Search

Beam polarization asymmetries for the p(gamma--,K+)Lambda and p(gamma--,K+)Sigma(0) reactions are measured for the first time for E(gamma)=1.5-2.4 GeV and 0.6cos((theta(c.m.)(K+))1.0 by using linearly polarized photons at the Laser-Electron-Photon facility at SPring-8 (LEPS). The observed asymmetries are positive and gradually increase with rising photon energy. The data are not consistent with theoretical predictions based on tree-level effective-Lagrangian approaches. Including the new results in the development of the models is, therefore, crucial for understanding the reaction mechanism and to test the presence of baryon resonances which are predicted in quark models but are thus far undiscovered.

Cross sections and polarization transfer observables in the 16O(p,p′) reactions at 392 MeV were measured at forward angles including 0°. The non‐spin‐flip (ΔS = 0) and spin‐flip (ΔS = 1) strengths in transitions to several discrete states and broad resonances in 16O were extracted using a model‐independent method. The giant resonances in the energy region of E x = 19–27 MeV were found to be predominantly excited by ΔL = 1 transitions. The strength distribution of spin‐dipole transitions with ΔS = 1 and ΔL = 1 were deduced. The obtained distribution was compared with a recent shell model calculation. Experimental results are reasonably explained by distorted‐wave impulse‐approximation calculations with the shell model wave functions.

The excitation and subsequent proton decay of the isovector spin-flip giant monopole resonance (IVSGMR) is studied via the 208Pb(3He,t) reaction at 410 MeV. In the inclusive spectrum (60+/-5)% of the non-energy-weighted sum-rule strength for this 2 variant Planck's over 2h omega resonance was found in the region 29Ex(208Bi)51 MeV. The central excitation energy and width of the IVSGMR are 37+/-1 MeV and 14+/-3 MeV, respectively. It is found that the branching ratio for proton decay is (52+/-12)% and that the deep neutron-hole states in 207Pb are strongly fed.

Cross sections, analyzing powers and spin rotation parameters of proton elastic scattering from 58Ni and 120Sn have been measured at intermediate energies. Obtained data have been analyzed in the framework of relativistic impulse approximations. In order to explain the 58Ni data, it was necessary to modify NN interactions in the nuclear medium by changing coupling constants and masses of σ and ω mesons. For 120Sn, by assuming the same modification of NN interactions and by using proton densities deduced from charge densities, the neutron density distribution was searched so as to reproduce 120Sn data at 300 MeV.

Dipole excitations in highly excited energy regions of (6)He and (7)He nuclei were investigated via the ((7)Li,(7)Be) reaction with an incident energy of 65A MeV at forward scattering angles. The resonances at Q approximately equal to -30 MeV observed commonly for both (6)Li and (7)Li targets were found to be excited via both spin-flip and spin-nonflip transitions with DeltaL = 1. Based on the observed excitation energy, width, and cross section of each resonance, the relevant resonances are inferred to be analogs of the dipole resonances of alpha clusters in the (6)Li and (7)Li nuclei.

We have constructed an experimental ensemble to measure polarization transfer observables in proton inelastic scattering at zero degrees. Excited states can simultaneously be measured for the excitation energy from 5 MeV to 35 MeV at Ep=400 MeV. A fast data acquisition system has been developed to endure the large background event rate originated by the primary beam itself. We have found the effective analyzing power of the focal plane polarimeter slightly depends on the treatment of two-ray events.

Polarization transfer (PT) coefficients in the 12C, 28Si(p,p′) reactions at a scattering angle of 0° are measured at Ep=392 MeV. The strength of the isoscalar central spin-dependent part (Vσ) of the effective nucleon-nucleon interaction is studied by using the sensitivity of the PT coefficients for the excitation of the 1+, T=0 state in 12C to the Vσ strength. It is found that distorted wave impulse approximation (DWIA) calculations employing the Franey and Love effective interaction well reproduce the measured PT coefficients.

Cross sections, analyzing powers and spin rotation parameters of proton elastic scattering from 58Ni and 120Sn have been measured at intermediate energies. By elastic scattering off N≃Z nuclei like 58Ni at intermediate energies we can study medium modification of the nucleon-nucleon (NN) interaction inside the nucleus, because proton distributions in target nuclei are constrained by charge distributions measured by electron scattering and neutron distributions can be assumed to be the same as proton’s. In order to explain our experimental data of 58Ni at large scattering angles, it was found to be necessary to use experimental densities deduced from charge densities measured by electron scattering and to modify the coupling constants and the masses of exchanged σ and ω mesons in the RIA, assuming linear dependencies of meson properties to nuclear densities. Parameters of the medium effect have been searched to reproduce the data. For N≠Z nuclei, neutron density distribution can be extracted from the elast...

We have measured cross sections and analyzing powers of elastic proton scattering from 12C, 58Ni, and 120Sn at energies from 200 MeV to 400 MeV. In addition, spin rotation parameters have been measured for 58Ni at Ep=300 MeV using the newly constructed focal plane polarimeter for the spectrometer Grand Raiden at RCNP. Results of calculations based on the relativistic impulse approximation are in good agreement with the measured spin observables, although the differential cross sections are overestimated.

A large focal‐plane polarimeter which uses inclusive scattering from carbon has been installed for the high resolution spectrometer ‘Grand Raiden’ at RCNP. A fast second‐level trigger system can reject events with small scattering angles. A special dipole magnet is added to the final stage of the spectrometer in order to rotate the spin direction. High resolution measurements of all spin observables for proton scattering are now able to be made with high efficiency over a broad energy range. The present system has been checked by the measurement of spin rotation parameters in proton elastic scattering at 300 MeV.

A race-track configuration, which consists of pairs of mirror and U-bend along with four poloidal divertors, is examined as a reactor operated in steady-state with the two-energy-component or the beam driven scheme. The each straight section is a long simple mirror, where the plasma is expected to be hydromagnetically stable stemming from the line tying on the magnetic neutral lines of the poloidal divertors and a dynamic stabilization of the radio-frequency electric field applied in the mirror sections. The 1=2 stellarator and the bumpy torus configurations are considered as the candidates of U-bend sections, especially the former configuration is examined related to the connection between mirror field and stellarator field which is produced with the circular coils and the ferro-magnetic materials. The T ion concentration in plasma is expected to be controllable by the ponderomotive force acting selectively on the T ions with the radio-frequency field applied at exits of the divertors. The estimation shows that the plasma Qp is about 3, and 80 percent or more of the reaction takes place in the mirror sections, assuming that the injection energy of neutral particles, E0 = 200keV, n = 1014cm-3, Te = 15 keV, and plasma loss time, Te = 0.477 sec.

Behavior of the ion sheath near an aperture of ion source is investigated via a nonlinear Poisson equation for an electric potential function in a cylindrical coordinate system. On the assumptions of free electrons with Maxwellian distribution and ion flow against the aperture, the sheath condition and the condition under which the plasma surface is concave are derived. These conditions are shown to depend on the aperture radius, potential of electrode U, electron temperature kT/sub e/ and initial ion velocity. The ion current through the aperture with maximum radius is found to increase significantly when U is greater than or equal to 20kT/sub e/. Behavior of the potential distribution and plasma boundary under various situations are also demonstrated by means of numerical calculations. (auth)

A new type of negative deuterium ion source for the neutral particle injection in the fusion research is proposed. The element of the ion source is made of a bilayer of vanadium or palladium metal and a silicon semiconductor. The D− ions are formed with the cascade processes which involve the dissociation of D2’s when they are dissolved into the element, the electronic resonance transition from the Si surface to D(1s) diffusing through the element, and the detachment of the resultant D− ion from the surface. The estimations show that in an ideal case, the obtainable current density of D− ions is about 27 mA/cm2 and that the neutral component leaving the surface is about 18.5% of the D− ion current.

Observations with a 27‐keV molecular ion injection experiment are described. In the experiment, an rf electric field is applied transversely to a containing magnetic mirror field in the mid‐region. The rf‐field intensity is proportional to r4, and the frequency relation is ω = 2.5ωci = 5ωcm, where r is the radius, and ωci and ωcm are the cyclotron frequencies of protons and hydrogen molecular ions, respectively. Accumulation of plasma greatly increases with an rf potential of about 1.4 kV, and a density of 7×107 particles/cm3 is obtained with an injection current of 2 mA. Perpendicular proton velocity distribution is well spread with an rf potential of about 1.4 kV. The spreading is caused during the process of deceleration of the injected molecular ions. Emissions at the second harmonic and the fourth harmonic of the proton cyclotron frequency are observed. Intensity of the fourth harmonic is reduced with a rise in strength of the rf field. As the rf field is switched off, there are plasma loss processes...

We propose the sequential reaction process $^{15}$O($p$,$\gamma)(\beta^{+}$)$^{16}$O as a new pathway to bypass of the $^{15}$O waiting point. This exotic reaction is found to have a surprisingly high cross section, approximately 10$^{10}$ times higher than the $^{15}$O($p$,$\beta^{+}$)$^{16}$O. These cross sections were calculated after precise measurements of energies and widths of the proton-unbound $^{16}$F low lying states, obtained using the H($^{15}$O,p)$^{15}$O reaction. The large $(p,\gamma)(\beta^{+})$ cross section can be understood to arise from the more efficient feeding of the low energy wing of the ground state resonance by the gamma decay. The implications of the new reaction in novae explosions and X-ray bursts are discussed., Comment: submitted

In recent experiments at GANIL and GSI, we studied the decay of $^{45}$Fe, according to theoretical predictions one of the most promissing cases for 2p radioactivity. Our results show for the first time clear evidence of this new radioactivity. In another experiment at GANIL, 2p emission was observed from excited states in $^{17}$Ne. In these complete kinematics measurements performed at the SPEG facility of GANIL, the angle between the two protons has been measured evidencing a $^{2}$He emission pattern. Both results will be presented and future studies are discussed.

Expérience GANIL; In experiments at the SISSI/LISE3 facility of GANIL, the doubly-magic nucleus 48Ni has been observed for the first time and decay information was gained for very proton-rich nuclei like $^{42}$Cr, $^{45}$Fe, and $^{49}$Ni, as $^{48}$Ni possible candidates for two-proton radioactivity. In the lighter-mass region, detailed studies of $^{21}$Mg and $^{25}$Si were performed and complete decay schemes for allowed decays were established.