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Laboratory studies of forbidden decay processes in stored ions
Stockholm University, Faculty of Science, Department of Physics. (Atomfysik)
2008 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Measurements of atomic and ionic data has been an active research area since the beginning of spectroscopic studies. The experimental data deduced from thesestudies are of great interest for our understanding of fundamental as well as applied physics. The metastability of certain energy levels has been used toexplain phenomena in widely different fields ranging from the principles of the laser to observations of forbidden spectral lines originating fromastrophysical objects. Eventhough measurements of radiative lifetimes have been carried out for many decades new interesting results are still found in theexplanation of phenomena observed in these studies. The technological development in the field of atomic physics has provided researchers with several toolswhich have opened up completely new possibilities in recent years. Atoms and ions can now be stored for long times which allows studies of extremely weakprocesses. In this thesis results from studies of weak radiative decays of metastable levels are presented. The measurements were carried out utilizing a laserprobing technique together with ions stored in the ion storage ring CRYRING at the Manne Siegbahn laboratory in Stockholm, Sweden. The longest radiativelifetime measured so far in a storage ring, 89 s in singly ionized barium, is presented along with a completely new method for determining extremelylong radiative lifetimes. The thesis also includes new interesting results from lifetime measurements in argon which revealed the unexpected importance of an E3 decay channel. This is to the best of our knowledge the first ever observation of an E3 transition rate of this magnitude in a singlycharged ion. All lifetime measurements are presented with complementary calculations by our collaborators at Université de Mons-Hainaut and Université de Liège, Belgium. The studies of BaII are also part of a collaboration with the Institute of solid state physics of the Bulgarian Academy of Sciences.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2008. , 61 p.
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-30244OAI: oai:DiVA.org:su-30244DiVA: diva2:242350
Presentation
2008-01-30, FA31, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 14:00 (English)
Opponent
Supervisors
Available from: 2010-09-14 Created: 2009-10-07 Last updated: 2010-09-14Bibliographically approved
List of papers
1. Laser-probing measurements and calculations of lifetimes of the 5d 2D3/2 and 5d 2D5/2 metastable levels in Ba II
Open this publication in new window or tab >>Laser-probing measurements and calculations of lifetimes of the 5d 2D3/2 and 5d 2D5/2 metastable levels in Ba II
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2007 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 75, no 5, 052506- p.Article in journal (Refereed) Published
Abstract [en]

The two metastable levels 5d 2D3∕2 and 5d 2D5∕2 in Ba II both show extremely long lifetimes of the order of several tens of seconds each. This has been found both by experiments and by theoretical predictions. The small transition probabilities associated with these two levels make them interesting and challenging for theoreticians as well as for experimentalists. Several calculations and measurements of these two lifetimes have been made previously but discrepancies between the results are present. This article presents values of τ=89.4±15.6 s for the 2D3∕2 level and τ=32.0±4.6 s for the 2D5∕2 level measured in a beam-laser experiment performed at the ion storage ring CRYRING. These values are supported by our new calculations resulting in τ=82.0 s for the 2D3∕2 level and τ=31.6 s for the 2D5∕2 level.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-25161 (URN)10.1103/PhysRevA.75.052506 (DOI)000246890400083 ()
Note
Part of urn:nbn:se:su:diva-7768Available from: 2008-05-27 Created: 2008-05-20 Last updated: 2017-12-13Bibliographically approved
2. Monitoring the weak collisional excitation of a stored ion beam reveals the radiative decay rate of extremely long-lived metastable levels
Open this publication in new window or tab >>Monitoring the weak collisional excitation of a stored ion beam reveals the radiative decay rate of extremely long-lived metastable levels
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2007 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 76, no 3, 030502- p.Article in journal (Refereed) Published
Abstract [en]

A fast ion beam stored in an ion storage ring will suffer from collisional interaction with the residual gas even in extreme ultrahigh vacuum. Normally these effects are negligible or easy to correct for. For measurements of extremely long radiative lifetimes of metastable levels we have found that correction for collisional effects is very important and usually limits the accuracy. We now suggest that by monitoring the process of collisional excitation of the metastable level of interest the lifetime value could be determined directly with improved accuracy. The method is applied to available data from our recent measurement of the 5d 2D5∕2 level in Ba+, yielding a value of 32.0±2.9 s, thus squeezing the error bar by 35%.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-25162 (URN)10.1103/PhysRevA.76.030502 (DOI)000249786000010 ()
Note
Part of urn:nbn:se:su:diva-7768Available from: 2008-05-27 Created: 2008-05-20 Last updated: 2017-12-13Bibliographically approved
3. Inclusion of Electric Octupole Contributions Explains the Fast Radiative Decays of Two Metastable States in Ar+
Open this publication in new window or tab >>Inclusion of Electric Octupole Contributions Explains the Fast Radiative Decays of Two Metastable States in Ar+
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2007 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 99, 213001- p.Article in journal (Refereed) Published
Abstract [en]

A laser probing investigation has yielded the lifetimes of the 3s23p4(1D)3d 2G7/2,9/2 metastable doublet states of Ar+. The results, obtained with the CRYRING ion storage ring of Stockholm, are 3.0±0.4 and 2.1±0.1  s, respectively. Comparisons with theoretical values calculated with two independent theoretical approaches, i.e., the pseudorelativistic Hartree-Fock method and the multiconfiguration Breit-Pauli approach, have allowed us to establish the unexpected and extraordinary strong contribution of an electric octupole (E3) transition to the ground state, in addition to the M1 decay channels to the 3d 2,4F states and the E2 contributions to the 4s 2P, 2D states.

National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-12437 (URN)10.1103/PhysRevLett.99.213001 (DOI)000251107500017 ()
Available from: 2008-01-15 Created: 2008-01-15 Last updated: 2017-12-13Bibliographically approved

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