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Boso, A., Lenzi, S. M., Recchia, F., Bonnard, J., Zuker, A. P., Aydin, S., . . . Valiente-Dobon, J. J. (2018). Neutron Skin Effects in Mirror Energy Differences: The Case of Mg-23-Na-23. Physical Review Letters, 121(3), Article ID 032502.
Open this publication in new window or tab >>Neutron Skin Effects in Mirror Energy Differences: The Case of Mg-23-Na-23
2018 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, no 3, article id 032502Article in journal (Refereed) Published
Abstract [en]

Energy differences between analogue states in the T = 1/2 Mg-23-Na-23 mirror nuclei have been measured along the rotational yrast bands. This allows us to search for effects arising from isospin-symmetrybreaking interactions (ISB) and/or shape changes. Data are interpreted in the shell model framework following the method successfully applied to nuclei in the f(7/2) shell. It is shown that the introduction of a schematic ISB interaction of the same type of that used in the f(7/2) shell is needed to reproduce the data. An alternative novel description, applied here for the first time, relies on the use of an effective interaction deduced from a realistic charge-dependent chiral nucleon-nucleon potential. This analysis provides two important results: (i) The mirror energy differences give direct insight into the nuclear skin; (ii) the skin changes along the rotational bands are strongly correlated with the difference between the neutron and proton occupations of the s(1/2) "halo" orbit.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-361688 (URN)10.1103/PhysRevLett.121.032502 (DOI)000439286800004 ()
Funder
EU, FP7, Seventh Framework Programme, 262010 ENSAR FP7/2007-2013 Available from: 2018-10-03 Created: 2018-10-03 Last updated: 2018-10-03Bibliographically approved
Luo, X. L., Modamio, V., Nyberg, J., Valiente-Dobon, J. J., Nishada, Q., de Angelis, G., . . . Wadsworth, R. (2018). Pulse pile-up identification and reconstruction for liquid scintillator based neutron detectors. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 897, 59-65
Open this publication in new window or tab >>Pulse pile-up identification and reconstruction for liquid scintillator based neutron detectors
2018 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 897, p. 59-65Article in journal (Refereed) Published
Abstract [en]

The issue of pulse pile-up is frequently encountered in nuclear experiments involving high counting rates, which will distort the pulse shapes and the energy spectra. A digital method of off-line processing of pile-up pulses is presented. The pile-up pulses were firstly identified by detecting the downward-going zero-crossings in the first-order derivative of the original signal, and then the constituent pulses were reconstructed based on comparing the pile-up pulse with four models that are generated by combining pairs of neutron and.. standard pulses together with a controllable time interval. The accuracy of this method in resolving the pile-up events was investigated as a function of the time interval between two pulses constituting a pile-up event. The obtained results show that the method is capable of disentangling two pulses with a time interval among them down to 20 ns, as well as classifying them as neutrons or gamma rays. Furthermore, the error of reconstructing pile-up pulses could be kept below 6% when successive peaks were separated by more than 50 ns. By applying the method in a high counting rate of pile-up events measurement of the NEutron Detector Array (NEDA), it was empirically found that this method can reconstruct the pile-up pulses and perform neutron-gamma discrimination quite accurately. It can also significantly correct the distorted pulse height spectrum due to pile-up events.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2018
Keywords
Pile-up, Digital, First-order derivative, Neutron-gamma discrimination, Liquid scintillator
National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:uu:diva-357373 (URN)10.1016/j.nima.2018.03.078 (DOI)000433206800010 ()
Funder
Swedish Research Council Available from: 2018-08-24 Created: 2018-08-24 Last updated: 2018-08-24Bibliographically approved
Clement, E., Michelagnoli, C., de France, G., Li, H. J., Lemasson, A., Dejeon, C. B., . . . Rudigier, M. (2017). Conceptual design of the AGATA 1 π array at GANIL. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 855, 1-12
Open this publication in new window or tab >>Conceptual design of the AGATA 1 π array at GANIL
2017 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 855, p. 1-12Article in journal (Refereed) Published
Abstract [en]

The Advanced GAmma Tracking Array (AGATA) has been installed at the GANIL facility, Caen-France. This setup exploits the stable and radioactive heavy-ions beams delivered by the cyclotron accelerator complex of GANIL. Additionally, it benefits from a large palette of ancillary detectors and spectrometers to address in-beam γ-ray spectroscopy of exotic nuclei. The set-up has been designed to couple AGATA with a magnetic spectrometer, charged-particle and neutron detectors, scintillators for the detection of high-energy γ rays and other devices such as a plunger to measure nuclear lifetimes. In this paper, the design and the mechanical characteristics of the set-up are described. Based on simulations, expected performances of the AGATA l π array are presented.

Keywords
AGATA spectrometer, GANIL facility, gamma-ray tracking, Pulse shape analysis, VAMOS plus plus spectrometer, NEDA detector, DIAMANT detector, PARIS LaBr3 detector, FATIMA LaBr3 detector, Plunger device
National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:uu:diva-322517 (URN)10.1016/j.nima.2017.02.063 (DOI)000399846900001 ()
Funder
EU, FP7, Seventh Framework Programme, 262010EU, Horizon 2020, 654002
Note

Title in WoS: Conceptual design of the AGATA 1 pi array at GANIL

Available from: 2017-05-29 Created: 2017-05-29 Last updated: 2017-05-29Bibliographically approved
Boso, A., Lenzi, S. M., Recchia, F., Bonnard, J., Aydin, S., Bentley, M. A., . . . Valiente-Dobon, J. J. (2017). Isospin Symmetry Breaking In Mirror Nuclei Mg-23-Na-23. Paper presented at Zakopane Conference on Nuclear Physics - Extremes of the Nuclear Landscape, AUG 28-SEP 04, 2016, Zakopane, POLAND. Acta Physica Polonica B, 48(3), 313-318
Open this publication in new window or tab >>Isospin Symmetry Breaking In Mirror Nuclei Mg-23-Na-23
2017 (English)In: Acta Physica Polonica B, ISSN 0587-4254, E-ISSN 1509-5770, Vol. 48, no 3, p. 313-318Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Jagiellonian University Press, 2017
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-321154 (URN)10.5506/APhysPolB.48.313 (DOI)000398717500011 ()
Conference
Zakopane Conference on Nuclear Physics - Extremes of the Nuclear Landscape, AUG 28-SEP 04, 2016, Zakopane, POLAND
Available from: 2017-05-02 Created: 2017-05-02 Last updated: 2017-05-02Bibliographically approved
Ralet, D., Nyberg, J. & Zielinska, M. (2017). Lifetime measurement of neutron-rich even-even molybdenum isotopes. Physical Review C, 95(3), Article ID 034320.
Open this publication in new window or tab >>Lifetime measurement of neutron-rich even-even molybdenum isotopes
2017 (English)In: Physical Review C, ISSN 2469-9985, Vol. 95, no 3, article id 034320Article in journal (Refereed) Published
Abstract [en]

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+11.3−9.1 ps for the 4+ state of 108Mo and τ=3.2+0.7−0.7 ps for the 6+ state of 102Mo. 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 108Mo which may be related to its well-pronounced triaxial shape indicated by the calculations.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-321284 (URN)10.1103/PhysRevC.95.034320 (DOI)000399143200002 ()
Available from: 2017-05-02 Created: 2017-05-02 Last updated: 2017-05-02Bibliographically approved
Ertoprak, A., Cederwall, B., Jakobsson, U., Nyako, B. M., Nyberg, J., Davies, P., . . . Xiao, Z. G. (2017). Lifetime Measurements With The Doppler Shift Attenuation Method Using A Thick Homogeneous Production Target — Verification of the Method. Paper presented at Zakopane Conference on Nuclear Physics - Extremes of the Nuclear Landscape, AUG 28-SEP 04, 2016, Zakopane, POLAND. Acta Physica Polonica B, 48(3), 325-329
Open this publication in new window or tab >>Lifetime Measurements With The Doppler Shift Attenuation Method Using A Thick Homogeneous Production Target — Verification of the Method
2017 (English)In: Acta Physica Polonica B, ISSN 0587-4254, E-ISSN 1509-5770, Vol. 48, no 3, p. 325-329Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Jagiellonian University Press, 2017
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-321155 (URN)10.5506/APhysPolB.48.325 (DOI)000398717500013 ()
Conference
Zakopane Conference on Nuclear Physics - Extremes of the Nuclear Landscape, AUG 28-SEP 04, 2016, Zakopane, POLAND
Available from: 2017-05-02 Created: 2017-05-02 Last updated: 2017-05-02Bibliographically approved
Klintefjord, M., Ljungvall, J., Gorgen, A., Lenzi, S. M., Garrote, F. L., Blazhev, A., . . . Dobon, J. J. (2017). Measurement of lifetimes in Fe-62,Fe-64, Co-61,Co-63, and Mn-59. PHYSICAL REVIEW C, 95(2), Article ID 024312.
Open this publication in new window or tab >>Measurement of lifetimes in Fe-62,Fe-64, Co-61,Co-63, and Mn-59
2017 (English)In: PHYSICAL REVIEW C, ISSN 2469-9985, Vol. 95, no 2, article id 024312Article in journal (Refereed) Published
Abstract [en]

Lifetimes of the 4(1)(+) states in Fe-62,Fe-64 and the 11/2(1)(-) states in Co-61,Co-63 and Mn-59 were measured at the Grand Accelerateur National d'Ions Lourds (GANIL) facility by using the Advanced Gamma Tracking Array (AGATA) and the large-acceptance variable mode spectrometer (VAMOS++). The states were populated through multinucleon transfer reactions with a U-238 beam impinging on a Ni-64 target, and lifetimes in the picosecond range were measured by using the recoil distance Doppler shift method. The data show an increase of collectivity in the iron isotopes approaching N = 40. The reduction of the subshell gap between the nu 2p(1/2) and nu 1g(9/2) orbitals leads to an increased population of the quasi-SU(3) pair (nu 1g(9/2), nu 2d(5/2)), which causes an increase in quadrupole collectivity. This is not observed for the cobalt isotopes withN < 40 for which the neutron subshell gap is larger due to the repulsive monopole component of the tensor nucleon-nucleon interaction. The extracted experimental B(E2) values are compared with large-scale shell-model calculations and with beyond-mean-field calculations with the Gogny D1S interaction. A good agreement between calculations and experimental values is found, and the results demonstrate in particular the spectroscopic quality of the Lenzi, Nowacki, Poves, and Sieja (LNPS) shell-model interaction.

National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-317948 (URN)10.1103/PhysRevC.95.024312 (DOI)000393743300002 ()
Available from: 2017-04-01 Created: 2017-04-01 Last updated: 2017-04-01Bibliographically approved
Siciliano, M., Valiente-Dobon, J. J., Goasduff, A., Bazzacco, D., Alahari, N., Benzoni, G., . . . Testov, D. (2017). Study Of Quadrupole Correlations In N = Z=5 0 Region Via Lifetime Measurements. Paper presented at Zakopane Conference on Nuclear Physics - Extremes of the Nuclear Landscape, AUG 28-SEP 04, 2016, Zakopane, POLAND. Acta Physica Polonica B, 48(3), 331-336
Open this publication in new window or tab >>Study Of Quadrupole Correlations In N = Z=5 0 Region Via Lifetime Measurements
2017 (English)In: Acta Physica Polonica B, ISSN 0587-4254, E-ISSN 1509-5770, Vol. 48, no 3, p. 331-336Article in journal (Refereed) Published
Abstract [en]

During the AGATA campaign at GANIL, the neutron-deficient Sn region was populated via a multi-nucleon transfer reaction in order to directly measure the lifetime of the first excited states with a plunger device, providing complementary information to previous results obtained with Coulomb excitation experiments. The AGATA gamma-ray array was used together with the VAMOS++ spectrometer to study the nuclei of interest.

Place, publisher, year, edition, pages
Jagiellonian University Press, 2017
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-321156 (URN)10.5506/APhysPolB.48.331 (DOI)000398717500014 ()
Conference
Zakopane Conference on Nuclear Physics - Extremes of the Nuclear Landscape, AUG 28-SEP 04, 2016, Zakopane, POLAND
Available from: 2017-05-02 Created: 2017-05-02 Last updated: 2017-05-02Bibliographically approved
Hüyük, T., Di Nitto, A., Jaworski, G., Gadea, A., Valiente-Dobón, J. J., Nyberg, J., . . . Wadsworth, R. (2016). Conceptual design of the early implementation of the NEutron Detector Array (NEDA) with AGATA. European Physical Journal A, 52(3), Article ID 55.
Open this publication in new window or tab >>Conceptual design of the early implementation of the NEutron Detector Array (NEDA) with AGATA
2016 (English)In: European Physical Journal A, ISSN 1434-6001, E-ISSN 1434-601X, Vol. 52, no 3, article id 55Article in journal (Refereed) Published
Abstract [en]

The NEutron Detector Array (NEDA) project aims at the construction of a new high-efficiency compact neutron detector array to be coupled with large $\gamma$ -ray arrays such as AGATA. The application of NEDA ranges from its use as selective neutron multiplicity filter for fusion-evaporation reaction to a large solid angle neutron tagging device. In the present work, possible configurations for the NEDA coupled with the Neutron Wall for the early implementation with AGATA has been simulated, using Monte Carlo techniques, in order to evaluate their performance figures. The goal of this early NEDA implementation is to improve, with respect to previous instruments, efficiency and capability to select multiplicity for fusion-evaporation reaction channels in which 1, 2 or 3 neutrons are emitted. Each NEDA detector unit has the shape of a regular hexagonal prism with a volume of about 3.23l and it is filled with the EJ301 liquid scintillator, that presents good neutron- $\gamma$ discrimination properties. The simulations have been performed using a fusion-evaporation event generator that has been validated with a set of experimental data obtained in the 58Ni + 56Fe reaction measured with the Neutron Wall detector array.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-293040 (URN)10.1140/epja/i2016-16055-8 (DOI)000372866900001 ()
Funder
Swedish Research Council Available from: 2016-05-11 Created: 2016-05-11 Last updated: 2017-11-30Bibliographically approved
Lalovic, N., Louchart, C., Michelagnoli, C., Perez-Vidal, R. M., Ralet, D., Gerl, J., . . . Stezowski, O. (2016). Performance of the AGATA gamma-ray spectrometer in the PreSPEC set-up at GSI. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 806, 258-266
Open this publication in new window or tab >>Performance of the AGATA gamma-ray spectrometer in the PreSPEC set-up at GSI
2016 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 806, p. 258-266Article in journal (Refereed) Published
Abstract [en]

In contemporary nuclear physics, the European Advanced GAmma Tracking Array (AGATA) represents a crucial detection system for cutting-edge nuclear structure studies. AGATA consists of highly segmented high-purity germanium crystals and uses the pulse-shape analysis technique to determine both the position and the energy of the y-ray interaction points in the crystals. It is the tracking algorithms that deploy this information and enable insight into the sequence of interactions, providing information on the full or partial absorption of the 7 ray. A series of dedicated performance measurements for an AGATA set-up comprising 21 crystals is described. This set-up was used within the recent PreSPEC-AGATA experimental campaign at the GSI Helmholtzzentrum fur Schwerionenforschung. Using the radioactive sources Co-56, Co-60 and Eu-152, absolute and normalized efficiencies and the peak-to-total of the array were measured. These quantities are discussed using different data analysis procedures. The quality of the pulse-shape analysis and the tracking algorithm are evaluated. The agreement between the experimental data and the Geant4 simulations is also investigated.

Keywords
Gamma-ray spectroscopy, Gamma-ray tracking, Nuclear structure, Pulse shape analysis, HPGe detectors
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-270410 (URN)10.1016/j.nima.2015.10.032 (DOI)000364856100035 ()
Available from: 2016-03-15 Created: 2015-12-28 Last updated: 2017-11-30
Identifiers
ORCID iD: orcid.org/0000-0001-6996-7605

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