| 1. |
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| 2. |
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| 3. |
- Ahlgren Cederlöf, Ebba, et al.
(författare)
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Lifetime measurement of the yrast 2+ state in 118Te
- 2023
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Ingår i: European Physical Journal A. - : Springer. - 1434-6001 .- 1434-601X. ; 59:12
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Tidskriftsartikel (refereegranskat)abstract
- The electromagnetic transition probabilities of the yrast 2+ states in the midshell Te isotopes, two protons above the closed shell at Sn, are of great importance for the understanding of nuclear collectivity in these isotopes and the role played by the neutron-proton interactions and cross-shell excitations. However, the large uncertainty of the experimental data for the midshell nucleus 118Te and the missing data for 116Te make it difficult to pin down the general trend of the evolution of transition probabilities as a function of the neutron number. In this work, the lifetime of the yrast 2+ state in 118Te was measured, with the aim of reducing the uncertainty of the previous measurement. The result is τ2+ = 7.46(19) ps. In addition, the lifetime of the 4+ state was measured to be τ4+ = 4.25(23) ps. The experimental transition rates are extracted from the measured lifetimes and compared with systematic large-scale shell-model calculations. The trend of the B(E2; 0+ → 2+) values in the midshell area is in good agreement with the calculations and the calculated B4/2 ratio provide evidence for 118Te as a near perfect harmonic vibrator.
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| 4. |
- Ahlgren Cederlöf, Ebba
(författare)
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The short, excited life of tellurium : Lifetime analysis of excited states in the Te midshell region
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this licentiate thesis, lifetimes of low lying excited states in the midshell region of tellurium isotopes are discussed. The nuclear lifetimes are interesting properties to study, since they are inversely proportional to the transition probabilities, which contain information on the underlying structure of the nucleus. By measuring the lifetime of a transition, information can be gained on e.g. the collectivity of the state.The main results presented in this thesis are the lifetime measurements of the 2+ → 0+ and 4+ → 2+ transitions in 118Te described in Paper I. The principal aim of this paper was to reduce the relative uncertainty in the 2+ lifetime, to better see the trend of the 2+ → 0+ transition probabilities over the tellurium isotopic chain.The work presented in Paper I is based on data from an experiment conducted in 2017 at the JYFL accelerator facility in Jyväskylä, Finland. In this experiment, excited states of were populated in the fusion-evaporation reaction 100Mo(22Ne,4n)118Te at a beam energy of 75 MeV. The lifetimes were extracted using the Recoil Distance Doppler Shift (RDDS) technique, with the Jurogam II γ-ray spectrometer coupled to the Differential Plunger for Unbound Nuclear States (DPUNS). Data analysis was performed using the Differential Decay Curve Method (DDCM) in coincidence mode. The lifetimes were determined to be τ2+ = 7.46(19) ps and τ4+ = 4.25(23) ps, in agreement with previous measurements, but with reduced uncertainty. In the case of the 2+ lifetime, the new result reduces the relative uncertainty of the lifetime from 16% to 2.5%, allowing for more precise tests of theoretical predictions.In addition to 118Te, an analysis of lifetimes of low-lying excited states in the odd-A nuclei 117Te and 119Te is ongoing and an experiment aiming to measure lifetimes in 116Te has been accepted. These nuclides will also be discussed in this thesis.
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| 5. |
- Andersson, Mikael, et al.
(författare)
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Gamma-ray track reconstruction using graph neural networks
- 2023
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 1048
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Tidskriftsartikel (refereegranskat)abstract
- Since the advent of the new generation of germanium detector arrays for low-energy nuclear physics experiments utilizing gamma-ray tracking, the challenges associated with track-reconstruction methods have been extensively studied. In the present work an approach based on recent developments in machine learning was used to address the problem. Here, a graph neural network was constructed and trained on data simulated in Geant4 in order to attempt track reconstruction of gamma rays below 1 MeV in a spherical shell geometry of pure germanium. Using a thick-shell geometry, and simulated data without energy-and position uncertainties the network achieved a reconstruction rate above 80% for complete tracks, and a combined peak-to-total value of 85% for energy spectra with four discrete peaks. For data with added noise, i.e. finite resolution in interaction-point position and energy, the corresponding peak-to-total ratio dropped to 74%. The track reconstruction was stable across multiplicities 1-10 but showed an increased error frequency in the energy range between 50 keV and 250 keV. To specifically study the complication of gamma tracks lost by out -scattering from the detector volume, a thin-shell (9 cm thickness) geometry was used together with a modified version of the GNN framework. By letting the GNN code identify and discriminate the out-scatter events, an improvement of the P/T value from 66% to 75% was found for the packed, noisy data. For the sake of comparison the new GNN model with existing gamma-ray tracking methods, a separate instance of the network was trained on slightly higher energies (up to 1.5 MeV) and multiplicities (up to 15) to evaluate 1.332 MeV photon cascade data in terms of P/T and photo-peak efficiency. The results for this GNN data set, with P/T values at 85% for single tracks and 74% for multiplicity 15, show clear promise when compared to the existing tracking methods.
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| 6. |
- Andgren, Karin, et al.
(författare)
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gamma-ray spectroscopy of At-197
- 2008
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 78:4, s. 044328-1-044328-8
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Tidskriftsartikel (refereegranskat)abstract
- Excited states of the extremely neutron-deficient nucleus At-197 have been studied in an in-beam experiment using the fusion-evaporation reaction Sn-118(Kr-82,p2n)At-197. gamma rays belonging to At-197 feeding the I-pi=(9/2(-)) ground state, as well as gamma rays feeding the 311-keV I-pi=(13/2(+)) isomer, decaying via the emission of gamma rays, and the 52-keV I-pi=(1/2(+)) alpha-decaying isomer have been identified using the recoil-alpha-decay tagging technique. Total Routhian surface calculations predict a near-spherical shape for the (9/2(-)) ground state and oblate shapes with beta(2) around -0.2 for the (1/2(+)) and the (13/2(+)) states. These predictions agree with our experimental findings.
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| 7. |
- Barday, R., et al.
(författare)
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ELECTRON BEAM POLARIMETRY AT LOW ENERGIES AND ITS APPLICATIONS
- 2011
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Ingår i: POLARIZED SOURCES, TARGETS AND POLARIMETRY. - : WORLD SCIENTIFIC PUBL CO PTE LTD. - 9789814324915 - 9789814462747 ; , s. 105-112
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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.
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| 8. |
- Bark, R A, et al.
(författare)
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Bandcrossings in Os-171
- 1999
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Ingår i: Nuclear Physics A. - 0375-9474 .- 1873-1554. ; 646:4, s. 399-413
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Tidskriftsartikel (refereegranskat)abstract
- The nucleus Os-171 has been populated using the reaction Sn-116(Ni-58,2pn). Four new bands are identified, and the previously known bands are extended in spin, to a maximum of 53/2 (h) over bar. One- and three-quasiparticle configurations are identified, and beta, gamma, and octupole configurations are assigned tentatively. The effects of a possible intruder configuration on the negative parity bands are tested using band-mixing calculations.
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| 9. |
- Bark, R A, et al.
(författare)
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Coexistence of triaxial and prolate shapes in Ir-171
- 1999
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Ingår i: Nuclear Physics A. - 0375-9474 .- 1873-1554. ; 657:2, s. 113-133
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Tidskriftsartikel (refereegranskat)abstract
- Excited states in Ir-171 have been observed for the first time. Gamma-rays were assigned to the nucleus by the recoil-decay tagging method, The ground-state band has a structure consistent with an h(11/2) proton coupled to a core of large triaxial deformation. At high spins, a bandcrossing occurs which is interpreted as a change in shape to a prolate deformation, Band-mixing calculations are performed for Ir171-175. These show that shape-coexistence between triaxial and prolate states in these nuclei follows the same systematics found in their Pt and Os neighbours. The systematics are also compared with deformations calculated for Ir171-179 using the code "Ultimate Cranker". Dipole bands were also observed, but tilted axis cranking calculations suggest that they are associated with a collective rotation.
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| 10. |
- Barucca, G., et al.
(författare)
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Feasibility studies for the measurement of time-like proton electromagnetic form factors from (p)over-barp -> mu(+)mu(-) at PANDA at FAIR
- 2021
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Ingår i: European Physical Journal A. - NEW YORK, USA : Springer Nature. - 1434-6001 .- 1434-601X. ; 57:1
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports on Monte Carlo simulation results for future measurements of the moduli of time-like proton electromagnetic form factors, vertical bar G(E)vertical bar and vertical bar G(M)vertical bar, using the (p) over barp -> mu(+)mu(-) reaction at PANDA (FAIR). The electromagnetic form factors are fundamental quantities parameterizing the electric and magnetic structure of hadrons. This work estimates the statistical and total accuracy with which the form factors can be measured at PANDA, using an analysis of simulated data within the PandaRoot software framework. The most crucial background channel is (p) over barp -> pi(+)pi(-), due to the very similar behavior of muons and pions in the detector. The suppression factors are evaluated for this and all other relevant background channels at different values of antiproton beam momentum. The signal/background separation is based on a multivariate analysis, using the Boosted Decision Trees method. An expected background subtraction is included in this study, based on realistic angular distributions of the background contribution. Systematic uncertainties are considered and the relative total uncertainties of the form factor measurements are presented.
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| 11. |
- Barucca, G., et al.
(författare)
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The potential of Λ and Ξ- studies with PANDA at FAIR
- 2021
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Ingår i: European Physical Journal A. - : Springer Nature. - 1434-6001 .- 1434-601X. ; 57:4
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Tidskriftsartikel (refereegranskat)abstract
- The antiproton experiment PANDA at FAIR is designed to bring hadron physics to a new level in terms of scope, precision and accuracy. In this work, its unique capability for studies of hyperons is outlined. We discuss ground-state hyperons as diagnostic tools to study non-perturbative aspects of the strong interaction, and fundamental symmetries. New simulation studies have been carried out for two benchmark hyperon-antihyperon production channels: p¯ p→ Λ¯ Λ and p¯ p→ Ξ¯ +Ξ-. The results, presented in detail in this paper, show that hyperon-antihyperon pairs from these reactions can be exclusively reconstructed with high efficiency and very low background contamination. In addition, the polarisation and spin correlations have been studied, exploiting the weak, self-analysing decay of hyperons and antihyperons. Two independent approaches to the finite efficiency have been applied and evaluated: one standard multidimensional efficiency correction approach, and one efficiency independent approach. The applicability of the latter was thoroughly evaluated for all channels, beam momenta and observables. The standard method yields good results in all cases, and shows that spin observables can be studied with high precision and accuracy already in the first phase of data taking with PANDA.
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| 12. |
- Bergman, Torbjörn, 1957-, et al.
(författare)
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Appendix : On definition and measurement
- 2021
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Ingår i: Coalition governance in Western Europe. - Oxford : Oxford University Press. - 9780198868484 ; , s. 727-748
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Bokkapitel (refereegranskat)abstract
- The appendix introduces our empirical study of the coalition life cycle. The structure of each country chapter is based on six core tables, each one capturing a major stage in the coalition life cycle. In the book chapters, the tables help structure the analysis and provide wealth of information and details of the coalition cycle. Nevertheless, the book chapters and this appendix only present a sample of the data and information that we have collected for this research project. For reasons of space, we have had to limit the presentation in the book chapters in terms of time-periods and variables. This appendix presents many more details that are important for readers who are not familiar with the definitions used in coalition research or interested in how particular variables where measured. In addition to the definitions and measurements presented in this appendix, all the data and all the variables are presented in an on-line data appendix at www.erdda.org.
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| 13. |
- Bergman, Torbjörn, 1957-, et al.
(författare)
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Coalition governance in Western Europe
- 2021
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Ingår i: Coalition governance in Western Europe. - Oxford : Oxford University Press. - 9780198868484 ; , s. 1-14
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Bokkapitel (refereegranskat)abstract
- This chapter describes the ambitions with the volume. First, we build on the lessons from earlier studies of governments in Western and Central Eastern Europe to deepen our understanding of the coalition life cycle, covering the three stages of a government's "life", beginning with the formation process, then turning to the governance stage, and lastly turning to the final phase when governments eventually terminate. Second, we seek to capture how recent changes in the Western European party systems, which are also described here, influence the various stages of the coalition life cycle. Third, we are in particular interested in how coalition partners cooperate and make policy once a government has formed, aiming to contribute to the growing literature on the topic of coalition governance. The chapter ends with a description of the content of the volume.
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| 14. |
- Bergman, Torbjörn, 1957-, et al.
(författare)
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Coalition governance patterns across Western Europe
- 2021
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Ingår i: Coalition governance in Western Europe. - Oxford : Oxford University Press. - 9780198868484 ; , s. 680-726
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Bokkapitel (refereegranskat)abstract
- We here summarize and compares the empirical results found by our country authors, focusing on the coalition life cycle in 17 countries. The chapter starts with a description of the changes that have occurred during the past decades in the party systems of Western Europe, and some institutional rules surrounding government formation and duration. We then turn to the comparing patterns of government formation across countries, showing that coalitions constitute almost 70 percent of the cabinets in Western Europe, and that the Scandinavian countries have been dominated by minority cabinets. Focusing on the coalition governance stage, we analyse the variation in the use of various control mechanisms across countries, for example showing that many coalition governments draft extensive contracts to control their partners in cabinet. The comparative data we present also shows that such agreements have become longer over time. Focusing on the last stage of the life cycle, we show that in a majority of countries, it is more common that a cabinet terminates early than serves the full term. There has also been a clear trend towards more government instability, even though the variation in cabinet duration across countries is large. We conclude this chapter by returning to the three coalition governance models described earlier in this volume, classifying the countries as being closer to one of the three models, based on a number of indicators and the information provided by our country experts.
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| 15. |
- Bergman, Torbjörn, 1957-, et al.
(författare)
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The three stages of the coalition life cycle
- 2021
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Ingår i: Coalition governance in Western Europe. - Oxford : Oxford University Press. - 9780198868484 ; , s. 15-40
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Bokkapitel (refereegranskat)abstract
- This chapter focuses on presenting the main research questions and answers provided in the literature on the different stages of the coalition life cycle. For example, focusing on the first stage, the formation stage, several researchers have tried to explain why specific types of governments form. Other scholars have asked why it take longer to form governments in some contexts. Other scholars have tried to explain how parties distribute ministerial and policy payoffs when forming a cabinet. Focusing on the second stage of the coalition life cycle, we review the growing literature on coalition governance, concentrating on three coalition governance models; the ministerial autonomy model, the coalition compromise model, and the PM dominated model – three models which make different assumptions about the actors that dominate the governance process in coalition governments. Focusing on the last phase of the coalition life cycle, the termination of governments, scholars have long aimed to explain the duration of cabinets, asking why some cabinets last longer than others. At the end of this chapter, we present some expectations about changes to the coalition life cycle which we are likely to observe considering the party system change we have seen in many Western European countries.
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| 16. |
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| 17. |
- Bäck, Henry, 1947, et al.
(författare)
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Den svenska politiken : Struktur, processer och resultat
- 2006
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- I Den svenska politiken ges en bred översikt över statsskicket och politiken. Med utgångspunkt i stats- och samhällsvetenskaplig forskning beskrivs och analyseras staten, EU, kommuner och landsting. Det politiska systemet gör det möjligt att fatta gemensamma beslut och skrida till gemensam handling i samhället. Till skillnad från andra system för gemensamt handlande verkar politiken genom att använda makt. För att kunna fånga maktutövningen i ett politiskt system krävs analytiska instrument i form av samhällsvetenskaplig teori. I boken behandlas särskilt det politiska systemets inbyggda kontrollmekanismer och den politiska processen. Formandet av den offentliga politiken illustreras med några centrala politikområden i den moderna svenska politiken. Här beskrivs och analyseras både det formella normativa ramverket och ”hur det verkligen går till”. För att begripa dagens svenska politik behöver vi kunna göra jämförelser i både tid och rum, och därför anläggs ett historiskt perspektiv och görs utblickar på andra länder.
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| 18. |
- Bäck, Henry, et al.
(författare)
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Den svenska politiken : Strukturer, processer och resultat
- 2011. - 3
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- I boken ges en bred översikt över statsskicket och politiken. Med utgångspunkt i stats- och samhällsvetenskaplig forskning beskrivs och analyseras staten, EU, kommuner och landsting. Läs mer Det politiska systemet gör det möjligt att fatta gemensamma beslut och skrida till gemensam handling i samhället. Till skillnad från andra system för gemensamt handlande verkar politiken genom att använda makt. För att kunna fånga maktutövningen i ett politiskt system krävs analytiska instrument i form av samhällsvetenskaplig teori. I boken behandlas särskilt det politiska systemets inbyggda kontrollmekanismer och den politiska processen. Formandet av den offentliga politiken illustreras med några centrala politikområden i den moderna svenska politiken. Här beskrivs och analyseras både det formella normativa ramverket och "hur det verkligen går till". För att begripa dagens svenska politik behöver vi kunna göra jämförelser i både tid och rum, och därför anläggs ett historiskt perspektiv och görs utblickar på andra länder.Stig Montin, docent i statsvetenskap vid Örebro universitet
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| 19. |
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| 20. |
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| 21. |
- Bäck, Hanna, et al.
(författare)
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The parties in government formation
- 2016. - 1
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Ingår i: The Oxford handbook of Swedish politics. - Oxford : Oxford University Press. - 9780199665679 ; , s. 206-223
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Bokkapitel (refereegranskat)
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| 22. |
- Bäck, Torbjörn, et al.
(författare)
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A TOF-PET system for educational purposes
- 2002
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576. ; 477, s. 82-82
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Tidskriftsartikel (refereegranskat)abstract
- A TOF-PET system has been designed and constructed for educational purposes. The aim of this system is to demonstrate the possibilities of positron emission tomography in general and the time-of-flight method in particular to the students of various courses at the Royal Institute of Technology, Stockholm, Sweden. The set-up consists of 48 small BaF2 crystals coupled to fast photomultipliers placed in a ring geometry. The signals of the photomultipliers are fed into fast constant fraction discriminators (CFD). The outputs of these are directed to a specially designed logic VME unit. which combines the CFD signals of 6 neighbouring channels to one signal by adding a different delay to each channel. The logic circuitry produces a prompt pulse for each event that serves as the start pulse for the 8-channel fast TDC. The delayed pulses act as the stop pulses for the TDC. In a computer. the measured times are converted into information about which the photomultipliers fired with the difference in the time of flight. The set-up is described and the results are presented.
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| 23. |
- Bäck, Torbjörn, et al.
(författare)
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An educational tool for demonstrating the TOF-PET technique
- 2001
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : AMERICAN PHYSICAL SOC. - 0168-9002 .- 1872-9576. ; 471:1-2, s. 200-204
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Tidskriftsartikel (refereegranskat)abstract
- A detector system for positron emission tomography with time-of-flight capability has been built to serve as an educational tool for undergraduate students. The set-up consists of 48 BaF2 scintillator crystals, each coupled to a fast photo-multiplier tube, mounted in a circular geometry. The analogue detector pulses are handled by fast constant fraction discriminators. A dedicated unit reduces the 48 channels to eight channels via delay-fine encoding, and the signals are then fed to an eight channel fast time-to-digital converter. A VME processor sorts the events and sends them to a workstation where the coincident events are extracted. The time resolution of the detectors together with fast VME based electronics allows for time-of-flight measurements to improve on the signal-to-noise ratio in the, reconstructed images. The system can be used for different types of exercises for the students, varying from the fundamentals of scintillator detectors to advanced image reconstruction. The set-up is described and some results are presented. (C) 2001 Elsevier Science B.V. All rights reserved.
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| 24. |
- Bäck, Torbjörn, et al.
(författare)
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First observation of gamma-rays from the proton emitter Au-171
- 2003
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Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 16:4, s. 489-494
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Tidskriftsartikel (refereegranskat)abstract
- Gamma-rays from the alpha- and proton-unstable nuclide Au-171 have been observed for the first time. The gamma-rays were correlated with both a proton- and an alpha-particle decay branch, confirming that the nucleus decays by alpha and proton emission from a single (11/2(-)) state. The measurement confirms the previously determined half-lives for these particle decays but the present values are of higher precision. In addition, a longer half-life than determined in previous work was measured for the proton-unstable tentative ground state. The results are discussed in relation to structures in neighbouring nuclei and compared with a Strutinsky-type TRS calculation.
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| 25. |
- Bäck, Torbjörn, et al.
(författare)
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Lifetime measurement of the first excited 2(+) state in (108)Te
- 2011
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 84:4, s. 041306-
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Tidskriftsartikel (refereegranskat)abstract
- The lifetime of the first excited 2(+) state in the neutron deficient nuclide (108)Te has been measured for the first time, using a combined recoil decay tagging and recoil distance Doppler shift technique. The deduced reduced transition probability is B(E2;0(g.s.)(+) -> 2(+)) = 0.39(-0.04)(+0.05)e(2)b(2). Compared to previous experimental data on neutron deficient tellurium isotopes, the new data point constitutes a large step (six neutrons) toward the N = 50 shell closure. In contrast to what has earlier been reported for the light tin isotopes, our result for tellurium does not show any enhanced transition probability with respect to the theoretical predictions and the tellurium systematics including the new data is successfully reproduced by state-of-the-art shell model calculations.
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