of the illuminated foil or the formation of the MOT when the \nyttrium foil is at room temperature and no trap is initially present. Subsequently, preliminary results \nobtained on the atomic desorption in a trap of 210Fr through a pulsed light will be shown. This \ntechnique seems to be promising to increase the atomic population of radioactive atoms traps.