M. Dozono

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(-0.021)(+0.025) fm in (208)Pb derived within a mean-field model [Phys. Rev. C 81, 051303 (2010)], thereby constraining the symmetry energy and its density dependence relevant to the description of neutron stars.

Candidate Resonant Tetraneutron State Populated by the He 4 (He 8, Be 8) Reaction

A candidate resonant tetraneutron state is found in the missing-mass spectrum obtained in the double-charge-exchange reaction ^{4}He(^{8}He,^{8}Be) at 186  MeV/u. The energy of the state is 0.83±0.65(stat)±1.25(syst)  MeV above the threshold of four-neutron decay with a significance level of 4.9σ. Utilizing the large positive Q value of the (^{8}He,^{8}Be) reaction, an almost recoilless condition of the four-neutron system was achieved so as to obtain a weakly interacting four-neutron system efficiently.

Three nucleon force effects in intermediate-energy deuteron analyzing powers for dp elastic scattering

A complete high precision set of deuteron analyzing powers for elastic deuteron-proton (dp) scattering at 250 MeV/nucleon (MeV/N) has been measured. The new data are presented together with data from previous measurements at 70, 100, 135 and 200 MeV/N. They are compared with the results of three-nucleon (3N) Faddeev calculations based on modern nucleon-nucleon (NN) potentials alone or combined with two models of three nucleon forces (3NFs): the Tucson-Melbourne 99 (TM99) and Urbana IX. At 250 MeV/N large discrepancies between pure NN models and data, which are not resolved by including 3NFs, were found at c.m. backward angles of {theta}{sub c.m.} > or approx. 120 deg. for almost all the deuteron analyzing powers. These discrepancies are quite similar to those found for the cross section at the same energy. We found small relativistic effects that cannot resolve the discrepancies with the data indicating that other, short-ranged 3NFs are required to obtain a proper description of the data.

Pygmy dipole resonance in 208Pb

Scattering of protons of several hundred MeV is a promising new spectroscopic tool for the study of electric dipole strength in nuclei. A case study of 208 Pb shows that, at very forward angles, J π = 1 − states are strongly populated via Coulomb excitation. A separation from nuclear excitation of other modes is achieved by a multipole decomposition analysis of the experimental cross sections based on theoretical angular distributions calculated within the quasiparticle-phonon model. The B(E1) transition strength distribution is extracted for excitation energies up to 9 MeV; that is, in the region of the so-called pygmy dipole resonance (PDR). The Coulomb-nuclear interference shows sensitivity to the underlying structure of the E1 transitions, which allows for the first time an experimental extraction of the electromagnetic transition strength and the energy centroid of the PDR.

Complete Set of Polarization Transfer Observables for the 12C( p,n) Reaction at 296 MeV and 0°

A complete set of polarization transfer observables has been measured for the 12 C( p , n ) reaction at T p =296 MeV and θ lab =0°. The measured polarization transfer observables indicate that the spin–dipole resonance at E x ≃7 MeV has greater 2 - strength than 1 - strength, which is consistent with recent experimental and theoretical studies. The total spin transfer Σ(0°) deduced from the polarization transfer observables indicates a predominance of the spin-flip strength in the continuum. The exchange tensor interaction at a large momentum transfer of Q ≃3.6 fm -1 is discussed.

Complete set of polarization transfer observables for the ^ O(p^^→, n^^→)^ F reaction at 296 MeV and 0 degrees

We report measurements of the cross section and a complete set of polarization transfer observables for the {sup 16}O(p-vector, n-vector){sup 16}F reaction at a bombarding energy of T{sub p} = 296 MeV and a reaction angle of {theta}{sub lab} = 0 deg. The data are compared with distorted-wave impulse approximation calculations employing the large configuration-space shell-model (SM) wave functions. The well-known Gamow-Teller and spin-dipole (SD) states at excitation energies of E{sub x} < or approx. 8 MeV have been reasonably reproduced by the calculations except for the spin-parity J{sup {pi}} = 2{sup -} state at E{sub x} = 5.86 MeV. The SD resonance at E{sub x} {approx_equal} 9.5 MeV appears to have more J{sup {pi}} = 2{sup -} strength than J{sup {pi}} = 1{sup -} strength, consistent with the calculations. The data show significant strength in the spin-longitudinal polarized cross section ID{sub L}(0 deg.) at E{sub x} {approx_equal} 15 MeV, which indicates the existence of the J{sup {pi}} = 0{sup -} SD resonance as predicted in the SM calculations.

Cross-sections and analyzing powers for

The cross-sections and analyzing powers for (p, n) reactions on He and He have been measured at a bombarding energy of Tp = 346 MeV and reaction angles of θlab = 9.4 –27. The energy transfer spectra for He(p, n) at large θlab (≥ 16 ) are dominated by quasielastic contributions, and can be reasonably reproduced by plane-wave impulse approximation (PWIA) calculations for quasielastic scattering. By contrast, the known L = 1 resonances in Li are clearly observed near the threshold in the He(p, n) spectra. Because these contributions are remarkable at small angles, the energy spectra are significantly different from those expected for quasielastic scattering. The data are compared with the PWIA calculations, and it is found that the quasielastic contributions are dominant at large θlab (≥ 22 ). The nuclear correlation effects on the quasielastic peak for He(p, n) are also discussed. PACS numbers: 25.40.Kv, 24.70.+s, 25.10.+s, 27.10.+h ∗wakasa@phys.kyushu-u.ac.jp; http://www.kutl.kyushu-u.ac.jp/~wakasa

(p,n)

22Mg, 30S, 34Ar and 38Ca have been investigated using (p,t) reactions at RCNP with the intent of identifying energy levels in nuclei that determine the reaction rates along the pathway of the αp‐process. These experiments exploit the high resolution and 0° capabilities of the Grand Raiden spectrometer and the WS beamline, which can deliver a fully dispersion matched beam to target. The level information is vital to understanding the nucleosynthesis occurring during explosive hydrogen burning, which, for example, is thought to occur during type I X‐ray bursts. In the case of 22Mg, new reaction rate calculations have been performed for the 18Ne(α,p)21Na reaction. The experimental technique will be discussed, and the experimental results will be presented.

reactions on

The cross sections and spin observables of the pd elastic scattering have been measured at 392 MeV. The results are compared with the prediction of Faddeev calculations with and without including a three nucleon force.

{}^{3}{\rm He}

Experimental method of measuring inelastic proton scattering with high-resolution at forward angles including zero degrees has been developed. An energy resolution of 20 keV and a scattering angle resolution of 0.5 degrees have been achieved as well as low background condition and a reliable background subtraction method. The experimental technique was applied to the 12C(p,p′) reaction for studying the property of the second 0+ state at 7.7 MeV and a broad bump around Ex~10 MeV, where the presence of a 2+ state was reported from the 12C(α,α′) measurement. Preliminary spectra and angular distributions are shown.