| 1. |
|
|
| 2. |
|
|
| 3. |
- Ahlgren Cederlöf, Ebba, et al.
(author)
-
Lifetime measurement of the yrast 2+ state in 118Te
- 2023
-
In: European Physical Journal A. - : Springer. - 1434-6001 .- 1434-601X. ; 59:12
-
Journal article (peer-reviewed)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.
|
|
| 4. |
- Ahlgren Cederlöf, Ebba
(author)
-
The short, excited life of tellurium : Lifetime analysis of excited states in the Te midshell region
- 2024
-
Licentiate thesis (other academic/artistic)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.
|
|
| 5. |
- Andersson, Mikael, et al.
(author)
-
Gamma-ray track reconstruction using graph neural networks
- 2023
-
In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 1048
-
Journal article (peer-reviewed)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.
|
|
| 6. |
- Barucca, G., et al.
(author)
-
Feasibility studies for the measurement of time-like proton electromagnetic form factors from (p)over-barp -> mu(+)mu(-) at PANDA at FAIR
- 2021
-
In: European Physical Journal A. - NEW YORK, USA : Springer Nature. - 1434-6001 .- 1434-601X. ; 57:1
-
Journal article (peer-reviewed)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.
|
|
| 7. |
- Barucca, G., et al.
(author)
-
The potential of Λ and Ξ- studies with PANDA at FAIR
- 2021
-
In: European Physical Journal A. - : Springer Nature. - 1434-6001 .- 1434-601X. ; 57:4
-
Journal article (peer-reviewed)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.
|
|
| 8. |
- Bergman, Torbjörn, 1957-, et al.
(author)
-
Appendix : On definition and measurement
- 2021
-
In: Coalition governance in Western Europe. - Oxford : Oxford University Press. - 9780198868484 ; , s. 727-748
-
Book chapter (peer-reviewed)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.
|
|
| 9. |
- Bergman, Torbjörn, 1957-, et al.
(author)
-
Coalition governance in Western Europe
- 2021
-
In: Coalition governance in Western Europe. - Oxford : Oxford University Press. - 9780198868484 ; , s. 1-14
-
Book chapter (peer-reviewed)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.
|
|
| 10. |
- Bergman, Torbjörn, 1957-, et al.
(author)
-
Coalition governance patterns across Western Europe
- 2021
-
In: Coalition governance in Western Europe. - Oxford : Oxford University Press. - 9780198868484 ; , s. 680-726
-
Book chapter (peer-reviewed)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.
|
|
| 11. |
- Bergman, Torbjörn, 1957-, et al.
(author)
-
The three stages of the coalition life cycle
- 2021
-
In: Coalition governance in Western Europe. - Oxford : Oxford University Press. - 9780198868484 ; , s. 15-40
-
Book chapter (peer-reviewed)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.
|
|
| 12. |
- Cederwall, Bo, 1964-, et al.
(author)
-
Isospin Properties of Nuclear Pair Correlations from the Level Structure of the Self-Conjugate Nucleus Ru 88
- 2020
-
In: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 124:6
-
Journal article (peer-reviewed)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.
|
|
| 13. |
-
Coalition governance in Western Europe
- 2021
-
Editorial collection (peer-reviewed)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.
|
|
| 14. |
- Davi, F., et al.
(author)
-
Technical design report for the endcap disc DIRC
- 2022
-
In: Journal of Physics G. - : Institute of Physics Publishing (IOPP). - 0954-3899 .- 1361-6471. ; 49:12
-
Journal article (peer-reviewed)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.
|
|
| 15. |
- Ding, B., et al.
(author)
-
Signature splitting of the g(7/2)[404]7/2(+) bands in Ba-131 and Ce-133
- 2021
-
In: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 104:6
-
Journal article (peer-reviewed)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.
|
|
| 16. |
- Eliasson, Linda, et al.
(author)
-
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
-
In: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 221
-
Journal article (peer-reviewed)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.
|
|
| 17. |
- Eliasson, Linda, et al.
(author)
-
Range-shifter effects on the stray field in proton therapy measured with the variance–covariance method
- 2022
-
In: Frontiers in Oncology. - : Frontiers Media SA. - 2234-943X. ; 12
-
Journal article (peer-reviewed)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.
|
|
| 18. |
- Eliasson, Linda
(author)
-
Towards nanodosimetry: therapeutic radiation measurements using the variance method
- 2022
-
Licentiate thesis (other academic/artistic)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.
|
|
| 19. |
- Ertoprak, Aysegul, et al.
(author)
-
Evidence for octupole collectivity in 172Pt
- 2020
-
In: European Physical Journal A. - : Springer. - 1434-6001 .- 1434-601X. ; 56:2
-
Journal article (peer-reviewed)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.
|
|
| 20. |
- Ertoprak, A., et al.
(author)
-
Lifetimes of core-excited states in semi-magic Rh-95
- 2020
-
In: European Physical Journal A. - : SPRINGER. - 1434-6001 .- 1434-601X. ; 56:11
-
Journal article (peer-reviewed)abstract
- Lifetimes of negative-parity states have been determined in the neutron deficient semi-magic (N = 50) nucleus Rh-95. The fusion-evaporation reaction Ni-58(Ca-40, 3p) was used to populate high-spin states in Rh-95 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/cm(2) metallic target. B(M1) and B(E2) reduced transition strengths are compared with predictions from large-scale shell-model calculations. state-of-the-art theory. Remarkably, the structural features up to moderate angular momentum of nuclei immediately below the N = Z = 50 shell closures can be described with high accuracy in a very simple way by shell-model calculations including only the g(9/2) and p(1/2) subshells. Of special interest is the neutron-proton pair coupling scheme which is expected to appear in the heaviest N=Z nuclei [1,2] and the seniority structure of the N = 50 isotones [3-7]. However, multiple core-excited states have been observed in the semi-magic nuclei of the Sn-100 region [8-10]. The theoretical study of those states is a challenging task, which requires a significantly larger model space for their interpretation. Transition probabilities between nuclear states provide important constraints for theoretical modelling of the structure of the nuclei of interest. Our previous lifetime study of the semimagic (N = 50) nucleus Ru-94 [ 11,12] provided information on the electromagnetic decay properties of neutron-core excited states. We now address lifetime measurements in its closest, more neutron deficient, isotone Rh-95 using the same DSAM technique. The experimental results have been interpreted within the framework of large-scale shell-model (LSSM) calculations.
|
|
| 21. |
- Guo, S., et al.
(author)
-
Evidence for pseudospin-chiral quartet bands in the presence of octupole correlations
- 2020
-
In: Physics Letters B. - : ELSEVIER. - 0370-2693 .- 1873-2445. ; 807
-
Journal article (peer-reviewed)abstract
- Three nearly degenerate pairs of doublet bands are identified in Ba-131. Two of them, with positive-parity, are interpreted as pseudospin-chiral quartet bands. This is the first time that a complete set of chiral doublet bands built on the pseudospin partners pi(d(5/2), g(7/2)) is observed. The chiral bands with opposite parity built on 3-quasiparticle configurations are directly connected by many E1 transitions, without involving an intermediary non-chiral configuration. The observed band structures in Ba-131 have been investigated by using the reflection-asymmetric particle rotor model. The energies and the electromagnetic transition ratios of the three pairs of doublet bands observed in Ba-131 are reproduced and they are interpreted as chiral doublet bands with three-quasiparticle configurations. It is the first time that multiple chiral bands are observed in the presence of enhanced octupole correlations and pseudospin symmetry.
|
|
| 22. |
- Liu, Xiaoyu, et al.
(author)
-
Evidence for spherical-oblate shape coexistence in Tc-87
- 2022
-
In: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 106:3
-
Journal article (peer-reviewed)abstract
- Excited states in the neutron-deficient nucleus Tc-87 have been studied via the fusion-evaporation reaction 54Fe(36Ar, 2n1p) Tc-87 at 115 MeV beam energy. The AGATA gamma-ray spectrometer coupled to the DIAMANT, NEDA, and Neutron Wall detector arrays for light-particle detection was used to measure the prompt coincidence of gamma rays and light particles. Six transitions from the deexcitation of excited states belonging to a new band in Tc-87 were identified by comparing gamma-ray intensities in the spectra gated under different reaction channel selection conditions. The constructed level structure was compared with the shell model and total Routhian surface calculations. The results indicate that the new band structure in 87Tc is built on a spherical configuration, which is different from that assigned to the previously identified oblate yrast rotational band.
|
|
| 23. |
- Wei, Rui, et al.
(author)
-
Exotic collective excitation patterns in triaxially deformed 131Ba
- 2024
-
In: Wuli xuebao. - : Chinese Academy of Sciences. - 1000-3290. ; 73:11
-
Journal article (peer-reviewed)abstract
- In the last two decades, several unique phenomena in triaxially deformed nuclei, such as chiral doublet bands and wobbling motion have been revealed. Up to now, there are still many open questions which require further experimental and theoretical studies. To explore the collective motion in 131Ba, an experiment was performed using the XTU Tandem accelerator in the Legnaro laboratory, Italy. High-spin states of 131Ba have been populated via the heavy-ion fusion-evaporation 122Sn(13C, 4n) reaction. g-rays, charged particles and neutrons emitted from the residues were detected by the GALILEO array, EUCLIDES silicon ball, and the Neutron Wall, respectively. A total of 1.2 ×109 triple- or higher-fold events were collected by the GALILEO data acquisition system. The g-g-g coincidence events were sorted into a three-dimensional histogram (cube) and the analysis was carried out with the RADWARE and GASPWARE software packages. Through analysis of the coincidences between g-rays, the most comprehensive level schemes of 131Ba to date was deduced from the present work. The extended level-scheme consists of 15 rotational bands, and newly observed transitions are marked in red. Three nearly degenerate pairs of doublet bands (Band 3–8) are identified in 131Ba. Two pairs of chiral doublets (Band 3–6) with configuration πh11/2(g7/2,d5/2)×νh11/2 are interpreted as a set of pseudospin-chiral quartet bands. The quartet bands are fed by another pair of chiral doublet bands (Band 7–8) built on a πh211/2×νh11/2 configuration via a series of enhanced E1 transitions. We extracted the energy displacement δE and the B(E1)/B(E2) branching ratios between the positive-parity band 3 and the negative-parity band 7 in 131Ba and in comparison with those in 124Ba, 224Th, 133Ce and 135Nd. The energy displacement δE and the B(E1)/B(E2) branching ratios in 131Ba are comparable with those in 124Ba but deviate appreciably from those in 224Th which has been reported to have stable octupole deformation. The results indicate the existence of octupole correlations in 131Ba without stable octupole deformation. A new rotational band (Band 10) discovered in the low-spin region exhibits a level structure similar to a wobbling band. Assuming it as a wobbling band, the wobbling frequency was extracted and compared with other reported wobbling bands in the neighboring nuclei. The wobbling frequency of this band decreases with increasing angular momentum, and even exhibits negative value at the highest spin. Considering that the wobbling phonon should contribute a positive amount to the excitation energy, this band is unlikely to be explained by this mechanism. The band may originate from other collective excitation mechanisms such as g vibration. The newly identified rotational band (Band 9) composed of M1 transitions is tentatively assigned as a magnetic rotational band through a systematic analysis of the level structure. Finally, the configurations of other 4 bands, Band 12-15, are also suggested based on previous researches and the extracted quasiparticle alignments.
|
|
| 24. |
- Zhang, Wei, et al.
(author)
-
Identification of excited states in Te55 52107
- 2021
-
In: Physical Review C. Nuclear Physics. - : American Physical Society. - 0556-2813 .- 1089-490X. ; 104:6
-
Journal article (peer-reviewed)abstract
- Excited states in the extremely neutron-deficient nucleus Te107 have been identified from two separate experiments using the recoil-decay tagging technique. Two connected structures were observed on the basis of γγ-coincidence relations and tentatively assigned as built on the mixed-parentage νg7/2d5/2 and νh11/2 intruder configurations. The observed structures were compared with large-scale shell-model calculations and total Routhian surface calculations. Collective behavior was discovered to persist in the νh11/2 band of Te107 which highlights the shape-polarizing effect of a single valence neutron occupying the h11/2 intruder orbit as the N=50 shell closure is approached.
|
|
