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Time-Resolved Spectroscopy and Intensity Measurements of Singly Charged Ions
Stockholm University, Faculty of Science, Department of Physics.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is mainly concerned with investigations of spontaneous radiatively decaying states in both negative and positive singly charged ions. When possible, the measured lifetime of the state has been combined with branching fractions in order to derive the absolute transition probability (A-value) between different quantum states. The radiative transition probability between two quantum states is a fundamental atomic property. Knowledge of this property can be used as a diagnostic tool in, for example, abundance and temperature determinations with applications in many fields, e.g. astronomy, plasma physics, atomic physics etc.

The focus of the experiments has been on lifetime measurements of long-lived metastable states. Lifetimes of long-lived metastable states are interesting in both theoretical aspects as well as the challenge it poses to the experimentalist. To perform such experiments, impact from the surrounding environment on the stored ions has to be kept to a minimum for extended periods of time. The metastable lifetimes presented here have been measured with time-resolved laser spectroscopic techniques in two different types of ion storage rings. One of them is a new type of unique cryogenically cooled storage ring made of purely electrostatic ion optical elements. As is demonstrated in this thesis, this device opens up a completely new time domain where lifetime measurements now can be performed. In addition, this thesis includes a discussion and preliminary studies of weak interactions otherwise limited by magnetic fields and/or thermal radiation from the environment. When available, the results have been compared to previous measurements and theoretical calculations which enables an evaluation of different methods and theoretical models.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2015. , 88 p.
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-113503ISBN: 978-91-7649-100-3 (print)OAI: oai:DiVA.org:su-113503DiVA: diva2:785588
Public defence
2015-03-20, sal FB42, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 6: Accepted.

Available from: 2015-02-26 Created: 2015-02-03 Last updated: 2015-02-26Bibliographically approved
List of papers
1. The FERRUM project: Transition probabilities for forbidden lines in [Fe II] and experimental metastable lifetimes
Open this publication in new window or tab >>The FERRUM project: Transition probabilities for forbidden lines in [Fe II] and experimental metastable lifetimes
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2009 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 508, no 1, 525-529 p.Article in journal (Refereed) Published
Abstract [en]

Context. Accurate transition probabilities for forbidden lines are important diagnostic parameters for low-density astrophysical plasmas. In this paper we present experimental atomic data for forbidden [Fe II] transitions that are observed as strong features in astrophysical spectra. Aims. We measure lifetimes for the 3d(6)((3)G)4s a (4)G(11/2) and 3d(6)((3)D)4s b (4)D(1/2) metastable levels in Fe II and experimental transition probabilities for the forbidden transitions 3d(7) a (4)F(7/2,9/2)-3d(6)((3)G)4s a (4)G(11/2). Methods. The lifetimes were measured at the ion storage ring facility CRYRING using a laser probing technique. Astrophysical branching fractions were obtained from spectra of Eta Carinae, obtained with the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. The lifetimes and branching fractions were combined to yield absolute transition probabilities. Results. The lifetimes of the a (4)G(11/2) and the b (4)D(1/2) levels have been measured and have the following values, tau = 0.75 +/- 0.10 s and tau = 0.54 +/- 0.03 s respectively. Furthermore, we have determined the transition probabilities for two forbidden transitions of a (4)F(7/2,9/2)-a (4)G(11/2) at 4243.97 and 4346.85 angstrom. Both the lifetimes and the transition probabilities are compared to calculated values in the literature.

Keyword
atomic data, methods: laboratory, techniques: spectroscopic, stars: individual: Eta Carinae
National Category
Atom and Molecular Physics and Optics Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-32215 (URN)10.1051/0004-6361/200913233 (DOI)000272417700054 ()
Available from: 2009-12-07 Created: 2009-12-07 Last updated: 2017-12-12Bibliographically approved
2. The FERRUM project: metastable lifetimes in Cr II
Open this publication in new window or tab >>The FERRUM project: metastable lifetimes in Cr II
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2012 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 420, no 2, 1636-1639 p.Article in journal (Refereed) Published
Abstract [en]

Parity forbidden radiative transitions from metastable levels are observed in spectra of low-density astrophysical plasmas. These lines are used as probes of the physical conditions, made possible due to the long lifetime of their upper level. In a joint effort, the FERRUM project aims to obtain new and accurate atomic data for the iron-group elements, and part of this project concerns forbidden lines. The radiative lifetimes of the metastable energy levels 3 d4(a 3 D)4 s c4 D 5/2 and 3 d4(a 3 D)4 s c4 D 7/2 of singly ionized chromium have been measured. The experiment has been performed at the ion storage ring CRYRING. We employed a laser-probing technique developed for measuring long lifetimes. In this article, we present the lifetimes of these levels to be t5/2= 1.28(16) s and t7/2= 1.37(7) s, respectively. A comparison with previous theoretical work shows good agreement and the result is discussed in a theoretical context.

Keyword
atomic data, methods: laboratory, techniques: spectroscopic, astronomical data bases: miscellaneous
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-67023 (URN)10.1111/j.1365-2966.2011.20152.x (DOI)000299417600056 ()
Funder
Swedish Research Council, 2006-3085Swedish Research Council, 2008-3736
Available from: 2011-12-22 Created: 2011-12-22 Last updated: 2017-12-08Bibliographically approved
3. Experimentally determined oscillator strengths in Rh II
Open this publication in new window or tab >>Experimentally determined oscillator strengths in Rh II
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2013 (English)In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 46, no 20, 205001- p.Article in journal (Refereed) Published
Abstract [en]

This paper presents new experimentally determined branching fractions and oscillator strengths (log gf) for lines originating from 17 levels belonging to 5 terms of the first excited odd configuration 4d(7)(D-4) 5p in Rh II. The intensity calibrated spectra of Rh II have been recorded with a Fourier transform spectrometer between 25000 and 45000 cm(-1) (2200-4000 angstrom). In this region, 49 lines have been identified and measured. By combining the branching fractions obtained from the spectra with previously measured lifetimes, log gf values are reported. The new results are compared with previous theoretical work.

National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-96881 (URN)10.1088/0953-4075/46/20/205001 (DOI)000325856800002 ()
Funder
Swedish Research Council, 2008-3736Swedish Research Council, 2006-3085
Note

AuthorCount:5;

Available from: 2013-11-28 Created: 2013-11-28 Last updated: 2017-12-06Bibliographically approved
4. The FERRUM project: Experimental transition probabilities from highly excited even 5s levels in Cr II
Open this publication in new window or tab >>The FERRUM project: Experimental transition probabilities from highly excited even 5s levels in Cr II
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2014 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 570, A34- p.Article in journal (Refereed) Published
Abstract [en]

We report lifetime measurements of the five levels in the 3d(4)(a(5)D)5s e(6)D term in Cr II at an energy around 83 000 cm(-1), and log(gf) values for 38 transitions from the investigated levels. The lifetimes are obtained using time-resolved, laser-induced fluorescence on ions from a laser-produced plasma. Since the levels have the same parity as the low-lying states directly populated in the plasma, we used a two-photon excitation scheme. This process is greatly facilitated by the presence of the 3d(4)(a(5)D)4p z(6)F levels at roughly half the energy difference. The f-values are obtained by combining the experimental lifetimes with branching fractions derived using relative intensities from a hollow cathode lamp recorded with a Fourier transform spectrometer.

Keyword
atomic data, methods: laboratory: atomic, techniques: spectroscopic
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-110200 (URN)10.1051/0004-6361/201424762 (DOI)000344158500140 ()
Note

AuthorCount:5;

Available from: 2014-12-09 Created: 2014-12-08 Last updated: 2017-12-05Bibliographically approved
5. First storage of ion beams in the Double Electrostatic Ion-Ring Experiment: DESIREE
Open this publication in new window or tab >>First storage of ion beams in the Double Electrostatic Ion-Ring Experiment: DESIREE
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2013 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 84, no 5, 055115- p.Article in journal (Refereed) Published
Abstract [en]

We report on the first storage of ion beams in the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. We have produced beams of atomic carbon anions and small carbon anion molecules (C-n(-), n = 1, 2, 3, 4) in a sputter ion source. The ion beams were accelerated to 10 keV kinetic energy and stored in an electrostatic ion storage ring enclosed in a vacuum chamber at 13 K. For 10 keV C-2(-) molecular anions we measure the residual-gas limited beam storage lifetime to be 448 s +/- 18 s with two independent detector systems. Using the measured storage lifetimes we estimate that the residual gas pressure is in the 10(-14) mbar range. When high current ion beams are injected, the number of stored particles does not follow a single exponential decay law as would be expected for stored particles lost solely due to electron detachment in collision with the residual-gas. Instead, we observe a faster initial decay rate, which we ascribe to the effect of the space charge of the ion beam on the storage capacity.

National Category
Accelerator Physics and Instrumentation
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-92036 (URN)10.1063/1.4807702 (DOI)000319999300073 ()
Funder
Swedish Research Council, 2011-6314, 2011-4047, 2012-3662Knut and Alice Wallenberg Foundation
Note

AuthorCount:34;

Available from: 2013-07-16 Created: 2013-07-15 Last updated: 2017-12-06Bibliographically approved
6. Storing keV negative ions for an hour: The lifetime of the metastable 2P1/2 level in 32S−
Open this publication in new window or tab >>Storing keV negative ions for an hour: The lifetime of the metastable 2P1/2 level in 32S−
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2015 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 114, no 14, 143003Article in journal (Refereed) Published
Abstract [en]

We use a novel electrostatic ion storage ring to measure the radiative lifetime of the upper level in the 3p 5  P 2  o 1/2 →3p 5  P 2  o 3/2   spontaneous radiative decay in S −  32   to be 503±54  sec . This is by orders of magnitude the longest lifetime ever measured in a negatively charged ion. Cryogenic cooling of the storage ring gives a residual-gas pressure of a few times 10 −14   mbar at 13 K and storage of 10 keV sulfur anions for more than an hour. Our experimental results differ by 1.3σ  from the only available theoretical prediction.

National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-114302 (URN)10.1103/PhysRevLett.114.143003 (DOI)000352192200009 ()
Funder
Swedish Research Council, 821-2013-1642Swedish Research Council, 621-2012-3662Swedish Research Council, 621-2011-4047Swedish Research Council, 621-2013-4084
Available from: 2015-02-26 Created: 2015-02-26 Last updated: 2017-12-04Bibliographically approved

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