Search results for "annihilation [dark matter]"
showing 10 items of 10 documents
'Cold' crystallization in nanostructurized 80GeSe2-20Ga2Se3 glass
2015
International audience; 'Cold' crystallization in 80GeSe 2-20Ga 2 Se 3 chalcogenide glass nanostructurized due to thermal annealing at 380°C for 10, 25, 50, 80, and 100 h are probed with X-ray diffraction, atomic force, and scanning electron microscopy, as well as positron annihilation spectroscopy performed in positron annihilation lifetime and Doppler broadening of annihilation line modes. It is shown that changes in defect-related component in the fit of experimental positron lifetime spectra for nanocrystallized glasses testify in favor of structural fragmentation of larger free-volume entities into smaller ones. Nanocrystallites of Ga 2 Se 3 and/or GeGa 4 Se 8 phases and prevalent GeSe…
Search for lepton flavor violating decays τ±→l± ω
2008
A search for lepton flavor violating decays of a {tau} to a lighter-mass charged lepton and an {omega} vector meson is performed using 384.1 fb{sup -1} of e{sup +}e{sup -} annihilation data collected with the BABAR detector at the Stanford Linear Accelerator Center PEP-II storage ring. No signal is found, and the upper limits on the branching ratios are determined to be {beta}({tau}{sup {+-}} {yields} e{sup {+-}}{omega}) < 1.1 x 10{sup -7} and {beta}({tau}{sup {+-}} {yields} {mu}{sup {+-}}{omega}) < 1.0 x 10{sup -7} at 90% confidence level.
Electromagnetic Structure of the Neutron from Annihilation Reactions
2022
The investigation of the fundamental properties of the nucleon is one of the most important topics in the modern hadron physics. Its internal structure and dynamics can be studied through the measurement of electromagnetic form factors which represent the simplest structure observables and serve as a test ground for our understanding of the strong interaction. Since the first attempt to measure the time-like form factors of the neutron, only four experiments published results on its structure from annihilation reactions. Due to the lack of statistics and experimental challenges, no individual determination of the form factors of the neutron has been possible so far. Modern developments of e…
Annihilation Characteristics of Confined 2D Positronium
2012
The 2D Positronium (2D Ps) atom confined in the 2D cave has been considered and its properties were compared with the 3D Positronium located in the infinity square well potential. Basing on the solution of Schrödinger equation for the 2D hydrogen atom the wave function of the 2D Ps was given. It allows us to calculate, for instance the angular correlation of the annihilation radiation (ACAR) of such a system. It was shown that the ACAR is much broad than ACAR for the 3D Ps and that for the Ps in the bubble model.
Precise energies of gamma rays from the 230Th and 228Th decay
1977
Abstract Energies up to 300 keV of prominent gamma rays from the decay of 230 Th, 228 Th and some of the 228 Th descendants have been precisely measured by use of Ge(Li) detectors.
Helium bubbles in metals: Molecular-dynamics simulations and positron states.
1987
By combining molecular-dynamics results for the aluminum-helium interface with positron-state calculations it is demonstrated that a positron is trapped at the surface of a He bubble in Al. The annihilation rate with Al electrons is similar to that at a clean surface, while simultaneously there is a significant annihilation rate with He electrons. This enables one to obtain a useful relation between the positron lifetime and helium densities in bubbles.
Test Measurements of Modernized Version of Two-Detector Doppler Spectrometer
1999
The quality of the annihilation quanta energy measurements (Doppler effect) has greatly increased when experimenters have begun to introduce Doppler apparatus modifications. In the basic version, the experimental set-up consisted of high energy resolution Ge(Li) detector, amplifier and multichannel analyser. A simple construction and short time of data acquisition were the main advantages of that version of the apparatus. Competitive, angular correlation of annihilation radiation (ACAR) method was better from the resolution point of view and not worse when considering the range of momentum distribution, but the ACAR method required high activity positron sources and data acquisition time wa…
Characterization of non-polar ZnO layers with positron annihilation spectroscopy
2008
We applied positron annihilation spectroscopy to study the effect of growth polarity on the vacancy defects in ZnO grown by metal-organic vapor phase deposition on sapphire. Both c-plane and a-plane ZnO layers were measured, and Zn vacancies were identified as the dominant defects detected by positrons. The results are qualitatively similar to those of earlier experiments in GaN. The Zn vacancy concentration decreases in c-plane ZnO by almost one order of magnitude (from high 10 cm−3 to low 10 cm−3) when the layer thickness is increased from 0.5 to 2 μm. Interestingly, in a-plane ZnO the Zn vacancy concentration is constant at a level of about 2×10 cm−3 in all the samples with thicknesses v…
Structural-relaxation phenomena in As–S glasses as probed by combined PAL/DBAR technique
2015
Abstract Experimental techniques exploring phenomena of positron–electron interaction, namely the positron annihilation lifetime spectroscopy and Doppler broadening of annihilation radiation, are shown to be very informative tools to study radiation- and thermally-induced phenomena in chalcogenide glasses of binary As–S system. Time-dependent processes of free-volume voids agglomeration (expansion), fragmentation (refining) and disappearing (contraction) are identified as main stages of physical aging in S-rich glasses, while a competitive channel of coordination topological defects formation associated with void charging becomes significant in a vicinity of near-stoichiometric glass compos…
Free-volume Study in GeS2-Ga2S3-CsCl Chalcohalide Glasses Using Positron Annihilation Technique
2015
Abstract Positron annihilation lifetime spectroscopy combined with Doppler broadening of annihilation radiation was applied to study free-volume entities in Ge-Ga-S glasses having different amount of CsCl additives. It is shown that the structural changes caused by CsCl additives can be adequately described by positron trapping modes determined within two-state model. The results testify in a favor of rather unchanged nature of corresponding free-volume voids responsible for positron trapping in the studied glasses, when mainly concentration of these traps is a subject to most significant changes with composition.