| 1. |
- Ahlgren Cederlöf, Ebba, et al.
(author)
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Lifetime measurement of the yrast 2+ state in 118Te
- 2023
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In: European Physical Journal A. - : Springer. - 1434-6001 .- 1434-601X. ; 59:12
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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.
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| 2. |
- Appagere, Gandharva
(author)
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Λ-Λ hyperons: the road to estimate the production cross-section in protonproton collisions
- 2024
-
Licentiate thesis (other academic/artistic)abstract
- In this study, we analyse the $\Lambda$-$\Lambda$ hyperon channel in proton-proton scattering, $pp \mapsto \Lambda\Lambda + K^+K^+, \,\,\Lambda\mapsto p+\pi^-$, with a proton beam energy of $4.5$ GeV using the High Acceptance Di-Electron Spectrometer (HADES) at GSI.The purpose of the study presented here is to measure the production cross-section for the $\Lambda$-$\Lambda$ channel. %at the above beam Kinetic energy. The following measurement will be the first at this energy scale (CoM: $\sqrt{s}=3.46$ GeV).We develop a multi-stage analysis strategy to first determine the acceptance-reconstruction efficiency for the $\Lambda$-$\Lambda$ channel from simulations produced according to phase space.The analysis of data is perforned for three different event selections: inclusive ($ pp \mapsto \Lambda\Lambda + X$), semi-exclusive ($ pp \mapsto \Lambda\Lambda + K^+ +X$) and the fully exclusive.For each selection, the data is represented by a two-dimensional histogram, where the axes correspond to the $p+\pi^-$ invariant mass of the respective $\Lambda$ candidate. %The same strategy was employed on the experimental data to build a $\Lambda$-$\Lambda$ 2D correlation matrix. The \sloppy{$\Lambda$-$\Lambda$ signal} is determined using a Statistical sideband analysis (SSB) and a Linear least squares (LLS) fit.The inclusive selection provides the most significant $\Lambda$-$\Lambda$ signal.Cross-section values corresponding to the two analyses are calculated as weighted average of the result of the three selections.The production cross-section for $\Lambda$-$\Lambda$ in $pp$ collisions at $\sqrt{s}=3.46$ GeV is measured \sloppy{to be $59\pm27$ nb} (one standard deviation uncertainity).
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| 3. |
- dos Santos Matias, Lucilio, et al.
(author)
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Characterization of the radiation field surrounding the Leksell Gamma Knife® and shielding applications
- 2023
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In: Applied Radiation and Isotopes. - 0969-8043 .- 1872-9800. ; 198
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Journal article (peer-reviewed)abstract
- The aim of this study is to improve the characterization and modeling of the radiation field surrounding the Leksell Gamma Knife®-PerfexionTM. The improved characterization of the radiation field enables more accurate shielding calculations to be performed for the areas adjacent to the treatment room. With the aid of a high-purity germanium detector and a satellite dose rate meter, ?-ray spectra and ambient dose equivalent H*(10) data were acquired at various locations in the field of a Leksell Gamma Knife unit in a treatment room at Karolinska University Hospital, Sweden. These measurements were used to validate the results of the PEGASOS Monte Carlo simulation system with a PENELOPE kernel. The levels of the radiation that passes through the shielding of the machine (leakage radiation) are shown to be much lower than what is suggested by various bodies, e.g. the National Council on Radiation Protection and Measurements, to be used when calculating radiation shielding barriers. The results clearly indicate that Monte Carlo simulations may be used in structural shielding design calculations for γ? rays from the Leksell Gamma Knife.
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| 4. |
- Ertoprak, Aysegul, et al.
(author)
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Evidence for octupole collectivity in 172Pt
- 2020
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In: European Physical Journal A. - : Springer. - 1434-6001 .- 1434-601X. ; 56:2
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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.
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| 5. |
- Ertoprak, A., et al.
(author)
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Lifetimes of core-excited states in semi-magic Rh-95
- 2020
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In: European Physical Journal A. - : SPRINGER. - 1434-6001 .- 1434-601X. ; 56:11
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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.
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| 6. |
- Liu, X., et al.
(author)
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Evidence for enhanced neutron-proton correlations from the levelstructure of the N= Z+ 1 nucleus 8743Tc44
- 2021
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In: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 104:2
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Journal article (peer-reviewed)abstract
- The low-lying excited states in the neutron-deficient N = Z + 1 nucleus (87)(43)Tcc(44) have been studied via the fusion-evaporation reaction Fe-54(Ar-36, 2n1p)Tc-87 at the Grand Accelerateur National d'Ions Lourds (GANIL), France. The AGATA spectrometer was used in conjunction with the auxiliary NEDA, Neutron Wall, and DIAMANT detector arrays to measure coincident prompt gamma rays, neutrons, and charged particles emitted in the reaction. A level scheme of Tc-87 from the (9/2(g.s.)(+)) state to the (33/2(1)(+)) state was established based on six mutually coincident gamma-ray transitions. The constructed level structure exhibits a rotational behavior with a sharp backbending at (h) over bar omega approximate to 0.50 MeV. A decrease in alignment frequency and increase in alignment sharpness in the odd-mass isotonic chains around N = 44 is proposed as an effect of the enhanced isoscalar neutron-proton interactions in odd-mass nuclei when approaching the N = Z line.
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| 7. |
- Liu, Xiaoyu, et al.
(author)
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Evidence for spherical-oblate shape coexistence in Tc-87
- 2022
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In: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 106:3
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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.
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| 8. |
- Mistry, A. K., et al.
(author)
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The DESPEC setup for GSI and FAIR
- 2022
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In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 1033, s. 166662-
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Journal article (peer-reviewed)abstract
- The DEcay SPECtroscopy (DESPEC) setup for nuclear structure investigations was developed and commissioned at GSI, Germany in preparation for a full campaign of experiments at the FRS and Super-FRS. In this paper, we report on the first employment of the setup in the hybrid configuration with the AIDA implanter coupled to the FATIMA LaBr3(Ce) fast-timing array, and high-purity germanium detectors. Initial results are shown from the first experiments carried out with the setup. An overview of the setup and function is discussed, including technical advancements along the path.
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| 9. |
- Perez-Vidal, R. M., et al.
(author)
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Evidence of Partial Seniority Conservation in the pi g9/2 Shell for the N=50 Isotones
- 2022
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In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 129:11
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Journal article (peer-reviewed)abstract
- The reduced transition probabilities for the 4+1 -2+1 and 2+1 -0+1 transitions in 92Mo and 94Ru and for the 4+1 -2+1 and 6+1 -4+1 transitions in 90Zr have been determined in this experiment making use of a multinucleon transfer reaction. These results have been interpreted on the basis of realistic shell-model calculations in the f5=2, p3=2, p1=2, and g9=2 proton valence space. Only the combination of extensive lifetime information and large scale shell-model calculations allowed the extent of the seniority conservation in the N = 50 g9=2 orbital to be understood. The conclusion is that seniority is largely conserved in the first 71g9=2 orbital.
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| 10. |
- Polettini, M., et al.
(author)
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Decay studies in the A∼225 Po-Fr region from the DESPEC campaign at GSI in 2021
- 2022
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In: Il Nuovo Cimento. - : Società Italiana di Fisica. - 2037-4909. ; 45:5
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Journal article (peer-reviewed)abstract
- The HISPEC-DESPEC collaboration aims at investigating the structure of exotic nuclei formed in fragmentation reactions with decay spectroscopy measurements, as part of the FAIR Phase-0 campaign at GSI. This paper reports on first results of an experiment performed in spring 2021, with a focus on beta-decaystudies in the Po-Fr nuclei in the 220 < A <230 island of octupole deformation exploiting the DESPEC setup. Ion-beta correlations and fast-timing techniques are being employed, giving an insight into this difficult-to-reach region.
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