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8 pags., 10 figs., 3 tabs., The Borromean drip-line nucleus Ne-17 has been suggested to possess a two-proton halo structure in its ground state. In the astrophysical rp-process, where the two-proton capture reaction O-15(2p,gamma) Ne-17 plays an important role, the calculated reaction rate differs by several orders of magnitude between different theoretical approaches. To add to the understanding of the Ne-17 structure we have studied nuclear and electromagnetic dissociation. A 500 MeV/u Ne-17 beam was directed toward lead, carbon, and polyethylene targets. Oxygen isotopes in the final state were measured in coincidence with one or two protons. Different reaction branches in the dissociation of Ne-17 were disentangled. The relative populations of s and d states in F-16 were determined for light and heavy targets. The differential cross section for electromagnetic dissociation (EMD) shows a continuous internal energy spectrum in the three-body system O-15 + 2p. The Ne-17 EMD data were compared to current theoretical models. None of them, however, yields satisfactory agreement with the experimental data presented here. These new data may facilitate future development of adequate models for description of the fragmentation process., This project is supported by NAVI, GSI-TU Darmstadt cooperation, HIC for FAIR, EMMI, and BMBF and from DFG through Grant No. SFB1245 and from BMBF via Project No. 05P15RDFN1, and from the Spanish Ministry by research grant FPA2015-64969-P. C.A.B. acknowledges support by the US DOE Grant No. DE-FG02-08ER41533 and the US NSF Grant No. 1415656.

Open Access funded by SCOAP3 - Sponsoring Consortium for Open Access Publishing in Particle Physics, One-neutron knockout reactions from Borromean nuclei are analyzed using a profile function analysis technique. The profile function, which is derived as the square root of the variance of the measured fragment + neutron momenta as a function of their relative energy, is shown to be very sensitive to the angular momentum of the knocked out neutron. Three cases are studied here: 7He, where the profile function analysis shows a presence of (s1/2)2 component in the 8He ground-state wave-function, 10Li, where the presence of a 11(2)% d-wave contribution to the relative energy spectrum above 1.5 MeV is found and, finally, the presence of a major s contribution around 0.5 MeV relative energy in the 13Be case and that the observed decay to the 12Be 2+ state originates in a d state in 13Be. © 2012 Elsevier Open access under CC BY license., Financial support from the Swedish Research Council and the Spanish Ministry through the research grant FPA2009-07387 is also acknowledged.

States in the N = 28 nucleus Ar-46 have been studied by a two-neutron transfer reaction at REX-ISOLDE (CERN). A beam of radioactive Ar-44 at an energy of 2.16 AMeV and a tritium-loaded titanium target were used to populate Ar-46 by the H-3(Ar-44, p) two-neutron transfer reaction. Protons emitted from the target were identified in the T-REX silicon detector array. The excitation energies of states in Ar-46 have been reconstructed from the measured angles and energies of recoil protons. Angular distributions for three final states were measured and based on the shape of the differential cross section an excited state at 3695 keV was identified as J(pi) = 0(+). The angular differential cross section for the population of different states are compared to calculations using a reaction model employing both sequential and direct transfer of two neutrons. Results are compared to shell-model calculations using state-of-the-art effective interactions.

At the continuous wave (cw) Superconducting Darmstadt Electron Linear Accelerator S-DALINAC, a new method has been developed for the determination of the electric ( α ¯ ) and magnetic ( β ¯ ) polarizabilities of the proton and the deuteron. For that purpose the energy and angular dependence of the differential cross-section for elastic γ p and γ d scattering of bremsstrahlung photons in the energy range between 20 and 100 MeV is measured by detecting the recoiling proton (deuteron) in coincidence with the scattered bremsstrahlung photon. α ¯ and β ¯ are then found by means of a best fit to a theoretical description of the scattering cross-section with these quantities as open parameters. The experimental setup consists of a bremsstrahlung photon facility, two specially designed high pressure hydrogen (deuterium) ionization chambers which serve as targets and detectors of the recoil proton (deuteron), NaI gamma spectrometers and several additional detectors for beam diagnostics and normalization. The whole setup was tested using bremsstrahlung photon beams with endpoint energies of 60 and 79.3 MeV. The results of the test experiments show that future high-statistics measurements are feasible.

A method for the identification of energetic charged particles has been investigated based on the employment of pulse-shape discrimination (PSD) in a silicon detector in addition to conventional time-of-flight (ToF) techniques. The method makes use of the fact that, at fixed energy, the particle's velocity, or ToF, is a measure of the particle's mass A while the time structure of the current pulse in a silicon energy detector, used as the ToF stop, permits identification of nuclear charges Z. In the measurements presented here, ToF and PSD methods were applied simultaneously. We used micro-channel plate (MCP) detectors as fast time pick-offs and surface-barrier (SB) n-type Si detectors made from homogeneously neutron-transmutation-doped (n-TD) silicon. As the particles, products from the reactions of a 400 MeV 20Ne beam impinging on 12C, 27Al and 208Pb targets were employed. With using fast current-sensitive pre-amplifiers for the 250 and 800 μ m SB detectors a major progress in particle identification with respect to both, mass A and charge Z was achieved. In addition, using a stack of two closely mounted n-TD SB detectors, a timing measurement between the two detectors permitted to study PSD in the rear detector with the time trigger derived from the foremost one. Finally, the internal PSD method was implemented which determines pulse rise-time in single detectors from analyzing differentiated preamplifier timing signals.

The unbound isotopes 10Li, 12Li and 13Li have been observed after nucleon-knockout reactions at relativistic energies with 11Li and 14Be beams impinging on a liquid hydrogen target. The channels , and were analysed in the ALADIN-LAND setup at GSI. The 10Li data confirm earlier findings, while the 12Li and 13Li nuclei were observed for the first time. The relative-energy spectrum shows that the ground state of 12Li can be described as a virtual s-state with a scattering length of -13.7(1.6) fm. A broad energy spectrum was found for the channel. Based on the assumption that the relative-energy spectrum is dominated by a correlated background presumably stemming from initial correlations in the 14Be ground-state, evidence for a 13Li resonance at 1.47(31) MeV above the threshold with a width around 2 MeV has been found.

J. Marganiec et al.; 9 pags.; 11 figs.; 2 tabs., © 2015, SIF, Springer-Verlag Berlin Heidelberg. Two-proton decay of the unbound Tz = -2 nucleus 16Ne , produced in one-neutron knockout from a 500 MeV/u 17Ne beam, has been studied at GSI. The ground state, at a resonance energy 1.388(15) MeV, (Γ = 0.082(15) MeV) above the 14O +p+p threshold, and two narrow resonances at Er = 3.220(46) MeV and 7.57(6) MeV have been investigated. A comparison of the energy difference between the first excited 2+ state and the 0+ ground state in 16Ne with its mirror nucleus 16C reveals a small Thomas-Ehrman shift (TES) of +70(46) keV. A trend of the TES for the T = 2 quintet is obtained by completing the known data with a prediction for 16F obtained from an IMME analysis. The decay mechanisms of the observed three resonances were revealed from an analysis of the energy and angular correlations of the 14O +p+p decay products. The ground state decay can be considered as a genuine three-body (democratic) mode and the excited states decay sequentially via states in the intermediate nucleus 15F , the 3.22 MeV state predominantly via the 15F ground-state resonance, while the 7.57 MeV state decays via the 5/2+ resonance in 15F at 2.8 MeV above the 14O +p+p threshold. Further, from an analysis of angular correlations, the spin-parity of the 7.57 MeV state has been determined as IП = 2+ and assigned as the third 2+ state in 16Ne based on a comparison with 16C., This work is partly supported by the Helmholtz International Center for FAIR within the framework of the LOEWE program launched by the State of Hesse, by the German Federal Ministry for Education and Research (BMBF), EU(EURONS), ExtreMe Matter Institute EMMI, GSI-TU Darmstadt cooperation, Nuclear Astrophysics Virtual Institutes NAVI. Financial support from the Swedish Research Council, the Spanish grants FPA-2010-17142, MICCIN FPA2009-14604-C02-01, FPA2012- 39404-C02-01and MINECO FPA 2012-32443 are also acknowledged. One of us (BJ) is a Helmholtz International Fellow

A search for the J(pi) = 1/2(-) spin-orbit partner of the J(pi) = 3/2(-) ground state in He-7 has been performed with the Li-7(d, He-2) charge-exchange reaction. The experimental results are incompatible with recent claims of such a state at very low excitation energy [M. Meister, et al., Phys. Rev. Lett. 88 (2002) 102501]. A decomposition of the spectrum is performed taking into account known resonances and quasifree charge-exchange reactions on Li-7 as well as on triton and He-4 clusters in the Li-7 ground state. A possible resonance at an excitation energy E-x approximate to 1.45 MeV with a width Gamma approximate to 2.0 MeV is suggested when the quasifree charge-exchange process on Li-7 is constrained by a measurement of the Li-6(d, He-2) reaction. Gamow-Teller strengths for transitions to the lowest states in He-7 deduced from the differential cross sections are in remarkable agreement with results from ab initio quantum Monte Carlo calculations. (c) 2006 Elsevier B.V. All rights reserved.

The one-neutron transfer reaction Li-9 + H-2 -> Li-8 + t has been investigated in an inverse kinematics experiment by bombarding a deuterated polypropylene target with a 2.36 MeV/u Li-9 beam from the post-accelerator REX-ISOLDE at CERN. Excitation energies in Li-8 as well as angular distributions of the tritons were obtained and spectroscopic factors deduced. (c) 2006 Elsevier B.V. All rights reserved.

20 pages, 2 tables, 9 figures, 1 appendix.-- PACS nrs.: 25.60.-t; 27.20.+n; 25.70.De; 25.75.Gz.-- Printed version published Sep 5, 2005., Dissociation of He-6 on a lead target has been studied at 240 MeV/u. The four-momenta of the two neutrons in coincidence with alpha-particles have been measured and used to reconstruct the three-body energy and angular correlations in the final state. For the first time, three-body correlations were included in the analysis of the He-6 dissociation data, and compared with calculations assuming a dipole mode for the electromagnetic dissociation. In addition, the experimental data have been analyzed using a series expansion of the final transition amplitude into hyperspherical functions, showing the importance of both nn and alpha n final-state interactions. It is shown that the dissociation process is governed by a transition of one neutron from the p-shell in the 6He ground state to the s-shell in the continuum further indicating that the role of the transition through an intermediate He-5(3/2(-)) state is more important than expected., This work was supported by the BMBF under Contracts 06 DA 115, 06 OF 112 and 06 MZ 174 and by GSI via Hochschulzusammenarbeitsvereinbarungen under Contracts DA RICK, OF ELZ and partly supported by the Polish Committee of Scientific Research under Contract PBZ/PB03/113/09, EC under contract ERBCHGE-CT92-0003, CICYT under contract AEN92-0788-C02-02 (MJGB) and RFBR grant No. 04-02-17251. One of us (B.J.) acknowledges the support through an Alexander von Humbold Research Award.

Breakup reactions were used to study the ground-state configuration of the neutron-rich isotope 23O. The 22O fragments produced in one-nucleon removal from 23O at 938 MeV/nucleon in a carbon target were detected in coincidence with de-exciting γ rays, allowing to discern between 22O ground-state and excited-states contributions. From the comparison of exclusive experimental momentum distributions for the one-neutron removal channel to theoretical momentum distributions calculated in an Eikonal model for the knockout process, and spin and parity assignment of I π = 1/2+ was deduced for the 23O ground state. This result solved the existent experimental discrepancy.

4 pages, 4 figures.-- Printed version published Dec 27, 2004.-- Issue title: "Proceedings of the Sixth International Conference on Radioactive Nuclear Beams (RNB6)" (Argonne, Illinois, US, Sep 22-26, 2003)., One-nucleon removal reactions at relativistic energies have been used as a spectroscopic tool to characterise the ground state properties of several neutron-rich isotopes in the sd-shell. Using the FRS at GSI, the longitudinal momentum distributions of the emerging fragments after one-nucleon removal were measured. The relative contributions of the remaining fragments in their ground and excited states have been determined from measurements of γ rays in coincidence with the longitudinal momentum distributions. In particular the breakup of O-23 has been investigated. The interpretation of our measurements, in the framework of a simple theoretical model, favours a spin and parity assignment of 1/2+ for the O-23 ground state in agreement with shell model predictions.

4 pages, 4 figures.-- Issue title: Proceedings of the 8th International Conference on Clustering Aspects of Nuclear Structure and Dynamics (Nara, Japan, Nov 24-29, 2003)., The particle unbound nucleus Li-10 has been investigated at the newly constructed post-accelerator REX-ISOLDE at CERN via the Li-9 +d --> Li-10 +p reaction at 2.36 MeV/u. We present here the preliminary analysis of our first data from REX-ISOLDE.

19 pages, 7 figures, 2 tables, 2 appendices.-- PACS nrs.: 27.10.+h; 25.60.Gc.-- Printed version published Jul 28, 2003., Erratum to this paper (error in the calculation of resonance parameters) published in Nuclear Physics A 739(3-4): 353-354 (2004), http://dx.doi.org/10.1016/j.nuclphysa.2004.04.115, The unbound hydrogen isotopes H-4,H-5 have been studied in the one-proton knockout channel of He-6 (240 MeV/u) impinging on a carbon target. The triton fragments originating from this channel were detected in coincidence with neutrons. Relative energy spectra as well as energy and angular correlations have been studied for the t+n and t+n+n systems. The analysis of the energy and angular correlations by the method of hyperspherical harmonic expansion allows to determine the relative weights of the most relevant partial waves in the three-body t+n+n final state. It is shown that the neutrons to a large extent occupy the p-shell and that the I-π = 1/2(+) state is strongly populated as expected for the H-5 ground state. No evidence for a narrow resonance in the t+n+n system is obtained, instead a broad structure peaked at 3 MeV above the threshold with about 6 MeV as a full width at half maximum is observed. The two-body t+n system reveals a resonance compatible with earlier results for H-4., This work was supported by the BMBF under Contracts 06 DA 820, 06 OF 112 and 06 MZ 864 and by GSI via Hochschulzusammenarbeitsvereinbarungen under Contracts DA RICK, OF ELZ, MZ KRK and partly supported by the Polish Committee of Scientific Research under Contract PBZ/PB03/113/09, EC under contract ERBCHGE-CT92-0003, CICYT under contract AEN92-0788-C02-02 (MJGB) and RFBR grant No. 01-02-16685. One of us (B.J.) acknowledges the support through an Alexander von Humboldt Research Award.

One-proton removal reactions of 936 MeV/u 8 B have been studied with carbon and lead as breakup targets. Using the FRS at GSI, the longitudinal momentum distributions of the 7 Be fragments and the one-proton removal cross section of 8 B were measured. The relative contributions of the breakup channels leading to 7 Be in its ground state and excited state at 429 keV ( 7 Be ∗ ) have been determined from measurements of γ rays in coincidence with the fragments from the one-proton removal reaction. The experimental breakup data are discussed in the context of a theoretical ( α+ 3 He + p ) three-body model. The combined data from the two targets allow a determination of the weight of the 7 Be ∗ component in the 8 B ground state wave function as (13.3±2.2%)

The reactions Ni-58(e, e') and M-58(p, p) have been studied at kinematics favorable for the excitation of J(pi) = 2(-) states by isovector spin-flip transitions with DeltaL = 1. There are states at an excitation energy E-X approximate to 10 MeV which are strongly excited in electron scattering but not in proton scattering, suggesting a predominantly orbital character. This is taken as direct evidence for the so-called twist mode in nuclei in which different layers of nuclear fluid in the upper and lower hemisphere counterrotate against each other. Microscopic quasiparticle-phonon model calculations which predict sizable orbital M2 strength at this excitation energy yield indeed a current flow pattern of the strongest transitions consistent with a twist-like motion. (C) 2002 Published by Elsevier Science B.V.

We report on the first observation of the unbound proton-rich nucleus 15Ne. Its ground state and first excited state were populated in two-neutron knockout reactions from a beam of 500 MeV/u 17Ne. The 15Ne ground state is found to be unbound by 2.522(66) MeV. The decay proceeds directly to 13O with simultaneous two-proton emission. No evidence for sequential decay via the energetically allowed 2- and 1- states in 14F is observed. The 15Ne ground state is shown to have a strong configuration with two protons in the (sd) shell around 13O with a 63(5)% (1s1/2)2 component.

F. Wamers et al.; 4 pags.; 2 figs. Open Access funded by Creative Commons Atribution Licence 2.0, We have studied one-proton-removal reactions of about 500 MeV/u17Ne beams on a carbon target at the R3B/LAND setup at GSI by detecting beam-like 15Op and determining their relative-energy distribution. We exclusively selected the removal of a 17Ne halo proton, and the Glauber-model analysis of the 16F momentum distribution resulted in an s 2 contribution in the 17Ne ground state of about 40 %. C Owned by the authors, published by EDP Sciences, 2014, This work was supported by the Alliance Program of the Helmholtz Association (HA216/EMMI), by the German Federal Ministry for Education and Research (BMBF) (project 05P12RDFN8) by HIC for FAIR, by Eurons (European Commission contract no. 506065), and by GSI.

The present article is the third out of three on a study of the 40 Ca(e,e′ x ) reaction discussing the role of direct and statistical contributions to the decay of the observed giant resonance strengths. The proton and α decay modes leading to low-lying final states in 36 Ar and 39 K were investigated. The branching ratios for the p 0 , p 123 , α 0 and α 1 channels are compared to statistical model calculations. In the excitation region of dominant isoscalar E2 strength ( E x =12–18 MeV) good agreement is observed. Model predictions of direct E2 decay for the ( α 0 + α 1 )/(p 0 +p 1 ) ratio describe the data poorly. In the isovector E1 excitation region large excess strength is found in the population of low-lying states in 39 K. A fluctuation analysis shows the direct contributions to the p 0 , p 1 channels to be ⩾85%. The presence of preequilibrium components is indicated by the significant nonstatistical decay to the p 3 level which has a dominant ‘phonon⊗hole’ structure. Cross correlations reveal no significant branching between the different channels. The correlations between different electron scattering angles in the p 0 , p 1 and p 3 decay result in an interaction radius compatible with the whole nucleus acting as an emitting source.

The present article is the second out of three on a study of the 40 Ca(e,e′ x ) reaction discussing the multipole decomposition of the measured cross sections and the analysis of angular correlations. The decomposition of the strongly overlapping E0, E1 and E2 giant resonance strengths using the (e,e′ x ; x =p, α ) reaction in 40 Ca is discussed for excitation energies between 10 and about 21 MeV. Two extraction methods are presented based on the variation of the form factors for the different multipoles. The resulting B (E1) strength distribution is in good agreement with ( γ , x ) photoabsorption data. The summed B (E2) and B (E0) strength is highly fragmented and spread out over the energy region investigated. Microscopic continuum RPA calculations including the coupling of the basic particle–hole states to the low-lying surface vibrations are capable of reproducing the strength distributions quite accurately. Exhaustion of the energy-weighted sum rules (EWSR) for the various decay channels is presented. A complete decomposition of E0, E1 and E2 contributions in 40 Ca is possible for (e,e′ α ) angular correlations populating the 36 Ar ground state. Contrary to expectations, the form factors of isoscalar E0 and E2 strengths in the 40 Ca(e,e′ α 0 ) reaction exhibit increasing differences towards smaller momentum transfers. Angular correlations for proton decay into low-lying states of 39 K are compared to a self-consistent continuum RPA calculation which allows a systematic description of the strong variations observed as a function of 40 Ca excitation energy and momentum transfer. The success implies that direct knock-out models of the 40 Ca(e,e′p) reaction are too simple. Furthermore, the shapes of the angular correlations seem to be determined largely by the final-state interaction, in particular by charge exchange reactions in the nuclear medium.

The 40 Ca(e,e′ x ; x =p, α ) reaction has been measured in the giant resonance excitation region for E x ≃8–26 MeV. The present article is the first out of three describing the experiments and giving an overview of the results. Data were taken at four momentum transfers in the range q =0.26–0.66 fm −1 . Angular correlations for decay to the ground state and low-lying states of 39 K and 36 Ar could be extracted as a function of excitation energy in 40 Ca. Excitation energy spectra integrated over the particle emission angle were generated for the various resolved decay channels. Comparisons of the giant resonance cross-section distributions with results using other electromagnetic or hadronic probes have been made and good agreement is found in most cases.

One-neutron removal cross-sections ( \(\)) of 17, 19C in various targets at about 900 MeV/nucleon, and one-proton removal cross-sections ( \(\)) of 8, 10B at about 1400 MeV/nucleon were measured using the fragment separator FRS at GSI. A significant increase of \(\) for 19C compared to its neighbors was observed. The same behavior was found for \(\) for the neutron-deficient nucleus 8B compared to the stable isotope 10B. These results support a one-neutron halo structure in 19C and a one-proton halo in 8B.

The coupling between bound quantum states and those in the continuum is of high theoretical interest. Experimental studies of bound drip-line nuclei provide ideal testing grounds for such investigations since they, due to the feeble binding energy of their valence particles, are easy to excite into the continuum. In this Letter, continuum states in the heaviest particle-stable Be isotope, 14Be, are studied by employing the method of inelastic proton scattering in inverse kinematics. New continuum states are found at excitation energies E∗=3.54(16) MeV and E∗=5.25(19) MeV. The structure of the earlier known 2+1 state at 1.54(13) MeV was confirmed with a predominantly (0d5/2)2 configuration while there is very clear evidence that the 2+2 state has a predominant (1s1/2, 0d5/2) structure with a preferential three-body decay mechanism. The region at about 7 MeV excitation shows distinct features of sequential neutron decay via intermediate states in 13Be. This demonstrates that the increasing availability of energetic beams of exotic nuclei opens up new vistas for experiments leading towards a new understanding of the interplay between bound and continuum states.

The coupling between bound quantum states and those in the continuum is of high theoretical interest. Experimental studies of bound drip-line nuclei provide ideal testing grounds for such investigations since they, due to the feeble binding energy of their valence particles, are easy to excite into the continuum. In this Letter, continuum states in the heaviest particle-stable Be isotope, Be14, are studied by employing the method of inelastic proton scattering in inverse kinematics. New continuum states are found at excitation energies E*=3.54(16) MeV and E*=5.25(19) MeV. The structure of the earlier known 21+ state at 1.54(13) MeV was confirmed with a predominantly (0d5/2)2 configuration while there is very clear evidence that the 22+ state has a predominant (1s1/2, 0d 5/2) structure with a preferential three-body decay mechanism. The region at about 7 MeV excitation shows distinct features of sequential neutron decay via intermediate states in Be13. This demonstrates that the increasing availability of energetic beams of exotic nuclei opens up new vistas for experiments leading towards a new understanding of the interplay between bound and continuum states. © 2013 American Physical Society.

The 48Ca(e,e(')n) reaction has been investigated for excitation energies 11-25 MeV and momentum transfers 0.22-0.43 fm(-1) at the superconducting Darmstadt electron linear accelerator S-DALINAC. Electric dipole and quadrupole plus monopole strength distributions are extracted from a multipole decomposition of the spectra. Their fragmented structure is described by microscopic calculations allowing for coupling of the basic particle-hole excitations to more complex configurations. Comparison of the excitation spectrum of the residual nucleus 47Ca with statistical model calculations reveals a 39(5)% contribution of direct decay to the damping of the giant dipole resonance.

Dissociation of a 240 MeV/u beam of He-6, incident on carbon and lead targets, has been studied in kinematically complete experiments to investigate low-lying excitation modes in the halo nucleus He-6. It is shown that alignment effects characterize the inelastic scattering and allow an unambiguous assignment of the spin of a narrow resonance observed in the excitation energy spectrum. The differential cross sections for the He-6 inelastic scattering on carbon and lead targets were deduced from the measured moments of the two neutrons and the a-particle. An analysis of these distributions shows that quadrupole and, possibly, monopole excitations characterize the hadronic interaction, while the dipole mode is dominating in Coulomb dissociation. Neither theoretically predicted new resonance states in He-6 nor nuclear excitation of a dipole mode were found. Direct evidence has been obtained for strong suppression of Coulornb post-acceleration in direct Coulomb breakup in a lead target.

The Radioactive Beam Experiment REX-ISOLDE [1-3] is a pilot experiment at ISOLDE (CERN) testing the new concept of post acceleration of radioactive ion beams by using charge breeding of the ions in a high charge state ion source and the efficient acceleration of the highly charged ions in a short LINAC using modern ion accelerator structures. In order to prepare the ions for the experiments singly charged radioactive ions from the on-line mass separator ISOLDE will be cooled and bunched in a Penning trap, charge bred in an electron beam ion source (EBIS) and finally accelerated in the LINAC. The LINAC consists of a radiofrequency quadrupole (RFQ) accelerator, which accelerates the ions up to 0.3 MeV/u, an interdigital H-type (IH) structure with a final energy between 1.1 and 1.2 MeV/u and three seven gap resonators, which allow the variation of the final energy. With an energy of the radioactive beams between 0.8 MeV/u and 2.2 MeV/u a wide range of experiments in the field of nuclear spectroscopy, astrophysics and solid state physics will be addressed by REX-ISOLDE.

Precision studies of the reaction [sup 3]He( e,thinspe[sup [prime]]p) using the three-spectrometer facility at the Mainz microtron MAMI are presented. All data are for quasielastic kinematics at [vert bar][rvec q][vert bar]=685 MeV/c . Absolute cross sections were measured at three electron kinematics. For the measured missing momenta range from 10 to 165 MeV/c , no strength is observed for missing energies higher than 20thinspthinspMeV. Distorted momentum distributions were extracted for the two-body breakup and the continuum. The longitudinal and transverse nature of the cross sections is well described by a widely used prescription of the off-shell electron-nucleon cross section. The results are compared to modern three-body calculations and to previous data. [copyright] [ital 1999] [ital The American Physical Society]

4 pages, 3 figures.-- PACS nrs.: 27.20.+n, 24.70.+s, 25.60.Gc., Peripheral fragmentation of a 287 MeV/nucleon beam of the halo nucleus Li-11 incident on a carbon target has been studied in a fragment-neutron coincidence experiment. The momentum distribution of the Li-10 fragments gives access to the momentum distribution of the removed neutron in Li-11. From the shape of the distribution, the (1s(1/2))(2) contribution to the mixture of (1s(1/2))(2) and (0p(1/2))(2) components in the ground-state wave function was determined to he (45 ± 10)%. The angular correlation between the knocked out neutron and the one from the decay of Li-10 shows a skew distribution signaling interference of these two different parity states., This work was supported by the BMBF under Contracts No. 06 DA 820, No. 06 OF 112, and No. 06 MZ 476, and by GSI via Hochschulzusammenarbeitsvereinbarungen under Contracts No. DA RICK, No. OF ELZ, and No. MZ KRK, and partly supported by the Polish Committee of Scientific Research under Contract No. PBZ/PB03/113/09, EC under Contract No. ERBCHGE-CT92-0003, CICYT under Contract No. AEN92-0788-C02-02(M. J.G.B.), and WTZ under Contract No. RUS 609-96. One of us (B. J.) acknowledges support from an Alexander von Humboldt Research Award.

Recent examples of giant resonance spectroscopy with electron scattering at the S-DALINAC are presented. Strength distributions and decay properties of electric resonances in 48 Ca are investigated with the (e,e′n) reaction. First results of a systematic search for spin and orbital magnetic quadrupole modes in 180° scattering are presented for 48 Ca and 90 Zr.

The longitudinal momentum distribution of Be fragments after fragmentation of B and the one-proton removal cross section (σ-1p) in a carbon target were measured at 1440 MeV/u with the fragment separator FRS used as an energy-loss spectrometer. The results show a narrow momentum distribution with a FWHM value of 91 ± 5 MeV/c and a large cross-section, σ-1p = 98 ± 6 mb. Both these results support the interpretation of a spatially extended proton orbit forming a halo in the B ground state. The momentum distribution and the one-proton removal cross section are shown to be reproduced with a three-body wave function for 8B where the target is treated as a black disc in the breakup process. © 1999 Published by Elsevier Science B.V. All rights reserved. (Less)

T. Aumann et al. ; 11 pags.; 6 figs.; 2 tabs. ; PACS number(s): 27.20.1n, 25.60.Gc, 25.70.De, 29.30.Hs

The nuclei ${}^{48}\mathrm{Ca}$ and ${}^{90}\mathrm{Zr}$ were investigated in $180\ifmmode^\circ\else\textdegree\fi{}$ high-resolution inelastic electron scattering for momentum transfers $q\ensuremath{\simeq}0.35--0.8$ ${\mathrm{fm}}^{\ensuremath{-}1}$. The complete $M2$ strength could be extracted in both nuclei up to excitation energies of about 15 MeV. Second-random-phase approximation calculations successfully describe the strong fragmentation of the experimental strength distributions. Contrary to previous experimental findings, suggesting a severe reduction, the deduced quenching of $M2$ spin matrix elements is comparable to the $M1$ case. A quantitative reproduction of the data requires the presence of appreciable orbital strength which can be interpreted as a torsional elastic vibration (``twist mode'').

The extremely weak $l$-forbidden ${1d}_{3/2}\ensuremath{\rightarrow}{2s}_{1/2}$ magnetic dipole ( $M1$) transition from the ground state of ${}^{32}\mathrm{S}$ to a ${J}^{\ensuremath{\pi}}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1}^{+}$ state at ${E}_{x}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}7.003\phantom{\rule{0ex}{0ex}}\mathrm{MeV}$ was investigated by 165\ifmmode^\circ\else\textdegree\fi{} and 180\ifmmode^\circ\else\textdegree\fi{} electron scattering. The extracted strength of $0.0040(5){\ensuremath{\mu}}_{N}^{2}$ represents the smallest $B(M1)\ensuremath{\uparrow}$ value ever measured in electron scattering. A combined analysis with the isospin-analogous Gamow-Teller (GT) decays of the ${J}^{\ensuremath{\pi}}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1}^{+}$ ground states of ${}^{32}\mathrm{Cl}$ and ${}^{32}\mathrm{P}$ is performed. Empirical corrections of Brown and Wildenthal to the magnetic operators reasonably account for the data. Corrections derived from microscopic approaches are less successful pointing towards a fundamental, not yet understood problem in the description of the effective $M1$ and GT operators.

Studies of nuclei far off the line of stability are one of the main topics in nuclear structure physics. The search for states with spatially extended low-density matter distributions, so-called “halos”, found predominantly in light neutron-rich nuclei is of central importance. Halo-breakup experiments were performed in complete kinematics with relativistic secondary beams of energies of 0.2–0.4 GeV/u at GSl. For the examples of the two-neutron halo nuclei 6 He and 11 Li results of angular, energy and momentum correlation measurements after breakup into a core fragment and valence neutrons are given and single-particle ground-state properties and large low-lying multipole strength near the threshold for particle emission will be discussed.

A new experimental method for a precise determination of the proton charge radius with elastic electron proton scattering at low momentum transfers is shown to be feasible, using a novel technique where the recoil protons are detected in a set of Si detectors.

Low energy single nucleon transfer reactions are proposed as a tool to investigate the structure of nuclei far off stability. Experimental concepts and conditions are discussed, in particular high resolution γ-ray spectroscopy after single nucleon pickup reactions. Nuclear structure is described by Skyrme Hartree-Fock calculations including pairing. As representative examples, binding energies, radii and wave functions for Mg and Sn isotopes are calculated. In the neutron deficient Mg isotopes a proton skin is found. At the neutron driplines the Mg and Sn isotopes develop extended neutron skins. The nuclear structure results are used in DWBA and EFR-DWBA transfer calculations. Single nucleon transfer reactions of 32,36Mg and exotic Sn beams on targets ranging from 2H to 24Mg in inverse kinematics are explored. The one-nucleon transfer cross sections decrease strongly for high-Z targets. An impact parameter analysis shows that the transfer process is selective on the tails of the wave functions. The largest cross sections are obtained for 2H and 9Be targets at incident energies of E lab = 2-5 MeV/u. The energy-momentum dependence is closely related to the special properties of wave functions of weakly bound states. Two-neutron (p,t) stripping reactions are studied for a 6He projectile. A strong competition of sequential and direct processes is found at low energies.

13 pags, 5 figures.-- PACS nrs.: 24.60.−t; 25.70.Ef; 27.20.+n., Momentum distributions and invariant mass spectra from the breakup of He-6 ions with an energy of 240 MeV/u interacting with a carbon target have been studied. The data were used to extract information about the reaction mechanism which is influenced by the structure of He-6. It is found that the dominant reaction mechanism is a two-step process: knock out of one neutron followed by the decay of the He-5 resonance. The shape of the (α+n) two-body invariant mass spectrum is interpreted as mainly reflecting the 5He ground state which is a J(π) = 3/2(-) resonance. However, no evidence for correlations between cu particles and neutrons is observed in the momentum widths of the distributions. It is demonstrated that a combined analysis of the two-body invariant mass spectrum and an appropriate correlation function may be used to determine the properties of the intermediate resonance., This work was supported by the German Federal Minister for Education and Research (BMBF) under Contracts 06 DA 820, 06 OF 474 and 06 MZ 476 and by GSI via Hochschulzusammenarbeitsvereinbarungen under Contracts DARIK, OF ELK, MZ KRK and partly supported by the Polish Committee of Scientific Research under Contract PB2/P03B/113/09, EC under Contract ERBCHGE-CT92-0003 and CICYT under Contract AEN92-0788-C02-02 (MJGB) and by Deutsche Forschungsgemeinschaft (DFG) under Contract 436 RUS 130/127/1. One of us (B.J.)acknowledges the support through an Alexander von Humboldt Research Award.

The differential coincident pion electroproduction cross section in the 3 He(e,e π + ) 3 H reaction has been measured with high resolution with the three-spectrometer set-up at the Mainz Microtron (MAMI) electron accelerator. Measurements were performed at the four incident energies E 0 = 855, 675, 600, and 555 MeV at fixed four-momentum transfer Q 2 = 0.045 GeV 2 , with the pions detected in parallel kinematics. This enables a separation of the measured cross section into the transverse and longitudinal structure functions by means of the Rosenbluth method. The experimental data are compared to model calculations, in which the elementary pion production amplitude includes the standard Born-amplitudes and also delta and higher resonance terms. Three-body Fadeev wave functions are used and the final state interaction of the outgoing pion is taken into account. The calculation describes the data only after medium modifications of the delta and of the pion are included.

The first experiments with exotic nuclei in the ESR heavy ion storage ring already indicated the new possibilities for nuclear structure research in storage and cooler rings [1–6]. The present status and future possibilities for nuclear reaction studies in storage rings will be addressed in this paper.

The angular correlation between momenta of 5He and its decay products has been calculated for the peripheral fragmentation of 6He using a two-step model in a sudden approximation: (1) One neutron knock-out leading to the unbound nucleus 5He. (2) Subsequent decay of 5He undisturbed by the target in an α-particle and a neutron. Angular correlations measured in a recent experiment dealing with the peripheral fragmentation of 240 MeV/u 6He on a carbon target can be well described by a dominant 5He 3/2− ground state configuration plus a small admixture of ≈ 7% of the first excited 1/2− state. The influence of an s-state admixture as well as a contribution of the momentum transfer to the correlation function are investigated.

Heavy-ion cooler and storage rings offer a rich field of new and unique possibilities to study nuclear structure. Cooling creates beams of high phase space density for high-resolution experiments. In first experiments atomic masses of more than hundred new nuclides were measured with high precision. Future experiments with cooled energetic beams of exotic nuclei allow high precision nuclear structure studies in direct reactions such as (d, p), (p, p′), or Coulomb breakup. The extension of these investigations to electron scattering in a heavy-ion-electron collider will be discussed.

It is demonstrated by the example of the E{sub x}=16.28MeV, J{sup {pi}};T=1{sup -};6 state in {sup 90}Zr that a high-resolution {sup 90}Zr( e,e{sup {prime}}p){sup 89}Y experiment can provide a nearly model-independent full characterization of all relevant spectroscopic properties of an isobaric analog state. The proton angular correlation data and branching ratios determine the total and partial widths into radiative and particle decay channels. A phenomenological wave function is deduced from the form factor. {copyright} {ital 1997} {ital The American Physical Society}

The systematics of fusion-evaporation reactions in the mass-symmetric system Ar1Ca are studied for incident energies of 5–30 MeV/nucleon. The measurement of the resulting evaporation residues in coincidence with emitted neutrons permits a clear identification of central collisions and a separation of equilibrium and preequilibrium contributions. The total neutron multiplicities and the total average mass loss of the system both show a tendency of soft saturation. Above about 20 MeV/nucleon the increase of the energy removal is entirely due to preequilibrium emission of light particles. The total excitation energy of the evaporation residues approaches a maximum value, but the excitation energy per nucleon rises linearly without any sign of saturation. At even higher projectile energies the production of evaporation residues is dramatically reduced and they become indistinguishable from spectatorlike fragments resulting from less central collisions. Thus, the longstanding question of a limiting excitation energy in hot nuclei can probably not be solved by experimental studies of fusion-evaporation reactions. @S0556-2813~97!04304-5#

An experimental study of beta-delayed charged particles (H, He, Be) from Li-11 shows a beta-feeding to an excited state at 18.15(15) MeV in Be-11 with a large Gamow-Teller strength, B-GT greater than or equal to 1.6. Branching ratios and reduced widths of 2-, 3- and 5- particle decay channels of this state are extracted, A strong suppression of the neutron branch from the 18 MeV state to the Be-10(g.s.) is observed, We suggest that the measured partial width may be sensitive to the (p(1/2))(2) component in the Li-11 halo, A rough estimate indicates that the (p(1/2))(2) component is not the dominant one in the halo wave-function.

New values for the $\ensuremath{\gamma}$ ray intensities following the $\ensuremath{\beta}$ decay of ${}^{11}$Li are presented. Special emphasis is put on the determination of the Gamow-Teller transition ${}^{11}$Li $\ensuremath{\rightarrow}$ ${}^{11}$Be (1/2${}^{\ensuremath{-}}$, 320 keV) to the only bound excited state in ${}^{11}$Be. We show that a shell-model calculation can simultaneously reproduce the half-life of ${}^{11}$Li and the newly measured branching ratio to the ${1/2}^{\ensuremath{-}}$ state provided the ${}^{11}$Li ground state wave function contains about 50% of $s$-wave neutron components.