Showing papers by "A. Bracco published in 2017"
Centre national de la recherche scientifique1, Université Paris-Saclay2, Spanish National Research Council3, University of Cologne4, University of Strasbourg5, University of Lyon6, Daresbury Laboratory7, University of Liverpool8, Lund University9, Uppsala University10, University of Valencia11, Hungarian Academy of Sciences12, Polish Academy of Sciences13, University of Surrey14
21 May 2017-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: The Advanced GAmma Tracking Array (AGATA) has been installed at the GANIL facility, Caen-France as discussed by the authors, where it 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.
Abstract: The Advanced GAmma Tracking Array (AGATA) has been installed at the GANIL facility, Caen-France. This set-up 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 1π array are presented.
64 citations
TL;DR: This result makes ^{66}Ni a unique nuclear system, apart from ^{236,238}U, in which a retarded γ transition from a 0^{+} deformed state to a spherical configuration is observed, resembling a shape-isomerlike behavior.
Abstract: A search for shape isomers in the ^{66}Ni nucleus was performed, following old suggestions of various mean-field models and recent ones, based on state-of-the-art Monte Carlo shell model (MCSM), all considering ^{66}Ni as the lightest nuclear system with shape isomerism. By employing the two-neutron transfer reaction induced by an ^{18}O beam on a ^{64}Ni target, at the sub-Coulomb barrier energy of 39 MeV, all three lowest-excited 0^{+} states in ^{66}Ni were populated and their γ decay was observed by γ-coincidence technique. The 0^{+} states lifetimes were assessed with the plunger method, yielding for the 0_{2}^{+}, 0_{3}^{+}, and 0_{4}^{+} decay to the 2_{1}^{+} state the B(E2) values of 4.3, 0.1, and 0.2 Weisskopf units (W.u.), respectively. MCSM calculations correctly predict the existence of all three excited 0^{+} states, pointing to the oblate, spherical, and prolate nature of the consecutive excitations. In addition, they account for the hindrance of the E2 decay from the prolate 0_{4}^{+} to the spherical 2_{1}^{+} state, although overestimating its value. This result makes ^{66}Ni a unique nuclear system, apart from ^{236,238}U, in which a retarded γ transition from a 0^{+} deformed state to a spherical configuration is observed, resembling a shape-isomerlike behavior.
48 citations
Istituto Nazionale di Fisica Nucleare1, University of Milan2, Beihang University3, University of Tokyo4, Katholieke Universiteit Leuven5, Michigan State University6, University of Brighton7, Osaka University8, University of Surrey9, University of York10, Tohoku University11, University of Oslo12, ATOMKI13, University of Padua14, Japan Atomic Energy Agency15, Autonomous University of Madrid16, Spanish National Research Council17, Istanbul University18
TL;DR: In this paper, the level structures of 70Co and 70Ni, populated from the β decay of 70Fe, have been investigated using β-delayed γ-ray spectroscopy following in-flight fission of a 238U beam.
32 citations
TL;DR: In this article, a low-energy enhancement in the γ-ray strength functions of 56,57Fe up to a factor of 30 over common theoretical E1 models is confirmed.
Abstract: Nuclear level densities and γ-ray strength functions of 56,57Fe have been extracted from proton-γ coincidences. A low-energy enhancement in the γ-ray strength functions up to a factor of 30 over common theoretical E1 models is confirmed. Angular distributions of the low-energy enhancement in 57Fe indicate its dipole nature, in agreement with findings for 56Fe. The high statistics and the excellent energy resolution of the large-volume LaBr3(Ce) detectors allowed for a thorough analysis of γ strength as function of excitation energy. Taking into account the presence of strong Porter–Thomas fluctuations, there is no indication of any significant excitation energy dependence in the γ-ray strength function, in support of the generalized Brink–Axel hypothesis.
26 citations
TL;DR: In this article, the isospin characters of low-energy dipole excitations in unstable nuclei were investigated, for the first time, in unstable nuclear cores, using distorted-wave Born approximation to extract independently the isovector and isoscalar dipole strengths.
25 citations
CERN1, University of Milan2, Spanish National Research Council3, Complutense University of Madrid4, Katholieke Universiteit Leuven5, University of Surrey6, Technische Universität Darmstadt7, Aarhus University8, University of Jyväskylä9, University of Cologne10, University of Bordeaux11, University of Huelva12
TL;DR: In this paper, a detailed analysis of the measured decay half-lives and decay scheme of the odd-A Ba isotope is presented, giving a first insight in the structure of this neutron-rich nucleus.
Abstract: Neutron-rich Ba isotopes are expected to exhibit octupolar correlations, reaching their maximum in isotopes around mass A = 146. The odd-A neutron-rich members of this isotopic chain show typical patterns related to non-axially symmetric shapes, which are however less marked compared to even-A ones, pointing to a major contribution from vibrations. In the present paper we present results from a recent study focused on $^{148 –150}Cs$ β-decay performed at the ISOLDE Decay Station equipped with fast-timing detectors. A detailed analysis of the measured decay half-lives and decay scheme of $^{149}Ba$ is presented, giving a first insight in the structure of this neutron-rich nucleus.
16 citations
TL;DR: In this paper, the isovector giant dipole resonance (IVGDR) decay was measured in the compound nuclei $^{80}\mathrm{Zr}$ and $^{81}\mathm{Rb}$ at an excitation energy of ${E}^{*}=54$ MeV.
Abstract: The isovector giant dipole resonance (IVGDR) $\ensuremath{\gamma}$ decay was measured in the compound nuclei $^{80}\mathrm{Zr}$ and $^{81}\mathrm{Rb}$ at an excitation energy of ${E}^{*}=54$ MeV. The fusion reaction $^{40}\mathrm{Ca}+^{40}\mathrm{Ca}$ at ${E}_{\mathrm{beam}}=136$ MeV was used to form the compound nucleus $^{80}\mathrm{Zr}$, while the reaction $^{37}\mathrm{Cl}+^{44}\mathrm{Ca}$ at ${E}_{\mathrm{beam}}=95$ MeV was used to form the compound nucleus $^{81}\mathrm{Rb}$ at the same excitation energy. The IVGDR parameters extracted from the analysis were compared with the ones found at higher excitation energy (${E}^{*}=83$ MeV). The comparison allows one to observe two different nuclear mechanisms: (i) the IVGDR intrinsic width remains constant with the excitation energy in the nucleus $^{81}\mathrm{Rb}$; (ii) the isospin-violating spreading width (i.e., Coulomb spreading width) remains constant with the excitation energy in the nucleus $^{80}\mathrm{Zr}$. The experimental setup used for the $\ensuremath{\gamma}$-ray detection was composed by the AGATA demonstrator array coupled to the large-volume ${\mathrm{LaBr}}_{3}$:Ce detectors of the ${\mathrm{HECTOR}}^{+}$ array.
13 citations
Istituto Nazionale di Fisica Nucleare1, University of Padua2, University of Valencia3, University of Birmingham4, Technische Universität Darmstadt5, Autonomous University of Madrid6, University of Surrey7, University of Milan8, University of Cologne9, University of Florence10, University of Brighton11, University of Paris-Sud12, Istanbul University13, University of Turin14, Université libre de Bruxelles15, Uppsala University16
TL;DR: In this paper, the shape evolution in the neutron-rich platinum isotopes towards the N = 126 shell closure was investigated via in-beam γ-ray spectroscopy in order to study the shape of the nucleus.
Abstract: The neutron-rich nucleus
ucleus{200}{Pt} is investigated via in-beam \gamma-ray spectroscopy in order to study the shape evolution in the neutron-rich platinum isotopes towards the N = 126 shell closure. The two-neutron transfer reaction
ucleus{198}{Pt}(
ucleus{82}{Se},
ucleus{80}{Se})
ucleus{200}{Pt} is used to populate excited states of
ucleus{200}{Pt}. The Advanced Gamma Ray Tracking Array (AGATA) demonstrator coupled with the PRISMA spectrometer detects \gamma rays coincident with the
ucleus{80}{Se} recoils, the binary partner of
ucleus{200}{Pt}. The binary partner method is applied to extract the \gamma-ray transitions and build the level scheme of
ucleus{200}{Pt}. The level at 1884\,keV reported by Yates et. al [Phys. Rev. C 37, 1889] was confirmed to be at 1882.1\,keV and assigned as the (6^+_1) state. An additional \gamma ray was found and it presumably de-excites the (8^+_1) state. The results are compared with state-of-the-art beyond mean-field calculations, performed for the even-even
ucleus{190-204}{Pt} isotopes, revealing that
ucleus{200}{Pt} marks the transition from the \gamma-unstable behaviour of lighter Pt nuclei towards a more spherical one when approaching the N=126 shell closure.
12 citations
University of Cologne1, University of Padua2, Istituto Nazionale di Fisica Nucleare3, University of Birmingham4, Saitama University5, University of Milan6, University of Manchester7, University of Rochester8, Lawrence Berkeley National Laboratory9, University of Valencia10, University of Surrey11, University of Oslo12, Spanish National Research Council13, University of Strasbourg14, TRIUMF15, University of Turin16, National Physical Laboratory17, University of Copenhagen18, University of Lyon19, Daresbury Laboratory20, Lawrence Livermore National Laboratory21
TL;DR: Vogt et al. as mentioned in this paper investigated the transitional nuclei Xe132 and Xe133 after multinucleon transfer (MNT) and fusion-evaporation reactions.
Abstract: Author(s): Vogt, A; Siciliano, M; Birkenbach, B; Reiter, P; Hadynska-Klȩk, K; Wheldon, C; Valiente-Dobon, JJ; Teruya, E; Yoshinaga, N; Arnswald, K; Bazzacco, D; Blazhev, A; Bracco, A; Bruyneel, B; Chakrawarthy, RS; Chapman, R; Cline, D; Corradi, L; Crespi, FCL; Cromaz, M; De Angelis, G; Eberth, J; Fallon, P; Farnea, E; Fioretto, E; Fransen, C; Freeman, SJ; Fu, B; Gadea, A; Gelletly, W; Giaz, A; Gorgen, A; Gottardo, A; Hayes, AB; Hess, H; Hetzenegger, R; Hirsch, R; Hua, H; John, PR; Jolie, J; Jungclaus, A; Karayonchev, V; Kaya, L; Korten, W; Lee, IY; Leoni, S; Liang, X; Lunardi, S; MacChiavelli, AO; Menegazzo, R; Mengoni, D; Michelagnoli, C; Mijatovic, T; Montagnoli, G; Montanari, D; Muller-Gatermann, C; Napoli, D; Pearson, CJ; Podolyak, Z; Pollarolo, G; Pullia, A; Queiser, M; Recchia, F; Regan, PH; Regis, JM; Saed-Samii, N; Sahin, E; Scarlassara, F; Seidlitz, M; Siebeck, B; Sletten, G; Smith, JF; Soderstrom, PA; Stefanini, AM; Stezowski, O; Szilner, S; Szpak, B; Teng, R; Ur, C; Warner, DD; Wolf, K; Wu, CY; Zell, KO | Abstract: The transitional nuclei Xe132 and Xe133 are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in Xe136+Pb208 MNT reactions employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (ii) in the Xe136+Pt198 MNT reaction employing the GAMMASPHERE spectrometer in combination with the gas-detector array CHICO, and (iii) as an evaporation residue after a Te130(α,xn)Xe134-xn fusion-evaporation reaction employing the HORUS γ-ray array at the University of Cologne. The high-spin level schemes are considerably extended above the Jπ=(7-) and (10+) isomers in Xe132 and above the 11/2- isomer in Xe133. The results are compared to the high-spin systematics of the Z=54 as well as the N=78 and N=79 chains. Furthermore, evidence is found for a long-lived (T1/2â‰1μs) isomer in Xe133 which closes a gap along the N=79 isotones. Shell-model calculations employing the SN100PN and PQM130 effective interactions reproduce the experimental findings and provide guidance to the interpretation of the observed high-spin features.
12 citations
TL;DR: The Long Range Plan for Nuclear Research in Europe (LRTNE) was released after approximately 20 months of work for its preparation as discussed by the authors. But it was not a special day for NuPECC.
Abstract: 19 June 2017 was a special day for NuPECC. Indeed, that day the “Long Range Plan for Nuclear Research in Europe” was released after approximately 20 months of work for its preparation. From the tim...
10 citations
TL;DR: The Long Range Plan for Nuclear Research in Europe (LRTNE) was released after approximately 20 months of work for its preparation as discussed by the authors. But it was not a special day for NuPECC.
Abstract: 19 June 2017 was a special day for NuPECC. Indeed, that day the “Long Range Plan for Nuclear Research in Europe” was released after approximately 20 months of work for its preparation. From the tim...
University of Cologne1, University of Padua2, Istituto Nazionale di Fisica Nucleare3, University of Birmingham4, Saitama University5, University of Surrey6, University of Milan7, Commissariat à l'énergie atomique et aux énergies alternatives8, University of Manchester9, University of Rochester10, Lawrence Berkeley National Laboratory11, University of Valencia12, Uppsala University13, Spanish National Research Council14, University of Turin15, University of Copenhagen16, Daresbury Laboratory17
TL;DR: In this article, the high-spin structures of the N = 81 isotones 135Xe and 137Ba are investigated after multinucleontransfer (MNT) and fusion-evaporation reactions.
Abstract: The high-spin structures of the N = 81 isotones 135Xe and 137Ba are investigated after multinucleontransfer (MNT) and fusion-evaporation reactions. Both nuclei are populated in (i) 136Xe+238U and (ii) 136Xe+208Pb MNT reactions employing the high-resolution Advanced Gamma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (iii), in the 136Xe+198Pt MNT reaction employing the -ray array GAMMASPHERE in combination with the gas detector array Chico, and (iv) via a 11B+130Te fusion-evaporation reaction. The high-spin level schemes of 135Xe and 137Ba are considerably extended to higher energies. The 2058-keV (19=2 ) state in 135Xe is identified as an isomer, completing the systematics for the N = 81 isotones. Its half-life is measured to be 8.6(10) ns, corresponding to a transition probability of B(E2; 19=2 ! 15=2 ) = 0:539(69) W.u. Latest shell model calculations considering 132Sn as a closed core reproduce the experimental findings and provide guidance to the interpretation of the new levels. The experimentally deduced reduced quadrupole transition probabilities of the isomeric states are compared to shell-model predictions.
TL;DR: In this paper, lifetime measurements were performed by using the Cologne plunger device for deep inelastic reactions and the Recoil Distance Doppler Shift technique to investigate the neutron effective single-particle energy sequence above the $78}\mathrm{Ni}$ core.
Abstract: Background: While the $N=50$ shell-gap evolution towards $^{78}\mathrm{Ni}$ is presently in the focus of nuclear structure research, experimental information on the neutron effective single-particle energy sequence above the $^{78}\mathrm{Ni}$ core remain scarce. Direct nucleon-exchange reactions are indeed difficult with presently available post-accelerated radioactive-ion beams (especially for high orbital-momentum orbitals) in this exotic region.Purpose: In this study we probe the evolution of the $\ensuremath{
u}1{g}_{7/2}$ effective single-particle energy which is a key to understanding the possible evolution of the spin-orbit splitting due to the proton-neutron interaction in the $^{78}\mathrm{Ni}$ region. To achieve this goal, a method based on lifetime measurements is used for the first time. The obtained lifetimes of the $7/{2}_{1}^{+}$ states in $^{87}\mathrm{Kr}$ and $^{85}\mathrm{Se}$ are used to investigate the $\ensuremath{
u}1{g}_{7/2}$ evolution.Method: Yrast and near-yrast states in the light $N=51$ isotones $^{85}\mathrm{Se}$ and $^{87}\mathrm{Kr}$ were populated via multinucleon transfer reactions, using a $^{82}\mathrm{Se}$ beam and a $^{238}\mathrm{U}$ target at the LNL tandem-ALPI facility. The prompt $\ensuremath{\gamma}$ rays were detected by the AGATA Demonstrator and particle identification was performed using the PRISMA spectrometer. Lifetime measurements were performed by using the Cologne plunger device for deep inelastic reactions and the Recoil Distance Doppler Shift technique.Results: We obtain ${\ensuremath{\tau}}_{(7/{2}_{1}^{+})}=0.{4}_{\ensuremath{-}0.4}^{+1.6}$ ps for $^{87}\mathrm{Kr}$. In the case of $^{85}\mathrm{Se}$ an upper limit of 3(2) ps is obtained for the ${\ensuremath{\tau}}_{7/{2}_{1}^{+}}$ value.Conclusion: For $^{87}\mathrm{Kr}$, the measured $(7/{2}_{1}^{+})$ lifetime is consistent with a core-coupled ${2}^{+}\ensuremath{\bigotimes}\ensuremath{
u}2{d}_{5/2}$ configuration for this state. This result is consistent with that obtained by direct reaction, which validates our method. For $^{85}\mathrm{Se}$, the measured $7/{2}_{1}^{+}$ lifetime limit indicates a very small contribution of the $\ensuremath{
u}1{g}_{7/2}$ configuration to the wave function of this state.
28 Jun 2017
TL;DR: In this article, the authors present advances in nuclear structures studies of neutron-rich systems, focusing on experimental activities based on γ and particle spectroscopy, which require the use of the most advanced detection setups, such as the European array AGATA and also arrays of large size scintillators.
Abstract: Advances in nuclear structures studies of neutron-rich systems are presented, focusing on experimental activities based on γ and particle spectroscopy—ideal probes of the multifaceted nature of the atomic nucleus. Emphasis is given to recent highlights obtained in world’s leading laboratories, in Europe and Japan, by large international collaborations in which the Nuclear Physics group of Milano University has played a key role. In particular, experiments are described taking advantage of both stable and radioactive ion beams, as well as intense neutron beams. They require the use of the most advanced detection setups, such as the European array AGATA, based on γ-ray tracking techniques, and also arrays of large size scintillators. Measurements of cross sections of thermonuclear fusion reactions at astrophysically relevant energies, performed by the LUNA collaboration, are also briefly discussed. Finally, research and developments of detectors based on novel scintillators materials are presented, being a significant part of the activity carried out at the Milano Physics Department.