First Measurement of the 96^{96}Ru(p,γ\gamma)97^{97}Rh Cross Section for the p-Process with a Storage Ring

This work presents a direct measurement of the $^{96}$Ru($p, \gamma$)$^{97}$Rh cross section via a novel technique using a storage ring, which opens opportunities for reaction measurements on unstable nuclei. A proof-of-principle experiment was performed at the storage ring ESR at GSI in Darmstadt, where circulating $^{96}$Ru ions interacted repeatedly with a hydrogen target. The $^{96}$Ru($p, \gamma$)$^{97}$Rh cross section between 9 and 11 MeV has been determined using two independent normalization methods. As key ingredients in Hauser-Feshbach calculations, the $\gamma$-ray strength function as well as the level density model can be pinned down with the measured ($p, \gamma$) cross section. Furthermore, the proton optical potential can be optimized after the uncertainties from the $\gamma$-ray strength function and the level density have been removed. As a result, a constrained $^{96}$Ru($p, \gamma$)$^{97}$Rh reaction rate over a wide temperature range is recommended for $p$-process network calculations.Comment: 10 pages, 7 figs, Accepted for publication at PR

Measurements of proton-induced reactions on ruthenium-96 in the ESR at GSI

8th International Conference on Nuclear Physics at Storage Rings Stori11, October 9-14, 2011 Laboratori Nazionale di Frascati, Italy. Storage rings offer the possibility of measuring proton- and alpha-induced reactions in inverse kinematics. The combination of this approachwith a radioactive beamfacility allows, in principle, the determination of the respective cross sections for radioactive isotopes. Such data are highly desired for a better understanding of astrophysical nucleosynthesis processes like the p-process. A pioneering experiment has been performed at the Experimental Storage Ring (ESR) at GSI using a stable 96Ru beam at 9-11 AMeV and a hydrogen target. Monte-Carlo simulations of the experiment were made using the Geant4 code. In these simulations, the experimental setup is described in detail and all reaction channels can be investigated. Based on the Geant4 simulations, a prediction of the shape of different spectral components can be performed. A comparison of simulated predictions with the experimental results shows a good agreement and allows the extraction of the cross section

Coulomb dissociation of N 20,21

Neutron-rich light nuclei and their reactions play an important role in the creation of chemical elements. Here, data from a Coulomb dissociation experiment on N20,21 are reported. Relativistic N20,21 ions impinged on a lead target and the Coulomb dissociation cross section was determined in a kinematically complete experiment. Using the detailed balance theorem, the N19(n,γ)N20 and N20(n,γ)N21 excitation functions and thermonuclear reaction rates have been determined. The N19(n,γ)N20 rate is up to a factor of 5 higher at

Experimental Study of collective electric dipole mode in neutron rich nickel nuclei [23.11.2009]

OnTEAM metadata: GDSID: DOC-2010-Oct-78; Attribute ID: LIBRARY-thesis_diss-2010-016; Title: [GSI Diss 2010-13] Experimental Study of collective electric dipole mode in neutron rich nickel nuclei [23.11.2009]; Author(s): Le Bleis, Tudi; Corporate author(s): ; Publication date: 20101015; Creator: manton; Creation date: 15.10.2010 14:59:50; Change date: 15.10.2010 15:22:07; Access: Welt; Attribute type: Text.Thesis.Diss; Directory path: ['GSI Publications', 'GSI as Publisher']; Attribute path: ['Infrastructure', 'Library and Documentation', 'thesis_diss', 'Added in 2010']; File name(s): ['DOC-2010-Oct-78-1.pdf']; File title(s): ['']; File access: ['GSI-intern'

Experimental Study of Collective Electric Dipole Mode in Neutron-Rich Nickel Nuclei

As a response to an external perturbation, a nucleus can be collectively excited. Amongthose collective excitations exist the giant resonances, which have been extensively studiedin stable nuclei. However, their evolution as the isospin asymmetry increases is not so wellknown. Theoretical models predict the appearance of a new component in the isovectorelectric dipole response, the pygmy dipole resonance. Recently, experimental methods ofinvestigating giant resonances for unstable nuclei have been developed. The observation ofa concentration of strength below the giant dipole resonance (GDR) has been reported inneutron-rich nuclei, in particular, by the LAND collaboration at GSI, on neutron-rich Snisotopes.The pygmy dipole resonance, which can macroscopically be interpreted as an oscillationof the neutron-skin against an isospin-saturated core, provides valuable information forthe nuclear structure of instable nuclei. We report on another experiment performed ina different mass region, i.e. the neutron-rich Ni nuclei. The experiment is based on theheavy-ion induced electromagnetic excitation at relativistic energies (around 500 MeV/u)technique. This excitation mechanism is almost identical to that of real photons.The interaction is studied in a kinematically complete setup. The projectile is detected andidentified before hitting the target. All the products of the decay from the resonance aredetected and their momenta measured.Recent development increases the modular behaviour of the setup. Particularly the devel-opment of new electronic modules and data acquisition system. A libraries-based softwarefor VME modules has been developed.After the experiment, all the detectors have been calibrated and integrated cross sectionshave been determined. Using measurements on C, Sn and Pb targets, a model for thenuclear contribution to the cross section has been established.The measured one-neutron and one-neutron-one-proton electromagnetic dissociation crosssection from the stable 58Ni, 127(6) mb, is in agreement with the published cross section127(12) mb, measured with a direct γ absorption.One- and two-neutron electromagnetic dissociation cross sections have been determined for67−69Ni. Compared with a semi-classical calculation, the measurements present a shift ofthe dipole strength to lower energies. This shift cannot be explained by an underlyinggiant quadrupole resonance. Calculations were done using a simple model for the pygmydipole resonance, located at 9 MeV and 11 MeV, according to results of a random-phaseapproximation prediction and of a measurement using (γ, γ′) reaction. The observed excesswould be consistent with a pygmy dipole resonance located at 11 MeV and exhausting8.2(9)% of the energy weighted sum rule, or exhausting 5.2(6)% of the sum rule if thepygmy were located at 9 MeV.Although further analysis is required in order to determine the details of its strength dis-tribution, the appearance of a low-lying (“pygmy”) dipole mode in 68Ni seems evident fromthe present experiment

Etude expérimentale du mode collectif et électrique dans les noyaux du Ni riches en neutrons

Le travail présenté dans cette thèse a consisté pour une part à préparer des expériences sur les noyaux à asymétrie en isospin. En particulier, j ai développé un nouveau système de lecture des modules VME pour le système d acquisition des données associé à ces expériences. J ai conservé autant que possible la modularité du système expérimental: l ajout ou le retrait de modules doit rester simple autant que possible.Pour la seconde part, l étude expérimentale d une concentration de force dipolaire à basse énergie est présentée. Cette présentation inclue les outils théoriques utilisés, le mécanisme de réaction, le montage expérimental, la calibration des détecteurs et la détermination des sections efficaces. Ces dernières sont consistantes pour le 58Ni avec des mesures publiées obtenues en cinématiques directe. Une GDR seule ne peut expliquer les sections efficaces intégrales obtenues pour les émissions de neutrons à partir des noyaux de 67-69Ni. En particulier, ces sections efficaces sont consistantes avec une résonance pygmée localisée à 11MeV et représentant 8.2(9)% de la règle de somme TRK pour le 68Ni.The work of this thesis consisted on one hand, the preparation of experiments on isospin-asymmetric nuclei. In particular, I developed a new read-out for VME modules for the data acquisition system associated with those experiments. I developed this new read-out trying to keep the modularity of the experimental setup: adding and removing modules should be kept as easy as possible.On the other hand, an experiment on the low-lying dipolar strength is presented, from the theoretical tools involved to integrated cross-sections via the reaction mechanism, the experimental setup, the calibration of the detectors and the determination of the cross-section. In particular I found that the integral cross-section for 58Ni obtained by the Coulomb excitation is consistent with published results obtained by excitation in normal kinematics. The study of the dipolar response of 67-69Ni shows that the GDR cannot describe the measured cross sections. In particular the cross sections 68Ni are consistent with a pygmy resonance located at 11MeV and exhausting 8.2(9)% of the TRK sum rule.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Exclusive measurements of quasi-free proton scattering reactions in inverse and complete kinematics

Quasi-free scattering reactions of the type (p, 2p) were measured for the first time exclusively in complete and inverse kinematics, using a 12C beam at an energy of ∼400 MeV/u as a benchmark. This new technique has been developed to study the single-particle structure of exotic nuclei in experiments with radioactive-ion beams. The outgoing pair of protons and the fragments were measured simultaneously, enabling an unambiguous identification of the reaction channels and a redundant measurement of the kinematic observables. Both valence and deeply-bound nucleon orbits are probed, including those leading to unbound states of the daughter nucleus. Exclusive (p, 2p) cross sections of 15.8(18) mb, 1.9(2) mb and 1.5(2) mb to the low-lying 0p-hole states overlapping with the ground state (3/2−) and with the bound excited states of 11B at 2.125 MeV (1/2−) and 5.02 MeV (3/2−), respectively, were determined via γ -ray spectroscopy. Particle-unstable deep-hole states, corresponding to proton removal from the 0s-orbital, were studied via the invariant-mass technique. Cross sections and momentum distributions were extracted and compared to theoretical calculations employing the eikonal formalism. The obtained results are in a good agreement with this theory and with direct-kinematics experiments. The dependence of the proton–proton scattering kinematics on the internal momentum of the struck proton and on its separation energy was investigated for the first time in inverse kinematics employing a large-acceptance measurement

Well developed deformation in Si42

Excited states in Si38,40,42 nuclei have been studied via in-beam γ-ray spectroscopy with multinucleon removal reactions. Intense radioactive beams of S40 and S44 provided at the new facility of the RIKEN Radioactive Isotope Beam Factory enabled γ-γ coincidence measurements. A prominent γ line observed with an energy of 742(8) keV in Si42 confirms the 2 + state reported in an earlier study. Among the γ lines observed in coincidence with the 2 +→0 + transition, the most probable candidate for the transition from the yrast 4 + state was identified, leading to a 41+ energy of 2173(14) keV. The energy ratio of 2.93(5) between the 21+ and 41+ states indicates well-developed deformation in Si42 at N=28 and Z=14. Also for Si38,40 energy ratios with values of 2.09(5) and 2.56(5) were obtained. Together with the ratio for Si42, the results show a rapid deformation development of Si isotopes from N=24 to N=28. © 2012 American Physical Society.link_to_subscribed_fulltex

In-beam γ -ray spectroscopy of 38,40,42Si

Excited states in the nuclei 38,40,42 Si have been studied using in-beam Γ-ray spectroscopy following multi-nucleon removal reactions to investigate the systematics of excitation energies along the Z=14 isotopic chain. The most probable candidates for the transition from the yrast 4 + state were tentatively assigned among several γ lines newly observed in the present study. The energy ratios between the 21 + and 41 + states were obtained to be 2.09(5), 2.56(5) and 2.93(5) for 38,40,42Si, respectively, indicating a rapid development of deformation in Si isotopes from N=24 to, at least, N=28. © Owned by the authors, published by EDP Sciences, 2014.link_to_subscribed_fulltex