| 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
-
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)
-
The short, excited life of tellurium : Lifetime analysis of excited states in the Te midshell region
- 2024
-
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
-
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
-
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
-
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
-
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
-
Ingår i: European Physical Journal A. - NEW YORK, USA : Springer Nature. - 1434-6001 .- 1434-601X. ; 57:1
-
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
-
Ingår i: European Physical Journal A. - : Springer Nature. - 1434-6001 .- 1434-601X. ; 57:4
-
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)
-
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
-
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)
-
Coalition governance in Western Europe
- 2021
-
Ingår i: Coalition governance in Western Europe. - Oxford : Oxford University Press. - 9780198868484 ; , s. 1-14
-
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)
-
Coalition governance patterns across Western Europe
- 2021
-
Ingår i: Coalition governance in Western Europe. - Oxford : Oxford University Press. - 9780198868484 ; , s. 680-726
-
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
-
Ingår i: Coalition governance in Western Europe. - Oxford : Oxford University Press. - 9780198868484 ; , s. 15-40
-
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
-
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)
-
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)
-
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
-
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
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : AMERICAN PHYSICAL SOC. - 0168-9002 .- 1872-9576. ; 471:1-2, s. 200-204
-
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)
-
First observation of gamma-rays from the proton emitter Au-171
- 2003
-
Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 16:4, s. 489-494
-
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)
-
Lifetime measurement of the first excited 2(+) state in (108)Te
- 2011
-
Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 84:4, s. 041306-
-
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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| 26. |
- Bäck, Torbjörn, et al.
(författare)
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Observation of superdeformed states in Mo-88
- 1999
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Ingår i: European Physical Journal A. - New York : SPRINGER VERLAG. - 1434-6001 .- 1434-601X. ; 6:4, s. 391-397
-
Tidskriftsartikel (refereegranskat)abstract
- High-spin states in Mo-88 were studied using the GAMMASPHERE germanium detector array in conjunction with the MICROBALL CsI(TI) charged-particle detector system. Three gamma-ray cascades with dynamic moments of inertia showing similar characteristics to superdeformed rotational bands observed in the neighbouring A = 80 region have been identified and assigned to the nucleus Mo-88. The quadrupole moment of the strongest band, deduced by the Residual Doppler Shift Method, corresponds to a quadrupole deformation of beta(2) approximate to 0.6. This confirms the superdeformed nature of this band. The experimental data are interpreted in the framework of total routhian surface calculations. All three hands are assigned to two-quasi-particle proton configurations at superdeformed shape.
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| 27. |
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| 28. |
- Bäck, Torbjörn, et al.
(författare)
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Spectroscopy of the neutron-deficient nuclide Pt-171
- 2003
-
Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 17:1, s. 1-5
-
Tidskriftsartikel (refereegranskat)abstract
- A number of previously unobserved gamma-rays emitted from the neutron-deficient nuclide Pt-171 have been identified using the recoil decay tagging technique. The level scheme has been updated using information from gamma-gamma coincidences and angular distribution measurements. To further confirm the assignments of the gamma-rays to Pt-171, the events were correlated with the alpha-decay of the daughter nucleus Os-167.
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| 29. |
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| 30. |
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| 31. |
- Bäck, Torbjörn, et al.
(författare)
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Transition probabilities near Sn-100 and the stability of the N, Z=50 shell closure
- 2013
-
Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 87:3, s. 031306-
-
Tidskriftsartikel (refereegranskat)abstract
- Recent B(E2; 0(g.s.)(+) -> 2(1)(+)) measurements in light tin isotopes have revealed surprisingly large values relative to standard shell model predictions, generating an unexpected asymmetry in the B(E2) values with respect to the neutron midshell. This effect has triggered various speculations as to its origin, such as a possible weakening of the N, Z = 50 shell closure. Here we present new shell model calculations to investigate the origin of the observed asymmetric character of the B(E2) values in the tin isotopes. By including the effects of the neutron g(9/2) orbital below the N = 50 shell gap it is shown that Pauli blocking effects may play an important role near the N = 50 shell closure. A new set of single-particle energies and monopole interactions, fitted to the experimental data in the region, together with the isospin-dependent effective charge suggested by Bohr and Mottelson is shown to reproduce the experimental transition rate values in the Sn isotopic chain.
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| 32. |
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| 33. |
- Cederwall, Bo, et al.
(författare)
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Collective rotational-vibrational transition in the very neutron-deficient nuclei (171,172)-Pt
- 1998
-
Ingår i: Physics Letters B. - AMSTERDAM, NETHERLANDS : ELSEVIER SCIENCE. - 0370-2693 .- 1873-2445. ; 443:1-4, s. 69-76
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Tidskriftsartikel (refereegranskat)abstract
- Excited states have been identified for the first time in very neutron deficient Pt-171.172 nuclei using the recoil-or-decay tagging technique. The ground-state band in Pt-172 has been established up to I-pi = 8+. A similar level sequence, presumably built on the I-pi = 13/2(+) state, is observed for Pt-171. The data are compared with theoretical calculations based on the mean field approach and the random phase approximation and are put into the context of the systematics of platinum isotopes. (C) 1998 Elsevier Science B.V. All rights reserved.
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| 34. |
- Cederwall, Bo, et al.
(författare)
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Evidence for a spin-aligned neutron-proton paired phase from the level structure of 92Pd
- 2011
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 469:7328, s. 68-71
-
Tidskriftsartikel (refereegranskat)abstract
- Shell structure and magic numbers in atomic nuclei were generally explained by pioneering work(1) that introduced a strong spin-orbit interaction to the nuclear shell model potential. However, knowledge of nuclear forces and the mechanisms governing the structure of nuclei, in particular far from stability, is still incomplete. In nuclei with equal neutron and proton numbers (N = Z), enhanced correlations arise between neutrons and protons (two distinct types of fermions) that occupy orbitals with the same quantum numbers. Such correlations have been predicted to favour an unusual type of nuclear superfluidity, termed isoscalar neutron-proton pairing(2-6), in addition to normal isovector pairing. Despite many experimental efforts, these predictions have not been confirmed. Here we report the experimental observation of excited states in the N = Z = 46 nucleus Pd-92. Gamma rays emitted following the Ni-58(Ar-36,2n)Pd-92 fusion-evaporation reaction were identified using a combination of state-of-the-art high-resolution c-ray, charged-particle and neutron detector systems. Our results reveal evidence for a spin-aligned, isoscalar neutron-proton coupling scheme, different from the previous prediction(2-6). We suggest that this coupling scheme replaces normal superfluidity (characterized by seniority coupling(7,8)) in the ground and low-lying excited states of the heaviest N = Z nuclei. Such strong, isoscalar neutron-proton correlations would have a considerable impact on the nuclear level structure and possibly influence the dynamics of rapid proton capture in stellar nucleosynthesis.
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| 35. |
- Cederwall, Bo, et al.
(författare)
-
Favoured superdeformed states in 89TC
- 1999
-
Ingår i: European Physical Journal A. - New York : Springer-Verlag New York. - 1434-6001 .- 1434-601X. ; 6:3, s. 251-255
-
Tidskriftsartikel (refereegranskat)abstract
- A superdeformed band consisting of a cascade of ten gamma-ray transitions has been identified and assigned to the nucleus Tc-89, close to the proton dripline. The quadrupole moment of the band (Q(t) = 6.7(-2.3)(+3.0) eb, as measured by the Residual Doppler Shift Method) as well as a large dynamic moment of inertia point to a highly elongated shape. With a relative population of approximately 15% of the gamma-ray flux in the Tc-89 exit channel, thp band is among the most intense superdeformed bands observed to date.
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| 36. |
- Cederwall, Bo, 1964-, et al.
(författare)
-
Isospin Properties of Nuclear Pair Correlations from the Level Structure of the Self-Conjugate Nucleus Ru 88
- 2020
-
Ingår i: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 124:6
-
Tidskriftsartikel (refereegranskat)abstract
- The low-lying energy spectrum of the extremely neutron-deficient self-conjugate (N = Z) nuclide 88Ru has been measured using the combination of the Advanced Gamma Tracking Array (AGATA)spectrometer, the NEDA, and Neutron Wall neutron detector arrays, and the DIAMANT charged particle detector array. Excited states in 88 Ru were populated via the 54 Feð 36 Ar; 2nγÞ 88 Ru fusion-evaporationreaction at the Grand Accélérateur National d’Ions Lourds (GANIL) accelerator complex. The observed γ-ray cascade is assigned to 88 Ru using clean prompt γ-γ-2-neutron coincidences in anticoincidence with the detection of charged particles, confirming and extending the previously assigned sequence of low-lying excited states. It is consistent with a moderately deformed rotating system exhibiting a band crossing at a rotational frequency that is significantly higher than standard theoretical predictions with isovector pairing, as well as observations in neighboring N > Z nuclides. The direct observation of such a “delayed” rotational alignment in a deformed N 1⁄4 Z nucleus is in agreement with theoretical predictions related to the presence of strong isoscalar neutron-proton pair correlations.
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| 37. |
-
Coalition governance in Western Europe
- 2021
-
Samlingsverk (redaktörskap) (refereegranskat)abstract
- Coalitions among political parties govern most European democracies. Coalition Governance in Western Europe brings the study of the full coalition life cycle up to date in 16 West European countries. It also introduces the first such analysis of Croatia. The volume provides information and analyses of the full cycle, from pre-electoral alliances to coalition formation and portfolio distribution, governing in coalitions, and the stages that eventually lead to government termination. In recent years, this takes place in a context of party system fragmentation, polarization, and newcomer populist parties. The volume captures these changes and examines the implication for the parties in government. While earlier research on Western Europe tends to stress that coalition partners emphasize coalition compromise and mutual supervision, there are some countries where the prime minister heavily dominates coalition governance. There is also some evidence of 'ministerial government', but less so than in Central Eastern Europe. This volume presents systematic information on political institutions, political parties, coalitions, and coalition governance in Western Europe and Croatia.
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| 38. |
- Davi, F., et al.
(författare)
-
Technical design report for the endcap disc DIRC
- 2022
-
Ingår i: Journal of Physics G. - : Institute of Physics Publishing (IOPP). - 0954-3899 .- 1361-6471. ; 49:12
-
Tidskriftsartikel (refereegranskat)abstract
- PANDA (anti-proton annihiliation at Darmstadt) is planned to be one of the four main experiments at the future international accelerator complex FAIR (Facility for Antiproton and Ion Research) in Darmstadt, Germany. It is going to address fundamental questions of hadron physics and quantum chromodynamics using cooled antiproton beams with a high intensity and and momenta between 1.5 and 15 GeV/c. PANDA is designed to reach a maximum luminosity of 2 × 1032 cm−2 s. Most of the physics programs require an excellent particle identification (PID). The PID of hadronic states at the forward endcap of the target spectrometer will be done by a fast and compact Cherenkov detector that uses the detection of internally reflected Cherenkov light (DIRC) principle. It is designed to cover the polar angle range from 5° to 22° and to provide a separation power for the separation of charged pions and kaons up to 3 standard deviations (s.d.) for particle momenta up to 4 GeV/c in order to cover the important particle phase space. This document describes the technical design and the expected performance of the novel PANDA disc DIRC detector that has not been used in any other high energy physics experiment before. The performance has been studied with Monte-Carlo simulations and various beam tests at DESY and CERN. The final design meets all PANDA requirements and guarantees sufficient safety margins.
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| 39. |
- Davies, P. J., et al.
(författare)
-
The role of core excitations in the structure and decay of the 16(+) spin-gap isomer in Cd-96
- 2017
-
Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 767, s. 474-479
-
Tidskriftsartikel (refereegranskat)abstract
- The first evidence for beta-delayed proton emission from the 16(+) spin gap isomer in Cd-96 is presented. The data were obtained from the Rare Isotope Beam Factory, at the RIKEN Nishina Center, using the BigRIPS spectrometer and the EURICA decay station. beta p branching ratios for the ground state and 16(+) isomer have been extracted along with more precise lifetimes for these states and the lifetime for the ground state decay of Cd-95. Large scale shell model (LSSM) calculations have been performed and WKB estimates made for l = 0, 2, 4 proton emission from three resonance-like states in Ag-96, that are populated by the beta decay of the isomer, and the results compared to the new data. The calculations suggest that l = 2 proton emission from the resonance states, which reside similar to 5 MeV above the proton separation energy, dominates the proton decay. The results highlight the importance of core-excited wavefunction components for the 16(+) state.
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| 40. |
- Ding, B., et al.
(författare)
-
Signature splitting of the g(7/2)[404]7/2(+) bands in Ba-131 and Ce-133
- 2021
-
Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 104:6
-
Tidskriftsartikel (refereegranskat)abstract
- Excited states in Ba-131 and Ce-133 were studied using in-beam gamma-ray spectroscopy through the Sn-122(C-13, 4n) Ba-133 and Te-125(C-12, 4n) Ce-133 reactions, respectively. A strongly coupled band, associated with the nu g(7/2) [404]7/2(+) configuration, was identified in Ba-131 and Ce-133. It is the first time to observe the nu g(7/2) [404]7/2(+) bands in the N = 75 isotones. The signature partners exhibit considerable energy splitting in comparison with those in the pi g(7/2) [404]7/2(+) bands in the odd-A Ta and Re isotopes. Extensive cranked shell model and quasiparticle-plus-triaxial-rotor model calculations reveal the origin of the signature splitting, which depends not only on the triaxiality, but also on the configuration mixing with nearby low- j orbitals.
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| 41. |
- Doncel, Maria, et al.
(författare)
-
Lifetime measurement of the first excited 2(+) state in Te-112
- 2015
-
Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 91:6
-
Tidskriftsartikel (refereegranskat)abstract
- The lifetime of the 2(+) --> 0(g.s.)(+) transition in the neutron-deficicient nucleus Te-112 has been measured for the first time using the DPUNS plunger and the recoil distance Doppler shift technique. The deduced value for the reduced transition probability is B(E2 :0(g.s.)(+) --> 2(+)) = 0.46 +/- 0.04 e(2)b(2), indicating that there is no unexpected enhancement of the B(E2 :0(g.s.)(+) --> 2(+)) values in Te isotopes below the midshell. The result is compared to and discussed in the framework of large-scale shell-model calculations.
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| 42. |
- Doncel, Maria, et al.
(författare)
-
Spin-dependent evolution of collectivity in Te 112
- 2017
-
Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 96:5
-
Tidskriftsartikel (refereegranskat)abstract
- The evolution of collectivity with spin along the yrast line in the neutron-deficient nucleus Te112 has been studied by measuring the reduced transition probability of excited states in the yrast band. In particular, the lifetimes of the 4+ and 6+ excited states have been determined by using the recoil distance Doppler-shift method. The results are discussed using both large-scale shell-model and total Routhian surface calculations.
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| 43. |
- Eliasson, Linda, et al.
(författare)
-
Low-pressure measurements of energy depositions in nanometre objects with a single ionisation chamber in a 60 Co beam using the variance-covariance method
- 2024
-
Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 221
-
Tidskriftsartikel (refereegranskat)abstract
- Dose -mean lineal energies were measured using the variance-covariance method and commercial ionisation chambers in a therapy level 60 Co field at several different air pressures. The results confirmed the trend from previous studies and the experimental data was extended down to a simulated object diameter of 4.2 nm using a low -noise electrometer. The variance-covariance method was adapted to consecutive charge integrations from a single ionisation chamber and used to correct for signal variations due to pressure drifts in the ion chamber. Monte Carlo simulations using MCNP 6.2 were performed, and the results follow the trend of the experimental values in the nanometric region.
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| 44. |
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| 45. |
- Eliasson, Linda, et al.
(författare)
-
Range-shifter effects on the stray field in proton therapy measured with the variance–covariance method
- 2022
-
Ingår i: Frontiers in Oncology. - : Frontiers Media SA. - 2234-943X. ; 12
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements in the stray radiation field from a proton therapy pencil beam at energies 70 and 146 MeV were performed using microdosimetric tissue- equivalent proportional counters (TEPCs). The detector volumes were filled with a propane-based tissue-equivalent gas at low pressure simulating a mean chord length of 2 mm in tissue. Investigations were performed with and without a beam range shifter, and with different air gaps between the range shifter and a solid water phantom. The absorbed dose, the dose-mean lineal energy, and the dose equivalent were determined for different detector positions using the variance–covariance method. The influence from beam energy, detector- and range-shifter positions on absorbed dose, LET, and dose equivalent were investigated. Monte Carlo simulations of the fluence, detector response, and absorbed dose contribution from different particles were performed with MCNP 6.2. The simulated dose response for protons, neutrons, and photons were compared with, and showed good agreement with, previously published experimental data. The simulations also showed that the TEPC absorbed dose agrees well with the ambient absorbed dose for neutron energies above 20 MeV. The results illustrate that changes in both dose and LET variations in the stray radiation field can be identified from TEPC measurements using the variance–covariance method. The results are in line with the changes seen in the simulated relative dose contributions from different particles associated with different proton energies and range-shifter settings. It is shown that the proton contribution scattered directly from the range shifter dominates in some situations, and although the LET of the radiation is decreased, the ambient dose equivalent is increased up to a factor of 3.
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| 46. |
- Eliasson, Linda
(författare)
-
Towards nanodosimetry: therapeutic radiation measurements using the variance method
- 2022
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Understanding how radiation damage occurs in human tissue seems to lie in the knowledge of energy depositions in DNA-size volumes, with diameters typically around a few nanometres. In such small volumes the energy transfers are stochastic and described using distributions of events along a particle track and relevant mean values. Usually, two main quantities are used to describe nanodosimetric characteristics: ionisation clus- ter sizes and lineal energies. The former give a distribution of the number of ionisation events while the latter give the distribution of the energy imparted per mean chord length in the volume of interest. The dose-mean lineal energy is the mean value of the dose-weighted distribution of lineal energy. Both quantities are independent of the deposited dose and depends only on the radiation quality. In the work presented here, dose-mean lineal energies were determined using commercial ion chambers and tissue-equivalent proportional counters containing gas at low pressures, simulating volumes of object sizes in the micro- and nanometre ranges. The variance method was used, where the dose-mean energy imparted during a fixed integration time was measured instead of the energy imparted by each single event. This method is valuable both in high-intensity beams where single-event methods are challenged by e.g. pileup, and in small volumes where the signals from single events are weak and need strong amplifications. To adjust for slow variations in e.g. the radiation beam, gas pressure and applied voltages, the covariance-adjusted variance-covariance method was used and further developed so that only one single detector was required. Paper I describes microdosimetric measurements using tissue-equivalent proportional counters placed in the stray field from a therapeutic proton beam at the Skandion clinic in Uppsala, Sweden. By comparing dose-mean lineal energies with and without the use of a range shifter it could be shown that proton scattering from this range shifter contributed to an increased absorbed dose in some positions. Paper II describes nanodosimetric measurements in a therapy-level 60Co field using commercial ion chambers. Using low-noise electronics, the dose-mean lineal energy down to simulated mean chord lengths of 2.8 nm in unit density in air could be measured. Both papers are steps toward nanodosimetric measurements in therapeutic hadron beams, where the dose-mean lineal energy can give a better understanding and de- scription of radiation quality in radiation therapy.
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| 47. |
- Erni, W., et al.
(författare)
-
Technical design report for the PANDA (AntiProton Annihilations at Darmstadt) Straw Tube Tracker
- 2013
-
Ingår i: European Physical Journal A. Hadrons and Nuclei. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 49:2
-
Tidskriftsartikel (refereegranskat)abstract
- This document describes the technical layout and the expected performance of the Straw Tube Tracker (STT), the main tracking detector of the PANDA target spectrometer. The STT encloses a Micro-Vertex-Detector (MVD) for the inner tracking and is followed in beam direction by a set of GEM stations. The tasks of the STT are the measurement of the particle momentum from the reconstructed trajectory and the measurement of the specific energy loss for a particle identification. Dedicated simulations with full analysis studies of certain proton-antiproton reactions, identified as being benchmark tests for the whole PANDA scientific program, have been performed to test the STT layout and performance. The results are presented, and the time lines to construct the STT are described.
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| 48. |
- Ertoprak, Aysegul, et al.
(författare)
-
Evidence for octupole collectivity in 172Pt
- 2020
-
Ingår i: European Physical Journal A. - : Springer. - 1434-6001 .- 1434-601X. ; 56:2
-
Tidskriftsartikel (refereegranskat)abstract
- Excited states in the extremely neutron-deficient nucleus 172Pt were populated via 96Ru(78Kr,2p) and 92Mo(83Kr,3n) reactions. The level scheme has been extended up to an excitation energy of ~ 5 MeV and tentative spin-parity assignments up to Iπ = 18+. Linear polarization and angular distribution measurements were used to determine the electromagnetic E1 character of the dipole transitions connecting the positive-parity ground-state band with an excited side-band, firmly establishing it as a negative-parity band. The lowest member of this negative-parity structure was firmly assigned spin-parity 3-. In addition, we observed an E3 transition from this 3- state to the ground state, providing direct evidence for octupole collectivity in 172Pt. Large-scale shell model (LSSM) and total Routhian surface (TRS) calculations have been performed, supporting the interpretation of the 3- state as a collective octupole-vibrational state.
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| 49. |
- Ertoprak, Aysegul, et al.
(författare)
-
Lifetime measurements of core-excited states in semi-magic 95Rh
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Lifetimes of negative-parity states have been determined in the semi-magic (N=50) nucleus 95Rh. The fusion-evaporation reaction 58Ni(40Ca, 3p) was used to populate high-spin states in 95Rh at the Grand Accelerateur National d'Ions Lourds (GANIL) accelerator facility. The results were obtained using the Doppler Shift Attenuation Method (DSAM) based on the Doppler broadened line shapes produced during the slowing down process of the residual nuclei in a thick 6~ mg/cm2 metallic target. B(M1) and B(E2) reduced transition strengths are compared with predictions from large-scale shell-model calculations.
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| 50. |
- Ertoprak, Aysegul, et al.
(författare)
-
LIFETIME MEASUREMENTS WITH THE DOPPLER SHIFT ATTENUATION METHOD USING A THICK HOMOGENEOUS PRODUCTION TARGET - VERIFICATION OF THE METHOD
- 2017
-
Ingår i: Acta Physica Polonica B. - : Jagiellonian University Press. - 0587-4254 .- 1509-5770. ; 48:3, s. 325-329
-
Tidskriftsartikel (refereegranskat)abstract
- Doppler Shift Attenuation Method (DSAM) analysis of excited-state lifetimes normally employs thin production targets mounted on a thick stopper foil ("backing") serving to slow down and stop the recoiling nuclei of interest in a well-defined manner. Use of a thick, homogeneous production target leads to a more complex analysis as it results in a substantial decrease in the energy of the incident projectile which traverses the target with an associated change in the production cross section of the residues as a function of penetration depth. Here, a DSAM lifetime analysis using a thick homogeneous target has been verified using the Doppler broadened lineshapes of gamma rays following the decay of highly excited states in the semi-magic (N = 50) nucleus Ru-94. Lifetimes of excited states in the Ru-94 nucleus have been obtained using a modified version of the LINESHAPE package from the Doppler broadened lineshapes resulting from the emission of the gamma rays, while the residual nuclei were slowing down in the thick (6 mg/cm(2)) metallic Ni-58 target. The results have been validated by comparison with a previous measurement using a different (RDDS) technique.
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