| 1. |
- Aktas, Özge
(författare)
-
Gamma-ray Spectroscopy ofNeutron-rich 111 Mo, 85,87 Ge andSelf-Conjugate 88 Ru Far From Stability
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The neutron-deficient self-conjugate (N=Z) nucleus 8844 Ru 44 was populatedvia the heavy ion fusion evaporation reaction 54 Fe( 36 Ar, 2n) 88 Ru in an ex-periment performed at the GANIL accelerator laboratory in France. Usingthe AGATA γ-ray spectrometer together with ancillary detectors, promptγ − γ − 2n coincidence and charge particle anticoincidence analysis was per-formed for the low-lying energy spectrum of 88 Ru. The results confirm thepreviously assigned γ-ray cascade and extend it to the 14 + level. The levelscheme is consistent with a deformed rotational system. However, the rota-tional frequency of the alignment of the valence nucleons has a significantlyhigher value than what is predicted by theoretical calculations performedwithout isoscalar neutron-proton pairing. By including isoscalar pairing, anagrement is obtained with the experimentally observed delayed rotationalalignment.Excited states in the neutron-rich nuclei 109 Mo and 111 Mo were studiedfollowing nucleon knock-out reactions. Seven γ-ray transitions, some of themin prompt mutual coincidence, were identified for the first time in 111 Mo usingthe DALI2 and MINOS detector systems at the BigRIPS and ZeroDegree elec-tromagnetic fragment separator at the RIBF, RIKEN, Japan. Total Routhiansurface (TRS) and Particle-Plus-Rotor calculations have been performed toinvestigate the predicted shape coexistence and its effect on the structure ofnuclei in this region of the nuclear chart. Following the results of the calcula-tions, theoretical level schemes are proposed for positive and negative paritystates and compared with the experimental findings.Gamma-ray transitions have been identified for the first time in the ex-tremely neutron-rich (N = Z + 25) nucleus 87 Ge following nucleon knockoutreactions studied at the RIBF, RIKEN, Japan. Previously unknown γ-raytransitions between excited states in 85 Ge were also observed and placed ina tentative level scheme. The results are compared with large-scale shell-model calculations and potential energy surface calculations based on thetotal Routhian surface formalism. The neutron-rich titanium isotopes havebeen studied, and preliminary results are presented in this work. For the odd-even 57,59,61 Ti isotopes several gamma-ray transitions has been identified forthe first time. For the even-even isotopes 56,58,60 Ti the previously knowndecays from 2 + and 4 + spin-parity states, are confirmed with the currentpreliminary analysis.
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| 2. |
- Barucca, G., et al.
(författare)
-
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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| 3. |
- Barucca, G., et al.
(författare)
-
PANDA Phase One
- 2021
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Ingår i: European Physical Journal A. - : Springer Nature. - 1434-6001 .- 1434-601X. ; 57:6
-
Tidskriftsartikel (refereegranskat)abstract
- The Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, provides unique possibilities for a new generation of hadron-, nuclear- and atomic physics experiments. The future antiProton ANnihilations at DArmstadt (PANDA or PANDA) experiment at FAIR will offer a broad physics programme, covering different aspects of the strong interaction. Understanding the latter in the non-perturbative regime remains one of the greatest challenges in contemporary physics. The antiproton-nucleon interaction studied with PANDA provides crucial tests in this area. Furthermore, the high-intensity, low-energy domain of PANDA allows for searches for physics beyond the Standard Model, e.g. through high precision symmetry tests. This paper takes into account a staged approach for the detector setup and for the delivered luminosity from the accelerator. The available detector setup at the time of the delivery of the first antiproton beams in the HESR storage ring is referred to as the Phase One setup. The physics programme that is achievable during Phase One is outlined in this paper.
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| 4. |
- Barucca, G., et al.
(författare)
-
Study of excited Ξ baryons with the P¯ ANDA detector
- 2021
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Ingår i: European Physical Journal A. - : Springer Nature. - 1434-6001 .- 1434-601X. ; 57:4
-
Tidskriftsartikel (refereegranskat)abstract
- The study of baryon excitation spectra provides insight into the inner structure of baryons. So far, most of the world-wide efforts have been directed towards N∗ and Δ spectroscopy. Nevertheless, the study of the double and triple strange baryon spectrum provides independent information to the N∗ and Δ spectra. The future antiproton experiment P¯ANDA will provide direct access to final states containing a Ξ¯ Ξ pair, for which production cross sections up to μb are expected in p¯p reactions. With a luminosity of L= 10 31 cm- 2 s- 1 in the first phase of the experiment, the expected cross sections correspond to a production rate of ∼106events/day. With a nearly 4 π detector acceptance, P¯ANDA will thus be a hyperon factory. In this study, reactions of the type p¯p → Ξ¯ +Ξ∗ - as well as p¯p → Ξ¯ ∗ +Ξ- with various decay modes are investigated. For the exclusive reconstruction of the signal events a full decay tree fit is used, resulting in reconstruction efficiencies between 3 and 5%. This allows high statistics data to be collected within a few weeks of data taking.
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| 5. |
- Barucca, G., et al.
(författare)
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The potential of Λ and Ξ- studies with PANDA at FAIR
- 2021
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Ingår i: European Physical Journal A. - : Springer Nature. - 1434-6001 .- 1434-601X. ; 57:4
-
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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| 6. |
- Bradbury, J., et al.
(författare)
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Lifetime measurements using a plunger device and the EUCLIDES Si array at the GALILEO gamma-ray spectrometer
- 2020
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 979
-
Tidskriftsartikel (refereegranskat)abstract
- The GALILEO gamma-ray spectrometer, installed at the Laboratori Nazionali di Legnaro (LNL), benefits from intense stable beams provided by the Tandem-ALPI-PIAVE accelerator complex and from radioactive beams to be delivered in the near future by the SPES facility. The spectrometer is complemented with a variety of ancillary devices to allow for nuclear structure and reaction studies. The 4 pi Si-ball array EUCLIDES coupled to the GALILEO gamma-ray spectrometer represents one of the commonly used setup for experiments aiming at spectroscopic studies. High-efficiency detection of light-charged particles in a fusion-evaporation reaction guarantees good discrimination of different reaction channels and provides essential information for the kinematic reconstruction. In this paper we discuss a configuration of the EUCLIDES array developed for the lifetime measurements of nuclear excited states populated in a fusion-evaporation reaction. In such a configuration a part of the EUCLIDES detectors is disassembled allowing for the installation of a plunger device in the reaction chamber. The reduced configuration of EUCLIDES provides high detection efficiency necessary for reliable light charged-particle discrimination. We report on the commissioning experiment focused on the Ni-58(Ni-58,3p)I-113 reaction. The lifetimes of 11/2(-) and 15/2(-) states were measured by applying the Recoil Distance Doppler Shift method to be equal to 206(20) ps and 7.9(12) ps correspondingly and were in good agreement with the values cited in the literature. Thus, the combination of the GALILEO and EUCLIDES arrays, and the plunger device has resulted in a powerful experimental setup to determine lifetimes of excited states in neutron-deficient nuclei in the picosecond range.
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| 7. |
- Cederwall, Bo, 1964-
(författare)
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A novel 3D-imaging and characterisation technique for special nuclear materials in radioactive waste
- 2023
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Ingår i: EPJ NUCLEAR SCIENCES & TECHNOLOGIES. - : EDP Sciences. - 2491-9292. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- A novel technique for non-destructive assay (NDA) of radioactive waste called ARCTERIX (Advanced Radwaste Characterisation based on Tomographically Enhanced Radiation Imaging without X-rays) is presented. The concept is based on a 3D-tomographic imaging technique for special nuclear materials - neutron-gamma emission tomography (NGET). ARCTERIX takes the NGET principle from its original application area of nuclear security systems into the realm of radioactive waste assay with its special characteristics and challenges. By adding localisation and imaging of SNM inside shielded waste containers to the array of existing techniques used for radioactive waste characterisation, ARCTERIX complements the state of the art in passive and active NDA interrogation methods. It is aimed primarily at the class of mixed, long-lived radioactive waste that is commonly called "legacy" or "historic" waste which has special safety, security and safeguards concerns due to its mixed composition, commonly poor documentation, and the frequent presence of SNM. The ARCTERIX concept provides rapid imaging and characterisation of nuclear materials in radioactive waste with a high degree of automation and high throughput capabilities, making it possible to quickly scan large radioactive waste inventories for the presence of special nuclear materials with minimal manual intervention. The first ARCTERIX prototype system has demonstrated a high technological readiness for the implementation of the technique in a commercial stand-alone system for rapid assessment of radioactive waste drums or in a system operating in conjunction with established techniques.
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| 8. |
- 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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| 9. |
- Chishti, M.M.R., et al.
(författare)
-
Response of the FAst TIMing Array (FATIMA) for DESPEC at FAIR Phase-0
- 2023
-
Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier B.V.. - 0168-9002 .- 1872-9576. ; 1056
-
Tidskriftsartikel (refereegranskat)abstract
- The Monte-Carlo simulated response for γ-ray detection of the FAst TIMing Array (FATIMA) for exploitation within the DEcay SPECtroscopy (DESPEC) experimental system at the FAIR Phase-0 facility at Darmstadt, Germany is presented. In this configuration, FATIMA consisted of 36 LaBr3(Ce) detectors surrounding the AIDA, position-sensitive charged-particle active stopper. The decay of the Iπ=8+ isomer-fed decay cascade in 96Pd, measured in the first DESPEC experiment at the FAIR-0 facility was used to validate the simulations. The experimental data yielded in-situ full-energy peak efficiency values for FATIMA of 11.2(11)%, 6.8(7)%, 3.8(4)% and 2.1(4)% at 106, 325, 684 and 1415 keV respectively, consistent with the values derived from the simulated response.
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| 10. |
- Ciemala, M., et al.
(författare)
-
Testing ab initio nuclear structure in neutron-rich nuclei : Lifetime measurements of second 2(+) state in C-16 and O-20
- 2020
-
Ingår i: Physical Review C. - : AMER PHYSICAL SOC. - 2469-9985 .- 2469-9993. ; 101:2
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Tidskriftsartikel (refereegranskat)abstract
- To test the predictive power of ab initio nuclear structure theory, the lifetime of the second 2(+) state in neutron-rich O-20, tau(2(2)(+)) = 150(-30)(+80) fs, and an estimate for the lifetime of the second 2(+) state in C-16 have been obtained for the first time. The results were achieved via a novel Monte Carlo technique that allowed us to measure nuclear state lifetimes in the tens-to-hundreds of femtoseconds range by analyzing the Doppler-shifted gamma-transition line shapes of products of low-energy transfer and deep-inelastic processes in the reaction O-18 (7.0 MeV/u) + Ta-181. The requested sensitivity could only be reached owing to the excellent performances of the Advanced gamma-Tracking Array AGATA, coupled to the PARIS scintillator array and to the VAMOS++ magnetic spectrometer. The experimental lifetimes agree with predictions of ab initio calculations using two- and three-nucleon interactions, obtained with the valence-space in-medium similarity renormalization group for O-20 and with the no-core shell model for C-16. The present measurement shows the power of electromagnetic observables, determined with high-precision gamma spectroscopy, to assess the quality of first-principles nuclear structure calculations, complementing common benchmarks based on nuclear energies. The proposed experimental approach will be essential for short lifetime measurements in unexplored regions of the nuclear chart, including r-process nuclei, when intense beams, produced by Isotope Separation On-Line (ISOL) techniques, become available.
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| 11. |
- Clement, E., et al.
(författare)
-
Spectroscopic quadrupole moments in 124Xe
- 2023
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Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 107:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: The Xe isotopic chain with four valence protons above the Z = 50 shell closure is an ideal laboratory for the study of the evolution of nuclear deformation. At the N = 82 shell closure, 136Xe presents all characteristics of a doubly closed shell nucleus with a spherical shape. In the very neutron-deficient isotopes close to N = 50, the alpha-decay chain of Xe was investigated to probe the radioactive decay properties near the drip-line and the magicity of 100Sn. Additionally, the Xe isotopes present higher order symmetries in the nuclear deformation such as the octupole degree of freedom near N = 60 and N = 90 or O(6) symmetry in stable isotopes.Purpose: The relevance of the O(6) symmetry has been investigated by measuring the spectroscopic quadrupole moment of the first excited states in 124Xe. In the O(6) symmetry limit, the spectroscopic quadrupole moment of collective states is expected to be null.Method: A stable 124Xe beam with energies of 4.03A MeV and 4.11A MeV was used to bombard a natW target at the GANIL facility. Excited states were populated via the safe Coulomb excitation reaction. The collision of the heavy ions with a large Z at low energy make this reaction sensitive to the diagonal E2 matrix element of the excited states. The recoils were detected in the VAMOS++ magnetic spectrometer and the gamma rays in the AGATA tracking array. The least squares fitting code GOSIA was used for the analysis to extract both E2 and M1 transitional and E2 diagonal matrix elements.Results: The rotational ground state band was populated up to the 8+1 state as well as the 2+2 and 4+2 states. Using high precision spectroscopic data to constrain the GOSIA fit, the spectroscopic quadrupole moments of the 2+1 , 4+1 , and 6+1 states were determined for the first time.Conclusions: The spectroscopic quadrupole moments were found to be negative, large, and constant in the ground state band underlining the prolate axially deformed ground state band of 124Xe. The present experimental data confirm that the is broken in 124Xe.
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| 12. |
- Das, Biswarup, et al.
(författare)
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Broken seniority symmetry in the semimagic proton mid-shell nucleus Rh 95
- 2024
-
Ingår i: Physical Review Research. - : American Physical Society (APS). - 2643-1564. ; 6:2
-
Tidskriftsartikel (refereegranskat)abstract
- Lifetime measurements of low-lying excited states in the semimagic (N=50) nucleus Rh95 have been performed by means of the fast-timing technique. The experiment was carried out using γ-ray detector arrays consisting of LaBr3(Ce) scintillators and germanium detectors integrated into the DESPEC experimental setup commissioned for the Facility for Antiproton and Ion Research (fair) Phase-0, Darmstadt, Germany. The excited states in Rh95 were populated primarily via the β decays of Pd95 nuclei, produced in the projectile fragmentation of a 850 MeV/nucleon Xe124 beam impinging on a 4g/cm2Be9 target. The deduced electromagnetic E2 transition strengths for the γ-ray cascade within the multiplet structure depopulating from the isomeric Iπ=21/2+ state are found to exhibit strong deviations from predictions of standard shell model calculations which feature approximately conserved seniority symmetry. In particular, the observation of a strongly suppressed E2 strength for the 13/2+→9/2+ ground state transition cannot be explained by calculations employing standard interactions. This remarkable result may require revision of the nucleon-nucleon interactions employed in state-of-the-art theoretical model calculations, and might also point to the need for including three-body forces in the Hamiltonian.
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| 13. |
- Davi, F., et al.
(författare)
-
Technical design report for the endcap disc DIRC
- 2022
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Ingår i: Journal of Physics G. - : Institute of Physics Publishing (IOPP). - 0954-3899 .- 1361-6471. ; 49:12
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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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| 14. |
- de Angelis, G., et al.
(författare)
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AGATA : nuclear structure advancements with fusion-evaporation reactions
- 2023
-
Ingår i: European Physical Journal A. - : Springer Nature. - 1434-6001 .- 1434-601X. ; 59:7
-
Tidskriftsartikel (refereegranskat)abstract
- Nuclear-structure studies using fusion reactions are reviewed in terms of prospects for advancement using the next generation of ?-ray tracking arrays such as AGATA. Properties discussed include those of light N = Z nuclei and rotational behaviour in heavy nuclei at high values of angular momentum and internal excitation energy.
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| 15. |
- 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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| 16. |
- Ertoprak, Aysegul, et al.
(författare)
-
Evidence for octupole collectivity in 172Pt
- 2020
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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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| 17. |
- Ertoprak, Aysegul, 1987-
(författare)
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Experimental Studies of the Neutron Deficient Atomic Nuclei 94Ru, 95Rh and 172Pt via their Electromagnetic Properties : Du som saknar dator/datorvana kan kontakta Pär Olsson, polsson@kth.se för information
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis reports new results obtained from studies of the neutron deficient atomic nuclei 94Ru, 95Rh and 172Pt using two different experimental set-ups. In the first part, lifetimes of highly excited states in nuclei near the N=50 closed-shell (94Ru and 95Rh) were deduced from an analysis of the Doppler broadened transition lineshapes measured following the 58Ni(40Ca,4p) and 58Ni(40Ca,3p) fusion-evaporation reactions at the Grand Accelerateur National d'Ions Lourds (GANIL) accelerator complex situated in Caen, France. Doppler Shift Attenuation Method (DSAM) lifetime analysis was performed on the Doppler broadened peaks in energy spectra from γ-rays emitted from excited states in the nuclei of interest while they were slowing down in a thick 6 mg/cm2 metallic 58Ni target. For 94Ru, eight excited-state lifetimes in the angular momentum range I= (13-20)h have been measured in total, five of which were determined for the first time. For the lifetime analysis of 95Rh, three lifetime values have been obtained. One of them, the lifetime of the 39/21- excited state, has been measured for the first time. In the other cases, the lifetimes of the previously measured 29/22- and 37/21- excited states have been obtained. The corresponding B(M1) and B(E2) reduced transition strengths have been deduced and are discussed within the framework of large-scale shell model (LSSM) calculations. In the second part, the extremely neutron deficient 172Pt nucleus has been studied. Excited states in 172Pt were populated using the 96Ru(78Kr,2p) and 92Mo(83Kr,3n) reactions at the Accelerator Laboratory of the University of Jyväskylä (JYFL), Finland. Prompt γ-rays were detected using the JUROGAM high-purity germanium detector array at the target position while the identification and decay spectroscopy of 172Pt was performed using the RITU gas-filled separator in conjunction with the GREAT spectrometer. The Recoil Decay Tagging (RDT) technique was used for the selection of prompt γ-rays. The known positive-parity band has been extended and the negative-parity structure has been established on top of the lowest member of the negative parity band which has now been firmly assigned as spin-parity 3-. Moreover, the newly observed E3 transition provides a link between the negative parity band with the ground state. The observations of this E3 transition together with several E1 transitions connecting the negative-parity structure with the ground-state band is consistent with the presence of octupole collectivity in 172Pt. Furthermore, this is the first observation of an E3 transition connecting the negative parity band with the ground-state band in the Pt-Os-W region. The experimental results were interpreted in terms of LSSM and total routhian surface calculations. With the support of these theoretical calculations, evidence for octupole collectivity in 172Pt is proposed.
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| 18. |
- Ertoprak, A., et al.
(författare)
-
Lifetimes of core-excited states in semi-magic Rh-95
- 2020
-
Ingår i: European Physical Journal A. - : SPRINGER. - 1434-6001 .- 1434-601X. ; 56:11
-
Tidskriftsartikel (refereegranskat)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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| 19. |
- Fougeres, Chloe, et al.
(författare)
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Search for Na-22 in novae supported by a novel method for measuring femtosecond nuclear lifetimes
- 2023
-
Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- Classical novae are thermonuclear explosions in stellar binary systems, and important sources of Al-26 and Na-22. While ? rays from the decay of the former radioisotope have been observed throughout the Galaxy, Na-22 remains untraceable. Its half-life (2.6 yr) would allow the observation of its 1.275 MeV ?-ray line from a cosmic source. However, the prediction of such an observation requires good knowledge of its nucleosynthesis. The Na-22(p, ?)Mg-23 reaction remains the only source of large uncertainty about the amount of Na-22 ejected. Its rate is dominated by a single resonance on the short-lived state at 7785.0(7) keV in Mg-23. Here, we propose a combined analysis of particle-particle correlations and velocity-difference profiles to measure femtosecond nuclear lifetimes. The application of this method to the study of the Mg-23 states, places strong limits on the amount of Na-22 produced in novae and constrains its detectability with future space-borne observatories. The authors report a particle-particle correlation and velocity-difference profile method to measure nuclear lifetime. The results obtained for excited states of 23Mg are used to constrain the production of 22Na in the astrophysical novae explosions.
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| 20. |
- Girard-Alcindor, V., et al.
(författare)
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New narrow resonances observed in the unbound nucleus F 15
- 2022
-
Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 105:5
-
Tidskriftsartikel (refereegranskat)abstract
- The structure of the unbound F15 nucleus is investigated using the inverse kinematics resonant scattering of a radioactive O14 beam impinging on a CH2 target. The analysis of H1(O14,p)O14 and H1(O14,2p)N13 reactions allowed the confirmation of the previously observed narrow 1/2- resonance, near the two-proton decay threshold, and the identification of two new narrow 5/2- and 3/2- resonances. The newly observed levels decay by 1p emission to the ground of O14, and by sequential 2p emission to the ground state of N13 via the 1- resonance of O14. Gamow shell model (GSM) analysis of the experimental data suggests that the wave functions of the 5/2- and 3/2- resonances may be collectivized by the continuum coupling to nearby 2p- and 1p-decay channels. The observed excitation function H1(O14,p)O14 and resonance spectrum in F15 are well reproduced in the unified framework of the GSM.
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| 21. |
- Gorska, M., et al.
(författare)
-
Nuclear structure aspects of the heaviest N similar to Z nuclei south of Sn-100
- 2023
-
Ingår i: 13TH INTERNATIONAL SPRING SEMINAR ON NUCLEAR PHYSICS PERSPECTIVES AND CHALLENGES IN NUCLEAR STRUCTURE AFTER 70 YEARS OF SHELL MODEL, ISS 2022. - : IOP Publishing.
-
Konferensbidrag (refereegranskat)abstract
- Ever-lasting interest in the structure of Sn-100 and neighbouring nuclei is still well justified by the fact that it is the heaviest doubly-magic nucleus with N=Z. State-of-the-art experimental techniques involving stable and radioactive beam facilities have enabled access to these exotic nuclei. In particular, the analysis of experimental data obtained in two DESPEC experiments at GSI Darmstadt extends the information on the shell structure and its evolution towards N = Z = 50, and allows the study of seniority conservation and proton-neutron interaction in the g(9/2) orbit. Several theoretical approaches for shell-model investigations are discussed and their predictive power assessed. The calculated systematics of the reduced transition probabilities for high- to medium-spin states in N similar to Z isotopes with active g(9/2) orbit is presented for the first time.
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| 22. |
- Guo, S., et al.
(författare)
-
Evidence for pseudospin-chiral quartet bands in the presence of octupole correlations
- 2020
-
Ingår i: Physics Letters B. - : ELSEVIER. - 0370-2693 .- 1873-2445. ; 807
-
Tidskriftsartikel (refereegranskat)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.
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| 23. |
- Guo, S., et al.
(författare)
-
Pseudospin partner bands in Ba-130
- 2020
-
Ingår i: Physical Review C. Nuclear Physics. - : American Physical Society (APS). - 0556-2813 .- 1089-490X. ; 102:4
-
Tidskriftsartikel (refereegranskat)abstract
- The high-spin states in Ba-130 have been investigated using the Sn-122(C-13, 5n) reaction and the GALILEO array coupled to the EUCLIDES and Neutron Wall ancillary detectors. The level scheme has been extended to an excitation energy of approximate to 12 MeV and spin 28. Two sets of pseudospin partner bands have been identified built on pi h(11/2)(g(7/2), d(5/2)) and nu h(11/2)(S-1/2, d(3/2)) configurations. The assignments are supported by calculations using the projected shell model and the particle rotor model.
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| 24. |
- Jazrawi, S., et al.
(författare)
-
Commissioning the FAst TIMing array (FATIMA) at FAIR Phase-0 : Half-lives of excited states in the N=50 isotones 96Pd and 94Ru
- 2022
-
Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 200
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reports results of the first experiment of the DESPEC Phase-0 campaign at GSI, which focused on the study of neutron-deficient nuclei approaching 100Sn. These data provide the first extended commissioning experiment for the DESPEC collaboration within NuSTAR. We present results on electromagnetic transition rates associated with the decays from excited states populated following the formation of I pi = 8+ proton 'seniority -isomer' states in the N = 50 isotones 94Ru and 96Pd. Direct half-life measurements via gamma-gamma coincidences using the FATIMA detector array consisting of 36 LaBr3(Ce) scintillators have determined the reduced matrix elements associated with decays between low-lying states in these semi-magic nuclei. The extracted half-lives for yrast I pi = 6+ and 4+ states in 96Pd and the 6+ state in 94Ru are consistent with the published, highest-precision values for these nuclei.
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| 25. |
- Korten, W., et al.
(författare)
-
Physics opportunities with the Advanced Gamma Tracking Array : AGATA
- 2020
-
Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 56:5
-
Forskningsöversikt (refereegranskat)abstract
- New physics opportunities are opening up by the Advanced Gamma Tracking Array, AGATA, as it evolves to the full 4 pi instrument. AGATA is a high-resolution gamma -ray spectrometer, solely built from highly segmented high-purity Ge detectors, capable of measuring gamma rays from a few tens of keV to beyond 10 MeV, with unprecedented efficiency, excellent position resolution for individual gamma -ray interactions, and very high count-rate capability. As a travelling detector AGATA will be employed at all major current and near-future European research facilities delivering stable and radioactive ion beams.
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| 26. |
- Liu, X., et al.
(författare)
-
Evidence for enhanced neutron-proton correlations from the levelstructure of the N= Z+ 1 nucleus 8743Tc44
- 2021
-
Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 104:2
-
Tidskriftsartikel (refereegranskat)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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| 27. |
- Liu, Xiaoyu, et al.
(författare)
-
Evidence for spherical-oblate shape coexistence in Tc-87
- 2022
-
Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 106:3
-
Tidskriftsartikel (refereegranskat)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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| 28. |
- Liu, Xiaoyu
(författare)
-
Experimental Studies of the Neutron Deficient Atomic Nuclei 88Ru and 87Tc, and the Diagonalization of the General Pairing Hamiltonian
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This doctoral thesis consists of two parts: the experimental study of the neutron-deficient atomic nuclei 88Ru and 87Tc, and the computational study on the diagonalization of general pairing Hamiltonian. In the first part, which constitutes the main content of the thesis, the low-lying excited states in the N = Z nucleus 88Ru and N = Z + 1 nucleus 87Tc were studied via fusion-evaporation reactions induced by 115 MeV 36 Ar ions bombarding6 mg/cm 2 thick metallic 54 Fe target foils at the Grand Accélérateur Nationald’Ions Lourds (GANIL), Caen, France. The prompt γγ-neutron and charged-particle coincidences from the de-excitation of the reactions were measured by the AGATA γ-ray spectrometer coupled to the auxiliary NEDA, Neutron Wall, and DIAMANT detector arrays. The results for 88 Ru confirmed and extended the previous level scheme to a tentative (14+) state. The constructed level structure exhibits a moderately deformed rotational behavior but shows a band crossing at a significantly higher rotational frequency compared with neighboring nuclei with N > Z. Such band crossings are associated with quasiparticle alignment within the standard isovector pairing scheme. The observation of a “delayed” rotation alignment in the deformed N = Znucleus is consistent with theoretical predictions related to the existence of strong isoscalar neutron-proton pair condensate. The yrast band in 87 Tc from the (9/2+) state to the (33/2+) state was established based on six mutually coincident γ-ray transitions. The constructed yrast band exhibits a sharp backbending at ~ω ≈ 0.50 MeV. In the odd-A isotonic chains around N = 44, approaching the N = Z line, the observed decrease in alignment frequency and increase in alignment sharpness were proposed as an effect of the enhanced isoscalar neutron-proton interactions. In addition to the yrast band in 87 Tc, six new mutually coincident γ-ray transitions were identified by comparing the γ-ray intensities in the spectra gated under different reaction channel selection conditions. The constructed level scheme was compared with shell model and TRS calculations. The results indicate that these low-lying states exhibit spherical behavior different from the previously identified oblate yrast band, and the band might be built on a (7/2 +1 ) ground state.In the second part, an OpenMP parallel Fortran program, PairDiag, for the diagonalization of the general pairing Hamiltonian in deformed systems was developed. In the program, the ‘01’ inversion algorithm is used to generate the seniority-zero basis vectors; all the non-zero Hamiltonian matrix elements are evaluated “on the fly” by the scattering operators and a search algorithm; the matrix diagonalization is achieved by the Lanczos + QR algorithm. The PairDiag program is packaged in a Fortran module and can be easily used to replace the BCS approximation in other nuclear structure programs.
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| 29. |
- Llewellyn, R. D. O., et al.
(författare)
-
Establishing the Maximum Collectivity in Highly Deformed N = Z Nuclei
- 2020
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 124:15
-
Tidskriftsartikel (refereegranskat)abstract
- The lifetimes of the first excited 2(+) states in the N = Z nuclei Zr-80, Y-78, and Sr-76 have been measured using the gamma-ray line shape method following population via nucleon-knockout reactions from intermediate-energy rare-isotope beams. The extracted reduced electromagnetic transition strengths yield new information on where the collectivity is maximized and provide evidence for a significant, and as yet unexplained, odd-odd vs even-even staggering in the observed values. The experimental results are analyzed in the context of state-of-the-art nuclear density-functional model calculations.
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| 30. |
- Llewellyn, R. D. O., et al.
(författare)
-
Spectroscopy of proton-rich Zr-79 : Mirror energy differences in the highly-deformed fpg shell
- 2020
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 811
-
Tidskriftsartikel (refereegranskat)abstract
- Energy differences between isobaric analogue states have been extracted for the A = 79, Zr-79/Y-79 mirror pair following their population via nucleon-knockout reactions from intermediate-energy rare-isotope beams. These are the heaviest nuclei where such measurements have been made to date. The deduced mirror energy differences (MED) are compared with predictions from a new density-functional based approach, incorporating isospin-breaking effects of both Coulomb and nuclear charge-symmetry breaking and configuration mixing.
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| 31. |
- Lv, B. F., et al.
(författare)
-
Evidence against the wobbling nature of low-spin bands in 135Pr
- 2022
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 824
-
Tidskriftsartikel (refereegranskat)abstract
- The electromagnetic character of the ΔI=1 transitions connecting the 1- to 0-phonon and the 2- to 1-phonon wobbling bands should be dominated by an E2 component, due to the collective motion of the entire nuclear charge. In the present work it is shown, based on combined angular correlation and linear polarization measurements, that the mixing ratios of all analyzed connecting transitions between low-lying bands in 135Pr interpreted as 0-, 1-, and 2-phonon wobbling bands, have absolute values smaller than one. This indicates predominant M1 magnetic character, which is incompatible with the proposed wobbling nature. All experimental observables are instead in good agreement with quasiparticle-plus-triaxial-rotor model calculations, which describe the bands as resulting from a rapid re-alignment of the total angular momentum from the short to the intermediate nuclear axis.
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| 32. |
- Lv, B. F., et al.
(författare)
-
Experimental evidence for transverse wobbling bands in Nd-136
- 2022
-
Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 105:3
-
Tidskriftsartikel (refereegranskat)abstract
- The nature of two high-spin bands in Nd-136 built on the two-quasiparticle configuration pi h(11/2)(2), predicted by the triaxial projected shell model as good candidates of transverse wobbling bands, are investigated experimentally. The mixing ratio of one Lambda I = 1 transition connecting the one-phonon and the zero-phonon wobbling bands is established from a high-statistics JuroGam II gamma-ray spectroscopy experiment by using the combined angular correlation and linear polarization method. The resulting wobbling excitation energy and ratios of reduced electromagnetic transition probabilities are in good agreement with results of a new particle-rotor model which rigidly couples the total angular momentum of two quasiparticles to a triaxial core in an orthogonal geometry, confirming thus the transverse wobbling nature of the bands.
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| 33. |
- Lv, B. F., et al.
(författare)
-
Refined description of the positive-parity bands and the extent of octupole correlations in Ba-120
- 2022
-
Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 105:4
-
Tidskriftsartikel (refereegranskat)abstract
- Three new negative-parity bands have been identified in 120Ba, two of them forming a strongly coupled band. The previously known negative-parity band is significantly extended to high spin, while the lower part of the yrare positive-parity band has been modified. From the analysis of the band properties and comparison with the neighboring nuclei a coherent description of all bands is achieved. In particular, a simple explanation of the evolution of the positive-parity bands at high spin is proposed, including the possible occupation of the ??f7/2[541]1/2??? intruder orbital. Cranked Nilsson-Strutinsky calculations reveal similar quadrupole deformations but different triaxiality of the bands, while particle number conserving cranked shell model calculations qualitatively reproduce the experimental data and support the assigned configurations. The new measured ratios of reduced transition probabilities B(E1)/B(E2) complete the systematics in the 118???124Ba nuclei, exhibiting a decrease with decreasing neutron number, and are compared with the known values in the 116???120Xe nuclei, which are larger. Extended calculations with the quadrupole and octupole collective Hamiltonian based on the relativistic Hartree-Bogoliubov model employing the relativistic DD-PC1 density functional nicely reproduce the decreasing trend towards lower neutron numbers for Ba and Xe nuclei, as well as the larger values in Xe nuclei, but are much larger in amplitude than the experimental values. On the other hand, particle number conserving cranked shell model calculations without octupole deformation overestimate the low-spin values, while those with octupole deformation included reproduce the experimental values in 120Ba, suggesting the possible existence of moderate octupole collectivity in the negative-parity bands of nuclei in this mass region.
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| 34. |
- Lv, B. F., et al.
(författare)
-
Tilted precession bands in Nd 135
- 2021
-
Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 103:4
-
Tidskriftsartikel (refereegranskat)abstract
- Two new excited bands built on the πh11/2 configuration have been identified in Nd135 in addition to the known πh11/2 band. The energy spectra of the excited bands and the available electromagnetic transition probabilities are in good agreement with theoretical results obtained using quasiparticle-plus-triaxial-rotor model calculations. The properties of the bands identify them as tilted precession bands instead of wobbling bands. Our results give a new insight into the interpretation of the low-lying bands in odd-A mass nuclei, and can stimulate future studies to address the nuclear triaxiality.
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| 35. |
- Mistry, A. K., et al.
(författare)
-
The DESPEC setup for GSI and FAIR
- 2022
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 1033, s. 166662-
-
Tidskriftsartikel (refereegranskat)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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| 36. |
- Pasqualato, G., et al.
(författare)
-
Shape evolution in even-mass 98-104Zr isotopes via lifetime measurements using the γ γ-coincidence technique
- 2023
-
Ingår i: European Physical Journal A. - : Springer. - 1434-6001 .- 1434-601X. ; 59:11
-
Tidskriftsartikel (refereegranskat)abstract
- The Zirconium (Z = 40) isotopic chain has attracted interest for more than four decades. The abrupt lowering of the energy of the first 2(+) state and the increase in the transition strength B(E2; 2(1)(+) -> 0(1)(+) ) going from Zr-98 to Zr-100 has been the first example of "quantum phase transition" in nuclear shapes, which has few equivalents in the nuclear chart. Although a multitude of experiments have been performed to measure nuclear properties related to nuclear shapes and collectivity in the region, none of the measured lifetimes were obtained using the Recoil Distance Doppler Shift method in the gamma gamma-coincidence mode where a gate on the direct feeding transition of the state of interest allows a strict control of systematical errors. This work reports the results of lifetime measurements for the first yrast excited states in Zr98-104 carried out to extract reduced transition probabilities. The new lifetime values in gamma gamma-coincidence and gamma-single mode are compared with the results of former experiments. Recent predictions of the Interacting Boson Model with Configuration Mixing, the Symmetry Conserving Configuration Mixing model based on the Hartree-Fock- Bogoliubov approach and the Monte Carlo Shell Model are presented and compared with the experimental data.
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| 37. |
- Pereira-López, X., et al.
(författare)
-
In-beam γ -ray spectroscopy of 94 Ag
- 2023
-
Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 59:3
-
Tidskriftsartikel (refereegranskat)abstract
- A recoil-beta-tagging experiment has been performed to study the excited T= 0 and T= 1 states in the odd–odd N= Z nucleus 94Ag, populated via the 40Ca(58Ni,1p3n)94Ag reaction. The experiment was conducted using the MARA recoil separator and JUROGAM3 array at the Accelerator Laboratory of the University of Jyväskylä. Through correlating fast, high-energy beta decays at the MARA focal plane with prompt γ rays emitted at the reaction target, a number of transitions between excited states in 94Ag have been identified. The timing characteristics of these transitions confirm that they fall within decay sequences that feed the short-lived T= 1 ground state of 94Ag. The transitions are proposed to proceed within and between the sets of states with T= 0 and T= 1. Possible correspondence between some of these transitions from analog states in 94Pd has been discussed, and shell-model calculations including multipole and monopole electromagnetic effects have been presented, in order to enable predictions of the decay patterns between the T= 0 and T= 1 states and to allow a theoretical set of Coulomb energy differences to be calculated for the A= 94 T= 1 analog states.
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| 38. |
- Perez-Vidal, R. M., et al.
(författare)
-
Evidence of Partial Seniority Conservation in the pi g9/2 Shell for the N=50 Isotones
- 2022
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 129:11
-
Tidskriftsartikel (refereegranskat)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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| 39. |
- Petrache, C. M., et al.
(författare)
-
High- K three-quasiparticle isomers in the proton-rich nucleus Nd 129
- 2023
-
Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 108:1
-
Tidskriftsartikel (refereegranskat)abstract
- Three three-quasiparticle isomers, one at an excitation energy of 2.3 MeV with T1/2=0.48(4)μs, and two shorter-lived with unknown half-lives at slightly lower energies have been identified in Nd129 using the MARA + JUROGAM 3 setup and the recoil tagging technique. All three isomers present decay patterns characteristic of high-K isomers. The known 6.7 s β-decaying isomer previously assigned to the 5/2+ level is now assigned to the new 7/2- ground state. A new low-spin 5/2+ isomeric state with a half-life of a few tens of nanoseconds has been identified, while a previously known 2.6 s β-decay activity was assigned to the band head of the ν1/2+[411] band. The transitions depopulating the high-K isomers to low-lying states also establish the relative energies of three low-lying one-quasiparticle bands, leading to a new spin-parity assignment of 7/2- to the ground state of Nd129. The partial half-lives of the depopulating transitions suggest spin-parities 21/2+, 19/2+, and 17/2+ for the three high-K isomers. The properties of the band built on the 21/2+ isomeric state suggest a one neutron-two proton configuration. Based on the results of extensive calculations with different models, we also assign one neutron-two proton configurations to the 19/2+ and 17/2+ isomeric states. The assigned configurations of the 17/2+ and 21/2+ isomeric states involve the π9/2+[404] orbital, which is identified in three-quasiparticle bands of proton-rich A≈130 nuclei.
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| 40. |
- Petrache, C. M., et al.
(författare)
-
Multiple chiral bands in 137 Nd
- 2020
-
Ingår i: European Physical Journal A. - : Springer Nature. - 1434-6001 .- 1434-601X. ; 56:8
-
Tidskriftsartikel (refereegranskat)abstract
- Two new bands have been identified in 137Nd from a high-statistics JUROGAM II gamma-ray spectroscopy experiment. Constrained density functional theory and particle rotor model calculations are used to assign configurations and investigate the band properties, which are well described and understood. It is demonstrated that these two new bands can be interpreted as chiral partners of previously known three-quasiparticle positive- and negative-parity bands. The newly observed chiral doublet bands in 137Nd represent an important support to the existence of multiple chiral bands in nuclei. The present results constitute the missing stone in the series of Nd nuclei showing multiple chiral bands, which becomes the most extended sequence of odd–even and even-even nuclei presenting multiple chiral bands in the Segré chart.
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| 41. |
- Petrache, C. M., et al.
(författare)
-
Signatures of enhanced octupole correlations at high spin in Nd 136
- 2020
-
Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 102:1
-
Tidskriftsartikel (refereegranskat)abstract
- Experimental signatures of moderately enhanced octupole correlations at high spin in Nd136 are indicated for the first time. The extracted dipole moments of two negative-parity bands are only two times smaller than those of the lanthanide nuclei with N≈90 which present well-established octupole correlations. Calculations using the cranked quasiparticle random phase approximation and a model of quadrupole-octupole rotations with octupole vibrations reveal the structure of the bands and the enhanced octupole correlations at high spin in Nd136.
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| 42. |
- Petrovic, Jana, 1992-, et al.
(författare)
-
Performance Evaluation of an Imaging Radiation Portal Monitor System
- 2022
-
Ingår i: Applied Sciences. - : MDPI AG. - 2076-3417. ; 12:18
-
Tidskriftsartikel (refereegranskat)abstract
- An organic scintillator-based radiation portal monitor (RPM) prototype system with imaging capabilities has been developed based on the neutron-gamma emission tomography technique. The technique enables rapid detection and precise location of small amounts of special nuclear materials, such as plutonium, using time and energy correlations between fast neutrons and gamma rays from spontaneous fission with low false-alarm rates. These capabilities, in addition to state-of-the-art detection of various gamma-emitting sources, enables the novel imaging RPM concept to efficiently address global security threats from terrorism and the proliferation of nuclear weapons. The detector approach is simple and versatile and can easily be adapted for different applications in nuclear security, public safety, nuclear emergency response, and radiological surveying. In this work, basic performance parameters of the imaging RPM prototype system developed at KTH have been evaluated.
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| 43. |
- Petrovic, Jana, et al.
(författare)
-
Rapid imaging of special nuclear materials for nuclear nonproliferation and terrorism prevention
- 2021
-
Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 7:21
-
Tidskriftsartikel (refereegranskat)abstract
- We introduce a neutron-gamma emission tomography (NGET) technique for rapid detection, three-dimensional imaging, and characterization of special nuclear materials like weapons-grade plutonium and uranium. The technique is adapted from fundamental nuclear physics research and represents a previously unexplored approach to the detection and imaging of small quantities of these materials. The method is demonstrated on a radiation portal monitor prototype system based on fast organic scintillators, measuring the characteristic fast time and energy correlations between particles emitted in nuclear fission processes. The use of these correlations in real time in conjunction with modern machine learning techniques provides unprecedented imaging efficiency and high spatial resolution. This imaging modality addresses global security threats from terrorism and the proliferation of nuclear weapons. It also provides enhanced capabilities for addressing different nuclear accident scenarios and for environmental radiological surveying.
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| 44. |
- Polettini, M., et al.
(författare)
-
Decay studies in the A∼225 Po-Fr region from the DESPEC campaign at GSI in 2021
- 2022
-
Ingår i: Il Nuovo Cimento. - : Società Italiana di Fisica. - 2037-4909. ; 45:5
-
Tidskriftsartikel (refereegranskat)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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| 45. |
- Polettini, M., et al.
(författare)
-
DESPEC Phase-0 campaign at GSI
- 2021
-
Ingår i: NUOVO CIMENTO C-COLLOQUIA AND COMMUNICATIONS IN PHYSICS. - : SOC ITALIANA FISICA. - 2037-4909. ; 44:2-3
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports preliminary results of the DESPEC campaign at GSI, focused on the study of neutron-deficient nuclei approaching Sn-100. The results presented show the isomeric decays of excited states with I-pi = 14(+) and 8(+) in Pd-96 and Pd-94, respectively. The detailed characterisation of the DESPEC set-up and analysis methodologies, proven in this experimental run, are crucial for the future campaigns.
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| 46. |
- Siciliano, M., et al.
(författare)
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Pairing-quadrupole interplay in the neutron-deficient tin nuclei : First lifetime measurements of low-lying states in Sn-106,Sn-108
- 2020
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Ingår i: Physics Letters B. - : ELSEVIER. - 0370-2693 .- 1873-2445. ; 806
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Tidskriftsartikel (refereegranskat)abstract
- The lifetimes of the low-lying excited states 2(+) and 4(+) have been directly measured in the neutron-deficient Sn-106,Sn-108 isotopes. The nuclei were populated via a deep-inelastic reaction and the lifetime measurement was performed employing a differential plunger device. The emitted gamma rays were detected by the AGATA array, while the reaction products were uniquely identified by the VAMOS++ magnetic spectrometer. Large-Scale Shell-Model calculations with realistic forces indicate that, independently of the pairing content of the interaction, the quadrupole force is dominant in the B(E2; 2(1)(+) -> 0(g.s)(+)) values and it describes well the experimental pattern for Sn104-114 ; the B(E2;(+)(4) -> 2(1)(+)) values, measured here for the first time, depend critically on a delicate pairing-quadrupole balance, disclosed by the very precise results in Sn-108.
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| 47. |
- Testov, D. A., et al.
(författare)
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Octupole correlations near Te 110
- 2021
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Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 103:4
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Tidskriftsartikel (refereegranskat)abstract
- The lifetime of the 2+ and 9-, 11-, 13-, 15- states in the neutron-deficient Te110 was measured for the first time using the recoil distance Doppler shift technique. The reported value of the reduced transition probability B(E2;0g.s+→2+)=4.3(8)×103e2fm4 supports the systematic for even-mass Te isotopes and was interpreted in the framework of the large-scale shell model and cranked shell model calculations. The measured reduced transition probabilities in the negative-parity yrast band revealed the upward trend towards the high spins. The enhanced collectivity is discussed in terms of the tilted axis cranking approach and the symmetry configuration mixing method with the Gogny D1S interaction.
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| 48. |
- Trombetta, Débora M., et al.
(författare)
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Investigation on the use of coincidences between fast neutrons and gamma rays for the detection of special nuclear materials
- 2021
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Ingår i: International Journal of Nuclear Security. - : University of Tennessee. - 2376-9955. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- The emergence of new methodologies with promising applications that could impact nuclear security and emergency preparedness detection systems in the near future motivate the development of computational tools that allow the theoretical investigation of the relevant design parameters for such detection systems. Here, we present Monte Carlo simulations using the MCNP6 code to investigate the use of fast neutron-neutron and gamma-neutron coincidences in addition to conventional methods for detection of special nuclear materials (SNM) using inorganic scintillator detectors. The results show fair agreement between MCNP6 and MCNP-PoliMi simulations for neutron-neutron coincidences and that coincident detection of gamma rays and fast neutrons has a potential for enhancing the sensitivity for detection of SNM compared with conventional gamma-ray, single-neutron, and fast neutron-neutron coincidence detection schemes.
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| 49. |
- Wei, Rui, et al.
(författare)
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Exotic collective excitation patterns in triaxially deformed 131Ba
- 2024
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Ingår i: Wuli xuebao. - : Chinese Academy of Sciences. - 1000-3290. ; 73:11
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Tidskriftsartikel (refereegranskat)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.
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| 50. |
- Yaneva, A., et al.
(författare)
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FAST-TIMING MEASUREMENT IN 96Pd: IMPROVED ACCURACY FOR THE LIFETIME OF THE 4+1 STATE
- 2023
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Ingår i: Acta Physica Polonica B, Proceedings Supplement. - : Jagiellonian University. - 1899-2358 .- 2082-7865. ; , s. 1-1
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Konferensbidrag (refereegranskat)abstract
- Direct lifetime measurements via γ–γ coincidences using the FATIMA fast-timing LaBr3(Ce) array were performed for the excited states below previously reported isomers. In the N = 50 semi-magic 96Pd nucleus, lifetimes below the Iπ = 8+ seniority isomer were addressed as a benchmark for further analysis. The results for the Iπ = 2+ and 4+ states confirm the published values. Increased accuracy for the lifetime value was achieved for the 4+ state.
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