Search

We report on first results from experiments using the ( α , α ′ γ ) reaction at E α = 136 MeV to investigate bound electric dipole (E1) excitations building the so-called Pygmy Dipole Resonance (PDR) in the semi-magic nucleus 140Ce. The method of ( α , α ′ γ ) allows the separation of E1 excitations from states of higher multipolarity, provides an excellent energy resolution and therefore allows a detailed analysis for each single state. Studying bound E1 excitations in α-scattering experiments at intermediate energies becomes feasible for the first time even in nuclei with a high level density. The surprising results of the first experiment on 140Ce point to a splitting of the PDR in this nucleus.

The possible existence of \eta'-nucleus bound states has been put forward through theoretical and experimental studies. It is strongly related to the \eta' mass at finite density, which is expected to be reduced because of the interplay between the $U_A(1)$ anomaly and partial restoration of chiral symmetry. The investigation of the C(p,d) reaction at GSI and FAIR, as well as an overview of the experimental program at GSI and future plans at FAIR are discussed., Comment: 7 pages, 3 figures; talk at the International Conference on Exotic Atoms and Related Topics (EXA2014), Vienna, Austria, 15-19 September 2014. in Hyperfine Interactions (2015)

The TRI mu P facility, under construction at KVI, requires the production and separation of short-lived and rare isotopes. Direct reactions, fragmentation and fusion-evaporation reactions in normal and inverse kinematics are foreseen to produce nuclides of interest with a variety of heavy-ion beams from the superconducting cyclotron AGOR. For this purpose, we have designed, constructed and commissioned a versatile magnetic separator that allows efficient injection into an ion catcher, i.e., gas-filled stopper/cooler or thermal ionizer, from which a low energy radioactive beam will be extracted. The separator performance was tested with the production and clean separation of Na-21 ions, where a beam purity of 99.5% could be achieved. For fusion-evaporation products, some of the features of its operation as a gas-filled recoil separator were tested. (c) 2006 Elsevier B.V. All rights reserved.

The reaction Ni-58((p) over right arrow, (p) over right arrow (/)) has been studied at small scattering angles and an incident beam energy of 172 MeV. We extract cross sections and analyzing powers for elastic scattering and transitions to vibrational states at low excitation energies. The data are compared to DWBA98 calculations using different widely used effective projectile-target interactions and the quasiparticle-phonon model including complex configurations for the nuclear structure input. The comparison with the experimental data reveals surprising discrepancies for elastic scattering observables at forward angles, whereas the prominent inelastic transitions to low-lying states are well described. (c) 2005 Elsevier B.V. All rights reserved.

We are investigating the feasibility of nuclear physics experiments designed to overcome the loopholes of observer-dependent reality and satisfying the counterfactuality condition. In a first approach, we have measured polarization correlations of 1 S 0 proton pairs produced in 12C(d, 2He) and 1H(d, 2He) reactions in one setting. The results of these measurements are used to test the Bell and Wigner–Belinfante inequalities against the predictions of quantum mechanics.

The direct particle decay of the isoscalar giant dipole resonance (ISGDR) has been studied in Pb-208 using the (alpha,alpha'p) and (alpha,alpha'n) reactions at a bombarding energy of 200 MeV. The direct-decay channels of proton and neutron emissions were observed in coincidence with the scattered a-particles in order to study the population of proton-hole states in Tl-207 and neutron-hole states in Pb-207. The results of the partial and total branching ratios allowed us to test recently performed continuum-RPA (CRPA) calculations for the ISGDR and thereby to learn about its microscopic structure.

Spin-isospin excitations of the medium-mass nucleus Co-58 were studied using the (n, p)-type (d,He-2) charge-exchange reaction at an incident energy E-d = 170 MeV and small scattering angles. The achieved energy resolution of 130 keV, full width at half maximum, allowed the extraction of Gamow-Teller strength to 13 peaks at excitation energies lower than 4.1 MeV in the residual nucleus Co-58 and is consistent with the results of a multipole-decomposition analysis. The identification of Gamow-Teller transitions is possible by comparison of the measured cross sections with DWBA calculations. The results are used to discuss the relevance of the Gamow-Teller strength distribution at low excitation energy with regard to electron-capture rates used in calculations for the final stage of a massive star. (C) 2003 Elsevier B.V. All rights reserved.

Gamow-Teller transitions in fp-shell nuclei have been studied using the 58 Ni( d , 2 He) charge exchange reaction at an incident energy of 170 MeV and forward angles. The measurements have been performed at AGOR using the Big-Bite Spectrometer and the EuroSuperNova focal-plane detection system. The unprecedented energy resolution of about 130 keV FWHM for excitations in the residual nucleus 58 Co allowed for the first time the extraction of single transitions in the β + direction up to about 4 MeV excitation. The impact on electron-capture rates in astrophysical environments has been evaluated.

International audience; Isoscalar giant resonances in exotic nuclei can be studied using inelastic alpha scattering in inverse kinematics. In particular, the compression modes, i.e. isoscalar giant monopole and dipole resonances, are very interesting because they can furnish information on the different terms of the nuclear incompressibility, especially if measured in long isotopic chains including nuclei far from the valley of stability. As beams of exotic nuclei have relatively low intensities thick targets have to be used in order to get a reasonable yield. However, this leads to degradation of the energy resolution and stops low-energy recoil particles. Two good alternatives exist. The first method is to use an active target, such as MAYA, which is a time-projection chamber and therefore can be used for detection of low-energy recoil particles. Furthermore, its thickness can be increased by increasing the length of the detection volume or the gas pressure without severe loss of energy resolution. The second method is to use a storage ring for storing the exotic nuclei, which then interact with target nuclei from a gas-jet target. Here, the luminosity and hence the yield are increased because the exotic nuclei circulate in the ring at a frequency of around 106 turns/s. Low-energy recoil particles traverse the gas-jet with little loss of energy and can be detected in solid-state detectors. Pioneering experiments with both methods have been performed for inelastic scattering of secondary 56Ni beam off helium nuclei. Here, preliminary results of the experiment with the active target MAYA will be presented.

At intermediate energies, the (d, He-2) charge-exchange reaction can be used to observe Gamow-Teller strength in the direction. He-2 denotes the two-proton system being in the singlet S-1(0) state. In the present experiment the two protons, which in the laboratory frame are emitted into the forward direction, have been momentum analyzed and detected in coincidence by the same spectrometer and detector. Protons from deuteron breakup processes can induce a large accidental coincidence background because of the much larger breakup cross-section as compared to the (d, He-2) cross-section. Nevertheless, background-free He-2 spectra with a resolution of 145 keV at an incident energy of 170 MeV are obtained, allowing the identification of many levels with high precision in the residual nuclei. The essential features of the detection system and the data-acquisition and analysis techniques which make our (d 2 He) experiments possible are described. Two nuclei, C-12 and Mg-24, have been used as a test case. (C) 2002 Elsevier Science B.V. All rights reserved.

The investigation of light-ion induced direct reactions using stored and cooled radioactive beams, interacting with internal targets of storage rings, can lead to substantial advantages over external target experiments, in particular for direct reaction experiments in inverse kinematics at very low momentum transfer, q. This new and challenging experimental technique enables high-resolution measurements down to very low q and provides a gain in luminosity from accumulation and recirculation of the stored beams. For performing first experiments of this kind a dedicated experimental setup housing several DSSD (Double-sided Silicon Strip Detector) and Si(Li) detectors for recoil particles, well suited for meeting the demanding UHV (Ultra High Vacuum) conditions of a storage ring, was recently designed, constructed and installed at the internal target of the ESR storage ring at GSI. From the interaction of a stored 56Ni beam with an internal H2 target, good quality differential cross section data for elastic proton scattering, measured with the aim to determine the radial shape of the nuclear matter distribution of 56Ni, were obtained. Preliminary results are presented. Being the first reaction experiment ever performed with a stored radioactive beam on a world-wide scale, this experiment can be considered as a breakthrough for nuclear structure and astrophysics studies, and, in addition, as a successful proof-of-principle of the new experimental concept. In addition, preliminary results from a feasibility study on inelastic α-scattering from 58Ni in inverse kinematics, where it was demonstrated that the Isoscalar Giant Monopole Resonance in 58Ni can be investigated by the present technique down to CM angles below 1 degree, are discussed. Such an experiment, performed in the future with the doubly magic 56Ni, would provide important information on the EOS of nuclear matter.

A series of measurements have been performed at KVI to obtain the vector analyzing power Ay Of the H-2((p) over right arrow, pd) reaction as a function of incident beam energy at energies of 120, 135, 150, and 170 MeV. For all these measurements, a range of upsilon (c.m) from 30 degrees to 170 degrees has been covered. The purpose of these investigations is to observe possible spin-dependent effects beyond two-nucleon forces. When compared to the,predictions of Faddeev calculations, based on two-nucleon forces only, significant deviations are observed at all energies and at center-of-mass angles between 70 degrees and 130 degrees. The addition of present-day three-nucleon forces does not improve the description of the data, demonstrating the still insufficient understanding of the properties of three-nucleon systems.

Decay via proton emission of isobaric analog states (IAS’s) in 91 Nb was studied using the 90 Zr(α, t) reaction at E�=180 MeV. This study provides information about the damping mechanism of these states. Decay to the ground state and low-lying phonon states in 90 Zr was observed. The experimental data are compared with theoretical predictions wherein the IAS ‘single-particle’ proton escape widths are calculated in a continuum RPA approach. The branching ratios for decay to the phonon states are explained using a simple model.

The giant resonance regions of 90 Zr, 116 Sn, 144 Sm and 208 Pb were investigated using 240 MeV α particle scattering at small angles including 0°. E1 strengths corresponding to 91±11%, 89±10%, 105±12% and 95±13% of the isoscalar E1 energy-weighted sum rule were identified beteen 18≤E x ≤31 MeV, 16≤E x ≤30 MeV, 15≤E x ≤27 MeV and 15≤E x ≤25 MeV with centroid energies of 24.8±0.4 MeV, 22.5±0.3 MeV, 21.6±0.3 MeV and 19.3±0.3 MeV and rms widths of 3.2±0.2 MeV, 3.5±0.2 MeV, 3.2±0.2 MeV and 2.5±0.2 MeV for 90 Zr, 116 Sn, 144 Sm and 208 Pb, respectively. Parameters obtained for the isoscalar giant monopole resonance, isoscalar giant quadrupole resonance and high energy octupole resonance are in agreement with accepted values.

Gamow-Teller (GT) transitions and $M1$ transitions from or to the ground states are analogous in the pair of $T=1/2$ mirror nuclei, if the excited states hold the mirror-symmetry properties. In order to study the mirror-symmetry structure of the $A=27$ mirror nuclei ${}^{27}\mathrm{Al}$ and ${}^{27}\mathrm{Si},$ experimental data on GT transition strengths obtained from ${}^{27}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{Si}}}^{27}\mathrm{Al}$ $\ensuremath{\beta}$ decay and from a good-resolution ${}^{27}\mathrm{Al}{(}^{3}\mathrm{He}{,t)}^{27}\mathrm{Si}$ reaction at 150 MeV/nucleon and 0\ifmmode^\circ\else\textdegree\fi{} have been compared with $M1$ transition strengths obtained from $\ensuremath{\gamma}$ decay in ${}^{27}\mathrm{Al}$ and ${}^{27}\mathrm{Al}(\ensuremath{\gamma},{\ensuremath{\gamma}}^{\ensuremath{'}})$ reaction. Good overall correspondence of transitions is observed for states up to nearly 9 MeV in excitation energy, where the particle-decay channel becomes important. The difference of excitation energies of analog states in the mirror nuclei are about 250 keV at this excitation energy. From a comparison of $B(M1)$ and $B(\mathrm{GT})$ strengths of the analogous transitions, the contribution of the isoscalar and the orbital terms in the $M1$ operator is found to become prominent in weak $M1$ transitions.

The cross section for the He-3(e, e'd)p reaction has been measured for a range of missing momentum p, at incident electron energies of 370 and 576 MeV and for values of the three-momentum transfer q of 412, 504, and 604 MeV/c. The longitudinal and transverse structure functions have been separated for q = 412 and 504 MeV/c. The data are compared to exact three-body Faddeev calculations and calculations based on a covariant, gauge-invariant diagrammatic expansion. In general, fair to good agreement is observed, but there are some differences between the data and the calculations, especially for the q dependence and for the transverse structure function W-T.

The European physical journal / Web of Conferences 66, 03093 (2014). doi:10.1051/epjconf/20146603093, Published by EDP Sciences, Les Ulis

The isoscalar giant dipole resonance (ISGDR) in ${}^{208}\mathrm{Pb}$ has been investigated using inelastic scattering of 200 MeV $\ensuremath{\alpha}$ particles at and near 0\ifmmode^\circ\else\textdegree\fi{} where the angular distribution of the ISGDR can be clearly differentiated from those of other modes. The ``difference of spectra'' technique was employed to separate the ISGDR from the high-energy octupole resonance (HEOR). These data provide the clearest evidence yet for the ISGDR adjacent to the HEOR. With these results, all expected isoscalar $\ensuremath{\lambda}\ensuremath{\le}3$ resonances in ${}^{208}\mathrm{Pb}$ have been identified.

Elastic electron scattering off Si-30 and P-31 was studied in an effective momentum-transfer range of 1.8-3.0 fm(-1). The form-factor data were analyzed together with existing data sets for these nuclei and for S-32 in a model-independent Fourier-Bessel expansion. For P-31 the M1 contribution was subtracted following an established parametrization. Results of Hartree-Fock (HF) calculations, performed for these three nuclei in a spherical basis and in an axially deformed basis, are compared to experiment. Occupancies have been determined which, when used in the spherical-basis HF calculations, lead to a good description of the elastic form-factor data. The deformed-basis calculations have been used to study the influence of the deformation on the calculated binding energies and ground-state charge densities. In all calculations the influence of using different effective nucleon-nucleon interactions was investigated. The resulting differences in 2s(1/2) in occupancy are combined with results from previous existing (e,e'p) experiments to yield ''absolute occupancies'' for the 2s(1/2) orbital. The deduced 2s(1/2) occupancies for Si-30 and S-32 are 0.24(4) and 1.35(19), respectively.

Using inelastic $\alpha$-scattering at extremely forward angles, including $0^\circ$, the strength distributions of the isoscalar giant monopole resonance (ISGMR) have been measured in the $^{204,206,208}$Pb isotopes in order to examine the proposed mutually enhanced magicity (MEM) effect on the nuclear incompressibility. The MEM effect had been suggested as a likely explanation of the "softness" of nuclear incompressibility observed in the ISGMR measurements in the Sn and Cd isotopes. Our experimental results rule out any manifestation of the MEM effect in nuclear incompressibility and leave the question of the softness of the open-shell nuclei unresolved still., Comment: Accepted for publication in Physics Letters B. Very minor changes in text

The isoscalar giant dipole resonance (ISGDR) in 208 Pb has been investigated using inelastic scattering of 200 MeV α particles at and near 0° where the angular distribution of the ISGDR can be clearly differentiated from other modes. The “difference of spectra” technique was employed to separate the contribution from the high-energy octupole resonance (HEOR). Preliminary angular distribution data provide clear evidence for the ISGDR adjacent to the HEOR.

We performed a missing-mass spectroscopy experiment of the 12C(p, d) reaction in order to search for η′-mesic nuclei. Excitation spectrum of 11C around the η′-meson production threshold was successfully obtained with a high-statistical sensitivity and sufficiently good energy resolution. Since no peak structure associated with the formation of η′-mesic nuclei was observed, we set constraints on the formation cross sections of η′-mesic states and on the η′-nucleus interaction.

The energy of the charge-exchange Anti-analog Giant Dipole Resonance (AGDR) has been calculated for the 208Pb isotope using the state-of-the-art fully self-consistent relativistic proton-neutron quasiparticle random-phase approximation based on the Relativistic Hartree-Bogoliubov model. It is shown that the AGDR centroid energy is very sensitively related to the corresponding neutron-skin thickness. The neutron-skin thickness of 208Pb has been determined very precisely by comparing the theoretical results with the available experimental data on E(AGDR). The result DR(pn)= 0.161(42) agrees nicely with the previous experimental results., Comment: arXiv admin note: substantial text overlap with arXiv:1302.6007, arXiv:1205.2325

A cross section enhancement, persisting to high momentum transfer, has been observed around 1HBAR omega in excitation energy in spectra from inelastic proton-, alpha- and electron scattering on Zr-90, Sn-116, Pt-196 and Pb-208. Data are presented for (p,p') at 201 MeV, (alpha,alpha') at 120 MeV and analyzed together with existing data obtained with 133.8 MeV polarized ((p) over right arrow,p') on Sn-116 and electron-scattering data on Sn-116 and Pt-196. Two different interpretations of the observed enhancement are discussed: that of the incoherent sum of all 1HBAR omega cross section and alternatively the sum over the isoscalar normal modes of all multipolarities.

Fragmentation and splitting of the Gamow-Teller (GT) strength has been observed in a systematic study of the ${(}^{3}$He,t) charge-exchange reaction at E${(}^{3}$He)=200 MeV over the entire range of stable Sn isotopes. Triton energy spectra were observed with a high-resolution magnetic spectrometer at angles near \ensuremath{\theta}=0\ifmmode^\circ\else\textdegree\fi{} where \ensuremath{\Delta}L=0 transitions are enhanced. Excitation energies, widths, 0\ifmmode^\circ\else\textdegree\fi{} cross sections, and strengths B(GT) were determined. A theoretically predicted configuration splitting of the main Gamow-Teller component into two components, expected to be dominant near A=118 at the onset of the filling of the 1${\mathit{h}}_{11/2}$ neutron orbital, could not be observed. This may be due to the fact that the total widths of the resonances of 5--6 MeV exceed the predicted splitting. A comparison of the 0\ifmmode^\circ\else\textdegree\fi{} cross sections for the transitions to the Gamow-Teller resonances and the isobaric analog states leads to strengths B(GT) for the main Gamow-Teller components of typically 65% of the sum-rule value of 3(N-Z). Three to four additional Gamow-Teller fragments (``pygmy resonances'') were observed in all final nuclei at lower excitation energies. The excellent energy resolution of the experiment made it possible to observe a pronounced fine structure in these low-lying resonances which is believed to be due to coupling to two-particle--two-hole doorway states. Also seen with all target nuclei was a systematic sequence of strong ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$=${1}^{+}$ states near the ground states in all Sb isotopes (${\mathit{E}}_{\mathit{x}}$=0 to 220 keV). In addition, strong \ensuremath{\Delta}L=1 resonances were observed in all nuclei at excitation energies of typically 20 MeV. Furthermore, nonresonant background from quasifree charge exchange was observed. An average of \ensuremath{\sim}85% of all excess neutrons seems to contribute to this background in approximate agreement with results from (e,e'p) experiments.

The gamma-decay of the anti-analog of the giant dipole resonance (AGDR) has been measured to the isobaric analog state excited in the p(124Sn,n) reaction at a beam energy of 600 MeV/nucleon. The energy of the transition was also calculated with state-of-the-art self-consistent random-phase approximation (RPA) and turned out to be very sensitive to the neutron-skin thickness (\DeltaR_(pn)). By comparing the theoretical results with the measured one, the \DeltaR_(pn) value for 124Sn was deduced to be 0.175 \pm 0.048 fm, which agrees well with the previous results. The energy of the AGDR measured previously for ^(208)Pb was also used to determine the \DeltaR_(pn) for ^(208)Pb. In this way a very precise \DeltaR_(pn) = 0.181 \pm 0.031 neutron-skin thickness has been obtained for 208Pb. The present method offers new possibilities for measuring the neutron-skin thicknesses of very exotic isotopes., 5 pages, 3 figures

High-momentum components of proton momentum distributions in $^{208}\mathrm{Pb}$ have been studied from 300 to 500 MeV/c with the ($e,{e}^{\ensuremath{'}}p$) reaction. Cross sections were measured with 180 keV excitation-energy resolution for transitions to the low-lying ${\mathrm{\textonehalf{}}}^{+}$, ${\frac{3}{2}}^{+}$, ${\frac{11}{2}}^{\ensuremath{-}}$, ${\frac{5}{2}}^{+}$, and ${\frac{7}{2}}^{+}$ states in $^{207}\mathrm{Tl}$. The data are compared to distorted-wave impulse-approximation calculations with mean-field wave functions and with wave functions that include nucleon-nucleon correlations. The data are substantially larger than mean-field predictions. The observed excess strength at low excitation energy appears to be mainly due to long-range correlations and not to short-range and tensor correlations.

The microscopic structure of both the Gamow-Teller resonance (GTR) at Eχ = 15.6 MeV and the spin-flip ΔL=1 resonances at higher excitation energies in 208Bi has been investigated by observing their direct proton decay to the 3p12, 2f52, 3p32, 1i32 and 2f72 neutron-hole states in 207Pb, following their excitation via the 208Pb (3He,t) reaction at E(3He) = 450 MeV. Decay protons were measured at backward angles in coincidence with tritons detected at very forward angles including θ = 0°. The total widths of the resonances as well as total and partial proton escape widths were determined and compared to theoretical estimates for the GTR. Using the same experimental set-up and conditions proton decay of the spin-flip ΔL=1 resonances in 12C was also measured.

Spin-isospin excitations in nuclei have been studied by means of the ( 3 He,t) reactions at 450 MeV. The Gamow-Teller (GT) resonances are found to be strongly excited. A fine structure of the giant Gamow Teller resonances in medium-heavy nuclei is observed with an energy resolution of 130 keV. The volume integrals of the effective interactions J στ and J τ have been determined experimentally. The importance of high resolution observation of the ( 3 He,t) reactions at intermediate energies, both, to study the double β decay processes and to measure the detection sensitivities for solar neutrino experiments is discussed.

The statistical γ-ray decay of the compound nucleus 154 Dy ∗ formed at an excitation energy of 69 MeV is studied in three angular-momentum windows 〈 J 〉 = 31,42 and 50ℏ. The GDR strength function extracted from the data indicates a constant centroid energy for the resonance E GDR = 15.2 ± 0.5 MeV, a small deformation of the nuclear shape for all spin regions and an increase in the resonance width with increasing angular momentum. The latter might indicate larger shape fluctuations at higher angular momenta. A systematical study of the dependence of the extracted strength function with different methods of analysis is presented, and their discrepancies discussed.

The (Pb(He,t)Bi)-Pb-208-He-3-Bi-208 reaction has been studied with the RCNP ring cyclotron at E(He-3) = 450 MeV using the magnetic spectrometer Grand Raiden at theta = 0-degrees. The Gamow-Teller resonance is strongly excited at this bombarding energy. Its microscopic structure has been investigated by measuring the direct proton decay to the neutron-hole states in Pb-207. The branching ratio for proton emission of a few % is much smaller than that for the decay of the isobaric analog state. The total width of the Gamow-Teller resonance as well as its total and partial escape widths have been determined. Several recent theoretical estimates for the escape width differ from the measured values by factors of approximately 2.5.

Spin-isospin excitations in nuclei have been studied by means of the (3He,t) reactions at 450 MeV on the targets sBe, natC, *%ii, 58Ni, 62Ni, seZr, l18Sn, **OSn, 124Sn, and 154Sm. The new spectrometer “Grand Raiden” was employed for the (3He,t) study for the first time. Observed (3He,t) spectra at 0’ show remarkable similarity with those from the (p,n) results at intermediate energies, suggesting a simple direct reaction mechanism for the (3He,t) reaction at 450 MeV. The GamowTeller (GT) resonances and the spin-flip AL=1 resonances are excited very strongly. A fine structure of the GT resonances in medium-heavy nuclei is observed with an energy resolution of 210 keV. It is demonstrated that the (3He,t) reaction at 450 MeV is a powerful tool to study the spin-isospin excitations in nuclei.

The rise time of stellar x-ray bursts is a signature of thermonuclear runaway processes in the atmosphere of neutron stars and is highly sensitive to a series of ($\ensuremath{\alpha}$,$p$) reactions via high-lying resonances in $sd$-shell nuclei. Lacking data for the relevant resonance levels, the stellar reaction rates have been calculated using statistical, Hauser-Feshbach models, assuming a high-level density. This assumption may not be correct in view of the selectivity of the ($\ensuremath{\alpha}$,$p$) reaction to natural parity states. We measured the ${}^{28}$Si($p$,$t$)${}^{26}$Si reaction with a high-resolution spectrometer to identify resonance levels in ${}^{26}$Si above the $\ensuremath{\alpha}$-emission threshold at 9.164 MeV excitation energy. These resonance levels are used to calculate the stellar reaction rate of the ${}^{22}$Mg($\ensuremath{\alpha}$,$p$)${}^{25}$Al reaction and to test the validity of the statistical assumption.

The ([sup 3]He,[ital t]) charge-exchange reaction has been studied at [ital E]([sup 3]He)=200 MeV and angles near 0[degree] on targets of [sup 117]Sn and [sup 120]Sn. Fragmentation of the giant Gamow-Teller resonance into separate components of the particle-hole type has been observed in good agreement with theoretical predictions. These components are connected with what is usually referred to in the literature as direct-, core-polarization-, and back-spin-flip Gamow-Teller strength. The observed cross sections near [theta]=0[degree] suggest contributions from the isovector spin-flip interaction as well as the isovector tensor interaction. A theoretically predicted configuration splitting of the main Gamow-Teller component into two components involving the 1[ital h][sub 11/2] neutron orbital could not uniquely be identified. The data are compatible, though, with such a splitting since the observed widths of the main Gamow-Teller components in [sup 117]Sb and [sup 120]Sb exceed the predicted splittings.

Expérience GANIL, Spectrometre LISE; International audience; The goal of the present paper is to attempt to clarify the nuclear reaction mechanism leading to the production of fragments at zero degree with neutron number larger than that in the 48Ca projectile, at about 60 MeV per nucleon. The production cross sections of the extremely neutron-rich Si and P isotopes were measured. Concerning the nuclear reaction mechanism leading to the production of these isotopes, one should probably refer to a particular type of transfer mechanism, which results in low excitation energy for the fragments, rather than to the ‘genuine' fragmentation mechanism. An upper limit of about 0.05 pb was estimated for the production cross section for the 47P isotope for which no count was observed.

To study the Gamow-Teller (GT) transitions to the pf-shell nucleus Cu-64, the Ni-64(He-3,t)Cu-64 experiment was performed at the Research Center for Nuclear Physics (RCNP) Ring Cyclotron, Osaka, using a He-3 beam of 140 MeV/nucleon. The outgoing tritons were momentum analyzed by the Grand Raiden spectrometer at 0(degrees). A high energy resolution of 32 keV (full width at half-maximum) allowed the separation of individual levels in the excitation-energy region from 0 to 3.5 MeV. In addition to the ground state (gs), known to be a J(pi)=1(+) GT state, many low-lying states showed L=0 nature, suggesting that they are candidates for GT states. Because the GT strength B(GT) for the gs transition is known from the beta-decay measurement, the strengths for the excited states could be determined using the proportionality between the B(GT) and the reaction cross section extrapolated to q=0 momentum transfer. At higher excitation energies, the level density becomes high and the so-called GT giant resonance dominates the spectrum. The lower and the upper limits of the strength contained in this energy region were estimated. Our results show that less than 55% of the strength predicted by the Ikeda sum rule is located in the excitation-energy region from 0 to 17 MeV..

The excitation and subsequent proton decay of the isoscalar giant dipole resonance (ISGDR) in $^{208}$Pb have been investigated via the $^{208}$Pb($\alpha, \alpha^{\prime}p)^{207}$Tl reaction at 400 MeV. Excitation of the ISGDR has been identified by the difference-of-spectra method. The enhancement of the ISGDR strength at high excitation energies observed in the multipole-decomposition-analysis of the singles $^{208}$Pb($\alpha,\alpha^{\prime}$) spectra is not present in the excitation energy spectrum obtained in coincidence measurement. The partial branching ratios for direct proton decay of ISGDR to low-lying states of $^{207}$Tl have been determined and the results are compared with predictions of continuum random-phase-approximation (CRPA) calculations., Comment: 12 pages, 4 figures; accepted for publication in Physics Letters B

Electron scattering experiments on $^{65}\mathrm{Cu}$ and $^{71}\mathrm{Ga}$ have been performed both at forward and backward angles in order to study the transition charge and current densities of the first excited state in these nuclei. The shape and strength of these densities in $^{65}\mathrm{Cu}$ as well as the strong quenching of the transition charge density in $^{71}\mathrm{Ga}$ relative to that of $^{65}\mathrm{Cu}$ and to single-particle estimates can be understood as resulting from pairing correlations and core polarization. The results are also supported by particle vibration coupling model calculations.

Inelastic electron scattering to levels of the ground-state band and the {gamma} band in {sup 150}Nd was studied in a momentum transfer range of 0.5 to 2.8 fm{sup {minus}1}. The extracted transition charge densities were compared to microscopic Hartree-Fock-Boguliubov calculations. The overall agreement between the data and the calculations is good, indicating that the dynamic properties of the rotational collective degrees of freedom in statically deformed nuclei can be well described in this microscopic model.

The 96Mo(d,2He)96Nb charge-exchange reaction was investigated at an incident energy of Ed=183.5 MeV. An excitation-energy resolution of 110 keV was achieved. The experiment was performed at KVI, Groningen, using the magnetic spectrometer BBS at three angular positions: 0°,2.5°, and 6°. We found that below 6 MeV almost the entire Gamow-Teller (GT+) strength is concentrated in a single state at 0.69 MeV excitation energy. As Mo96 is the daughter of the ?? decay nucleus Zr96, the present result provides information about the nuclear matrix elements active in the 2??? decay of Zr96.

The (d,He-2) charge-exchange reaction on the double-beta decay (beta beta) nucleus Zn-64 has been studied at an incident energy of 183 MeV. The two protons in the S-1(0) state (indicated as He-2) were both momentum analyzed and detected simultaneously by the BBS magnetic spectrometer and its position-sensitive detector. He-2 spectra with a resolution of about 115 keV (FWHM) have been obtained allowing identification of many levels in the residual nucleus Cu-64 with high precision. Zn-64 is one of the rare cases undergoing a beta beta decay in beta(+) direction. In the experiment presented here, Gamow-Teller (GT(+)) transition strengths have been extracted. Together with the GT(-) transition strengths from Ni-64(He-3,t) data to the same intermediate nucleus Cu-64, the nuclear matrix elements of the beta beta decay of Zn-64 have been evaluated. Finally, the GT(+/-) distributions are compared with shell-model calculations and a critical assessment is given of the various residual interactions presently employed for the pf shell.

The Gamow-Teller strength for the transition from the ground state of (13)C to the T=1/2,J(pi)=3/2(-) excited state at 3.51 MeV in (13)N is extracted via the (13)C((3)He,t) reaction at 420 MeV. In contrast to results from earlier (p,n) studies on (13)C, a good agreement with shell-model calculations and the empirical unit cross-section systematics from other nuclei is found. The results are used to study the analog (13)N(e(-),nu(e))(13)C reaction, which plays a role in the pre-explosion convective phase of type Ia supernovae. Although the differences between the results from the ((3)He,t) and (p,n) data significantly affect the deduced electron-capture rate and the net heat deposition in the star resulting from this transition, the overall effect on the pre-explosive evolution is small.

The excitation-energy region up to 23 MeV in Ni-58 has been investigated with the (p,p(')) reaction at an incident energy of 172 MeV and forward angles favoring the excitation of the spin-dipole mode in the continuum. The measured cross sections, spin-flip cross sections, and spin-flip probabilities are compared to microscopic reaction-model calculations using various effective projectile-target interactions. The nuclear structure input, which takes into account one-particle one-hole (1p1h) as well as two-particle-two hole (2p2h) excitations, allows for a reasonable description of the continuum region well above the particle-decay thresholds. However, considerable problems remain in the description of spin-flip resonances at lower excitation energies, which cannot be explained by a quenching of the spin-isospin interaction.

The Ni-64(d,He-2)Co-64 reaction was studied at the AGOR cyclotron of KVI, Groningen, with the Big-Bite Spectrometer and the EuroSuperNova detector using a 171-MeV deuteron beam. An energy resolution of about 110 keV was achieved. In addition to the J(pi) = 1(+) ground state, several other 1(+) states could be identified in Co-64 and the strengths of the corresponding Gamow-Teller transitions were determined. The obtained strength distribution was compared with theoretical predictions and former (n,p) experimental results and displayed a good agreement. Due to the good energy resolution, detailed spectroscopic information was obtained, which supplements the data base needed for network calculations for supernova scenarios.

The direct and statistical neutron decay of the isoscalar giant dipole resonance was studied in Zr-90, Sn-116, and Pb-208 using the (alpha,alpha(')n) reaction at a bombarding energy of 200 MeV. The spectra of fast decay neutrons populating valence hole-states of the Z,N-1 nuclei were analyzed, and estimates for the branching ratios were determined. The results were compared to recent continuum random-phase approximation calculations.

Decay by proton emission from high-lying states in Nb-91, populated in the Zr-90(alpha,t) reaction at E-alpha=180 MeV, has been investigated. Decay to the ground state and semidirect decay to the low-lying (2(+),5(-), and 3(-)) phonon states in Zr-90 were observed. It was found that these phonon states play an important role in the damping process of the single-particle states. An optical-model coupled-channel approach was used successfully to describe the direct and semidirect parts of the decay.