| 1. |
- Akkoyun, S., et al.
(författare)
-
AGATA - Advanced GAmma Tracking Array
- 2012
-
Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002 .- 0167-5087 .- 1872-9576. ; 668, s. 26-58
-
Tidskriftsartikel (refereegranskat)abstract
- The Advanced GAmma Tracking Array (AGATA) is a European project to develop and operate the next generation γ-ray spectrometer. AGATA is based on the technique of γ-ray energy tracking in electrically segmented high-purity germanium crystals. This technique requires the accurate determination of the energy, time and position of every interaction as a γ ray deposits its energy within the detector volume. Reconstruction of the full interaction path results in a detector with very high efficiency and excellent spectral response. The realisation of γ-ray tracking and AGATA is a result of many technical advances. These include the development of encapsulated highly segmented germanium detectors assembled in a triple cluster detector cryostat, an electronics system with fast digital sampling and a data acquisition system to process the data at a high rate. The full characterisation of the crystals was measured and compared with detector- response simulations. This enabled pulse-shape analysis algorithms, to extract energy, time and position, to be employed. In addition, tracking algorithms for event reconstruction were developed. The first phase of AGATA is now complete and operational in its first physics campaign. In the future AGATA will be moved between laboratories in Europe and operated in a series of campaigns to take advantage of the different beams and facilities available to maximise its science output. The paper reviews all the achievements made in the AGATA project including all the necessary infrastructure to operate and support the spectrometer. © 2011 Elsevier B.V. All rights reserved.
|
|
| 2. |
- Ali, Safdar, et al.
(författare)
-
Electron-ion recombination of H- and He-like sulfur
- 2011
-
Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 44:22, s. 225203-
-
Tidskriftsartikel (refereegranskat)abstract
- Electron-ion recombination of sulfur ions with electrons in the energy range of 1.6-3 keV was studied at the Stockholm Refrigerated Electron Beam Ion Trap. We obtained the KLn dielectronic recombination (DR) cross sections up to n = 5 for H-like and He-like sulfur ions by observing the x-rays from the trapped ions. A fully relativistic distorted wave approximation method was used for calculating the DR cross sections, while the resonance energies were obtained with a multiconfiguration Dirac-Fock approach using the GRASP II code. The calculations agree with the experimental results within the experimental error bars. Additionally, the obtained total DR resonance strengths were used to check the behaviour of a scaling formula for low-Z, He-like iso-electronic sequence (Watanabe et al 2001 J. Phys. B: At. Mol. Opt. Phys. 34 5095).
|
|
| 3. |
- Ali, Safdar, et al.
(författare)
-
Photo-recombination studies at R-EBIT with a Labview control and data = quisition system
- 2011
-
Ingår i: Journal of Instrumentation. - 1748-0221. ; 6, s. C01016-
-
Tidskriftsartikel (refereegranskat)abstract
- Equipment at the Stockholm Refrigerated Electron Beam Ion Trap (R-EBIT) was developed for photo-recombination studies. A LabView-based event mode data acquisition and R-EBIT control system was implemented. The energies of KLL dielectronic recombination resonances in Li- to C-like argon ions were determined and compared with theoretical calculations performed using a distorted wave approximation. The theoretical and experimental peak positions for Li-, Be-, and C-like argon ions agree within the error bars. For B-like argon we observe an energy shift of 9 eV between the experimentally obtained peak position and the calculated result.
|
|
| 4. |
- Barday, R., et al.
(författare)
-
ELECTRON BEAM POLARIMETRY AT LOW ENERGIES AND ITS APPLICATIONS
- 2011
-
Ingår i: POLARIZED SOURCES, TARGETS AND POLARIMETRY. - : WORLD SCIENTIFIC PUBL CO PTE LTD. - 9789814324915 - 9789814462747 ; , s. 105-112
-
Konferensbidrag (refereegranskat)abstract
- Low energy (E-k similar to 100 keV) Mott scattering polarimetry is a widely established technique to measure the polarization of an electron beam. We analyze the feasibility of Mott scattering at energies up to 20 MeV. For further studies of the electron spin dynamics in the scattering process a correlation between the linear polarization of bremsstrahlung radiation and the electron beam polarization has been measured for the first time using a planar HPGe Compton polarimeter at the 100 keV source of polarized electrons at TU Darmstadt.
|
|
| 5. |
- Böhm, Sebastian, et al.
(författare)
-
First results from the Stockholm Electron Beam Ion Trap
- 2007
-
Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 58:303, s. 303-306
-
Tidskriftsartikel (refereegranskat)abstract
- A new laboratory for highly charged ions is being built up at Stockholm university. An electron beam ion trap (EBIT) (3T magnet,≤30 keV electron beam) was installed. It is used for spectroscopic studies, precision mass measurements, electron ion collisions, and highlycharged ion surface studies. Here we report about a fast ion-extraction scheme from ebit and first results using a time-of-flight detection as well as a labview based operational system of ebit.
|
|
| 6. |
- Gumberidze, Alexandre, et al.
(författare)
-
Angular Distribution of Characteristic Radiation Following the Excitation of He-Like Uranium in Relativistic Collisions
- 2021
-
Ingår i: Atoms. - : MDPI AG. - 2218-2004. ; 9:2
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present an experimental and theoretical study of excitation processes for the heaviest stable helium-like ion, that is, He-like uranium occurring in relativistic collisions with hydrogen and argon targets. In particular, we concentrate on angular distributions of the characteristic K alpha radiation following the K -> L excitation of He-like uranium. We pay special attention to the magnetic sub-level population of the excited 1s2l(j) states, which is directly related to the angular distribution of the characteristic K alpha radiation. We show that the experimental data can be well described by calculations taking into account the excitation by the target nucleus as well as by the target electrons. Moreover, we demonstrate for the first time an important influence of the electron-impact excitation process on the angular distributions of the K alpha radiation produced by excitation of He-like uranium in collisions with different targets.
|
|
| 7. |
- Hobein, Matthias, 1981-, et al.
(författare)
-
Optimization of the Stockholm R-EBIT for the production and extraction of highly charged ions
- 2010
-
Ingår i: Journal of Instrumentation. - 1748-0221. ; 5:C11003
-
Tidskriftsartikel (refereegranskat)abstract
- We describe a refrigerated EBIT (R-EBIT) commissioned at the AlbaNova Research Center at Stockholm University. As an innovative solution, the superconducting magnet and the trapping drift tubes of the R-EBIT are cooled to a temperature of 4 K by a set of two cooling heads connected to helium compressors. This dry, i.e. liquid helium and liquid nitrogen free, system is easily operated and creates highly charged ions at a fraction of the cost of traditional liquid-cooled systems. A pulsed and continuous gas injection system was developed to feed neutral particles into the electron beam in the trap region. This improves significantly the highly charged ion production and R-EBIT performance. Fast extraction of ions from the R-EBIT yields very short ( < 100 ns), charge-separated ion bunches which can be either analysed using a straight time-of-flight section or sent to experimental beam lines following selection in a bending magnet. An emittance meter was used to measure the emittance of the ions extracted from the R-EBIT. The extracted ions were also re-trapped in a cylindrical Penning trap and properties of the re-trapped ions have been measured using the emittance meter. Results of these measurements are reported in this publication.
|
|
| 8. |
- Khaplanov, Anton, et al.
(författare)
-
A gamma-ray polarimeter based on a single segmented planar HPGe detector
- 2008
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 593:3, s. 459-465
-
Tidskriftsartikel (refereegranskat)abstract
- The polarization sensitivity of a segmented planar HPGe detector has been measured. For this purpose 662 keV photons from a Cs-137 source which were Compton scattered at approximate to 90 degrees in a coaxial germanium detector were utilized as a source of partially linearly polarized gamma radiation of the energy; approximate to 288 keV. The detector has a 50 x 50 x 21 mm sensitive volume and 5 x 5 electrical segmentation of the cathode contact. The degree of linear polarization is determined through the analysis of the directions of Compton scatterings inside the detector. The locations of the Compton scattering interactions and of the subsequent photo-absorption interactions have been determined with the help of pulse shape analysis (PSA), provided that these interactions are in two different segments of the planar detector. A comparison with a polarization analysis using the position resolution defined by the physical segmentation (without the use of PSA) was also performed. It is demonstrated that the use of PSA enables a much higher polarization sensitivity for events where the 288 keV photons scatter between adjacent pixels. Such events constitute 90% of the data for the 288 keV photons and are even more important for gamma-rays of lower energies.
|
|
| 9. |
- Khaplanov, Anton, et al.
(författare)
-
Position sensitivity of segmented planar HPGe detectors for the DESPEC project at FAIR
- 2008
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 592, s. 325-333
-
Tidskriftsartikel (refereegranskat)abstract
- One of the proposed germanium detector systems for the upcoming DESPEC array at the FAIR facility consists of triple modules of electrically segmented planar high-purity germanium detectors. In this work, the position sensitivity obtained by means of pulse shape analysis (PSA) for simulated gamma-ray interactions has been studied for the possible segmentation patterns for such detectors-the double-sided strip detector (DSSD) and the one-sided pixelated geometry. An over-all similar number of readout channels has been considered for each case, resulting in 8 + 8 strips and 16 pixels. It has been found that the higher physical granularity of the DSSD results in a significantly higher position resolution, as well as in a somewhat lower probability of merging multiple interaction points. A drawback of the DSSD geometry is the inability to assign the interactions to the correct voxels for certain complex multiple interaction patterns. This effect has been studied in detail. Finally, a comparison has been made with the existing 25-pixel planar detector at KTH [A. Khaplanov, et al., Nucl. Instr. and Meth. A 580 (2007) 1075; L. Milechina, B. Cederwall, Nucl. Instr. and Meth. A 550 (2005) 278)].
|
|
| 10. |
- Khaplanov, Anton, et al.
(författare)
-
Position sensitivity of the proposed segmented germanium detectors for the DESPEC project
- 2009
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 604:1/2, s. 56-59
-
Tidskriftsartikel (refereegranskat)abstract
- The DESPEC HPGe array is a part of the NuSTAR project at FAIR, Germany. It is aimed at the spectroscopy of the stopped decaying exotic nuclei. Segmented gamma-ray tracking detectors are proposed for this array in order to maximize detection efficiency and background suppression when searching for very rare events. Two types of detector modules-stacks of three 16-fold segmented planar crystals and 12- and 16-fold segmented clover detectors-have been investigated and compared from the point of view of the achievable position resolution using pulse shape analysis (PSA). To this end, detector signals from realistic gamma-ray interactions have been calculated. These signals were treated by PSA in order to reconstruct the photon interaction locations. Comparing the initial interaction locations to the reconstructed ones, it was found that the double-sided strip planar detector yielded position reconstruction errors at least a factor 2 lower than the other detectors considered
|
|
| 11. |
- Kojouharov, I., et al.
(författare)
-
The GSI HPGe detector scanner - A sophisticated device based on PET technique
- 2007
-
Ingår i: 2007 IEEE Nuclear Science Symposium Conference Record. - : IEEE. - 1424409233 - 9781424409235 ; , s. 2213-2215
-
Konferensbidrag (refereegranskat)abstract
- A new 3D HPGe detector scanner based on PET technique has been proposed and implemented. The scanning technology utilizes a 2D position sensitive detector array made of fibre scintillation detectors ordered in cone geometry and read out by position sensitive photomultipliers. This allows simultaneous scanning of numerous coordinate points. The third coordinate of the interaction point in the germanium volume to be scanned is obtained by measuring y-rays Compton scattered by 90° using collimated scintillation detectors. The first results of the proposed scanning technology clearly demonstrate the feasibility to obtain high quality data from a germanium detector within a reasonable time employing a moderate 1 MBq activity y source.
|
|
| 12. |
- Kovtun, Oleksiy, et al.
(författare)
-
Spin-orbit interaction in bremsstrahlung and its effect on the electron motion in a strong Coulomb field
- 2015
-
Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 92:6
-
Tidskriftsartikel (refereegranskat)abstract
- Linear polarization of bremsstrahlung x rays produced in collisions of longitudinally polarized 2.1-MeV electrons with gold atoms was studied using the Compton scattering technique. We observed that the angle of x-ray polarization is strongly correlated with the incoming electron polarization. This correlation reveals the dominance of the spin-orbit interaction in bremsstrahlung and indicates a striking effect of the electron spin on the electron motion in a strong Coulomb field. The results confirm the validity of the theoretical predictions in a computationally challenging energy regime.
|
|
| 13. |
- Kovtun, Oleksiy, et al.
(författare)
-
Strong effect of the electron spin on bremsstrahlung observed in the relativistic regime
- 2015
-
Ingår i: XXIX INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC, AND ATOMIC COLLISIONS (ICPEAC2015), PTS 1-12. - : Institute of Physics Publishing (IOPP).
-
Konferensbidrag (refereegranskat)abstract
- We have studied bremsstrahlung produced by polarized 2.1 MeV electrons colliding with a thin gold target. We have observed a strong correlation between the orientation of the electron spin and the angle of x-ray linear polarization at the x-ray high energy tip region. This indicates a dominance of the spin-orbit interaction in bremsstrahlung.
|
|
| 14. |
- Mahmood, Sultan, 1969-, et al.
(författare)
-
Recombination and electron impact excitation rate coefficients for S XV AND S XVI
- 2012
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 754:2, s. 86-
-
Tidskriftsartikel (refereegranskat)abstract
- Recombination and electron impact excitation of S14+ and S15+ ions was measured at the Stockholm refrigerated electron beam ion trap. The collision energy range was 1.4-3 keV, where we covered the KLL, KLM, KLN, and KLO dielectronic recombination resonances resulting in S13+ and S14+ ions. The recombination rates were obtained by detecting the charge state distribution with a newly developed time-of-flight technique. Resonance energies and cross sections calculated within the relativistic many-body perturbation theory for S15+ agree well with the experimental data. The temperature dependent rate coefficients have been extracted from the measured rates and compared with calculations from literature used for studies of collisionally ionized astrophysical plasmas. A good agreement for S15+ was obtained, while the plasma rates for S14+ were 23% lower than the so far published values. In addition to the time-of-flight spectra, the x-ray spectra, produced mainly by photo-recombination and excitation, have been also collected. The combination of these two measurements allowed us to separate the photo-recombination and the excitation spectra, and the excitation rate coefficients for summed intensities with known fractions of S14+ and S15+ ions were extracted.
|
|
| 15. |
- Maiorova, A. V., et al.
(författare)
-
Polarization studies on the two-step radiative recombination of highly charged, heavy ions
- 2009
-
Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 42:12
-
Tidskriftsartikel (refereegranskat)abstract
- Radiative recombination of a free electron into an excited state of a bare, high-Z ion is studied, together with its subsequent decay, within the framework of the density matrix theory and Dirac's relativistic equation. Special attention is paid to the polarization and angular correlations between the recombination and the decay photons. In order to perform a systematic analysis of these correlations the general expression for the double-differential recombination cross section is obtained by making use of the resonance approximation. Based on this expression, detailed computations for the linear polarization of x-ray photons emitted in the (e, 2 gamma) two-step recombination of uranium ions U92+ are carried out for a wide range of projectile energies.
|
|
| 16. |
- Orban, Istvan, 1980-, et al.
(författare)
-
Charge-state Selected Detection of Photons from Electron-Ion Interactions in an EBIT
- 2009
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114.
-
Tidskriftsartikel (refereegranskat)abstract
- A new approach provides charge-state selective recombination rate coefficients from TOF spectraof highly charged ions extracted from an EBIT. Experimentally derived dielectronic recombinationspectra are compared with results of relativistic many body perturbation theory calculations. Electronimpact excitation rate coefficients are also obtained from the experiment through the separationof the DR contribution in the X-ray spectra. The combination of TOF and X-ray measurementsoffers a powerful tool for the simultaneous extraction of atomic quantities for several charge states.
|
|
| 17. |
- Schuch, Reinhold, et al.
(författare)
-
The new Stockholm Electron Beam Ion Trap (S-EBIT)
- 2010
-
Ingår i: Journal of Instrumentation. - 1748-0221. ; 5, s. C12018-
-
Tidskriftsartikel (refereegranskat)abstract
- A new laboratory for highly charged ions is being built up at Stockholm University. A fully refrigerated electron beam ion trap (R-EBIT, 3 T magnet, 30 keV electron energy) was installed. It was used for spectroscopic studies, ion cooling experiments, electron ion collisions, and highly-charged ion surface studies. Here we report on an upgrade of this EBIT to a ``Super EBIT'' (S-EBIT, 4 T magnet, 260 keV electron energy). The high-voltage trapping system, the ion injection as well as the extraction scheme of S-EBIT and the LabView based operational system of S-EBIT are described.
|
|
| 18. |
- Tashenov, Stanislav
(författare)
-
Circular polarimetry with gamma-ray tracking detectors
- 2011
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 640:1, s. 164-169
-
Tidskriftsartikel (refereegranskat)abstract
- Measurement of circular polarization of gamma-rays with position sensitive solid state detectors is proposed. It is based on the transfer of the photon spin to the recoiled electron in the process of Compton scattering and subsequent detection of the electron spin polarization. Bremsstrahlung polarization correlations, in particular the left-right asymmetry of the photon emission from transversally polarized electrons, are used for this purpose. Compton scattering and electron bremsstrahlung events as well as the scattered and the bremsstrahlung photon absorptions take place inside the active volume of the position sensitive detector. These events are identified and their complete kinematics is reconstructed by means of gamma-ray tracking. No spin polarized targets and no inactive materials are needed for this technique. The proposed method is naturally integrated into the concept of a Compton telescope, allowing for the first time to build an imaging gamma-ray circular polarimeter. It should work in the energy region of several 100 key up to several 10 MeV.
|
|
| 19. |
- Tashenov, Stanislav, et al.
(författare)
-
Gamma-ray tracking and background suppression in the planned germanium array of DESPEC : A comparative analysis
- 2009
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 604:1-2, s. 64-66
-
Tidskriftsartikel (refereegranskat)abstract
- A new high efficiency gamma-ray spectrometer is being designed for the DESPEC project at FAIR. It should accomplish all types of decay studies with implanted radioactive ion beams. The gamma-ray tracking and imaging capabilities of the array will be its essential property allowing low background detection of the rare decay events. For this purpose two types of germanium detectors are considered, i.e. segmented planar and coaxial detectors. Several final array configurations based on these detectors, differently segmented, are evaluated and compared in this paper.
|
|
| 20. |
- Tashenov, Stanislav, et al.
(författare)
-
Hard X-ray polarimetry by means of Rayleigh scattering
- 2009
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 600:3, s. 599-603
-
Tidskriftsartikel (refereegranskat)abstract
- A new linear polarimetry technique based on Rayleigh scattering is introduced. Its properties are compared to the Compton technique. Experimental verification was realized using a 5 x 5 segmented planar HPGe pixel detector. In the proof-of-principle experiment a measurement of Rayleigh scattering off lead atoms was performed for linearly polarized; approximate to 53.3 keV photons at two scattering angles.
|
|
| 21. |
- Tashenov, Stanislav
(författare)
-
Identification of bremsstrahlung events in gamma-ray tracking detectors
- 2010
-
Ingår i: Journal of Instrumentation. - 1748-0221. ; 5
-
Tidskriftsartikel (refereegranskat)abstract
- Tracking of gamma-rays in position sensitive germanium and silicon detectors is a relatively new concept. In the energy region of a few hundred keV up to a few MeV it aims at identification of the sequence and positions of photon scattering points inside a detector. This is achieved by verifying the energy and momentum conservation laws for each Compton interaction as well as the scattering and absorption probabilities. By calculating multiple figures of merit, each favoring a specific class of events (e.g. full-energy, escape and bremsstrahlung), one can identify these events and increase the peak/total ratio of the full-energy spectrum. As an example, events where bremsstrahlung photons are produced by Compton recoiled electrons are identified. A further extension of this technique may allow identification of pair production events and extend the tracking analysis into a higher energy region of several MeV where pair production dominates.
|
|
| 22. |
- Tashenov, Stanislav, et al.
(författare)
-
Measurement of the Correlation between Electron Spin and Photon Linear Polarization in Atomic-Field Bremsstrahlung
- 2011
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 107:17, s. 173201-
-
Tidskriftsartikel (refereegranskat)abstract
- Atomic-field bremsstrahlung has been studied with a longitudinally polarized electron beam. The correlation between the initial orientation of the electron spin and the angle of photon polarization has been measured at the photon high energy tip region. In the time reversal this corresponds to a so-far unobserved phenomenon of production of longitudinally polarized electrons by photoionization of unpolarized atoms with linearly polarized photons. The results confirm the fully relativistic calculations for radiative recombination and suggest a new method for electron beam polarimetry.
|
|
| 23. |
- Tashenov, Stanislav, et al.
(författare)
-
TANGO-New tracking AlGOrithm for gamma-rays
- 2010
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 622:3, s. 592-601
-
Tidskriftsartikel (refereegranskat)abstract
- For spectroscopy, polarimetry and imaging purposes a new gamma-ray tracking algorithm has been developed featuring identification of Compton escape events. The rejection of these events results in a significant increase of the Peak/Total ratio. The initial photon energy is restored for these events. Although the energy resolution in the spectrum reconstructed from the escape events is lower than the one from the full-energy events, the Monte-Carlo simulations show that the combined spectrum has an increased detector full-energy efficiency of up to 130% compared to its intrinsic full-energy efficiency. The assumed geometrical origin of the photons is verified event-by-event. This enables separation of photons emitted from a target and from background sources. A linear polarization analysis of the gamma-lines can be performed. The efficiency of the algorithm and the Peak/Total ratio depending on the detector properties is discussed along with the proposed optimization schemes. The influence of the intrinsic properties of the scattering process like Compton profile and electron recoiling is discussed as well. The described algorithm deals with single photon events with energies of approximate to 100 keV up to a few MeV.
|
|
