Pygmy dipole resonance in 140Ce via inelastic scattering of 17O

The γ decay from the high-lying states of Ce140 excited via inelastic scattering of O17 at a bombarding energy of 340 MeV was measured using the high-resolution AGATA-demonstrator array in coincidence with scattered ions detected in two segmented ΔE-E silicon detectors. Angular distributions of scattered ions and emitted γ rays were measured, as well as their differential cross sections. The excitation of 1- states below the neutron separation energy is similar to the one obtained in reactions with the α isoscalar probe. The comparison between the experimental differential cross sections and the corresponding predictions using the distorted-wave Born approximation allowed us to extract the isoscalar component of identified 1- pygmy states. For this analysis the form factor obtained by folding microscopically calculated transition densities and optical potentials was used

Charged particle decay of hot and rotating 88^{88}Mo nuclei in fusion-evaporation reactions

A study of fusion-evaporation and (partly) fusion-fission channels for the $^{88}$Mo compound nucleus, produced at different excitation energies in the reaction $^{48}$Ti + $^{40}$Ca at 300, 450 and 600 MeV beam energies, is presented. Fusion-evaporation and fusion-fission cross sections have been extracted and compared with the existing systematics. Experimental data concerning light charged particles have been compared with the prediction of the statistical model in its implementation in the Gemini++ code, well suited even for high spin systems, in order to tune the main model parameters in a mass region not abundantly covered by exclusive experimental data. Multiplicities for light charged particles emitted in fusion evaporation events are also presented. Some discrepancies with respect to the prediction of the statistical model have been found for forward emitted $\alpha$-particles; they may be due both to pre-equilibrium emission and to reaction channels (such as Deep Inelastic Collisions, QuasiFission/QuasiFusion) different from the compound nucleus formation.Comment: 14 pages, 14 figure

Pygmy dipole resonance in Ce 140 via inelastic scattering of O 17

M. Krzysiek et al. ; 8 págs.; 7 figs. ; 2 tabs.The γ decay from the high-lying states of Ce140 excited via inelastic scattering of O17 at a bombarding energy of 340 MeV was measured using the high-resolution AGATA-demonstrator array in coincidence with scattered ions detected in two segmented ΔE-E silicon detectors. Angular distributions of scattered ions and emitted γ rays were measured, as well as their differential cross sections. The excitation of 1- states below the neutron separation energy is similar to the one obtained in reactions with the α isoscalar probe. The comparison between the experimental differential cross sections and the corresponding predictions using the distorted-wave Born approximation allowed us to extract the isoscalar component of identified 1- pygmy states. For this analysis the form factor obtained by folding microscopically calculated transition densities and optical potentials was used. ©2016 American Physical SocietyThis work has been partly supported by the stipend from Marian Smoluchowski Krakow Research Consortium ’Matter-Energy-Future’ as a Leading National Research Center (KNOW) and also by several grants: the Polish National Science Centre under Contracts No. 2015/17/B/ST2/01534, No. 2013/09/N/ST2/04093, No. 2013/08/M/ST2/00591, and No. 2011/03/B/ST2/01894; US-NSF Grants No. PHY-1204486 and No. PHY-1404343; Croatian Science Foundation under Project No. IP-2014-09-9159; the Spanish Ministerio de Economía y Competitividad under Contract No. FPA2014-57196-C5-4-P. Also, A. Gadea has been supported by MINECO, Spain, under Grant No. FPA2014-57196-C5; Generalitat Valenciana, Spain, under Grant No. PROMETEOII/2014/019; and the EU under the FEDER program. The research leading to these results has also received funding from the European Union Seventh Framework Programme FP7/2007-2013 under Grant Agreement No. 262010 - ENSAR.Peer Reviewe

Photoneutron measurements in the GDR region at ELI-NP

The Extreme Light Infrastructure - Nuclear Physics (ELI-NP) is a facility dedicated to nuclear physics research with extreme electromagnetic fields. The expected gamma-ray beams with energies up to 20 MeV, 0.5% relative energy resolution and similar to 10(8) photons per second intensity will allow precise photonuclear measurements. Nuclear structure experiments will involve photo-excitations of mainly low-spin collective states and the observation of the radiation emitted in the subsequent decays. Photoneutron reactions and elastic and inelastic photon scattering are proposed to be recorded using a mixed gamma-neutron detection system using LaBr3:Ce, CeBr3, BC501A and GS20 detectors. Photoneutron (gamma, xn) with x= 1,2 reactions cross sections measurements will be performed with a 4 pi flat efficiency neutron detection system dedicated for neutron multiplicity sorting experiments. The detection system is comprised of He-3 counters embedded in a moderator block. The paper will introduce the experimental setups dedicated to studies of the nuclear Giant Dipole Resonance excitation mode using the high energy resolution and high intensity ELI-NP gamma-ray beams. The feasibility studies performed using extensive Geant4 simulations, results of detector tests will be presented

Lifetime measurements of short-lived excited states, and shape changes in As 69 and Ge 66 nuclei

Background: The nuclear shape is a macroscopic feature of an atomic nucleus that is sensitive to the underlying nuclear structure in terms of collectivity and the interaction between nucleons. Therefore, the evolution of nuclear shapes has attracted many theoretical and experimental nuclear structure studies. The structure of the A≈70, N≈Z nuclei, lying far from the stability line, is interesting because a particularly strong proton-neutron correlation may occur here due to the occupation of the same orbits by nucleons of both types. In this region, different particle configurations drive a nucleus towards various deformed shapes: prolate, oblate, octupole, or nonaxial. These nuclear shapes change rapidly with nucleon number and also with angular momentum. This is reflected by a presence of different structures (bands) of excited states which exhibit a broad range of lifetimes. Purpose: The aim of this paper is to determine lifetimes of some high-spin excited states in As69 and Ge66 nuclei to examine the shape evolution in these neutron-deficient nuclei. Methods: Lifetimes of high-spin states in As69 and Ge66 have been measured by using the Doppler-shift attenuation technique with the GASP and recoil filter detector setup at the Laboratori Nazionali di Legnaro. The nuclei of interest were produced in the S32(95MeV)+0.8mg/cm2 Ca40 fusion-evaporation reaction. The strongest reaction channels 3p and α2p led to the As69 and Ge66 final nuclei, respectively. Using γ-γ-recoil coincidences we were able to determine very short lifetimes (in the femtosecond range) in the residual nuclei of interest. Results: In As69, the extracted lifetimes are τ=72 (-32, +45) fs for the 33/2+ state at 7897 keV and τ<85 fs for the 37/2+ state at 9820 keV. For the Ge66 case, the lifetime of the 11- state at 7130 keV is τ=122(±41) fs. Lifetimes in As69 and Ge66 reported in this paper have been measured for the first time in the present experiment. Conclusions: The results are discussed in the terms of deformation and shape evolution in As69 and Ge66. The quadrupole moments deduced from the measured lifetimes were compared with the cranked Woods-Saxon-Strutinsky calculations by means of the total Routhian surface method. It turns out that Band 3 in As69 shows an oblate-prolate shape transition, and above spin 33/2+ it corresponds to a prolate collective structure with β2≈0.27 and γ≈20. In turn, in Ge66 the negative-parity band built on the 7- state at 4205 keV corresponds to a triaxial shape with β2=0.33 and γ=31. Analysis of the transitional quadrupole moments derived from the experimental and theoretical ones points to a significant change of deformation in the As69 and Ge66 nuclei with increasing rotational frequency

Study of the γ decay of high-lying states in 208Pb via inelastic scattering of 17O ions

High-lying states in 208Pb nucleus were populated via inelastic scattering of a 17O beam at bombarding energy of 20 MeV/u. Their subsequent gamma decay was measured with the detector system AGATA Demonstrator based on HPGe detectors, coupled to an array of large volume LaBr3:Ce scintillators. Preliminary results in comparison with (γ,γ′) data, for states in the 5–8 MeV energy interval, seem to indicate that in that region the states belong to two different groups one with a isoscalar character and the other with a isovector nature. This is similar to what was observed in other stable nuclei with (α,α′γ) experiments. The multipolarity of the observed gamma transitions is determined with remarkable sensitivity thanks to angular distribution measurements. Data aiming at studying the neutron decay of the Giant Quadrupole Resonance in the 208Pb by the high resolution measurement of the following gamma decay are also presented in their preliminary form

Quadrupole collectivity in Ca 42 from low-energy Coulomb excitation with AGATA

A Coulomb-excitation experiment to study electromagnetic properties of Ca42 was performed using a 170-MeV calcium beam from the TANDEM XPU facility at INFN Laboratori Nazionali di Legnaro. γ rays from excited states in Ca42 were measured with the AGATA spectrometer. The magnitudes and relative signs of ten E2 matrix elements coupling six low-lying states in Ca42, including the diagonal E2 matrix elements of 21+ and 22+ states, were determined using the least-squares code gosia. The obtained set of reduced E2 matrix elements was analyzed using the quadrupole sum rule method and yielded overall quadrupole deformation for 01,2+ and 21,2+ states, as well as triaxiality for 01,2+ states, establishing the coexistence of a weakly deformed ground-state band and highly deformed slightly triaxial sideband in Ca42. The experimental results were compared with the state-of-the-art large-scale shell-model and beyond-mean-field calculations, which reproduce well the general picture of shape coexistence in Ca42

Superdeformed and Triaxial States in Ca 42

Shape parameters of a weakly deformed ground-state band and highly deformed slightly triaxial sideband in ^{42}Ca were determined from E2 matrix elements measured in the first low-energy Coulomb excitation experiment performed with AGATA. The picture of two coexisting structures is well reproduced by new state-of-the-art large-scale shell model and beyond-mean-field calculations. Experimental evidence for superdeformation of the band built on 0_{2}^{+} has been obtained and the role of triaxiality in the A∼40 mass region is discussed. Furthermore, the potential of Coulomb excitation as a tool to study superdeformation has been demonstrated for the first time