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

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