نتایج جستجو برای: positron
تعداد نتایج: 31378 فیلتر نتایج به سال:
Siemens Healthcare, Knoxville, TN, USA A new positron annihilation imaging modality is described that enables nondestructive measurement of the linear attenuation coefficients (LACs) of positron beams in heterogeneous materials. This positron attenuation tomography (PAT) technique utilizes a positron emission tomography (PET) system embedded within a uniform static magnetic field, such as is fo...
We study electron-positron in-flight annihilation as a potential source of quasi-monoenergetic photon (or gamma-ray) beams. A high-intensity tunable-energy (1.515 MeV) gamma source has many potential uses in medical, industrial and security applications. Several electron-positron collision geometries are considered: a) head-on; b) collinear; and c) positron beam incident on a fixed electron tar...
We present a new measurement of the cosmic-ray positron fraction e + =(e + + e) obtained from the rst balloon ight of the High Energy Antimatter Telescope (HEAT). Using a magnet spectrometer combined with a transition radiation detector, an electromagnetic calorimeter, and time-of-ight counters we have achieved a high degree of background rejection. Our results do not indicate a major contribut...
A precision measurement by AMS of the positron fraction in primary cosmic rays in the energy range from 0.5 to 500 GeV based on 10.9 million positron and electron events is presented. This measurement extends the energy range of our previous observation and increases its precision. The new results show, for the first time, that above ∼200 GeV the positron fraction no longer exhibits an increas...
Volkov states are exact solutions of the Dirac equation in presence an arbitrary plane wave. states, as well free photon not stable background plane-wave field but "decay" electrons/positrons can emit photons and transform into electron-positron pairs. By using corresponding Schwinger-Dyson equations within locally-constant approximation, we compute probabilities nonlinear single Compton scatte...
Positronium (Ps) formation in a ground state and 2s state of the hydrogen atom by positron impact has been studied within the framework of Eikonal direct approximation in the intermediate and high energy range. For this process, we compute Eikonal charge- exchange scattering amplitude, the differential and total cross sections by reducing the six-dimensional integrals to one-dimensional integra...
Positron annihilation spectroscopy is often used to analyze the local electronic structure of materials of technological interest. Reliable theoretical tools are crucial to interpret the measured spectra. Here, we propose a parameter-free gradient correction scheme for a local-density approximation obtained from high-quality quantum Monte Carlo data. The results of our calculations compare favo...
Positron Annihilation Spectroscopy is a valuable microscopic method to study radiation damage in nuclear reactor pressure vessel steels. At SCKoCEN, a new positron lifetime setup, suited to measure positron lifetimes in irradiated steel, is being constructed. The particularity of this setup is that the prompt count rate originating from the induced 60Co-activity in the steel is highly reduced. ...
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