K. Yako

Resolving the Discrepancy of 135 MeV pd Elastic Scattering Cross Sections and Relativistic Effects

Three precise measurements for elastic pd scattering at 135 MeV/A have been performed with the three different experimental setups. The cross sections are described well by the theoretical predictions based on modern nucleon-nucleon forces combined with three-nucleon forces. Relativistic Faddeev calculations show that relativistic effects are restricted to backward angles. This result supports the two measurements recently reported by RIKEN and contradicts the KVI data.

Analyzing power in elastic scattering of 6He from a polarized proton target at 71 MeV/nucleon

The vector analyzing power has been measured for the elastic scattering of neutron-rich {sup 6}He from polarized protons at 71 MeV/nucleon making use of a newly constructed solid polarized proton target operated in a low magnetic field and at high temperature. Two approaches based on local one-body potentials were applied to investigate the spin-orbit interaction between a proton and a {sup 6}He nucleus. An optical model analysis revealed that the spin-orbit potential for {sup 6}He is characterized by a shallow and long-ranged shape compared with the global systematics of stable nuclei. A semimicroscopic analysis with an {alpha}+n+n cluster folding model suggests that the interaction between a proton and the {alpha} core is essentially important in describing the p+{sup 6}He elastic scattering. The data are also compared with fully microscopic analyses using nonlocal optical potentials based on nucleon-nucleon g matrices.

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.

Determination of the Gamow–Teller quenching factor from charge exchange reactions on 90Zr

Abstract Double differential cross sections between 0°–12° were measured for the 90 Zr(n, p) reaction at 293 MeV over a wide excitation energy range of 0–70 MeV. A multipole decomposition technique was applied to the present data as well as the previously obtained 90 Zr(p, n) data to extract the Gamow–Teller (GT) component from the continuum. The GT quenching factor Q was derived by using the obtained total GT strengths. The result is Q = 0.88 ± 0.06 , not including an overall normalization uncertainty in the GT unit cross section of 16%.

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.

Analyzing power for proton elastic scattering from the neutron-rich He6 nucleus

Vector analyzing power for the proton-{sup 6}He elastic scattering at 71 MeV/nucleon has been measured for the first time, with a newly developed polarized proton solid target, which works at a low magnetic field of 0.09 T. The results are found to be incompatible with a t-matrix folding model prediction. Comparisons of the data with g-matrix folding analyses clearly show that the vector analyzing power is sensitive to the nuclear structure model used in the reaction analysis. The {alpha}-core distribution in {sup 6}He is suggested to be a possible key for understanding the nuclear structure sensitivity.

Precision measurement of vector and tensor analyzing powers in elastic deuteron-proton scattering

Abstract.High-precision vector and tensor analyzing powers of elastic deuteron-proton ( d + p) scattering have been measured at intermediate energies to investigate effects of three-nucleon forces. Angular distributions in the range of 70°-120° in the center-of mass frame for incident-deuteron energies Edlab = 130 and 180 MeV were obtained using the RIKEN facility. The beam polarization was unambiguously determined by measuring the ^12C (d, α)^10B(2+) reaction at 0°. Results of the measurements are compared with state-of-the-art three-nucleon calculations. The present modeling of nucleon-nucleon forces and its extension to the three-nucleon system is not sufficient to describe the high-precision data consistently and requires, therefore, further investigation.

Spin-isospin selectivity in three-nucleon forces

Abstract Precision data are presented for the break-up reaction, H 2 ( p → , p p ) n , within the framework of nuclear-force studies. The experiment was carried out at KVI using a polarized-proton beam of 190 MeV impinging on a liquid-deuterium target and by exploiting the detector, BINA. Some of the vector-analyzing powers are presented and compared with state-of-the-art Faddeev calculations including three-nucleon forces effect. Significant discrepancies between the data and theoretical predictions were observed for kinematical configurations which correspond to the H 2 ( p → , He 2 ) n channel. These results are compared to the H 2 ( p → , d ) p reaction to test the isospin sensitivity of the present three-nucleon force models. The current modeling of two and three-nucleon forces is not sufficient to describe consistently polarization data for both isospin states.

Neutron skin thickness of Zr-90 determined by charge exchange reactions

Charge exchange spin-dipole (SD) excitations of {sup 90}Zr are studied by the {sup 90}Zr(p,n) and {sup 90}Zr(n,p) reactions at 300 MeV. A multipole decomposition technique is employed to obtain the SD strength distributions in the cross-section spectra. For the first time, a model-independent SD sum rule value is obtained: 148{+-}12 fm{sup 2}. The neutron skin thickness of {sup 90}Zr is determined to be 0.07{+-}0.04 fm from the SD sum rule value.

Analyzing powers Ayy , Axx , Axz and Ay in the dd → 3Hen reaction at 270 MeV

The data on the tensor Ayy, Axx, Axz and vector Ay analyzing powers in the dd → Hen obtained at Td = 270 MeV in the angular range 0 ◦ – 110◦ in the c.m. are presented. The observed negative sign of the tensor analyzing powers Ayy, Axx and Axz at small angles clearly demonstrate the sensitivity to the ratio of the D and S wave component of the He wave function. However, the one-nucleon exchange calculations by using the standard He wave functions have failed to reproduce the strong variation of the tensor analyzing powers as a function of the angle in the c.m. PACS. 24.70.+s Polarization phenomena in reactions – 25.10.+s Nuclear reactions involving few-nucleon system – 21.45.+v Few-body systems