Showing papers by "A. Bracco published in 2014"
University of Milan1, University of Padua2, University of Cologne3, Royal Institute of Technology4, University of Strasbourg5, University of Paris-Sud6, University of Valencia7, University of Oslo8, Spanish National Research Council9, DSM10, Daresbury Laboratory11, Uppsala University12, University of Lyon13
TL;DR: In this paper, the properties of pygmy dipole states in Pb-208 were investigated using the distorted wave Born approximation approach, which gave a good description of the elastic scattering and of the inelastic excitation of the 2(+) and 3(-) states.
Abstract: The properties of pygmy dipole states in Pb-208 were investigated using the Pb-208(O-17, O-17'gamma) reaction at 340 MeV and measuring the gamma decay with high resolution with the AGATA demonstrator array. Cross sections and angular distributions of the emitted gamma rays and of the scattered particles were measured. The results are compared with (gamma, gamma') and (p, p') data. The data analysis with the distorted wave Born approximation approach gives a good description of the elastic scattering and of the inelastic excitation of the 2(+) and 3(-) states. For the dipole transitions a form factor obtained by folding a microscopically calculated transition density was used for the first time. This has allowed us to extract the isoscalar component of the 1(-) excited states from 4 to 8 MeV.
49 citations
University of Milan1, University of Cologne2, University of Padua3, Royal Institute of Technology4, University of Strasbourg5, Centre national de la recherche scientifique6, University of Valencia7, Technische Universität München8, University of Oslo9, University of Liverpool10, Spanish National Research Council11, Western Michigan University12, Michigan State University13, University of Salamanca14, DSM15, Daresbury Laboratory16, Uppsala University17, University of Lyon18
TL;DR: In this article, the gamma decay from the high-lying states of Sn-124 was measured using the inelastic scattering of O-17 at 340 MeV, and the emitted gamma rays were detected with high resolution with the AGATA demonstrator array and the scattered ions were detected in two segmented Delta E-E silicon telescopes.
46 citations
University of Padua1, Istituto Nazionale di Fisica Nucleare2, University of Milan3, University of Valencia4, GSI Helmholtz Centre for Heavy Ion Research5, National Physical Laboratory6, University of Surrey7, University of Warsaw8, Polish Academy of Sciences9, University of Brighton10, University of Santiago de Compostela11, Hungarian Academy of Sciences12, King Abdulaziz City for Science and Technology13, University of São Paulo14, University of Vigo15, University of Salamanca16, Technische Universität München17, Lund University18, Comenius University in Bratislava19, University of Delhi20, University of Cologne21
TL;DR: The role of allowed Gamow-Teller and first-forbidden β transitions in this mass region is discussed in this paper, where partial level schemes, proposed with the help of systematics and shell-model calculations, are presented.
Abstract: The fragmentation of relativistic uranium projectiles has been exploited at the Gesellschaft fur Schwerionenforschung laboratory to investigate the β decay of neutron-rich nuclei just beyond 208Pb. This paper reports on β-delayed γ decays of 211-213Tl, 215Pb, and 215-219Bi de-exciting states in the daughters 211-213Pb, 215Bi, and 215-219Po. The resulting partial level schemes, proposed with the help of systematics and shell-model calculations, are presented. The role of allowed Gamow-Teller and first-forbidden β transitions in this mass region is discussed. © 2014 American Physical Society.
22 citations
TL;DR: In this paper, the shape transition in the neutron-rich Os isotopes is studied by investigating the nucleus through in-beam γ-ray spectroscopy using a two-proton transfer reaction from a 198Pt target to a 82Se beam.
Abstract: The shape transition in the neutron-rich Os isotopes is studied by investigating the neutron-rich 196Os nucleus through in-beam γ-ray spectroscopy using a two-proton transfer reaction from a 198Pt target to a 82Se beam. The beam-like recoils were detected and identified with the large-acceptance magnetic spectrometer PRISMA, and the coincident γ rays were measured with the advanced gamma tracking array (AGATA) demonstrator. The de-excitation of the low-lying levels of the yrast-band of 196Os were identified for the first time. The results are compared with state-of-the-art beyond-mean-field calculations, performed for the even-even 188-198Os isotopes. The new results suggest a smooth transition in the Os isotopes from a more axial rotational behavior towards predominately vibrational nuclei through triaxial configurations. An almost perfect γ-unstable/triaxial rotor yrast band is predicted for 196Os which is in agreement with the experimentally measured excited states
22 citations
12 citations
TL;DR: In this paper, the half-lives of the 9/2 +, 13/2+, and 15 2+ yrast states in the 67Cu nucleus were determined by using the in-beam fast-timing technique.
Abstract: The half-lives of the 9/2 + , 13/2+ , and 15/2+ yrast states in the neutron-rich 67Cu nucleus were determined by using the in-beam fast-timing technique. The experimentally deduced E3 transition strength for the decay of the 9/2+ level to the 3/2- ground state indicates that the wave function of this level might contain a collective component arising from the coupling of the odd proton p3/2 with the 3- state in 66Ni. Theoretical interpretations of the 9/2+ state are presented within the particle-vibration weak-coupling scheme involving the unpaired proton and the 3- state from 66Ni and within shell-model calculations with a 56Ni core using the jj44b residual interaction. The shell model also accounts reasonably well for the other measured electromagnetic transition probabilities.
12 citations
10 citations
14 Apr 2014
TL;DR: In this article, a selection of the properties of large volume, cylindrical 3.5" x 8" LaBr 3 detectors coupled with a three-5" PMT and a special designed Voltage Divider (LABRVD) is discussed.
Abstract: A selection of the properties of large volume, cylindrical 3.5” x 8” LaBr 3 :Ce scintillation detectors coupled to a 3.5” PMT (model R10233-1000SEL from HAMAMATSU) and a special designed Voltage Divider (LABRVD) will be discussed. A number of 10 of such detectors constitute the HECTOR + array which, in fall 2012, measured at GSI coupled to the AGATA DEMOSTRATOR at the PRESPEC experimental setup. These crystals are among the largest ever produced and needed to be characterized. We have performed several tests and here we discuss, in particular, the energy resolution measured using monochromatic γ −ray sources and in-beam reactions producing γ −rays up to 22.6 MeV. As already measured in two previous works a saturation in the energy resolution was observed in case of high energy gamma rays. Crystal non-homogeneities and PMT gain drifts can affect the resolution of measurements especially in case of high energy γ −rays.
10 citations
University of Warsaw1, University of Valencia2, Spanish National Research Council3, University of Padua4, Polish Academy of Sciences5, Hungarian Academy of Sciences6, GSI Helmholtz Centre for Heavy Ion Research7, University of Surrey8, Lund University9, Istanbul University10, University of Santiago de Compostela11, University of Milan12, University of Salamanca13, University of Liverpool14, Autonomous University of Madrid15, University of York16
TL;DR: The absence of any sizable low-lying Gamow-Teller strength in the reported beta-decay experiment supports the hypothesis of a negligible role of coherent T=0 proton-neutron correlations in (62)Ga.
Abstract: Search for a new kind of superfluidity built on collective proton-neutron pairs with aligned spin is performed studying the Gamow-Teller decay of the T=1, Jπ=0+ ground state of Ge62 into excited states of the odd-odd N=Z nucleus Ga62. The experiment is performed at GSI Helmholtzzentrum fur Schwerionenforschung with the Ge62 ions selected by the fragment separator and implanted in a stack of Si-strip detectors, surrounded by the RISING Ge array. A half-life of T1/2=82.9(14) ms is measured for the Ge62 ground state. Six excited states of Ga62, populated below 2.5 MeV through Gamow-Teller transitions, are identified. Individual Gamow-Teller transition strengths agree well with theoretical predictions of the interacting shell model and the quasiparticle random phase approximation. The absence of any sizable low-lying Gamow-Teller strength in the reported beta-decay experiment supports the hypothesis of a negligible role of coherent T=0 proton-neutron correlations in Ga62. (Less)
10 citations
University of Padua1, University of Valencia2, Hungarian Academy of Sciences3, University of Surrey4, University of Santiago de Compostela5, GSI Helmholtz Centre for Heavy Ion Research6, University of Milan7, University of Brighton8, University of Vigo9, Indian Institute of Technology Roorkee10, University of Salamanca11, Technische Universität München12, Polish Academy of Sciences13, Lund University14, Comenius University in Bratislava15, University of Delhi16, University of Cologne17, University of Warsaw18
TL;DR: In this paper, the structure of the neutron-rich bismuth isotope 217Bi has been studied for the first time using the fragmentation of a primary 238U beam at the FRS-RISING setup at GSI.
Abstract: The structure of the neutron-rich bismuth isotope 217Bi has been studied for the first time. The fragmentation of a primary 238U beam at the FRS-RISING setup at GSI was exploited to perform γ-decay spectroscopy, since μs isomeric states were expected in this nucleus. Gamma rays following the decay of a t1/2=3 μs isomer were observed, allowing one to establish the low-lying structure of 217Bi. The level energies and the reduced electric quadrupole transition probability B(E2) from the isomeric state are compared to large-scale shell-model calculations.
6 citations
TL;DR: In this paper, the reduced transition strengths of the deexciting transitions from the first two excited states in 33Ar were measured in a relativistic Coulomb excitation experiment at the GSI Helmholtz center.
Abstract: Reduced transition strengths of the deexciting transitions from the first two excited states in 33Ar were
measured in a relativistic Coulomb excitation experiment at the GSI Helmholtz center. The radioactive ion
beam was produced by fragmentation of a primary 36Ar beam on a 9Be target followed by the selection of
the reaction product of interest via the GSI Fragment Separator. The 33Ar beam hit a secondary 197Au target
with an energy of approximately 145 MeV/nucleon. An array of high-purity germanium cluster detectors
and large-volume BaF2 scintillator detectors were employed for γ -ray spectroscopy at the secondary target
position. The Lund-York-Cologne Calorimeter was used to track the outgoing ions and to identify the nuclear
reaction channels. For the two lowest energy excited states of 33Ar the reduced transition strengths have been
determined. With these first results the Tz = −3/2 nucleus 33Ar is now, together with 21Na (Tz = −1/2),
the only neutron-deficient odd-A sd shell nucleus in which experimental transition strengths are available.
The experimental values are compared to results of shell-model calculations which describe simultaneously
mirror-energy differences and transition-strength values of mirror pairs in the sd shell in a consistent way
01 Mar 2014
TL;DR: In this article, a theoretical approach was developed to describe secondary particle emission in heavy ion collisions, with special regards to pre-equilibrium α-particle production, and the probabilities of neutron, proton and αparticle emission were evaluated for both the equilibrium and preequilibrium stages of the process.
Abstract: A theoretical approach was developed to describe secondary particle emission in heavy ion collisions, with special regards to pre-equilibrium α-particle production. The probabilities of neutron, proton and α-particle emission have been evaluated for both the equilibrium and pre-equilibrium stages of the process. Effects due the possible cluster structure of the projectile which has been excited during the collisions have been experimentally evidenced studying the double differential cross sections of p and α-particles emitted in the E=250MeV 16 O + 116 Sn reaction. Calculations within the present model with different clusterization probabilities have been compared to the experimental data.
TL;DR: In this paper, the soft dipole modes in 140 Ce, excited via inelastic scattering of weakly bound 17 O projectiles, were investigated for the first time, and the main aim was to investigate the splitting of the PDR into two parts: a low-energy isoscalar component dominated by neutron skin oscillations and a higher-energy component lying on the tail of the giant dipole resonance of a rather isovector character.
Abstract: The main aim of this study was a deeper understanding of the nuclear structure properties of the soft dipole modes in 140 Ce, excited via inelastic scattering of weakly bound 17 O projectiles. An important aim was to investigate the ‘splitting’ of the PDR into two parts: a low-energy isoscalar component dominated by neutron-skin oscillations and a higher-energy component lying on the tail of the giant dipole resonance of a rather isovector character. This was already observed for this nucleus, investigated in (α, α′) and (γ, γ′) experiments. The experiment was performed at Laboratori Nazionali di Legnaro, Italy. Inelastic scattering of 17 O ion beam at − 2 0M eV A 1 was
01 Mar 2014
TL;DR: In this article, the lifetime of the 9/2 + state of 65 Cu, at 2534 keV, has been measured by fast timing techniques, in order to establish wether such state arises from a weak coupling between a p3=2 proton and the 3 octupole vibration at 3.56 MeV in the 64 Ni core.
Abstract: The lifetime of the 9/2 + state of 65 Cu, at 2534 keV, has been measured by fast timing techniques, in order to establish wether such state arises from a weak coupling between a p3=2 proton and the 3 octupole vibration at 3.56 MeV in the 64 Ni core. The 65 Cu nucleus was populated by the reaction 7 Li + 64 Ni at 32 MeV, at the Horia Hu- lubei National Institute of Physics and Nuclear Engineering (NIPNE) in Bucharest, and its -decay was detected by the ROSPHERE array. The measured lifetime coresponds to a B(E3) reduced transition probability to the ground state equal to 8.89 W.u., in agreement with theoretical predictions in the weak coupling limit.
TL;DR: In this article, an exploratory experiment performed at REX-ISOLDE to investigate neutron-rich Sr, Y and Zr nuclei around mass A = 100 by cluster transfer reactions of radioactive 98Rb/98Sr beams on a 7Li target is presented.
Abstract: In this work, we present an exploratory experiment performed at REX-ISOLDE to investigate neutron-rich Sr, Y and Zr nuclei around mass A = 100 by cluster transfer reactions of radioactive 98Rb/98Sr beams on a 7Li target. The goal of the experiment is to test the potential of clustertransfer mechanism to study the low-lying structure of neutron-rich nuclei, performing, as a first case, a -spectroscopy study of the structure in deformed nuclei beyond N = 60 populated, so far, only via β decay and spontaneous fission experiments.
01 Mar 2014
TL;DR: In this article, isospin mixing induced by the Coulomb interaction has been studied in the compound nucleus 80 Zr at T 2 MeV produced in the fusion-evaporation reaction 40 Ca+40 Ca at E beam = 136 MeV.
Abstract: Isospin mixing induced by the Coulomb interaction has been studied in the compound nucleus 80 Zr at T~2 MeV produced in the fusion-evaporation reaction 40 Ca+ 40 Ca at E beam = 136 MeV. The isospin impurity was measured using the first step of the Giant Dipole Resonance γ decay. The preliminary value of the Coulomb spreading width has been extracted via statistical model analysis of the measured γ spectrum.
TL;DR: Low-energy enhancement of nuclear γ strength and its impact on astrophysical reaction rates and its effect on astrophysics reaction rates is studied.
Abstract: Larsen, Ann-Cecilie; Blasi, Nives; Bracco, Angela; Burger, Arnold; Camera, Franco; Eriksen, Tomas Kvalheim; Giacoppo, Francesca; Goriely, Stephan; Guttormsen, Magne Sveen; Gorgen, Andreas; Hagen, Trine Wiborg; Harissopulos, Sotirios; Koehler, Paul Edward; Leoni, Silvia; Million, Benedicte; Nyhus, Hilde-Therese; Renstrom, Therese; Rose, Sunniva Johanne; Ruud, Inger Eli; Schiller, Andreas Ulrich; Siem, Sunniva; Tornyi, Tamas Gabor; Tveten, Gry Merete; Voinov, Alexander; Wiedeking, Mathis.
Low-energy enhancement of nuclear γ strength and its impact on astrophysical reaction rates. The European Physical Journal Conferences 2014 ;Volum 66:07014.
01 Mar 2014
TL;DR: In this article, the 48 Ti on 40 Ca reactions have been studied at 300 and 600 MeV focusing on the fusion-evaporation (FE) and fusion-fission (FF) exit channels.
Abstract: The 48 Ti on 40 Ca reactions have been studied at 300 and 600 MeV focusing on the fusion-evaporation (FE) and fusion-fission (FF) exit channels. Energy spectra and multiplicities of the emitted light charged particles have been compared to Monte Carlo simulations based on the statistical model. Indeed, in this mass region (A 100) models predict that shape transitions can occur at high spin values and relatively scarce data exist in the literature about coincidence mea- surements between evaporation residues and light charged particles. Signals of shape transitions can be found in the variations of the lineshape of high energy gamma rays emitted from the de-excitation of GDR states gated on di erent region of angular mo- menta. For this purpose it is important to keep under control the FE and FF processes, to regulate the statistical model parameters and to control the onset of possible pre- equilibrium emissions from 300 to 600 MeV bombarding energy.
TL;DR: In this article, the editorial board of NuPECC is an expert board of the European Science Foundation (ESF), which is largely and continuously benefitting from this position.
Abstract: It has been decided by the editorial board to inform the readers in brief on the European Science Foundation (ESF). NuPECC is an expert board of this organization, which is largely and continuously benefitting from this position.
01 Mar 2014
TL;DR: In this article, a new measurement of the dynamical dipole emission was performed by studying 16 O + 116 Sn at 12 MeV/u, and the measured trend with beam energy does not confirm the rise and fall behavior previously reported for the same fused compound but with a much higher dipole moment.
Abstract: In heavy ion reactions, in the case of N/Z asymmetry between projectile and target, the process leading to complete fusion is expected to produce pre-equilibrium dipole γ -ray emission. It is generated during the charge equilibration process and it is known as Dynamical Dipole. A new measurement of the dynamical dipole emission was performed by studying 16 O + 116 Sn at 12 MeV/u. These data, together with those measured at 8.1 MeV/u and 15.6 MeV/u for the same reaction, provide the dependence on the Dynamical Dipole total emission yield with beam energy and they can be compared with theoretical expectations. The experimental results show a weak increase of the Dynamical Dipole total yield with beam energies and are in agreement with the prediction of a theoretical model based on the Boltzmann–Nordheim–Vlasov (BNV) approach. The measured trend with beam energy does not confirm the rise and fall behavior previously reported for the same fused compound but with a much higher dipole moment.
01 Sep 2014
TL;DR: The gamma decay of the giant dipole resonance (including its tail region) is an important tool to probe the properties of these states, and thus to test the predictions of mean field theories as discussed by the authors.
Abstract: The gamma decay of the giant dipole resonance (including its tail region) is an important tool to probe the properties of these states, and thus to test the predictions of mean field theories. This paper focuses on two main aspects concerning the electric dipole excitation in nuclei. These are the study of the isospin character of the low en- ergy tail of the Giant Dipole Resonance (GDR), the so-called Pygmy resonance, and the isospin mixing of nuclear systems at finite temperature. In the first case, the Pygmy reso- nance has been populated in the inelastic scattering reaction 17 O+ 124 Sn at 20 MeV/u. Its gamma decay has been measured using the AGATA Demonstrator and an array of 8 large volume LaBr3:Ce scintillators. In the second case, the gamma decay of the GDR in ther- malized nuclear systems, formed in fusion evaporation reactions, has been used to inves- tigate the isospin mixing in 80 Zr. For this work the reactions 40 Ca+ 40 Ca at 3.4 MeV/u and 37 Cl + 44 Ca at 2.6 MeV/u were used.
01 Mar 2014
TL;DR: In this article, a shape transition between a slightly prolate deformed to an oblate deformed ground state was deduced from the observed level schemes for even-even osmium isotopes.
Abstract: The neutron-rich isotopes of tungsten, osmium and platinum have different shapes in their ground states and present also shape transitions phenomena. Spectroscopic information for these nuclei is scarce and often limited to the gamma rays from the decay of isomeric states. For the neutron-rich even-even osmium isotopes 194 Os and 198 Os, a shape transition between a slightly prolate deformed to an oblate deformed ground state was deduced from the observed level schemes. For the even-even nucleus lying in between, 196 Os, no gamma ray transition is known. In order to elucidate the shape transition and to test the nuclear models describing it, this region was investigated through gamma-ray spectroscopy using the AGATA demonstrator and the large acceptance heavy-ion spectrometer PRISMA at LNL, Italy. A two-nucleon transfer from a 198 Pt target to a stable 82 Se beam was utilized to populate medium-high spin states of 196 Os. The analysis method and preliminary results, including the first life-time measurement of isomeric states with AGATA, are presented.
01 Mar 2014
TL;DR: In this paper, the heavy ion reaction 22 Ne+208 Pb at 128 MeV of bombarding energy has been studied using the PRISMA-CLARA experimental setup at Legnaro National Laboratories.
Abstract: The heavy ion reaction 22 Ne+208 Pb at 128 MeV of bombarding energy has been studied using the PRISMA-CLARA experimental setup at Legnaro National Laboratories. Elastic, inelastic and one nucleon transfer cross sections have been measured. The experimental results are presented in parallel with the analysis on existing data for the unstable 24 Ne nucleus, from the reaction 24 Ne+208 Pb at 182 MeV (measured at SPIRAL with the VAMOS-EXOGAM setup). The β 2 C charge deformation parameter for both 22 Ne and 24 Ne has been determined by a DWBA analysis of the experimental angular dis- tributions, showing a strong reduction for 24 Ne.
01 Jan 2014
TL;DR: In this article, with MINIBALL coupled to T-REX, the one-valence-proton Sb nucleus by the cluster transfer reaction of Sn on Li was investigated, and the results were used to perform advanced tests of different types of nuclear interactions, usually employed in the description of particle-phonon coupled excitations.
Abstract: We propose to investigate, with MINIBALL coupled to T-REX, the one-valence-proton Sb nucleus by the cluster transfer reaction of Sn on Li. The excited Sb will be populated by transfer of a triton into Sn, followed by the emission of an alpha particle (detected in T-REX) and 2 neutrons. The aim of the experiment is to locate states arising from the coupling of the valence proton of Sb to the collective low-lying phonon excitations of Sn (in particular the 3). According to calculations in the weak-coupling approach, these states lie in the 4 – 5 MeV excitation energy region and in the spin interval 1/2 19/2, i.e., in the region populated by the cluster transfer reaction. The results will be used to perform advanced tests of different types of nuclear interactions, usually employed in the description of particle-phonon coupled excitations. States arising from couplings of the proton with simpler core excitations, involving few nucleons only, will also be accessible, providing a very specific test of effective shell model interactions across the shell gap. Predictions for the reaction mechanism, the expected statistics and the observed γ transitions are based, in part, on the experience gained in a test experiment performed by this collaboration at REXISOLDE in November 2012, in preparation of the present research program. Requested shifts: 21 shifts (split into 1 run over 1 year)
Istituto Nazionale di Fisica Nucleare1, University of Padua2, University of Brighton3, Polish Academy of Sciences4, University of Surrey5, University of Warsaw6, University of Santiago de Compostela7, King Abdulaziz City for Science and Technology8, University of Milan9, University of Vigo10, University of Salamanca11, Hungarian Academy of Sciences12, Technische Universität München13, Lund University14, University of Delhi15, University of Cologne16, University of São Paulo17
TL;DR: The region of neutron-rich nuclei beyond 208Pb has been very difficult to explore due to its high mass and exoticity as discussed by the authors, however, recent experimental improvements allowed one to perform a quite extended isomer decay spectroscopy of these nuclei.
Abstract: The region of neutron-rich nuclei beyond 208Pb has been very difficult to explore due to its high mass and exoticity. However, recent experimental improvements allowed one to perform a quite extended isomer decay spectroscopy of these nuclei.
01 Nov 2014
TL;DR: The LaBr3:Ce scintillator offers the unique opportunity to study the β− radioactive decay of 138La, that is a 2nd order unique forbidden transition as discussed by the authors.
Abstract: The LaBr3:Ce scintillator offers the unique opportunity to study the β− radioactive decay of 138La, that is a 2nd order unique forbidden transition The 138La isotope is one of the rarest isotopes on earth (it is present as 009% in natural Lanthanum) and because of its extremely long lifetime, of the order of 1011 years, large amounts of 138La are needed for the measurement of the β− decay spectrum In literature, only one experimental measurement is present and the results are not reproduced by the standard nuclear theory A second measurement of the β− continuum is presented in this work For this measurement, two LaBr3:Ce scintillators (3″ × 3″) and two different experimental techniques were used The shape of the β− continuum spectrum, measured down to the energy of 2–3 keV, is found to be identical to the one previously measured and published On the other side, it is different from the theoretical published spectrum in particular below 75 keV