Nuclear spin polarized alkali beams (Li and Na): Production and acceleration

Recent improvements of the Heidelberg source for polarized heavy ions (PSI) are described. By means of optical pumping in combination with the existing multipole separation magnet the beam figure of merit (polarization2 x intensity) was doubled. 7Li and 23Na atomic beams can now be produced in pure hyperfine magnetic substates. Fast switching of the polarization is achieved by an adiabatic medium field transition. The hyperfine magnetic substate population is determined by laser-induced fluorescence spectroscopy. In routine operation atomic beams with nuclear polarization pα≥0.85 (α=z, zz) are obtained. The acceleration of polarized 23Na- ions by a 12 MV tandem accelerator introduces a new problem: the energy at the terminal stripper foil is not sufficient to produce a usable yield of naked ions. For partially stripped ions hyperfine interaction of the remaining electrons with the nuclear spin reduces the nuclear polarization. Using in addition the Heidelberg postaccelerator 23Na9+ beams of energies between 49 and 184 MeV were obtained with an alignment on target of Pzz≅0.45. 7Li beams have also been accelerated up to 45 MeV with an alignment of Pzz=0.69. (orig.)