Time of Flight system to investigate positronium cooling

A positronium Time of Flight (TOF) apparatus, conceived to work with continuous positron beams of intensity up to ~106 positrons/s, was developed. The geometry of the TOF chamber and the acquisition chain are described in detail. The performances of the set up were preliminary tested with a laboratory positron beam of ~5 × 103 positrons/s by measuring the Time of Flight of Ps emitted from oxidized nanochannels produced in a Si single crystal. A TOF spectrum of ~104 events was collected in 9 days with a time resolution of 8 ns. The analysis of the TOF spectrum is discussed. This apparatus is going to be assembled at the intense positron source NEPOMUC at FRM-II reactor, where the measurement time of each spectrum will be reduced to less than 2 h, making this TOF system appropriate to investigate positronium emission after cooling in porous materials held at cryogenic temperature.