Candidate Toroidal Electric Dipole Mode in the Spherical Nucleus ^{58}Ni.

Dipole toroidal modes appear in many fields of physics. In nuclei, such a mode was predicted more than 50 years ago, but clear experimental evidence was lacking so far. Using a combination of high-resolution inelastic scattering experiments with photons, electrons, and protons, we identify for the first time candidates for toroidal dipole excitations in the nucleus ^{58}Ni and demonstrate that transverse electron scattering form factors represent a relevant experimental observable to prove their nature.

Comprehensive Test of the Brink-Axel Hypothesis in the Energy Region of the Pygmy Dipole Resonance.

The validity of the Brink-Axel hypothesis, which is especially important for numerous astrophysical calculations, is addressed for ^{116,120,124}Sn below the neutron separation energy by means of three independent experimental methods. The γ-ray strength functions (GSFs) extracted from primary γ-decay spectra following charged-particle reactions with the Oslo method and with the shape method demonstrate excellent agreement with those deduced from forward-angle inelastic proton scattering at relativistic beam energies. In addition, the GSFs are shown to be independent of excitation energies and spins of the initial and final states.

Test of the Brink-Axel Hypothesis for the Pygmy Dipole Resonance.

The gamma strength function and level density of 1^{-} states in ^{96}Mo have been extracted from a high-resolution study of the (p[over →], p[over →]^{'}) reaction at 295 MeV and extreme forward angles. By comparison with compound nucleus γ decay experiments, this allows a test of the generalized Brink-Axel hypothesis in the energy region of the pygmy dipole resonance. The Brink-Axel hypothesis is commonly assumed in astrophysical reaction network calculations and states that the gamma strength function in nuclei is independent of the structure of the initial and final state.

Electric Dipole Polarizability of ^{48}Ca and Implications for the Neutron Skin.

The electric dipole strength distribution in ^{48}Ca between 5 and 25 MeV has been determined at RCNP, Osaka from proton inelastic scattering experiments at forward angles. Combined with photoabsorption data at higher excitation energy, this enables the first extraction of the electric dipole polarizability α_{D}(^{48}Ca)=2.07(22)  fm^{3}.

First Measurement of Collectivity of Coexisting Shapes Based on Type II Shell Evolution: The Case of ^{96}Zr.

Background: Type II shell evolution has recently been identified as a microscopic cause for nuclear shape coexistence.

Purpose: Establish a low-lying rotational band in ^{96}Zr.

Methods: High-resolution inelastic electron scattering and a relative analysis of transition strengths are used.

Nonquenched Isoscalar Spin-M1 Excitations in sd-Shell Nuclei.

Differential cross sections of isoscalar and isovector spin-M1 (0(+)→1(+)) transitions are measured using high-energy-resolution proton inelastic scattering at E(p)=295  MeV on (24)Mg, (28)Si, (32)S, and (36)Ar at 0°-14°. The squared spin-M1 nuclear transition matrix elements are deduced from the measured differential cross sections by applying empirically determined unit cross sections based on the assumption of isospin symmetry. The ratios of the squared nuclear matrix elements accumulated up to E(x)=16  MeV compared to a shell-model prediction are 1.

Complete electric dipole response and the neutron skin in 208Pb.

A benchmark experiment on (208)Pb shows that polarized proton inelastic scattering at very forward angles including 0° is a powerful tool for high-resolution studies of electric dipole (E1) and spin magnetic dipole (M1) modes in nuclei over a broad excitation energy range to test up-to-date nuclear models. The extracted E1 polarizability leads to a neutron skin thickness r(skin) = 0.156(-0.

Origin of low-energy quadrupole collectivity in vibrational nuclei.

The coupling of the giant quadrupole resonance to valence-space configurations is shown to be the origin of the formation of low-lying quadrupole-collective structures in vibrational nuclei with symmetric and mixed-symmetric character with respect to the proton-neutron degree of freedom. For the first time experimental evidence for this picture is obtained from electron- and proton scattering experiments on the nucleus ^{92}Zr that are sensitive to the relative phase of valence-space amplitudes by quantum interference.

Pair decay width of the Hoyle state and its role for stellar carbon production.

The pair decay width of the first excited 0+ state in 12C (the Hoyle state) is deduced from a novel analysis of the world data on inelastic electron scattering covering a wide momentum transfer range, thereby resolving previous discrepancies. The extracted value Γπ=(62.3±2.

Measurement of the reaction 2H(e,e') at 180 degrees close to the deuteron breakup threshold.

Inclusive inelastic electron scattering off the deuteron under 180 degrees has been studied at the S-DALINAC close to the breakup threshold at momentum transfers q=0.27 fm;{-1} and 0.74 fm;{-1} with good energy resolution sufficient to map in detail the spin flip M1 response, which governs the starting reaction pn-->dgamma of big-bang nucleosynthesis over most of the relevant temperature region.

Spin- and parity-resolved level densities from the fine structure of giant resonances.

Level densities of J pi=2+ and 2- states extracted from high-resolution studies of E2 and M2 giant resonances in 58Ni and 90Zr are used to test recent predictions of a possible parity dependence. The experimental results are compared to a combinatorial approach based on the Hartree-Fock-Bogoliubov model and to shell-model Monte Carlo calculations including both spin and parity projection. No parity dependence is observed experimentally, which is in agreement for 90Zr but in contrast with the model predictions for 58Ni.

High-energy-resolution inelastic electron and proton scattering and the multiphonon nature of mixed-symmetry 2+ states in 94Mo.

High-energy-resolution inelastic electron scattering (at the S-DALINAC) and proton scattering (at iThemba LABS) experiments permit a thorough test of the nature of proposed one- and two-phonon symmetric and mixed-symmetric 2+ states of the nucleus 94Mo. The combined analysis reveals the one-phonon content of the mixed-symmetry state and its isovector character suggested by microscopic nuclear model calculations. The purity of two-phonon 2+ states is extracted.

Gamow-Teller strength in the exotic odd-odd nuclei 138La and 180Ta and its relevance for neutrino nucleosynthesis.

The Gamow-Teller strength distributions below the particle threshold in 138La and 180Ta, deduced from high-resolution measurements of the (3He,t) reaction at 0 degrees, allow us to evaluate the role of charged-current reactions for the production of these extremely rare nuclides in neutrino-nucleosynthesis models. The analysis suggests that essentially all 138La in the Universe can be made that way. Neutrino nucleosynthesis also contributes significantly to the abundance of 180Ta but the magnitude depends on the unknown branching ratio for population of the long-lived isomer.

Structure of the Hoyle state in 12C.

The first excited 0(+) state in 12C (Hoyle state) has been predicted to be a dilute self-bound gas of bosonic alpha particles, similar to a Bose-Einstein condensate. To clarify this conjecture, precise electron scattering data on form factors of the ground state and the transition to the Hoyle state are compared with results of the fermionic molecular dynamics model, a microscopic alpha-cluster model, and an alpha-cluster model with reduced degrees of freedom (in the spirit of a Bose-Einstein condensed state). The data indicate clearly a dilute density with a large spatial extension of the Hoyle state.

Gamow-Teller strengths in the A = 14 multiplet: a challenge to the shell model.

A new experimental approach to the famous problem of the anomalously slow Gamow-Teller (GT) transitions in the beta decay of the A=14 multiplet is presented. The GT strength distributions to excited states in 14C and 14O were studied in high-resolution (d,2He) and (3He,t) charge-exchange reactions on 14N. No-core shell-model calculations capable of reproducing the suppression of the beta decays predict a selective excitation of Jpi=2+ states.

Fine structure of the Gamow-Teller resonance in 90Nb and level density of 1+ states.

The fine structure of the Gamow-Teller resonance in a medium-heavy nucleus is observed for the first time in a high-resolution 90Zr(3He,t)90Nb experiment at the Research Center for Nuclear Physics, Osaka. Using a novel wavelet analysis technique, it is possible to extract characteristic energy scales and to quantify their relative importance for the generation of the fine structure. This method combined with the selectivity of the reaction permits an extraction of the level density of 1+ states in 90Nb.

Comparison of a centered 32P source wire system with a noncentered 90Sr/Y brachytherapy system for intracoronary beta-radiation following PCI of diffuse in-stent restenosis.

Background: We investigated the potential impact of differences in effective radiation dose between the centered Guidant 32P source wire system and the noncentered Novoste 90Sr/Y BetaCath system on clinical and angiographic outcomes of intracoronary brachytherapy for the prevention of in-stent restenosis.

Methods: From 10/00 to 05/04, a total of 400 patients underwent percutaneous coronary intervention (PCI) with brachytherapy for diffuse in-stent restenosis at our institution. Following balloon dilatation, patient Group A (n=200) was treated with the centered 32P Galileo source wire system, patient Group B (n=200) was treated with the noncentered 90Sr/Y BetaCath radiation system.

Supernova inelastic neutrino-nucleus cross sections from high-resolution electron scattering experiments and shell-model calculations.

Highly precise data on the magnetic dipole strength distributions from the Darmstadt electron linear accelerator for the nuclei 50Ti, 52Cr, and 54Fe are dominated by isovector Gamow-Teller-like contributions and can therefore be translated into inelastic total and differential neutral-current neutrino-nucleus cross sections at supernova neutrino energies. The results agree well with large-scale shell-model calculations, validating this model.

Fine structure in the energy region of the isoscalar giant quadrupole resonance: characteristic scales from a wavelet analysis.

Fine structure in the energy region of the isoscalar giant quadrupole resonance in nuclei is observed in high-resolution proton scattering experiments at iThemba LABS over a wide mass range. A novel method based on wavelet transforms is introduced for the extraction of scales characterizing the fine structure. A comparison with microscopic model calculations including two-particle two-hole (2p2h) degrees of freedom identifies the coupling to surface vibrations as the main source of the observed scales.

Electron capture radioactive sources for intravascular brachytherapy: a feasibility study.

The feasibility of electron capture (EC) radionuclides as an alternative to the beta and high-energy gamma emitters presently in use for intravascular brachytherapy is investigated. A potential advantage of the low-energy x-ray radiation from EC isotopes may be an enhanced biological effectiveness with respect to the presently applied beta nuclides, but at the same time avoiding the shielding problems induced by the large penetrability of high-energy gamma rays. A survey considering the most important practical aspects such as dose delivery to the vessel walls in reasonable time spans, absorption properties, possible production of sources with the required specific activities and radiation safety reveals 71Ge as the most promising candidate.

Nature of low-energy dipole strength in nuclei: the case of a resonance at particle threshold in 208Pb.

A high-resolution (gamma,gamma') study of the electric dipole response in 208Pb at the S-DALINAC reveals a resonance structure centered around the neutron emission threshold. Microscopic quasiparticle phonon model calculations in realistic model spaces including the coupling to complex configurations are able to describe the data in great detail. The resonance is shown to result from surface density oscillations of the neutron skin relative to an approximately isospin-saturated core.

Deuteron breakup in the 2H(e,e' p) reaction at low momentum transfer and close to threshold.

Deuteron breakup has been studied in a 2H(e,e' p) coincidence experiment at low momentum transfer and for energies close to threshold. The longitudinal-plus-transverse ( L+T) and longitudinal-transverse ( LT) interference cross sections are deduced. Nonrelativistic calculations based on the Bonn potential and including leading order relativistic contributions, meson exchange currents, and isobar configurations describe the ( L+T) data well.

Giant resonances in the doubly magic nucleus 48Ca from the (e, e'n) reaction.

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.