| 26. |
- Boso, A., et al.
(författare)
-
Neutron Skin Effects in Mirror Energy Differences : The Case of Mg-23-Na-23
- 2018
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 121:3
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 27. |
- Crespi, F. C. L., et al.
(författare)
-
1(-) and 2(+) discrete states in Zr-90 populated via the (O-17, O-17 'gamma) reaction
- 2015
-
Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 91:2
-
Tidskriftsartikel (refereegranskat)abstract
- 2(+) and 1(-) states in Zr-90 were populated via the (O-17, O-17 'gamma) reaction at 340 MeV. The gamma decay was measured with high resolution using the AGATA (advanced gamma tracking array demonstrator array). Differential cross sections were obtained at few different angles for the scattered particle. The results of the elastic scattering and inelastic excitation of 2(+), 3(,)(-) and 1(-) states are compared with distorted-wave Born approximation (DWBA) calculations, using both the standard collective form factor and a form factor obtained by folding microscopically calculated transition densities. This allowed to extract the isoscalar component of the 1(-) state at 6.424 MeV. The comparison of the present (17O, 17O 'gamma) data with existing (gamma,gamma') and (p, p') data in the corresponding region of the gamma continuum (6-11 MeV), characterized by a large E1 component, shows completely different behaviors of the cross section as a function of the nuclear excitation energy. The comparison of the data with DWBA calculations suggests a decrease of the isoscalar strength in the cross section with increasing excitation energy.
|
|
| 28. |
- Ertoprak, Aysegul, et al.
(författare)
-
LIFETIME MEASUREMENTS WITH THE DOPPLER SHIFT ATTENUATION METHOD USING A THICK HOMOGENEOUS PRODUCTION TARGET - VERIFICATION OF THE METHOD
- 2017
-
Ingår i: Acta Physica Polonica B. - : Jagiellonian University Press. - 0587-4254 .- 1509-5770. ; 48:3, s. 325-329
-
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.
|
|
| 29. |
- Luo, X. L., et al.
(författare)
-
Pulse pile-up identification and reconstruction for liquid scintillator based neutron detectors
- 2018
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : ELSEVIER SCIENCE BV. - 0168-9002 .- 1872-9576. ; 897, s. 59-65
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 30. |
- Podolyák, Zs, et al.
(författare)
-
Role of the Δ Resonance in the Population of a Four-Nucleon State in the 56Fe → 54Fe Reaction at Relativistic Energies
- 2016
-
Ingår i: Physical Review Letters. - 0031-9007. ; 117:22
-
Tidskriftsartikel (refereegranskat)abstract
- The Fe54 nucleus was populated from a 56Fe beam impinging on a Be target with an energy of E/A=500 MeV. The internal decay via γ-ray emission of the 10+ metastable state was observed. As the structure of this isomeric state has to involve at least four unpaired nucleons, it cannot be populated in a simple two-neutron removal reaction from the 56Fe ground state. The isomeric state was produced in the low-momentum (-energy) tail of the parallel momentum (energy) distribution of 54Fe, suggesting that it was populated via the decay of the Δ0 resonance into a proton. This process allows the population of four-nucleon states, such as the observed isomer. Therefore, it is concluded that the observation of this 10+ metastable state in 54Fe is a consequence of the quark structure of the nucleons.
|
|
| 31. |
- Sahin, E., et al.
(författare)
-
Shell evolution beyond N=40 : Cu-69,Cu-71,Cu-73
- 2015
-
Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 91:3
-
Tidskriftsartikel (refereegranskat)abstract
- The level structure of the neutron-rich Cu-69, Cu-71, and Cu-73 isotopes has been investigated by means of multinucleon transfer reactions. The experiment was performed at Laboratori Nazionali di Legnaro using the AGATA Demonstrator array coupled to the PRISMA magnetic spectrometer. Lifetimes of excited states in Cu nuclei were measured with the recoil-distance Doppler-shift method. The resulting electromagnetic matrix elements for transitions from excited states in Cu-69,Cu-71,Cu-73 nuclei are used to assess the collective or single-particle character of these states. The results are compared with predictions of large-scale shell-model calculations, giving further insight into the evolution of the proton pf shell as neutrons fill the 1g(9/2) orbital.
|
|
| 32. |
- Söderström, Pär-Anders, 1980-, et al.
(författare)
-
Neutron detection and gamma-ray suppression using artificial neural networks with the liquid scintillators BC-501A and BC-537
- 2019
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : ELSEVIER SCIENCE BV. - 0168-9002 .- 1872-9576. ; 916, s. 238-245
-
Tidskriftsartikel (refereegranskat)abstract
- In this work we present a comparison between the two liquid scintillators BC-501A and BC-537 in terms of their performance regarding the pulse-shape discrimination between neutrons and gamma rays. Special emphasis is put on the application of artificial neural networks. The results show a systematically higher gamma-ray rejection ratio for BC-501A compared to BC-537 applying the commonly used charge comparison method. Using the artificial neural network approach the discrimination quality was improved to more than 95% rejection efficiency of gamma rays over the energy range 150 to 1000 keV for both BC-501A and BC-537. However, due to the larger light output of BC-501A compared to BC-537, neutrons could be identified in BC-501A using artificial neural networks down to a recoil proton energy of 800 keV compared to a recoil deuteron energy of 1200 keV for BC-537. We conclude that using artificial neural networks it is possible to obtain the same gamma-ray rejection quality from both BC-501A and BC-537 for neutrons above a low-energy threshold. This threshold is, however, lower for BC-501A, which is important for nuclear structure spectroscopy experiments of rare reaction channels where low-energy interactions dominates.
|
|
| 33. |
- Ceruti, S., et al.
(författare)
-
Isospin Mixing in Zr-80 : From Finite to Zero Temperature
- 2015
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 115:22
-
Tidskriftsartikel (refereegranskat)abstract
- The isospin mixing was deduced in the compound nucleus Zr-80 at an excitation energy of E* = 54 MeV from the gamma decay of the giant dipole resonance. The reaction Ca-40 + Ca-40 at E-beam = 136 MeV was used to form the compound nucleus in the isospin I = 0 channel, while the reaction Cl-37 + Ca-44 at E-beam = 95 MeV was used as the reference reaction. The. rays were detected with the AGATA demonstrator array coupled with LaBr3:Ce detectors. The temperature dependence of the isospin mixing was obtained and the zero-temperature value deduced. The isospin-symmetry-breaking correction delta(C) used for the Fermi superallowed transitions was extracted and found to be consistent with beta-decay data.
|
|
| 34. |
- Egea Canet, F. J., et al.
(författare)
-
A New Front-End High-Resolution Sampling Board for the New-Generation Electronics of EXOGAM2 and NEDA Detectors
- 2015
-
Ingår i: IEEE Transactions on Nuclear Science. - 0018-9499 .- 1558-1578. ; 62:3, s. 1056-1062
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents the final design and results of the FADC Mezzanine for the EXOGAM (EXOtic GAMma array spectrometer) and NEDA (Neutron Detector Array) detectors. The measurements performed include those of studying the effective number of bits, the energy resolution using HP-Ge detectors, as well as timing histograms and discrimination performance. Finally, the conclusion shows how a common digitizing device has been integrated in the experimental environment of two very different detectors which combine both low-noise acquisition and fast sampling rates. Not only the integration fulfilled the expected specifications on both systems, but it also showed how a study of synergy between detectors could lead to the reduction of resources and time by applying a common strategy.
|
|
| 35. |
- Egea Canet, F. J., et al.
(författare)
-
Digital Front-End Electronics for the Neutron Detector NEDA
- 2015
-
Ingår i: IEEE Transactions on Nuclear Science. - 0018-9499 .- 1558-1578. ; 62:3, s. 1063-1069
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents the design of the NEDA (Neutron Detector Array) electronics, a first attempt to involve the use of digital electronics in large neutron detector arrays. Starting from the front-end modules attached to the PMTs (PhotoMultiplier Tubes) and ending up with the data processing workstations, a comprehensive electronic system capable of dealing with the acquisition and pre-processing of the neutron array is detailed. Among the electronic modules required, we emphasize the front-end analog processing, the digitalization, digital pre-processing and communications firmware, as well as the integration of the GTS (Global Trigger and Synchronization) system, already used successfully in AGATA (Advanced Gamma Tracking Array). The NEDA array will be available for measurements in 2016.
|
|
| 36. |
- Ertoprak, Aysegul, et al.
(författare)
-
M1 and E2 transition rates from core-excited states in semi-magic Ru-94
- 2018
-
Ingår i: European Physical Journal A. - : Springer. - 1434-6001 .- 1434-601X. ; 54:9
-
Tidskriftsartikel (refereegranskat)abstract
- Lifetimes of high-spin states have been measured in the semi-magic (N = 50) nucleus Ru-94. Excited states in Ru-94 were populated in the Ni-58(Ca-40, 4p)Ru-94* fusion-evaporation reaction at the Grand Accelerateur National d'Ions Lourds (GANIL) accelerator complex. DSAM lifetime analysis was performed on the Doppler broadened line shapes in energy spectra obtained from gamma-rays emitted while the residual nuclei were slowing down in a thick 6 mg/cm(2) metallic Ni-58 target. In total eight excited-state lifetimes in the angular momentum range I = (13-20)h have been measured, five of which were determined for the first time. The corresponding B(M1) and B(E2) reduced transition strengths are discussed within the framework of large-scale shell model calculations to study the contribution of different particle-hole configurations, in particular for analyzing contributions from core-excited configurations.
|
|
| 37. |
- Montanari, D., et al.
(författare)
-
Pair neutron transfer in Ni-60+Sn-116 probed via gamma-particle coincidences
- 2016
-
Ingår i: PHYSICAL REVIEW C. - 2469-9985. ; 93:5
-
Tidskriftsartikel (refereegranskat)abstract
- We performed a gamma-particle coincidence experiment for the Ni-60 + Sn-116 system to investigate whether the population of the two-neutron pickup channel leading to Ni-62 is mainly concentrated in the ground-state transition, as has been found in a previous work [D. Montanari et al., Phys. Rev. Lett. 113, 052501 (2014)]. The experiment has been performed by employing the PRISMA magnetic spectrometer coupled to the Advanced Gamma Tracking Array (AGATA) demonstrator. The strength distribution of excited states corresponding to the inelastic, one-and two-neutron transfer channels has been extracted. We found that in the two-neutron transfer channel the strength to excited states corresponds to a fraction (less than 24%) of the total, consistent with the previously obtained results that the 2n channel is dominated by the ground-state to ground-state transition.
|
|
| 38. |
- Siciliano, M., et al.
(författare)
-
STUDY OF QUADRUPOLE CORRELATIONS IN N = Z=5 0 REGION VIA LIFETIME MEASUREMENTS
- 2017
-
Ingår i: Acta Physica Polonica B. - : Jagiellonian University Press. - 0587-4254 .- 1509-5770. ; 48:3, s. 331-336
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 39. |
- Testov, D., et al.
(författare)
-
High Resolution γ-Ray Spectrometry Using Galileo Array
- 2019
-
Ingår i: Eurasian Journal of Physics and Functional Materials. - : L.N. Gumilyov Eurasian National University. - 2522-9869. ; 3:1, s. 84-90
-
Tidskriftsartikel (refereegranskat)abstract
- The GALILEO γ-ray spectrometer has been constructed at the Legnaro National Laboratory of INFN (LNL-INFN). It can be coupled to advanced ancillary devices which allows nuclear structure studies employing the variety of in-beam γ-ray spectroscopy methods. Such studies benefit from reactions induced by the intense stable beams delivered by the Tandem-ALPI-PIAVE accelerator complex and by the radioactive beams which will be provided by the SPES facility. In this paper we outline two experiments performed within the experimental campaign at GALILEO coupled to the EUCLIDES Si-ball and the Neutron Wall array. The first one was aimed at spectroscopic studies in A=31 mirror nuclei and the second one at measurements of lifetimes of excited states in nuclei in the vicinity of 100Sn.
|
|
| 40. |
- Doncel, Maria, et al.
(författare)
-
Determination of lifetimes of nuclear excited states using the Recoil Distance Doppler Shift Method in combination with magnetic spectrometers
- 2017
-
Ingår i: European Physical Journal A. - : SPRINGER. - 1434-6001 .- 1434-601X. ; 53:10
-
Tidskriftsartikel (refereegranskat)abstract
- The current work presents the determination of lifetimes of nuclear excited states using the Recoil Distance Doppler Shift Method, in combination with spectrometers for ion identification, normalizing the intensity of the peaks by the ions detected in the spectrometer as a valid technique that produces results comparable to the ones obtained by the conventional shifted-to-unsifted peak ratio method. The technique has been validated using data measured with the gamma-ray array AGATA, the PRISMA spectrometer and the Cologne plunger setup. In this paper a test performed with the AGATA-PRISMA setup at LNL and the advantages of this new approach with respect to the conventional Recoil Distance Doppler Shift Method are discussed.
|
|
