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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 degrees in the center-of mass frame for incident-deuteron energies Ed (lab)(d) = 130 and 180 MeV were obtained using the RIKEN facility. The beam polarization was unambiguously determined by measuring the C-12(d,alpha)B-10(2(+)) reaction at 0 degrees. 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.

We report measurements of the cross section and a complete set of polarization observables for the Si 28 ( p → , n → ) P 28 ( 6 − ) reaction at a bombarding energy of 198 MeV. The data are compared with distorted wave impulse approximation calculations employing response functions normalized to inelastic electron scattering. The spin-longitudinal polarized cross section I D q is slightly over-predicted by the calculations, while the normal spin-transverse polarized cross section I D n is significantly under-predicted. The calculated in-plane spin-transverse I D p and spin-scalar I D 0 polarized cross sections agree well with the experimental data. These results are consistent with those for Si 28 ( p → , p → ′ ) Si 28 ( 6 − , T = 1 ) scattering at the same energy, and thus it is concluded that isospin-mixing effects are not responsible for the discrepancy between theory and experiment in the ( p → , p → ′ ) case. Energy half-off-shell effects as medium effects on the effective nucleon–nucleon interaction are also investigated and found to be too small to be responsible for the discrepancy.

Heavy-ion beam charge stripping at 2.7 MeV/u is studied, experimentally and theoretically, for different low-Z gas stripper targets.

Vector analyzing powers for proton elastic scattering from 8He at 71 MeV/nucleon have been measured using a solid polarized proton target operated in a low magnetic field of 0.1 T. The spin-orbit potential obtained from a phenomenological optical model analysis is found to be significantly shallower and more diffuse than the global systematics of stable nuclei, which is an indication that the spin-orbit potential is modified for scattering involving neutron-rich nuclei. A close similarity between the matter radius and the root-mean-square radius of the spin-orbit potential is also identified., Comment: 6 pages, 4 figures, accepted for publication in Physical Review C Rapid Communication

Development of a nondestructive, efficient electric-charge-stripping method is a key requirement for next-generation high-intensity heavy-ion accelerators such as the RIKEN Radioactive-Isotope Beam Factory. A charge stripper employing a low-$Z$ gas is an important candidate applicable to high-intensity uranium beams for replacing carbon-foil strippers. In this study, a high-beam-transmission charge-stripping system employing helium gas for $^{238}\mathrm{U}$ beams injected at $10.8\text{ }\text{ }\mathrm{MeV}/\mathrm{u}$ was developed and demonstrated for the first time. The charge-state evolution measured using helium in a thickness range of $0.24--1.83\text{ }\text{ }\mathrm{mg}/{\mathrm{cm}}^{2}$ is compared with theoretical predictions. Energy attenuation and energy spread due to the helium stripper are also investigated.

The vector analyzing power has been measured for the elastic scattering of neutron-rich 6He 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 6He nucleus. An optical model analysis revealed that the spin-orbit potential for 6He is characterized by a shallow and long-ranged shape compared with the global systematics of stable nuclei. A semimicroscopic analysis with a alpha+n+n cluster folding model suggests that the interaction between a proton and the alpha core is essentially important in describing the p+6He elastic scattering. The data are also compared with fully microscopic analyses using non-local optical potentials based on nucleon-nucleon g-matrices., 20 pages, 20 figures, accepted by Physical Review C

The charge-state distributions of U with energies of 14 and 15 MeV=nucleon were measured using nitrogen (N2) gas and carbon foil (C-foil) charge strippers. The most probable charge states of U with energies of 14 and 15 MeV=nucleon in N2 gas attain equilibrium at 60.8 and 62.4, whereas those in C-foils attain equilibrium at 75.8 and 76.7, respectively. Novel empirical formulas for the accurate prediction of the equilibrium charge states of U with energies 10–20 MeV=nucleon in gases and C-foil were derived by fitting the data in the energy range of 1–20 MeV=nucleon. The charge states predicted by using the formulas for gases and C-foil are in good agreement with the data in the energy range of 10–20 MeV=nucleon within an average of 0.23 and 0.21, respectively.

The RIKEN accelerator complex started feeding the next-generation exotic beam facility radioisotope beam factory (RIBF) with heavy-ion beams from 2007 after the successful commissioning of RIBF at the end of 2006. Many improvements made from 2007 to 2010 were instrumental in increasing the intensity of various heavy-ion beams. However, the available beam intensity of very heavy ion beams, especially uranium beams, is far below our goal of $1\text{ }\text{ }\mathrm{p}\ensuremath{\mu}\mathrm{A}$ ($6\ifmmode\times\else\texttimes\fi{}{10}^{12}\text{ }\text{ }\mathrm{particles}/\mathrm{s}$). In order to achieve this goal, upgrade programs are already in progress; the programs include the construction of a new 28-GHz superconducting electron cyclotron resonance ion source and a new injector linac. However, the most serious problem, that of a charge stripper for high-power uranium beams, still remains unsolved, despite extensive research and development work using large foils mounted on a rotating cylinder and a ${\mathrm{N}}_{2}$ gas stripper. A gas stripper is free from problems related to lifetime, though the equilibrium charge state in this stripper is considerably lower than that in a carbon foil, owing to the absence of the density effect. Nevertheless, the merits of gas strippers motivated us to develop a low-$Z$ gas stripper to achieve a higher equilibrium charge state even in gases. We measured the electron-loss and electron-capture cross sections of uranium ions in He gas as a function of their charge state at 11, 14, and $15\text{ }\text{ }\mathrm{MeV}/\mathrm{nucleon}$. The equilibrium charge states extracted from the intersection of the lines of the two cross sections were promisingly higher than those in ${\mathrm{N}}_{2}$ gas by more than 10. Simple simulations of charge development along the stripper thickness were performed by assuming the measured cross sections. The simulation results show that about $1\text{ }\text{ }\mathrm{mg}/{\mathrm{cm}}^{2}$ of He gas should be accumulated to achieve a charge state higher than that of ${\mathrm{N}}_{2}$ gas, notwithstanding the difficulty in accumulation of this helium amount owing to its fast dispersion. However, we now believe that the following two solutions can overcome this difficulty: a gas cell with a very large differential pumping system and a gas cell with a plasma window. Their merits and demerits are discussed in the paper.

The charge-state distributions and equilibrium charge states of uranium ($^{238}\mathrm{U}$) and xenon ($^{136}\mathrm{Xe}$) ions at $11\text{ }\text{ }\mathrm{MeV}/\mathrm{nucleon}$ were determined using a gas charge stripper. A differential pumping system facilitated the increase of the nitrogen gas thickness up to $1.3\text{ }\text{ }\mathrm{mg}/{\mathrm{cm}}^{2}$, which is sufficient for the most probable charge state to attain equilibrium. The charge states of $^{238}\mathrm{U}$ attain equilibrium at 56.0, 56.6, and 55.7 in ${\mathrm{N}}_{2}$, Ar, and ${\mathrm{CO}}_{2}$ media with thicknesses of 125, 79, and $126\text{ }\text{ }\ensuremath{\mu}\mathrm{g}/{\mathrm{cm}}^{2}$, respectively, while those of $^{136}\mathrm{Xe}$ attain equilibrium at 40.5, 40.1, and 40.3 in ${\mathrm{N}}_{2}$, Ar, and ${\mathrm{CO}}_{2}$ media with thicknesses of 163, 95, and $139\text{ }\text{ }\ensuremath{\mu}\mathrm{g}/{\mathrm{cm}}^{2}$, respectively. The equilibrium charge states of $^{136}\mathrm{Xe}$ are acceptable for acceleration by the subsequent cyclotron. The measured data of $^{238}\mathrm{U}$ were used to devise an empirical formula for the prediction of the equilibrium charge state in gaseous media over the energy region of $0.01--60\text{ }\text{ }\mathrm{MeV}/\mathrm{nucleon}$. The equilibrium charge state of $^{136}\mathrm{Xe}$ as predicted by the devised formula is in good agreement with the data.

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 data are presented for the break-up reaction, $^2{\rm H}(\vec p,pp)n$, 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 $^2{\rm H}(\vec p,^2$He$)n$ channel. These results are compared to the $^2{\rm H}(\vec p,d)p$ 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., 4 pages, 3 figures, submitted to PRL

We describe the neutron polarimeter NPOL3 for the measurement of polarization transfer observables $D_{ij}$ with a typical high resolution of $\sim$300 keV at $T_n$ $\simeq$ 200 MeV. The NPOL3 system consists of three planes of neutron detectors. The first two planes for neutron polarization analysis are made of 20 sets of one-dimensional position-sensitive plastic scintillation counters with a size of 100 cm $\times$ 10 cm $\times$ 5 cm, and they cover the area of 100 $\times$ 100 $\mathrm{cm}^2$. The last plane for detecting doubly scattered neutrons or recoiled protons is made of the two-dimensional position-sensitive liquid scintillation counter with a size of 100 cm $\times$ 100 cm $\times$ 10 cm. The effective analyzing powers $A_{y;\mathrm{eff}}$ and double scattering efficiencies $\epsilon_{\mathrm{D.S.}}$ were measured by using the three kinds of polarized neutrons from the ${}^{2}{\rm H}(\vec{p},\vec{n})pp$, ${}^{6}{\rm Li}(\vec{p},\vec{n}){}^{6}{\rm Be}(\mathrm{g.s.})$, and ${}^{12}{\rm C}(\vec{p},\vec{n}){}^{12}{\rm N}(\mathrm{g.s.})$ reactions at $T_p$ = 198 MeV. The performance of NPOL3 defined as $\epsilon_{\mathrm{D.S.}}(A_{y;\mathrm{eff}})^2$ are similar to that of the Indiana Neutron POLarimeter (INPOL) by taking into account for the counter configuration difference between these two neutron polarimeters., Comment: 28 pages, 18 figures, submitted to Nucl. Instrum. Methods Phys. Res. A

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., Comment: accepted by Physical Review Letter

The Gamow–Teller (GT) unit cross section, GT, is an essential quantity to deduce the GT transition strength, B(GT), from the (p, n) 0° cross section. (p, n) measurements at 200 and 300 MeV were performed using the Neutron Time-of-Flight (NTOF) facility at the Research Center for Nuclear Physics (RCNP). The GT values were determined, for the first time, for several nuclei in the region of A > 50 at Ep = 200 and 300 MeV. A significant difference between the B(GT) values obtained by (p, n) and (3He, t) measurements was found.

The vector analyzing power has been measured for the elastic scattering of neutron-rich 6He and 8He from polarized protons at 71 MeV/A making use of a newly constructed solid polarized proton target operated in a low magnetic field of 0.1 T and at a relatively high temperature of 100 K. An optical model analysis revealed that the spin-orbit potentials for 6He and 8He are characterized by shallow and long-ranged shape compared with the global systematics of stable nuclei. Such a characteristics reflect a diffused density distribution of the neutron-rich isotopes.