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The onset of antiprotonic X-ray transitions at high principal quantum numbers and the occurence of electronic X-rays in antiprotonic argon, krypton, and xenon has been analyzed with the help of Multiconfiguration Dirac-Fock calculations. The shell-by-shell ionisation by Auger electron emission, characterised by appearance and disappearance of X-ray lines, is followed through the antiprotonic cascade by considering transition and binding energies of both the antiproton and the remaining electrons. Electronic lines could be attributed partly to specific states of the antiprotonic atom de-excitation.
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The state dependent quenching mechanism of metastable antiprotonic He atoms by contaminants is suggested to explain existing experimental data. The effect of antiproton transfer from the antiprotonic He to noble gas contaminants is shown to play a significant role. Preliminary estimations have been done in the framework of the coupled channels model. The obtained results support the idea of strong dependence of quenching cross-sections on the antiprotonic states quantum numbers and enable to explain qualitatively existing discrepancies between experimental results, obtained for different contaminant densities. New observable effects are predicted.
A study of the gas pressure effect in the position resolution of an interacting X- or gamma-ray photon in a gas medium is performed. The intrinsic position resolution for pure noble gases (Argon and Xenon) and their mixtures with CO2 and CH4 were calculated for several gas pressures (1-10bar) and for photon energies between 5.4 and 60.0 keV, being possible to establish a linear match between the intrinsic position resolution and the inverse of the gas pressure in that energy range. In order to evaluate the quality of the method here described, a comparison between the available experimental data and the calculated one in this work, is done and discussed. In the majority of the cases, a strong agreement is observed.
The Large Underground Xenon (LUX) experiment operates at the Sanford Underground Research Facility to detect nuclear recoils from the hypothetical Weakly Interacting Massive Particles (WIMPs) on a liquid xenon target. Liquid xenon typically contains trace amounts of the noble radioactive isotopes $^{85}$Kr and $^{39}$Ar that are not removed by the in situ gas purification system. The decays of these isotopes at concentrations typical of research-grade xenon would be a dominant background for a WIMP search exmperiment. To remove these impurities from the liquid xenon, a chromatographic separation system based on adsorption on activated charcoal was built. 400 kg of xenon was processed, reducing the average concentration of krypton from 130 ppb to 3.5 ppt as measured by a cold-trap assisted mass spectroscopy system. A 50 kg batch spiked to 0.001 g/g of krypton was processed twice and reduced to an upper limit of 0.2 ppt.
The QED contribution to the energies of the circular (n,l=n-1), 2 ≤ n ≤ 19 transitions have been calculated for several kaonic atoms throughout the periodic table, using the current world average kaon mass. Calculations were done in the framework of the Klein-Gordon equation, with finite nuclear size and all-order Uelhing vacuum polarization corrections, as well as Kallen and Sabry and Wichmann and Kroll corrections. These energy level values are compared with other computed values. The circular transition energies are compared with available measured and theoretical transition energy. Electron screening is evaluated using a Dirac-Fock model for the electronic part of the wave function. The effect of electronic wavefunction correlation is evaluated for the first time.
A formula for the ionization rate in extremely intense electromagnetic field is proposed and used for numerical study of QED (quantum-electrodynamical) cascades in noble gases in the field of two counter-propagating laser pulses. It is shown that the number of the electron-positron pairs produced in the cascade increases with the atomic number of the gas where the gas density is taken to be reversely proportional to the atomic number. While the most electrons produced in the laser pulse front are expelled by the ponderomotive force from region occupied by the strong laser field there is a small portion of the electrons staying in the laser field for a long time until the instance when the laser field is strong enough for cascading. This mechanism is relevant for all gases. For high-$Z$ gases there is an additional mechanism associated with the ionization of inner shells at the the instance when the laser field is strong enough for cascading. The role of both mechanisms for cascade initiation is revealed.
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