THIN-FILMS FOR SLOW POSITRON GENERATION

The authors report on calculated slow-positron yields from mu m thick W(110) and Cu(111) single crystals in a transmission geometry to be used in conjunction with a **2**2Na beta ** plus source. The fast to slow positron moderation efficiencies were found to be comparable ( APP GRTH 10** minus **3) to the more conventional single-crystal moderators used in the backscattering geometry with a **5**8Co source. This allows the construction of more simplified slow-positron beams. The authors also calculate the brightness enhancement and efficiency of ultrathin single-crystal metal foils used for remoderation of the slow-positron beam. The results are consistent with recent experiments, while they are smaller than previous theoretical estimates.