LBE Paper
Liquid Lead Bismuth Target for Positron Production
Intro
Need for positrons
Intense positron sources are urgently needed for numerous applications, primarily for positron spectroscopy, which can have a huge impact on chemistry, physics, materials and biological science [1–4]. Additionally, high intensity positron beams are required to carry out gravitation experiments [5, 6] and to do chemistry with antimatter [7]. Finally, efficient positron traps also require an intense source of positrons [8, 9].
The easiest way to produce positron beams is to use e+-emitting sources, such as Na-22, which can have activity as high as 1 MBq. Another possibility is to generate positrons by pair production. In this case, an electron beam is stopped in a converter creating bremsstrahlung γ-rays. Provided that the energy of the primary electron beam is high enough, the generation probability of e-/e+ pairs is sufficiently high. Typically high Z material (such as tungsten) is preferred for positron production and moderation [10, 11]. For 10 MeV beam the optimum tungsten converter thickness is about 1.4 mm, and about 20% of the electron beam energy is converted into the x-rays.