| 1. |
- Gatchell, Michael, et al.
(författare)
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Commissioning of the DESIREE storage rings - a new facility for cold ion-ion collisions
- 2014
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Ingår i: XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013). - : Institute of Physics (IOP). ; 488:1
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Konferensbidrag (refereegranskat)abstract
- We report on the ongoing commissioning of the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. Beams of atomic carbon anions (C-) and smaller carbon anion molecules (C-2(-), C-3(-), C-4(-) etc.) have been produced in a sputter ion source, accelerated to 10 keV or 20 keV, and stored successfully in the two electrostatic rings. The rings are enclosed in a common vacuum chamber cooled to below 13 Kelvin. The DESIREE facility allows for studies of internally relaxed single isolated atomic, molecular and cluster ions and for collision experiments between cat-and anions down to very low center-of-mass collision energies (meV scale). The total thermal load of the vacuum chamber at this temperature is measured to be 32 W. The decay rates of stored ion beams have two components: a non-exponential component caused by the space charge of the beam itself which dominates at early times and an exponential term from the neutralization of the beam in collisions with residual gas at later times. The residual gas limited storage lifetime of carbon anions in the symmetric ring is over seven minutes while the 1/e lifetime in the asymmetric ring is measured to be about 30 seconds. Although we aim to improve the storage in the second ring, the number of stored ions are now sufficient for many merged beams experiments with positive and negative ions requiring milliseconds to seconds ion storage.
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| 2. |
- Gatchell, Michael, et al.
(författare)
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First results from the Double ElectroStatic Ion-Ring ExpEriment, DESIREE
- 2014
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Ingår i: XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013). - : Institute of Physics (IOP). ; 488
-
Konferensbidrag (refereegranskat)abstract
- We have stored the first beams in one of the rings of the double electrostatic ion-storage ring, DESIREE at cryogenic and at room temperature conditions. At cryogenic operations the following parameters are found. Temperature; T= 13K, pressure; p <10(-13) mbar, initial number of stored ions; N > 10(7) and storage lifetime of a C-2(-) beam; tau = 450 S.
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| 3. |
- Hartman, Henrik, et al.
(författare)
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First storage of ion beams in the Double Electrostatic Ion-Ring Experiment : DESIREE
- 2013
-
Ingår i: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 84:5
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Tidskriftsartikel (refereegranskat)abstract
- 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 (Cn-, 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 C2- 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.
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| 4. |
- Thomas, Richard D., et al.
(författare)
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DESIREE : Physics with cold stored ion beams
- 2015
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Ingår i: DR2013. - : EDP Sciences. ; 84, s. 01004-01004
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Konferensbidrag (refereegranskat)abstract
- Here we will briefly describe the commissioning of the Double ElectroStatic Ion Ring ExpEriment (DESIREE) facility at Stockholm University, Sweden. This device uses purely electrostatic focussing and deflection elements and allows ion beams of opposite charge to be confined under extreme high vacuum and cryogenic conditions in separate rings and then merged over a common straight section. This apparatus allows for studies of interactions between cations and anions at very low and well-defined centre-of-mass energies (down to a few meV) and at very low internal temperatures (down to a few K).
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| 5. |
- Thomas, Richard D., et al.
(författare)
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The double electrostatic ion ring experiment : A unique cryogenic electrostatic storage ring for merged ion-beams studies
- 2011
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 82:6, s. 065112-
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Tidskriftsartikel (refereegranskat)abstract
- We describe the design of a novel type of storage device currently under construction at Stockholm University, Sweden, using purely electrostatic focussing and deflection elements, in which ion beams of opposite charges are confined under extreme high vacuum cryogenic conditions in separate rings and merged over a common straight section. The construction of this double electrostatic ion ring experiment uniquely allows for studies of interactions between cations and anions at low and well-defined internal temperatures and centre-of-mass collision energies down to about 10 K and 10 meV, respectively. Position sensitive multi-hit detector systems have been extensively tested and proven to work in cryogenic environments and these will be used to measure correlations between reaction products in, for example, electron-transfer processes. The technical advantages of using purely electrostatic ion storage devices over magnetic ones are many, but the most relevant are: electrostatic elements which are more compact and easier to construct; remanent fields, hysteresis, and eddy-currents, which are of concern in magnetic devices, are no longer relevant; and electrical fields required to control the orbit of the ions are not only much easier to create and control than the corresponding magnetic fields, they also set no upper mass limit on the ions that can be stored. These technical differences are a boon to new areas of fundamental experimental research, not only in atomic and molecular physics but also in the boundaries of these fields with chemistry and biology. For examples, studies of interactions with internally cold molecular ions will be particular useful for applications in astrophysics, while studies of solvated ionic clusters will be of relevance to aeronomy and biology.
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| 6. |
- Bäckström, Erik, et al.
(författare)
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Experimentally determined oscillator strengths in Rh II
- 2013
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:20, s. 205001-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Bäckström, Erik, 1983-, et al.
(författare)
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Storing keV negative ions for an hour : The lifetime of the metastable 2P1/2 level in 32S−
- 2015
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 114:14
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Bäckström, Erik, et al.
(författare)
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The FERRUM project : metastable lifetimes in Cr II
- 2012
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 420:2, s. 1636-1639
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Bäckström, Erik, 1983-
(författare)
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Time-Resolved Spectroscopy and Intensity Measurements of Singly Charged Ions
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 10. |
- Chartkunchand, Kiattichart C., et al.
(författare)
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Radiative lifetimes of the bound excited states of Pt-
- 2016
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Ingår i: Physical Review A - Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 94:3
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Tidskriftsartikel (refereegranskat)abstract
- © 2016 American Physical Society.The intrinsic radiative lifetimes of the 5d106sS1/22 and 5d96s2 D3/22 bound excited states in the platinum anion Pt- have been studied at cryogenic temperatures at the Double ElectroStatic Ion Ring Experiment (DESIREE) facility at Stockholm University. The intrinsic lifetime of the higher-lying 5d106s S1/22 state was measured to be 2.54±0.10s, while only a lifetime in the range of 50-200 ms could be estimated for the 5d96s2 D3/22 fine-structure level. The storage lifetime of the Pt- ion beam was measured to be a little over 15 min at a ring temperature of 13K. The present study reports the lifetime of an atomic negative ion in an excited bound state with an electron configuration different from that of the ground state.
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| 11. |
- Gurell, Jonas, 1981-
(författare)
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High Resolution Spectroscopy of Singly Charged Ions : Applications of Laser and Fourier Transform Techniques
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents measurements of fundamental properties of singly charged ionic systems including spectral wavelengths, lifetimes of excited states and branching fractions with the main focus on time resolved laser spectroscopy of stored ions providing lifetime measurements of metastable states. The results of these measurements have been used to determine energy levels and transition probabilities of the studied systems. The included experimental data are compared with results from calculations which provides evaluations of different theoretical models. The presented results have been applied by others to the field of atomic astrophysics in order to deduce electron densities and elemental abundances in ejecta of the supermassive star eta Carinae and have also been followed by additional work of theoreticians interested in comparisons with laboratory data. The thesis is a result of several collaborations in which Stockholm University has been providing lifetime measurements of metastable states, Lund Observatory and the National Institute of Standards and Technology have been providing wavelength and branching fraction measurements, Lund Laser Centre has been providing lifetime measurements of short-lived states and calculations have been performed by theoretical physicists from Université de Mons-Hainaut, Université de Liège, Queen's University of Belfast and Laboratoire Aimé Cotton.
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| 12. |
- Gurell, Jonas, 1981-
(författare)
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Laboratory studies of forbidden decay processes in stored ions
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 13. |
- Gurell, Jonas, 1981-, et al.
(författare)
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Laser-probing measurements and calculations of lifetimes of the 5d 2D3/2 and 5d 2D5/2 metastable levels in Ba II
- 2007
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 75:5, s. 052506-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 14. |
- Gurell, Jonas, 1981-, et al.
(författare)
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The FERRUM project : Laboratory-measured transition probabilities for Cr II
- 2010
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 511:A68
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Tidskriftsartikel (refereegranskat)abstract
- Aims: We measure transition probabilities for Cr II transitions from the z ^4H_J, z ^2D_J, y ^4F_J, and y ^4G_J levels in the energy range 63000 to 68000 cm^{-1}. Methods:Radiative lifetimes were measured using time-resolved laser-induced fluorescence from a laser-produced plasma. In addition, branching fractions were determined from intensity-calibrated spectra recorded with a UV Fourier transform spectrometer. The branching fractions and radiative lifetimes were combined to yield accurate transition probabilities and oscillator strengths. Results: We present laboratory measured transition probabilities for 145 Cr II lines and radiative lifetimes for 14 Cr II levels. The laboratory-measured transition probabilities are compared to the values from semi-empirical calculations and laboratory measurements in the literature.
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| 15. |
- Gurell, Jonas, 1981-, et al.
(författare)
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The FERRUM project : Transition probabilities for forbidden lines in [Fe II] and experimental metastable lifetimes
- 2009
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 508:1, s. 525-529
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 16. |
- Hartman, Henrik, et al.
(författare)
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The FERRUM project : experimental and theoretical transition rates of forbidden [Sc II] lines and radiative lifetimes of metastable ScII levels
- 2008
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 480:2, s. 575-580
-
Tidskriftsartikel (refereegranskat)abstract
- Context. In many plasmas, long-lived metastable atomic levels are depopulated by collisions (quenched) before they decay radiatively. In low-density regions, however, the low collision rate may allow depopulation by electric dipole (E1) forbidden radiative transitions, so-called forbidden lines (mainly M1 and E2 transitions). If the atomic transition data are known, these lines are indicators of physical plasma conditions and used for abundance determination. Aims. Transition rates can be derived by combining relative intensities between the decay channels, so-called branching fractions (BFs), and the radiative lifetime of the common upper level. We use this approach for forbidden [Sc II] lines, along with new calculations. Methods. Neither BFs for forbidden lines, nor lifetimes of metastable levels, are easily measured in a laboratory. Therefore, astrophysical BFs measured in Space Telescope Imaging Spectrograph (STIS) spectra of the strontium filament of Eta Carinae are combined with lifetime measurements using a laser probing technique on a stored ion-beam (CRYRING facility, MSL, Stockholm). These quantities are used to derive the absolute transition rates (A-values). New theoretical transition rates and lifetimes are calulated using the CIV3 code. Results. We report experimental lifetimes of the Sc II levels 3d(2) a(3)P(0,1,2) with lifetimes 1.28, 1.42, and 1.24 s, respectively, and transition rates for lines from these levels down to 3d4s a(3)D in the region 8270-8390 angstrom. These are the most important forbidden [Sc II] transitions. New calculations for lines and metastable lifetimes are also presented, and are in good agreement with the experimental data.
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| 17. |
- Kamińska, Magdalena, et al.
(författare)
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Lifetime of the bound excited level in Ni
- 2016
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Ingår i: Physical Review A. - 1050-2947 .- 1094-1622. ; 93:1
-
Tidskriftsartikel (refereegranskat)abstract
- The intrinsic lifetime of the upper level in the bound-bound 3d(9) 4s(2) D-2(3/2) -> 3d(9) 4s(2) D-2(5/2) radiative transition in Ni- was measured to be 15.1 +/- 0.4 s. The experiment was performed at cryogenic temperatures in one of the ion-beam storage rings of the Double ElectroStatic Ion Ring ExpEriment facility at Stockholm University. The storage lifetime of the Ni- ion beam was measured to be close to 5 min at a ring temperature of 13 K.
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| 18. |
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| 19. |
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| 20. |
- Lundin, Peter, 1973-
(författare)
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Laser Spectroscopic Investigations of Decay Properties in Stored Ions
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Investigations and measurements of metastable states are in many ways very important. Spectroscopists, theorists and astrophysicists have all great interest and requirements regarding knowledge about such states and their properties. One of the interesting properties is the lifetime of each state and lifetime measurements are therefore of great importance. It is necessary to have a long observation time when performing investigations on metastable states in ions and there are some different methods to fulfill this requirement. One method to store ions is to use an ion storage ring in which the ions are bent in circle by a magnetic or an electrostatic field. The storage ring method combined with a laser probing technique constitutes the basis for the papers described in this thesis. The thesis also contains some theoretical background to the experiments together with explanations regarding the experimental setup, the procedure for the laser probing technique and the systematic effects that have to be considered. The thesis includes results from nine different positive and negative singly charged ions. The experimental and theoretical results are presented and compared. The experiments have been done in collaboration with E. Biémont's theoretical group in Belgium, with S. Johansson's astrophysical group in Lund and D. Hanstorp's group in Gothenburg.
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| 21. |
- Lundin, Peter, et al.
(författare)
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Metastable levels in ScII : lifetime measurements and calculations
- 2008
-
Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896 .- 0281-1847. ; 78:1, s. 015301-
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Tidskriftsartikel (refereegranskat)abstract
- The lifetime of the metastable level 3d(21)G(4) in a singly charged scandium has been experimentally investigated at the ion storage ring CRYRING. A laser probing technique has been used for the studies. We also report calculated lifetimes and transition rates for 10 metastable levels in Sc II, including the 3d(21)G(4) state, by calculations using configuration interaction wave functions. The lifetime of the (1)G(4) level is experimentally determined to be tau(exp) = 2.64 +/- 0.18 s and is in good agreement with the theoretical calculation tau(th) = 2.84 s.
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| 22. |
- Palmeri, Patrick, et al.
(författare)
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Lifetimes of metastable levels of singly ionized titanium : theory and experiment
- 2008
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 41:12
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents new theoretical lifetimes of metastable levels in singly ionized titanium, Ti II. Along with the lifetimes, transition probabilities for several decay channels from these metastable levels are presented. The calculations are supported by experimental lifetime determinations of the 3d3 b 2D5/2 and 3d2(3P)4s b 2P3/2 levels along with revised values of the previously published lifetimes of the 3d2(3P)4s b 4P5/2 and 3d2(3P)4s b 2P1/2 levels originating partly from a reanalysis utilizing a recently developed method applied on the previously recorded data and partly from new measurements. The presented theoretical investigation of lifetimes of metastable levels in Ti II shows that the HFR calculations are in general compatible with measurements performed using the ion storage ring CRYRING of Stockholm University. The transition probabilities of forbidden lines derived from the new lifetime values will be useful for the diagnostics of low density laboratory or astrophysical plasmas, particularly those encountered in the strontium filament found in the ejecta of η Carinae.
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| 23. |
- Schef, Peter, 1977-
(författare)
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Weak Atomic Interactions
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An atom or ion can change quantum state, usually through emission or absorption of a photon. The photon has the same energy as the energy difference between the states of the transition. The states, or energy levels, of an atom are quantized and light emitted, or absorbed, from the atom is therefore of specific wavelengths, giving spectral lines. The spectrum of an atomic ion is unique and contains information of the structure and energy levels of the ion. The spectrum of an atom can be used as a fingerprint in determinations of the abundance of the element in different objects.This thesis is focused on some weak effects observed by spectroscopy. Although the effects are weak, they turn out to be of great importance. According to quantum mechanics transitions between certain states are not allowed. Here the weak effects open the possibility for transitions. Spectral lines from forbidden transitions are very weak and difficult to observe under ordinary laboratorial conditions, but they are commonly observed from astrophysical objects and can be very useful for diagnostics of astrophysical plasmas. The first reported observation of forbidden lines was from an astrophysical object and at that time supposed to be from new, previous unknown, elements. If all possible decay channels from an energy level are forbidden, the energy level is metastable and has usually a lifetime 10$^8$ times longer than an ordinary excited state. Measurements of such long lifetimes are difficult since the ion need to be confined during the observation time. Confinement of ions can be achieved with a storage device, such as a storage ring or a trap, where the ions are stored without interacting with each other or the surroundings.A laser probing technique has been developed at the storage ring CRYRING, for measurements of lifetimes of metastable states. The technique has now been improved for measurement of longer lifetimes. The technique has also been modified to fit when measuring on negative ions. Results of lifetime measurements are reported and the techniques and methods used are described.Another weak effect is hyperfine interaction, which splits the energy levels of an atom or ion. Hyperfine splitting is very small and usually special spectral techniques are needed to resolve such structure. A laser can, in combination with an electromagnetic radio-frequency field, be used for accurate determination of hyperfine structures in atomic ions. Such measurements are also important for evaluation of astrophysical properties, since hyperfine structure can broaden the spectral lines. An experimental setup for such double resonance measurements has been developed and constructed. Results of experimental measurements are reported and the technique is described.
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| 24. |
- Schmidt, Henning T., et al.
(författare)
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Rotationally Cold OH- Ions in the Cryogenic Electrostatic Ion-Beam Storage Ring DESIREE
- 2017
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 119:7
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Tidskriftsartikel (refereegranskat)abstract
- We apply near-threshold laser photodetachment to characterize the rotational quantum level distribution of OH- ions stored in the cryogenic ion-beam storage ring DESIREE at Stockholm University. We find that the stored ions relax to a rotational temperature of 13.4 +/- 0.2 K with 94.9 +/- 0.3% of the ions in the rotational ground state. This is consistent with the storage ring temperature of 13.5 +/- 0.5 K as measured with eight silicon diodes but in contrast to all earlier studies in cryogenic traps and rings where the rotational temperatures were always much higher than those of the storage devices at their lowest temperatures. Furthermore, we actively modify the rotational distribution through selective photodetachment to produce an OH- beam where 99.1 +/- 0.1% of approximately one million stored ions are in the J = 0 rotational ground state. We measure the intrinsic lifetime of the J = 1 rotational level to be 145 +/- 28 s.
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| 25. |
- Söderström, Mats, et al.
(författare)
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Leukotriene C synthase in mouse mastocytoma cells. An enzyme distinct from cytosolic and microsomal glutathione transferases
- 1988
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Ingår i: Biochemical Journal. - : Portland Press. - 0264-6021 .- 1470-8728. ; 250:3, s. 713-718
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Tidskriftsartikel (refereegranskat)abstract
- Leukotriene C4 synthesis was studied in preparations from mouse mastocytoma cells. Enzymic conjugation of leukotriene A4 with glutathione was catalysed by both the cytosol and the microsomal fraction. The specific activity of the microsomal fraction (7.8 nmol/min per mg of protein) was 17 times that of the cytosol fraction. The cytosol fraction of the mastocytoma cells contained two glutathione transferases, which were purified to homogeneity and characterized. A microsomal glutathione transferase was purified from mouse liver; this enzyme was shown by immunoblot analysis to be present in the mastocytoma microsomal fraction at a concentration one-tenth or less of that in the liver microsomal fraction. Both the cytosolic and the microsomal glutathione transferases in the mastocytoma cells were identified with enzymes previously characterized, by determining specific activities with various substrates, sensitivities to inhibitors, reactions with antibodies, and physical properties. The purified microsomal glutathione transferase from liver was inactive with leukotriene A4 or its methyl ester as substrate. The cytosolic enzymes displayed activity with leukotriene A4, but their specific activities and intracellular concentrations were too low to account for the leukotriene C4 formation in the mastocytoma cells. The microsomal fraction of the cells contained an enzyme distinguishable by various criteria from the previously studied glutathione transferases. This membrane-bound enzyme, leukotriene C synthase (leukotriene A4:glutathione S-leukotrienyltransferase), appears to carry the main responsibility for the biosynthesis of leukotriene C4.
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| 26. |
- Söderström, Mats, et al.
(författare)
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Leukotriene C4 synthase : characterization in mouse mastocytoma cells
- 1990
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Ingår i: Methods in Enzymology. - : Elsevier. - 0076-6879 .- 1557-7988. ; 187, s. 306-312
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Tidskriftsartikel (refereegranskat)abstract
- The chapter presents a study on leukotriene C4 (LTC4) synthase, discussing the characterization in mouse mastocytoma cells. LTC4 is formed by conjugation of leukotriene A4 (LTA4) with glutathione (GSH). In biological systems, the reaction is catalyzed by a membrane-bound enzyme, leukotriene C4 synthase (EC 2.5.1.37). Cytosolic glutathione transferases, in particular, members of the class Mu, have been shown to catalyze formation of LTC4.The most efficient isoenzymes are transferase 6-6 isolated from rat brain, transferase 4-4 from rat liver, and transferase μ from human liver. The name leukotriene C4 synthase, used for the enzyme described in this chapter, has been adopted to distinguish the enzyme from the above glutathione transferases, which display broad substrate specificity. Reports from three groups of investigators have shown that LTC4 formation in rat basophilic leukemia cells is catalyzed by a membrane-bound enzyme. Leukotriene C4 synthase activity has been described and an enzyme partially purified from the microsomal fraction of guinea pig lung. The formation of LTC4 is especially high in mouse mastocytoma cells, the source from which LTC4 was first isolated. The partial purification of leukotriene C4 synthase from this source is described in the chapter.
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| 27. |
- Söderström, Mats, et al.
(författare)
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On the nature of leukotriene C4 synthase in human platelets
- 1992
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Ingår i: Archives of Biochemistry and Biophysics. - : Elsevier. - 0003-9861 .- 1096-0384. ; 294:1, s. 70-74
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Tidskriftsartikel (refereegranskat)abstract
- Leukotriene C4 is considered to play a major role in several important pathophysiological conditions, e.g., allergy, asthma, and shock. The present investigation demonstrates the presence in human platelets of a membrane-associated enzyme catalyzing the final step in the biosynthesis of leukotriene C4. This leukotriene C4 synthase was shown to be distinct from previously characterized "microsomal" and soluble glutathione transferases. The latter enzymes did not contribute significantly to the leukotriene A4 conjugating activity in platelets. As determined with leukotriene C4 synthase of a crude membrane fraction from human platelets, the Km value was 7 microM and the V value was 0.56 nmol x min-1 x mg-1 with leukotriene A4 as substrate. The enzyme was 20-fold more efficient with leukotriene A4 than with leukotriene A5 and 30-fold more efficient than with the unphysiological derivative leukotriene A4 methyl ester, as measured by the corresponding V/Km values; 14,15-leukotriene A4 was not a substrate. Platelets should be a useful source for the purification and further characterization of human leukotriene C4 synthase.
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