Positron sources for atomic physics experiments

The authors have demonstrated the possibility of producing strong and point-like positron sources by collection of the ion beams from an on-line mass separator. At ISOLDE beta ⁺ emission rates of 3.7*10⁹ Bq were obtained from ⁸¹Rb sources collected on an area smaller than 4.5 mm². When the activity is deposited on a transmission moderator, low-energy positron beams with high brightness can be produced. With a 6 mu m thick polycrystalline tungsten transmission moderator a brightness per energy of better than 800 s^-1 mm^-2 rad^-2 eV^-1 was achieved. This value could still be considerably increased by optimisation of the ion beam parameters and by means of a more efficient moderator.