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[en] We propose a detailed concept to raise the total energy of a positron beam by an amount of at least 10keV. The setup consists of a combination of a pre- and a main-buncher which is able to convert the continuous remoderated positron beam of NEPOMUC into pulses of about 2.5 ns width with a repetition rate of 5 MHz. This pulsed beam is suited for a new setup which elevates the beam energy by rf-fields. In contrast to existing rf-accelerators, the new setup has only negligible influence on the transversal beam phase space.
[en] The field of low energy positron physics has significantly expanded in recent years to include not only particle and atomic physics but also solid state and surface physics or materials science. The interaction of a positron with matter shows a wide variety. Roughly speaking, the use of a positron as a probe in materials science can be grouped into four categories: 1. an electronic structure probe, 2. a lattice defect probe, 3. a surface/interface probe, and 4. a micro probe. The advances in positron beam technology from an uncontrolled use as a white beam as born from radioactive nuclei to a well controlled use as a slow/monoenergetic and a high brightness beam expanded an object of study from the bulk to the depth specified surface/interface region and further to the three-dimensionally specified small region. In this report, I will review the status of present and future positron beams in Japan. At present, two slow positron facilities using Linacs as a slow positron generator are in operation. Several radioisotope-based laboratory beams are in operation. I begin with a survey of conditions surrounding positron beams in Japan. A second section will summarize several ways for the generation of positrons. Emphasis will be placed on three types of planned beams: 1. a Linac-based full scale factory, 2. a cyclotron-based mini-factory, and 3. a radioisotope-based laboratory beam dedicated to industrial research. (orig.)
[en] When energetic positrons are injected into liquids, up to 80% of them ultimately form positronium atoms. Most of the Ps atoms are formed by e+ + e- reaction in the end-of-track spurs. Such a spur contains several ion-electron pairs and the de-energized positron. A simple mechanism is presented. In liquid hydrocarbons an upper limit of the fraction of positrons that form Ps by the Ore mechanism is estimated to be 0.1. The data are ready for the development of a stochastic multipair spur model. The model would also apply to conventional radiolysis systems. (author)
[en] The condition and specific features of the non-dipole regime of radiation is discussed in the context of the results of the recent CERN experiment NA63 on measurement of the radiation power spectrum of 149 GeV electrons in thin tantalum targets. The first observation of a logarithmic dependence of radiation yield on the target thickness that was done there is the conclusive evidence of the effect of radiation suppression in a thin layer of matter, which was predicted many years ago, and which is the direct manifestation of the radiation of a relativistic electron with non-equilibrium own Coulomb field. The special features of the angular distribution of the radiation and its polarization in a thin target at non-dipole regime are proposed for a new experimental study.
[en] In the production of positrons by ultra-relativistic electrons channeling in a crystal-radiator the incident electrons produce X-ray radiation in the crystal that is not used by now. In present paper we consider the properties of 3 kinds of X-ray radiation as the parametric X-ray radiation, the characteristic X-ray radiation, the diffracted transition radiation emitted in the backward direction from the crystalline radiator of positrons. We found that these kinds of quasi-monochromatic radiations can be registered by an X-ray spectrometer simultaneously with the production of positrons. We propose the observation of backward-going X-rays for the diagnostics of the crystal-radiator and electron beam status during production of positrons. Such on-line diagnostics can contribute to the optimization of the positron production. The same 3 kinds of radiation can be used for the diagnostics of the crystal-radiator during production of a coherent bremsstrahlung by the ultrarelativistic electron beam in a crystal and also for the diagnostics of bent crystals that are used for the steering of the high-energy particle beams trajectory. Besides, the diffracted transition radiation can be considered as a source of intense quasimonochromatic tunable X-rays beam excited by the high-energy particle beam in a crystal.
[en] Using a narrow band positron beam, the response of a large high-resolution NaI(Ti) crystal to an incident positron beam was measured. It was found that nuclear interactions cause the appearance of additional peaks in the low energy tail of the deposited energy spectrum.
[en] The new positron (e+) magnetic beam presently under construction at UCL is described with particular attention to those features which will facilitate the implementation of a variety of experiments ranging from gaseous atomic scattering to surface and solid state studies. Some intended experiments on the new system are also briefly outlined. (orig.)