The ATHENA apparatus that recently produced and detected the first cold antihydrogen atoms is described. Its main features, which are described herein, are: an external positron accumulator, making it possible to accumulate large numbers of positrons; a separate antiproton catching trap, optimizing the catching, cooling and handling of antiprotons; a unique high resolution antihydrogen annihilation detector, allowing an clear determination that antihydrogen has been produced; an open, modular design making variations in the experimental approach possible and a ‘‘nested’’ Penning trap situated in a cryogenic, 3T magnetic field environment used for the mixing of the antiprotons and positrons

The temperature dependence of the light emission for pure CsI crystals has been measured with photomultipliers, and photodiodes with wavelength shifters from 80-300 K. The light yield at 80 K is N = 5 0 ; 0005; 000 photons per MeV. This number was deduced from the numberof electron-hole pairs produced in the photodiode, N eh = 3 9 ; 600 1; 200. The light yield at room temperature is lower by a factor of 15:8 1:0, giving 3; 200 400 photons per MeV. Decay times were measured with a photomultiplier. At room temperature two fast decay components were observed with decay times of 6 1 ns and 28 2 ns. Below 180 K only one component is observed and at 80 K the decay time is 1015 17 ns.

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