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- Andersson, M, et al.
(författare)
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Hyperfine-dependent lifetimes in Be-like ions
- 2009
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 79:3
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical investigations of hyperfine quenching of the two metastable levels 1s(2)2s2p P-3(0) and P-3(2) have been performed along the Be-like isoelectronic sequence for ions between Z=6-22. It is shown that the lifetime of the latter level is sensitive to hyperfine quenching in the beginning of the isoelectronic sequence, but the sensitivity decreases towards the high-Z end. It is also shown that the hyperfine dependent branching fraction between the 2s(2) S-1(0)-2s2p P-3(2) and the 2s2p P-3(1)-2s2p P-3(2) transitions can lead to some rather drastic changes in the spectra. Our predicted value of 0.677 s(-1) for the hyperfine-induced 2s(2) S-1(0)-2s2p P-3(0) transition rate for Ti-47(18+) are in disagreement with a recent experimental value of 0.56(3) s(-1). Our calculated values of this quenching are in agreement with other recent calculations all along the sequence.
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- Andersson, M., et al.
(författare)
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Hyperfine-interaction-dependent 4s4p P-3(2) lifetimes in Zn-like ions
- 2008
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 78:6
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical studies on hyperfine-interaction-dependent lifetimes of the 4s4p P-3(2) states of Zn-like ions are reported in this paper. A systematic investigation along the isoelectronic sequence shows that the lifetime of the 4s4p P-3(2) level is very sensitive to hyperfine interaction at the beginning of the sequence, but gets less sensitive going to the higher end. The intensity ratio between the 4s(2) S-1(0)-4s4p P-3(2) and the 4s4p P-3(1)-4s4p P-3(2) transitions was also investigated and it is shown that this ratio is very sensitive to hyperfine interaction. In some isotopes the two branches are dominated by transitions from different upper hyperfine levels. Our research also reveals that the hyperfine-induced electric dipole transitions contribute to the transitions of 4s(2) S-1(0)-4s4p P-3(2) at about the same level as, or even higher than, M2 transitions whenever the nucleus has a spin. This is true all along the isoelectronic sequence.
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- Andersson, M., et al.
(författare)
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Hyperfine-state-dependent lifetimes along the Ni-like isoelectronic sequence
- 2008
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 77:4, s. 12-042509
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Tidskriftsartikel (refereegranskat)abstract
- An investigation of the lifetime of the 3d(9)4s D-3(3) level along a part of the nickel-like isoelectronic sequence has been performed. The focus of this work has been to evaluate the importance of the hyperfine induced electric quadrupole channel of the 3d(10) S-1(0)-3d(9)4s D-3(3) transition for isotopes with nuclear spin. Comparisons between the magnetic octupole transition rate and the hyperfine-induced electric quadrupole transition rate shows that the hyperfine quenching is of importance along the whole isoelectronic sequence. At the low-Z end the hyperfine induced electric quadrupole transition channel dominates, being several orders of magnitude larger than the rate for the magnetic octupole transition channel, while for higher Z the two rates are of comparable size.
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- Huang, M, et al.
(författare)
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Multiconfiguration Dirac-Hartree-Fock calculations for intercombination lines in silicon-like ions
- 2005
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 38:5, s. 503-508
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports on multiconfiguration Dirac-Hartree-Fock calculations for intercombination lines in highly charged silicon-like ions. Results for wavelengths, fine structure, transition rates, branching ratios and lifetimes are reported and compared with other theories and experiments. A review of the experimental situation is presented, and deviations from expected smooth trends along the sequence are discussed.
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- Hutton, B F, et al.
(författare)
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Reducing the influence of spatial resolution to improve quantitative accuracy in emission tomography : A comparison of potential strategies
- 2006
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 569:2 SPEC. ISS., s. 462-466
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Tidskriftsartikel (refereegranskat)abstract
- The goal of this paper is to compare strategies for reducing partial volume effects by either minimizing the cause (i.e. improving resolution) or correcting the effect. Correction for resolution loss can be achieved either by modelling the resolution for use in iterative reconstruction or by imposing constraints based on knowledge of the underlying anatomy. Approaches to partial volume correction largely rely on knowledge of the underlying anatomy, based on well-registered high-resolution anatomical imaging modalities (CT or MRI). Corrections can be applied by considering the signal loss that results by smoothing the high-resolution modality to the same resolution as obtained in emission tomography. A physical phantom representing the central brain structures was used to evaluate the quantitative accuracy of the various strategies for either improving resolution or correcting for partial volume effects. Inclusion of resolution in the reconstruction model improved the measured contrast for the central brain structures but still underestimated the true object contrast (∼0.70). Use of information on the boundaries of the structures in conjunction with a smoothing prior using maximum entropy reconstruction achieved some degree of contrast enhancement and improved the noise properties of the resulting images. Partial volume correction based on segmentation of registered anatomical images and knowledge of the reconstructed resolution permitted more accurate quantification of the target to background ratio for individual brain structures. © 2006 Elsevier B.V. All rights reserved.
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| 10. |
- Liu, Y F, et al.
(författare)
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Charge state evolution of uranium in electron beam ion trap
- 2005
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Ingår i: Chinese Physics Letters. - 1741-3540. ; 22:8, s. 1891-1894
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Tidskriftsartikel (refereegranskat)abstract
- We present a calculation scheme with significant modifications and improvements for determining the ionization balance and the ion temperature evolution in an electron beam ion trap (EBIT). The scheme is applied to uranium and nitrogen ions using a specific set of EBIT operating parameters. The calculation results are compared to the experimental data. Rates for the individual atomic processes in EBIT, especially single and multiple charge exchange processes, are discussed. The time evolution of the ion temperatures for uranium and its coolant nitrogen are also given.
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