Experimental studies of exotic transitions in high-Z few-electron ions [Elektronische Ressource] / von Sergiy Trotsenko

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• Physik

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• Publié par: goethe_universitat_frankfurt_am_main
• Publié le: 01 janvier 2008
• Nombre de lectures: 42
• Langue: English
• Poids de l'ouvrage: 3 Mo

Extrait

Experimental Studies of Exotic Transitions in
High-Z Few-Electron Ions
Dissertation
zur Erlangung des Doktorgrades
der Naturwissenschaften
vorgelegt beim Fachbereich Physik
der Johann Wolfgang Goethe-Universit¨at
in Frankfurt am Main
von
Sergiy Trotsenko
aus Bogodukhiv
Frankfurt am Main 2008
(D30)vom Fachbereich Physik der Johann Wolfgang Goethe-Universit¨at
als Dissertation angenommen.
Dekan: Prof. Dr. D.-H. Rischke
Gutachter: Prof. Dr. Th. St¨ohlker
Prof. Dr. R. D¨orner
Datum der Disputation: 24.06.2009Contents
1 Introduction 13
2 The Structure of Few-electron systems 17
2.1 One-electron ions . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.2 Two-electron ions . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.3 Transition rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.3.1 Transition rates for H-like ions . . . . . . . . . . . . . . . 25
2.3.2 Transition rates for He-like ions . . . . . . . . . . . . . . . 25
3 Two-photon transitions 29
3.1 The simultaneous emission of two photons . . . . . . . . . . . . . 29
3.2 Two-photon decay in one-electron ions . . . . . . . . . . . . . . . 32
3.3 Two-photon decay in two-electron ions . . . . . . . . . . . . . . . 34
3.4 Dependence of the two-photon decay properties on the atomic
number Z . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.5 The 2E1 decay rate and energy distribution . . . . . . . . . . . . 38
3.6 Two-photon decay of ions with inner-shell vacancy . . . . . . . . . 41
3.7 Earlier Two-Photon Decay Experiments . . . . . . . . . . . . . . 42
4 Experimental Approach for Studying Exotic Transitions 47
4.1 Collisions of Highly Charged Ions. . . . . . . . . . . . . . . . . . . 47
4.2 Ionization and Excitation Processes . . . . . . . . . . . . . . . . . 48
4.3 Selective Generation of Excited States
in Few-Electron Ions . . . . . . . . . . . . . . . . . . . . . . . . . 50
4.3.1 Ionization and excitation probabilities . . . . . . . . . . . 52
12 CONTENTS
4.3.2 Simultaneous excitation and ionization
in the IPA framework . . . . . . . . . . . . . . . . . . . . 53
4.3.3 Relaxation of Electron Orbitals . . . . . . . . . . . . . . . 54
5 Experimental Facility 57
5.1 The GSI Accelerator Facility . . . . . . . . . . . . . . . . . . . . . 58
5.2 Experimental Storage Ring . . . . . . . . . . . . . . . . . . . . . . 59
5.3 The Gas-jet target at the ESR . . . . . . . . . . . . . . . . . . . . 62
5.4 X-ray Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
5.5 Experiments at the ESR . . . . . . . . . . . . . . . . . . . . . . . 66
6 Feasibility of the Exclusive Production of the K-shell vacancy 69
6.1 Selective ionization of the K-shell electron of Li-like Uranium . . 69
6.2 Selective ionization of the K-shell electron of Be-like Uranium . . 74
7 Measurement of the two-photon decay in He-like tin and
the data evaluation 77
7.1 The Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
7.2 Total x-ray spectrum . . . . . . . . . . . . . . . . . . . . . . . . . 80
7.3 Random subtraction . . . . . . . . . . . . . . . . . . . . . . . . . 81
7.4 Ionization spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . 82
7.5 Energy and Efficiency calibration . . . . . . . . . . . . . . . . . . 86
7.6 Spectra simulations . . . . . . . . . . . . . . . . . . . . . . . . . . 88
7.6.1 Relativistic Doppler shift . . . . . . . . . . . . . . . . . . . 89
7.6.2 Doppler broadening of the x-ray lines . . . . . . . . . . . . 90
7.6.3 Detector Response . . . . . . . . . . . . . . . . . . . . . . 90
8 Results and Discussions 93
9 Summary 99
10 Outlook 101
10.1 Further Applications: Two-Electron One-Photon transition in Li-
like Uranium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102CONTENTS 3
10.2 Two-Photon Decay in High-Z ions:
Further Development and New Challenges . . . . . . . . . . . . . 103
11 Zusammenfassung 107
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113List of Figures
1.1 Level scheme of the first excited levels of a He-like ion. . . . . . . . . . . 14
2.1 The mean value of the electric field strength <|E|> as a function of nuclear
charge (Z) for the most strongly bound states in H-like ions. . . . . . . . . 18
2.2 The level scheme according to the Dirac’s theory for the lowest atomic levels
in one-electron ions. The dashed lines represent the QED corrections to the
energy levels. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.3 Level scheme for a) a light(LS-coupling) and b) a heavy (jj-coupling) He-like
ion. Besides the decay mode of every ground state transition, the respective
Z-scaling of the transition rates are also presented. . . . . . . . . . . . . . 21
2.4 The different contributions to the absolute ionization potential in He-like sys-
2 1tems [7]. The data refer to the 1s S ground state. The corrections that0
lead to a reduction of the ionization potential are marked with a minus sign. 23
2.5 The absolute decay rates and lifetimes of the L → K transitions in He-like
ions as a function of the nuclear charge (for an explanation of 2E1-shape see
the next chapter). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3 32.6 Branching ratio for the radiative decay of the 1s2p P -level to the 1s2p S -2 1
state as a function of nuclear charge for He-like ions [17]. . . . . . . . . . . 26
3.1 Schematic of forbidden and allowed transitions with respect to the angular
momentum conservation law. . . . . . . . . . . . . . . . . . . . . . . . 29
13.2 Calculated typical energy distribution of the two-photon decay of the 2 S -0
stateofaHe-likeion. Theintensityisnormalizedtothemiddleofthedistribu-
tion. The photon energy is normalized to the energy difference (E ) between0
the initial and the final state (see equation 3.1). . . . . . . . . . . . . . . 30
56 LIST OF FIGURES
3.3 Calculated theoretical angular distribution of two-photon emission from
2ns− 1s transition (1 + cos θ); θ is the angle between the two photons
[79], [130], [59], [131]. . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.4 Level scheme of the first excited states of hydrogen. The scaling of the corre-
sponding transition rates with the atomic number Z is also given. . . . . . . 33
3.5 Level scheme of the first excited states of a He-like ion. The scaling of the
corresponding transition rates with the atomic number (Z) is also shown. . . 35
3.6 Theoretical energy distributions of the two-photon (2E1) decays in hydrogen
and helium [63]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.7 (Top panel) Comparison of relativistic and non-relativistic estimations of the
1decayratesforthe2 S state[61]. (Lowerpanel)Fullwidthathalfmaximum0
1(FWHM) of the two-photon energy distribution of the 2 S state ploted as a0
function of Z [62]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
1 13.8 Energy distribution of the 2 S - 1 S two-photon transition, calculated0 0
using a relativistic approach [63]. . . . . . . . . . . . . . . . . . . . . . 41
4.1 Impact parameter (b) in collision of ion (projectile) with atom (target). . . . 49
4.2 Production of the excited 1s2s state by selective K-shell ionization. One K-
shell electron is ionized without disturbing the remaining two electrons. . . . 50
4.3 Impact parameter dependent description of the ionization/excitation processes. 52
4.4 The 1s ionization and/or 2s excitation probabilities for relativistic1/2 1/2
89+398 MeV/u U → N collisions as a function of the impact parameter b(λ);2
with λ - Compton wavelength [104], [105]. . . . . . . . . . . . . . . . . . 54
5.1 Layout of the accelerator facility at GSI, showing the linear accelerator UNI-
LAC, the heavy-ion synchrotron SIS18, and the experimental storage ring ESR. 57
5.2 Calculated charge-state evolution as a function of target thickness for
300 MeV/u uranium ions impinging on Cu (top panel), Al (middle panel)
and C (bottom panel) targets. Colors of the lines define different charge-
states (black lines for bare ions, red - H-like, green - He-like, blue - Li-like
etc.) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58LIST OF FIGURES 7
5.3 Schematic of the storage and cooler ring ESR at GSI. The layout depicts the
beam guiding system (dipole bending magnets, quadrupoles and hexapoles)
as well as the most important installations for beam handling and diagnostics
(kicker, rf cavities, Schottky noise pick-up, electron cooler). The position of
the internal jet-target is marked in addition. . . . . . . . . . . . . . . . . 60
5.4 Layout of the electron cooler device used at the storage and cooler ring ESR.
Electronsproduced in the electrongun at a cathode temperature of≈ 1300 K
are guided by a≈0.1 T magnetic field co-propagating over a distance of 2 m
with the stored ion beam [93]. . . . . . . . . . . . . . . . . . . . . . . 61
92+5.5 Schottky frequency spectra for a circulating beam of U ions at 295MeV/u.
The broad distribution refers to the uncooled initial beam, measured directly
after injection into the ESR. The narrow distribution reflects the momentum
profile of a continuously cooled ion beam. . . . . . . . . . . . . . . . . . 61
5.6 Scheme of the Gas Jet target at the ESR[100]. . . . . . . . . . . . . . . . 62
5.7 The hi