Construction of a time-of-flight measurement system to study the low energy positronium production

To investigates the low energy positronium Ps. production in terms of target temperatures and materials, surface condition and so on, we adopt the time-of-flight TOF.method and perform extensive Monte Carlo simulation to design an apparatus. Under reasonable assumptions in the simulation with respect to an initial energy distribution of Ps, we examine how cleanly ortho-positronium oPs.is observed without being subject to large backgrounds of 2g decay from eqey annihilation. The simulation finds that the contribution of 2g events is suppressed by 10y6 smaller than the generated Ps by using the 2.5-cm thick W and 4.6-cm Pb collimators with slit gap of 1 mm. We inject slow positron beams on the W target installed in the TOF system and move the position of the target. Then we expect the position resolution of 1.5 mm resulting the accuracy of determining the oPs velocity 20%, corresponding to 1.1=106 cmrs for thermal Ps with 30 meV. q1999 Elsevier Science B.V. All rights reserved.