| 1. |
- Boso, A., et al.
(författare)
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ISOSPIN SYMMETRY BREAKING IN MIRROR NUCLEI Mg-23-Na-23
- 2017
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Ingår i: Acta Physica Polonica B. - : Jagiellonian University Press. - 0587-4254 .- 1509-5770. ; 48:3, s. 313-318
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Tidskriftsartikel (refereegranskat)abstract
- Mirror energy differences (MED) are a direct consequence of isospin symmetry breaking. Moreover, the study of MED has proved to give valuable information of several nuclear structure properties. We present the results of an experiment performed in GANIL to study the MED in mirror nuclei Mg-23-Na-23 up to high spin. The experimental values are compared with state-of-the-art shell model calculations. This permits to enlighten several nuclear structure properties, such as the way in which the nucleons alignment proceeds, the radius variation with J, the role of the spin-orbit interaction and the importance of isospin symmetry breaking terms of nuclear origin.
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| 2. |
- Ertoprak, Aysegul, et al.
(författare)
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Lifetime measurements of core-excited states in semi-magic 95Rh
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Lifetimes of negative-parity states have been determined in the semi-magic (N=50) nucleus 95Rh. The fusion-evaporation reaction 58Ni(40Ca, 3p) was used to populate high-spin states in 95Rh at the Grand Accelerateur National d'Ions Lourds (GANIL) accelerator facility. The results were obtained using the Doppler Shift Attenuation Method (DSAM) based on the Doppler broadened line shapes produced during the slowing down process of the residual nuclei in a thick 6~ mg/cm2 metallic target. B(M1) and B(E2) reduced transition strengths are compared with predictions from large-scale shell-model calculations.
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| 3. |
- Ertoprak, Aysegul, et al.
(författare)
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LIFETIME MEASUREMENTS WITH THE DOPPLER SHIFT ATTENUATION METHOD USING A THICK HOMOGENEOUS PRODUCTION TARGET - VERIFICATION OF THE METHOD
- 2017
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Ingår i: Acta Physica Polonica B. - : Jagiellonian University Press. - 0587-4254 .- 1509-5770. ; 48:3, s. 325-329
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Tidskriftsartikel (refereegranskat)abstract
- Doppler Shift Attenuation Method (DSAM) analysis of excited-state lifetimes normally employs thin production targets mounted on a thick stopper foil ("backing") serving to slow down and stop the recoiling nuclei of interest in a well-defined manner. Use of a thick, homogeneous production target leads to a more complex analysis as it results in a substantial decrease in the energy of the incident projectile which traverses the target with an associated change in the production cross section of the residues as a function of penetration depth. Here, a DSAM lifetime analysis using a thick homogeneous target has been verified using the Doppler broadened lineshapes of gamma rays following the decay of highly excited states in the semi-magic (N = 50) nucleus Ru-94. Lifetimes of excited states in the Ru-94 nucleus have been obtained using a modified version of the LINESHAPE package from the Doppler broadened lineshapes resulting from the emission of the gamma rays, while the residual nuclei were slowing down in the thick (6 mg/cm(2)) metallic Ni-58 target. The results have been validated by comparison with a previous measurement using a different (RDDS) technique.
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| 4. |
- Ertoprak, A., et al.
(författare)
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Lifetimes of core-excited states in semi-magic Rh-95
- 2020
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Ingår i: European Physical Journal A. - : SPRINGER. - 1434-6001 .- 1434-601X. ; 56:11
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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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| 5. |
- Ghazi Moradi, Farnaz, 1976-, et al.
(författare)
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Character of particle-hole excitations in Ru-94 deduced from gamma-ray angular correlation and linear polarization measurements
- 2014
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 89:1, s. 014301-
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Tidskriftsartikel (refereegranskat)abstract
- Linear polarization and angular correlations of gamma-rays depopulating excited states in the neutron-deficient nucleus Ru-94(44)50 have been measured, enabling firm spin-parity assignments for several excited states in this nucleus. The deduced multipolarities of strong transitions in the yrast structure were found to be mostly of stretched M1, E1, and E2 types and, in most cases, in agreement with previous tentative assignments. The deduced multipolarity of the 1869 keV and the connecting 257 and 1641 keV transitions indicates that the state at 6358 keV excitation energy has spin parity 12(1)(-) rather than 12(3)(+) as proposed in previous works. The presence of a 12(1)(-) state is interpreted within the framework of large-scale shell-model calculations as a pure proton-hole state dominated by the pi(p(1/2)(-1)circle times g(9/2)(-5)) and pi(p(3/2)(-1) g(9/2)(-5)) configurations. A new positive-parity state is observed at 6103 keV and is tentatively assigned as 12(2)(+). The 14(1)(-) state proposed earlier is reassigned as 13(4)(-) and is interpreted as being dominated by neutron particle-hole core excitations. The strengths of several E1 transitions have been measured and are found to provide a signature of core-excited configurations.
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| 6. |
- Ghazi Moradi, Farnaz, 1976-
(författare)
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Experimental Nuclear Structure Studies in the Vicinityof the N = Z Nucleus 100Sn and in the ExtremelyNeutron Deficient 162Ta Nucleus
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work covers spectroscopic studies of nuclei from different regions of the Segré chart whose properties illustrate the delicate balance between the forces in the atomic nucleus. Studies of nuclei far from stability offer new insights into the complex nucleon many-body problem. In nuclei with equal neutron and proton numbers (N = Z), the unique nature of the atomic nucleus as an object composed of two distinct types of fermions can be expressed as enhanced correlations arising between neutrons and protons occupying orbitals with the same quantum numbers. The bound N = Z nuclei with mass number A > 90 can only be produced in the laboratory at very low cross sections. The related problems of identifying and distinguishing such reaction products and their associated gamma rays have prevented a firm interpretation of their structure even for the lowest excited states until recently. In the present work the experimental difficulties of observation of excited states in the N = Z = 46 nucleus 92Pd have been overcome through the use of a highly efficient, state-of-the-art detector system; the EXOGAM-Neutron Wall-DIAMANT setup, and a prolonged experimental running period. The level spacings in the ground state band of 92Pd give the first experimental evidence for a new spin-aligned neutron-proton (np) paired phase, an unexpected effect of enhanced np correlations for N = Z nuclei in the immediate vicinity of the doubly magic nucleus 100Sn.Excited states in 94Ru and 95Rh nuclei close to the double magic shell Z = N = 50 have been studied in order to untangle the ambiguity of the spin and the parity of the lowest-lying states. The observed yrast structures are compared to results of large-scale shell model (LSSM) calculations and the strengths of hindered E1 transitions are used as a sensitive test of the LSSM parameters. The effect of single-particle-hole excitations is discussed in terms of the strength of hindered E1 transitions.Excited states of the odd-odd nucleus 162Ta have been observed using the JUROGAM/RITU experimental set-up. This nucleus is located in a transitional region in the nuclide chart which is between near-spherical nuclei and well-deformed nuclei, offering the possibility to study the emergence of collective phenomena and nuclear deformation (in particular the degree of triaxiality). The results, which are interpreted in the framework of the cranked shell model with total Routhian surface calculations, suggest an almost axially symmetric nuclear shape. The energy staggering between the signature partners of the yrast rotational bands has been deduced for eight odd-odd isotopes in the neighborhood of 162Ta nucleus and the special observed feature of signature inversion for these nuclei is discussed.
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| 7. |
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| 8. |
- Ralet, D., et al.
(författare)
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Lifetime measurement of neutron-rich even-even molybdenum isotopes
- 2017
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Ingår i: Physical Review C: covering nuclear physics. - : AMER PHYSICAL SOC. - 2469-9985 .- 2469-9993. ; 95:3
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Tidskriftsartikel (refereegranskat)abstract
- Background: In the neutron-rich A≈100 mass region, rapid shape changes as a function of nucleon number as well as coexistence of prolate, oblate, and triaxial shapes are predicted by various theoretical models. Lifetime measurements of excited levels in the molybdenum isotopes allow the determination of transitional quadrupole moments, which in turn provides structural information regarding the predicted shape change. Purpose: The present paper reports on the experimental setup, the method that allowed one to measure the lifetimes of excited states in even-even molybdenum isotopes from mass A=100 up to mass A=108, and the results that were obtained. Method: The isotopes of interest were populated by secondary knock-out reaction of neutron-rich nuclei separated and identified by the GSI fragment separator at relativistic beam energies and detected by the sensitive PreSPEC-AGATA experimental setup. The latter included the Lund-York-Cologne calorimeter for identification, tracking, and velocity measurement of ejectiles, and AGATA, an array of position sensitive segmented HPGe detectors, used to determine the interaction positions of the γ ray enabling a precise Doppler correction. The lifetimes were determined with a relativistic version of the Doppler-shift-attenuation method using the systematic shift of the energy after Doppler correction of a γ-ray transition with a known energy. This relativistic Doppler-shift-attenuation method allowed the determination of mean lifetimes from 2 to 250 ps. Results: Even-even molybdenum isotopes from mass A=100 to A=108 were studied. The decays of the low-lying states in the ground-state band were observed. In particular, two mean lifetimes were measured for the first time: τ=29.7-9.1+11.3 ps for the 4+ state of Mo108 and τ=3.2-0.7+0.7 ps for the 6+ state of Mo102. Conclusions: The reduced transition strengths B(E2), calculated from lifetimes measured in this experiment, compared to beyond-mean-field calculations, indicate a gradual shape transition in the chain of molybdenum isotopes when going from A=100 to A=108 with a maximum reached at N=64. The transition probabilities decrease for Mo108 which may be related to its well-pronounced triaxial shape indicated by the calculations.
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| 9. |
- Zheng, Y., et al.
(författare)
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gamma-ray linear polarization measurements and (g(9/2))(-3) neutron alignment in Ru-91
- 2013
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Ingår i: Physical Review C. Nuclear Physics. - : American Physical Society (APS). - 0556-2813 .- 1089-490X. ; 87:4, s. 044328-
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Tidskriftsartikel (refereegranskat)abstract
- Linear polarization measurements have been performed for gamma rays in Ru-91 produced with the Ni-58(Ar-36,2p1n gamma)Ru-91 reaction at a beam energy of 111 MeV. The EXOGAM Ge clover array has been used to measure the gamma-gamma coincidences, gamma-ray linear polarization, and gamma-ray angular distributions. The polarization sensitivity of the EXOGAM clover detectors acting as Compton polarimeters has been determined in the energy range 0.3-1.3 MeV. Several transitions have been observed for the first time. Measurements of linear polarization and angular distribution have led to the firm assignments of spin differences and parity of high-spin states in Ru-91. More specifically, calculations using a semiempirical shell model were performed to understand the structures of the first and second (21/2(+)) and (17/2(+)) levels. The results are in good agreement with the experimental data, supporting the interpretation of the nonyrast (21/2(+)) and (17/2(+)) states in terms of the J(max) and J(max) - 2 members of the seniority-three nu(g(9/2))(-3) multiplet.
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