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The Gamow-Teller (GT) strength distribution has been investigated in a high-resolution (³He,t) charge-exchange experiment on the double-beta (ββ) decaying nucleus 100Mo. The experiment was carried out at the Osaka University Research Center for Nuclear Physics (RCNP) with a 420 MeV incident³He beam and the Grand Raiden magnetic spectrometer. A final-state energy resolution of 33 keV was achieved. It was found that nearly the entire low-energy (up to ≈ 4 MeV) GT- strength is concentrated in the ground-state transition to 100Tc, which is interpreted as a result of the particular neutron and proton sub-shell occupancies. The impact on the matrix elements for the two-neutrino double-beta (2vββ) decay and the use of 100Mo as a neutrino detection material is discussed. [ABSTRACT FROM AUTHOR]

We report measurements of cross sections and analyzing powers for reaction angles of &thgr;lab = 0.0°-10.0° and complete sets of polarization transfer observables and induced polarizations at &thgr;lab = 0.0°-7.0° for the 208Pb(→p, →n) reaction at a bombarding energy of Tp = 296 MeV. A multipole decomposition technique was applied to the data to extract the Gamow-Teller (GT) and spin-dipole (SD) components from the continuum. The polarization observables were also used, for the first time, to separate the SD components into different spin-parity transfer (&Dgr;J&pgr; = 0-, 1-, and 2-) contributions. A significant strength with &Dgr;J&pgr; = 1+ is identified in the continuum beyond the GT giant resonance, which is due to configuration mixing effects and the isovector spin monopole (IVSM) contribution. The SD strength distributions were clearly dependent on &Dgr;J&pgr;, which is reasonably reproduced by Hartree-Fock (HF) plus random phase approximation (RPA) calculations that include the Skyrme interaction with tensor components [Phys. Rev. C 83, 054316 (2011)]. [ABSTRACT FROM AUTHOR]

We report measurements of cross sections and analyzing powers for nucleon-knockout (p,np) reactions of ²H, 6Li, and 12C at 296 MeV using the RCNP NPOL3 neutron detector and large acceptance spectrometer. The 1s and 1p knockout reactions were successfully separated with a separation-energy resolution of approximately 6 MeV. The resulting data were compared with plane-wave and distorted-wave impulse approximation calculations employing the nucleon-nucleon t matrix in free space. No significant differences were identified in the case of the present analyzing power data, in contrast to the significant reductions observed in (p,2p) values. The conventional Pauli blocking and nuclear binding effects with the g matrix and the relativistic effect of nucleon mass reduction in the nuclei are also discussed. [ABSTRACT FROM AUTHOR]

Differential cross sections of isoscalar and isovector spin-M1 (P+ → 1+) transitions are measured using high-energy-resolution proton inelastic scattering at Ep = 295 MeV on 24Mg, 28Si, 32S, and 36Ar at 0°-l 4°. 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 Ex = 16 MeV compared to a shell-model prediction are 1.01(9) for isoscalar and 0.61(6) for isovector spin-M1 transitions, respectively. Thus, no quenching is observed for isoscalar spin-M1 transitions, while the matrix elements for isovector spin-M1 transitions are quenched by an amount comparable with the analogous Gamow-Teller transitions on those target nuclei. [ABSTRACT FROM AUTHOR]

A complete high-precision set of deuteron analyzing powers for elastic deuteron-proton (dp) scattering at 250 and 294 MeV/nucleon has been measured. These data and previously existing data sets for the cross section at similar energies are compared to the results of three-nucleon Faddeev calculations based on modern nucleonnucleon (NN) potentials alone or combined with two models of three-nucleon forces: the Tucson-Melbourne 99 and Urbana IX. Large discrepancies between pure NN theory and data, which are not resolved by the current three-nucleon forces, were found at c.m. backward angles θc.m. ≳ 120° for all the deuteron analyzing powers and the cross section. Because only small relativistic effects were found for the deuteron analyzing powers and the cross section, the inclusion of short-range components of the three-nucleon force is probably required to get a better description of the data. [ABSTRACT FROM AUTHOR]

The Gamow-Teller (GT) strength distribution has been investigated in a high-resolution (3He,t) charge-exchange experiment on the double-beta (ßß) decaying nucleus 96Zr. The experiment was carried out at the Osaka University Research Center for Nuclear Physics (RCNP) with a 420 MeV incident 3He beam and the Grand Raiden magnetic spectrometer. A final-state energy resolution of 32 keV was achieved. A large fraction of the low-energy GT- strength is identified in a single state at 694 keV. A similar observation has been made in a 96Mo(d,2He)96Nb experiment at 120 keV resolution for the GT+ strength. It is found that this single state makes up nearly 100% of the nuclear matrix element for the 96Zr two-neutrino double-beta (2vßß) decay. [ABSTRACT FROM AUTHOR]

A 76Ge(³He,t)76As charge-exchange experiment at an incident energy of 420 MeV has been performed with an energy resolution of 30 keV. The Gamow-Teller GT- strength distribution in 76As, which is the intermediate nucleus in the double-beta (ββ) decay of 76Ge, has been extracted. An unusually strong fragmentation of the GT- strength is observed even at low excitation energies of Ex ⩽ 5 MeV. By combining the data with those for GT+ transitions from a recent 76Se(d,²He)76As measurement, the nuclear matrix element for the 76Ge 2νββ decay has been evaluated. A lack of correlation among the GT transition strengths feeding the same levels from the two different directions is observed. The impact on the 76Ge 2νββ decay nuclear matrix element is discussed. [ABSTRACT FROM AUTHOR]

The double-differential cross sections for the 116Cd(p,n) and 116Sn(n,p) reactions were measured at 300 MeV for studying the nuclear matrix element of the 116Cd ßß decay. A multipole decomposition technique was applied to the spectra to extract the Gamow-Teller (GT) component. The integrated GT strengths up to an excitation energy of 30 MeV in the intermediate nucleus 116In are 40 ± 6 and 11 ± 1 in the (p,n) and (n,p) spectra, respectively, including the component from the isovector spin monopole (IVSM). The spectra are compared with those obtained from a theoretical calculation with a quasiparticle random phase approximation, where the contribution from the IVSM component as well as the interference effect between the GT and IVSM components are fully taken into account. [ABSTRACT FROM AUTHOR]

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 208Pb shows that, at very forward angles, Jπ = 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(El) 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 £ 1 transitions, which allows for the first time an experimental extraction of the electromagnetic transition strength and the energy centroid of the PDR. [ABSTRACT FROM AUTHOR]

A benchmark experiment on 208Pb shows that polarized proton inelastic scattering at very forward angles including 00 is a powerful tool for high-resolution studies of electric dipole (El) and spin magnetic dipole (MI) modes in nuclei over a broad excitation energy range to test up-to-date nuclear models. The extracted El polarizability leads to a neutron skin thickness rSkin = 0. 156+0.025-0.021 fm in 208Pb 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. [ABSTRACT FROM AUTHOR]

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 θc.m. ≳ 120° 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. [ABSTRACT FROM AUTHOR]

A high-resolution (3He,t) charge-exchange experiment at an incident energy of 420 MeV has been performed on the double beta (ββ) decay nucleus 82Se. A detailed Gamow-Teller (GT-) strength distribution in 82Br has been extracted, which provides information to the ββ-decay nuclear matrix elements. Three strong and isolated transitions, which are to the 75, 1484 and the 2087 keV states in 82Br, are found to dominate the low-excitation region below ≈2.1 MeV. Above 2.1 MeV a sudden onset of a strong GT fragmentation is observed. The degree of fragmentation resembles a situation found in the neighboring A=76 system 76Ge, whereas the observed concentration of strength in the three low-lying states is reminiscent of the heavier neighbors 96Zr and 100Mo. The strong GT transition to the 75 keV (1+) state makes 82Se interesting for solar neutrino detection. The 82Se(νe,e-)82Br solar neutrino capture rate in a nonoscillation scenario is therefore evaluated to 668±12(stat)±60(sys) SNU, and some of the advantages of using selenium for solar neutrino studies are discussed. [ABSTRACT FROM AUTHOR]

A candidate resonant tetraneutron state is found in the missing-mass spectrum obtained in the double-charge-exchange reaction He4(He8,Be8) 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 (8He,8Be) reaction, an almost recoilless condition of the four-neutron system was achieved so as to obtain a weakly interacting four-neutron system efficiently. [ABSTRACT FROM AUTHOR]

To search for low-energy resonant structures in isospin T=3/2 three-body systems, we have performed the experiments ^{3}H(t,^{3}He)3n and ^{3}He(^{3}He,t)3p at intermediate energies. For the 3n experiment, we have newly developed a thick Ti-^{3}H target that has the largest tritium thickness among targets of this type ever made. The 3n experiment for the first time covered the momentum-transfer region as low as 15  MeV/c, which provides ideal conditions for producing fragile systems. However, in the excitation-energy spectra we obtained, we did not observe any distinct peak structures. This is in sharp contrast to tetraneutron spectra. The distributions of the 3n and 3p spectra are found to be similar, except for the displacement in energy due to Coulomb repulsion. Comparisons with theoretical calculations suggest that three-body correlations exist in the 3n and 3p systems, although not enough to produce a resonant peak.

The structure and decay of the most neutron-rich beryllium isotope, ^{16}Be, has been investigated following proton knockout from a high-energy ^{17}B beam. Two relatively narrow resonances were observed for the first time, with energies of 0.84(3) and 2.15(5) MeV above the two-neutron decay threshold and widths of 0.32(8) and 0.95(15) MeV, respectively. These were assigned to be the ground (J^{π}=0^{+}) and first excited (2^{+}) state, with E_{x}=1.31(6)  MeV. The mass excess of ^{16}Be was thus deduced to be 56.93(13) MeV, some 0.5 MeV more bound than the only previous measurement. Both states were observed to decay by direct two-neutron emission. Calculations incorporating the evolution of the wave function during the decay as a genuine three-body process reproduced the principal characteristics of the neutron-neutron energy spectra for both levels, indicating that the ground state exhibits a strong spatially compact dineutron component, while the 2^{+} level presents a far more diffuse neutron-neutron distribution.

A kinematically complete quasifree (p,pn) experiment in inverse kinematics was performed to study the structure of the Borromean nucleus ^{17}B, which had long been considered to have a neutron halo. By analyzing the momentum distributions and exclusive cross sections, we obtained the spectroscopic factors for 1s_{1/2} and 0d_{5/2} orbitals, and a surprisingly small percentage of 9(2)% was determined for 1s_{1/2}. Our finding of such a small 1s_{1/2} component and the halo features reported in prior experiments can be explained by the deformed relativistic Hartree-Bogoliubov theory in continuum, revealing a definite but not dominant neutron halo in ^{17}B. The present work gives the smallest s- or p-orbital component among known nuclei exhibiting halo features and implies that the dominant occupation of s or p orbitals is not a prerequisite for the occurrence of a neutron halo.

The formation of a dineutron in the ^{11}Li nucleus is found to be localized to the surface region. The experiment measured the intrinsic momentum of the struck neutron in ^{11}Li via the (p,pn) knockout reaction at 246  MeV/nucleon. The correlation angle between the two neutrons is, for the first time, measured as a function of the intrinsic neutron momentum. A comparison with reaction calculations reveals the localization of the dineutron at r∼3.6  fm. The results also support the density dependence of dineutron formation as deduced from Hartree-Fock-Bogoliubov calculations for nuclear matter.

We performed the first direct mass measurements of neutron-rich scandium, titanium, and vanadium isotopes around the neutron number 40 at the RIKEN RI Beam Factory using the time-of-flight magnetic-rigidity technique. The atomic mass excesses of ^{58-60}Sc, ^{60-62}Ti, and ^{62-64}V were measured for the first time. The experimental results show that the two-neutron separation energies in the vicinity of ^{62}Ti increase compared to neighboring nuclei. This shows that the masses of Ti isotopes near N=40 are affected by the Jahn-Teller effect. Therefore, a development of Jahn-Teller stabilization appears below the Cr isotopes, and the systematics in Sc, Ti, and V isotopes suggest that ^{62}Ti is located close to the peak of the Jahn-Teller effect.

The structure of a neutron-rich ^{25}F nucleus is investigated by a quasifree (p,2p) knockout reaction at 270A  MeV in inverse kinematics. The sum of spectroscopic factors of π0d_{5/2} orbital is found to be 1.0±0.3. However, the spectroscopic factor with residual ^{24}O nucleus being in the ground state is found to be only 0.36±0.13, while those in the excited state is 0.65±0.25. The result shows that the ^{24}O core of ^{25}F nucleus significantly differs from a free ^{24}O nucleus, and the core consists of ∼35% ^{24}O_{g.s.}. and ∼65% excited ^{24}O. The result may infer that the addition of the 0d_{5/2} proton considerably changes neutron structure in ^{25}F from that in ^{24}O, which could be a possible mechanism responsible for the oxygen dripline anomaly.

The key parameter to discuss the possibility of the pion condensation in nuclear matter, i.e., the so-called Landau-Migdal parameter g^{'}, was extracted by measuring the double-differential cross sections for the (p,n) reaction at 216  MeV/u on a neutron-rich doubly magic unstable nucleus, ^{132}Sn with the quality comparable to data taken with stable nuclei. The extracted strengths for Gamow-Teller (GT) transitions from ^{132}Sn leading to ^{132}Sb exhibit the GT giant resonance (GTR) at the excitation energy of 16.3±0.4(stat)±0.4(syst)  MeV with the width of Γ=4.7±0.8  MeV. The integrated GT strength up to E_{x}=25  MeV is S_{GT}^{-}=53±5(stat)_{-10}^{+11}(syst), corresponding to 56% of Ikeda's sum rule of 3(N-Z)=96. The present result accurately constrains the Landau-Migdal parameter as g^{'}=0.68±0.07, thanks to the high sensitivity of the GTR energy to g^{'}. In combination with previous studies on the GTR for ^{90}Zr and ^{208}Pb, the result of this work shows the constancy of this parameter in the nuclear chart region with (N-Z)/A=0.11 to 0.24 and A=90 to 208.

We perform the first direct mass measurements of neutron-rich calcium isotopes beyond neutron number 34 at the RIKEN Radioactive Isotope Beam Factory by using the time-of-flight magnetic-rigidity technique. The atomic mass excesses of ^{55-57}Ca are determined for the first time to be -18650(160), -13510(250), and -7370(990)  keV, respectively. We examine the emergence of neutron magicity at N=34 based on the new atomic masses. The new masses provide experimental evidence for the appearance of a sizable energy gap between the neutron 2p_{1/2} and 1f_{5/2} orbitals in ^{54}Ca, comparable to the gap between the neutron 2p_{3/2} and 2p_{1/2} orbitals in ^{52}Ca. For the ^{56}Ca nucleus, an open-shell property in neutrons is suggested.

The (^{12}N, ^{12}C) charge-exchange reaction at 175  MeV/u was developed as a novel probe for studying the isovector spin giant monopole resonance (IVSMR), whose properties are important for better understanding the bulk properties of nuclei and asymmetric nuclear matter. This probe, now available through the production of ^{12}N as a secondary rare-isotope beam, is exothermic, is strongly absorbed at the surface of the target nucleus, and provides selectivity for spin-transfer excitations. All three properties enhance the excitation of the IVSMR compared to other, primarily light-ion, probes, which have been used to study the IVSMR thus far. The ^{90}Zr(^{12}N,^{12}C) reaction was measured and the excitation energy spectra up to about 70 MeV for both the spin-transfer and non-spin-transfer channels were deduced separately by tagging the decay by γ emission from the ^{12}C ejectile. Besides the well-known Gamow-Teller and isobaric analog transitions, a clear signature of the IVSMR was identified. By comparing with the results from light-ion reactions on the same target nucleus and theoretical predictions, the suitability of this new probe for studying the IVSMR was confirmed.

The double-differential cross sections for the 48Ca(p,n) and 48Ti(n,p) reactions were measured at 300 MeV. A multipole decomposition technique was applied to the spectra to extract the Gamow-Teller (GT) components. The integrated GT strengths up to an excitation energy of 30 MeV in 48Sc are 15.3+/-2.2 and 2.8+/-0.3 in the (p,n) and (n,p) spectra, respectively. In the (n,p) spectra additional GT strengths were found above 8 MeV where shell models within the fp shell-model space predict almost no GT strengths, suggesting that the present shell-model description of the nuclear matrix element of the two-neutrino double-beta decay is incomplete.