نتایج جستجو برای: positron
تعداد نتایج: 31378 فیلتر نتایج به سال:
At a vacant lattice cell positron-ion repulsion is reduced leading to positron trapping. This causes observable changes in annihilation characteristics: the positron lifetime increases and the positron-electron momentum distribution narrows. Positron trapping in semiconductors is analogous to carrier capture. Due to the long-range Coulomb interaction, the charge state of a vacancy has a strong ...
At least three proposed future colliders (ILC, CLiC and LHeC) require a positron source with a yield greater than 10 e+s−1. An undulator-based positron source has the potential to provide the required yield. This design generates gamma rays by using a high energy electron beam traveling through a superconducting helical undulator. The gamma rays then pair produce in a titanium alloy target to p...
A production method for a positron microprobe using a beta+-decay radioisotope (22Na) source has been investigated. When a magnetically guided positron beam was extracted from the magnetic field, the combination of an extraction coil and a magnetic lens enabled us to focus the positron beam by a factor of 10 and to achieve a high transport efficiency (71%). A 150-nm-thick Ni(100) thin film was ...
BACKGROUND The value of performing post-therapy routine surveillance imaging in patients with Hodgkin lymphoma is controversial. This study evaluates the utility of positron emission tomography/computed tomography using 2-[18F]fluoro-2-deoxyglucose for this purpose and in situations with suspected lymphoma relapse. DESIGN AND METHODS We conducted a multicenter retrospective study. Patients wi...
The Positron Puzzle is a half-century old conundrum about the origin of Galactic $\gamma$-ray emission line at photon energies 511 keV, and shape its morphology, showing bulge-to-disk luminosity ratio $\sim 1$ - unlike any astrophysical source distribution. Positrons that have been cooled to eV scale capture electrons form intermediate bound state Positronium (Ps) which decays on nano-second ti...
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