Search Results (29 total)

Precise measurements of the reaction cross sections (σ_R) for ¹²C on Be, C, and Al targets and ¹¹Be on Be targets were performed in the energy range between 30 and 400 MeV/nucleon. The energy dependencies of σ_R for ¹²C, ¹¹Be, and ⁸B were compared to Glauber-type calculations performed using reliable nucleon-density distributions that are supported by experimental data. It was found that the Glauber-type calculations, which include the higher-order multiple scattering effect, the finite-range effect, and the Fermi-motion effect of nucleons in the nucleus, seem to provide a good prescription relating σ_R at intermediate energies to a proper nucleon-density distribution. This method provides a powerful tool with which to study the nuclear surface structure through the σ_R measurements.

The one- and two-neutron removal reactions from ¹⁷C and ¹⁸C as well as the reaction cross section of ¹⁸C have been studied using a carbon target at 80A MeV. The longitudinal momentum distributions of ^15,16C fragments from ¹⁷C and ^16,17C fragments from ¹⁸C were measured by a direct time-of-flight method. The width of ¹⁵C fragments from ¹⁷C is fairly smaller than that from other C isotopes. The experimental data are discussed within the framework of the Glauber model.

Interaction cross sections (σ_I) of ^72,76,80Kr on a C target were measured at the projectile fragment separator FRS at GSI. Effective matter radii of the nuclei were deduced by a Glauber model analysis so as to reproduce the experimental σ_I. An increase of matter radii toward the proton drip-line is observed. We compare the extracted radii to theoretical predictions, which are based on Skyrme-Hartree-Fock-Bogoliubov (SHFB) and on relativistic mean field (RMF) approaches. The enhancement of the matter radius observed in ⁷²Kr is discussed.

In order to clarify the difference of outcomes between our recent work [Y. Yuri et al., Phys. Rev. ST Accel. Beams 10, 104001 (2007)] and the work done by Los Alamos National Laboratory in the 1990s outlined in the Comment [R. E. Shafer, Phys. Rev. ST Accel. Beams 11, 039001 (2008)], we briefly summarize the former progress of the research and development on beam uniformization by means of the nonlinear focusing method, and insist on the newness of our recent publication in this Reply.

It has been known that uniformization of a beam with a Gaussian profile is possible utilizing odd-order nonlinear focusing in the beam transport system, and this has recently been employed for uniform beam irradiation. Here, we have theoretically studied uniformization of the transverse beam profile using nonlinear-focusing forces produced by multipole magnets in detail. In the case where the nonlinear field of the multipole magnet is given by an infinite power series, all the odd-order multipole strengths required for uniformization of a Gaussian beam and the extent of the resultant uniform region have been expressed using the Twiss parameters. We have shown the principle of uniformization using even-order nonlinear fields. We have also actually demonstrated the transformation of a beam with an asymmetric distribution into one with a uniform distribution by utilizing nonlinear focusing, especially with the sextupole and octupole fields. The validity of the formulas presented here was confirmed through particle-tracking simulations. A practical method to realize a uniform profile using beam collimation and octupole focusing is also presented.

We applied a time-resolved small-angle neutron scattering technique to the vesicle system of dimyristoylphosphatidylcholine for the first time to determine lipid kinetics. The observed kinetics could be explicitly represented by a simple model that includes two independent kinetic parameters, i.e., the rates of transbilayer and interbilayer exchange. This technique is perfectly suited for the determination of lipid exchange kinetics in equilibrium and applicable to evaluation of the activity of the factors relevant to lipid migration, such as translocase and lipid transfer proteins.

Production cross sections for the projectile fragmentation of a 1.05A GeV ⁸⁰Kr beam on a Be target were measured at the projectile fragment separator FRS at GSI. Cross sections were obtained for isotopes of the elements Ge to Kr close to the proton drip line. These data are compared to the results of the empirical parametrization EPAX and to abrasion-ablation calculations. We also compare the results to predictions of intranuclear-cascade calculations. The intranuclear-cascade calculations allow us to also compare well measured one-proton pickup cross sections.

The β-NQR (nuclear quadrupole resonance) signals of ⁸B (I^π=2⁺,T_1/2=770 ms) implanted in TiO₂ (rutile) have been detected to determine the electric quadrupole moment of ⁸B with high precision. The ratio of the quadrupole moments of ⁸B and ¹²B was determined as |Q(⁸B)/Q(¹²B)|=4.88±0.04. Combined with the known sign, the quadrupole moment of ⁸B was obtained as Q(⁸B)=+(64.5±1.4) mb, which is consistent with and more precise than the previously reported value. The experimental values of the Q moment, the proton and neutron radii and the density distribution of ⁸B were compared with several theoretical predictions and were found to be best reproduced by a microscopic cluster model, which suggests the existence of a proton halo.

For the first time, we obtained the g factor for the ground state of ²³Al by use of a β-NMR measurement. ²³Al has a small proton separation energy and is a potential proton-halo candidate. The obtained g factor, |g|=1.557±0.088, clearly shows the spin and parity, J^π=5/2⁺, for ²³Al, which is the same as that of its mirror partner, ²³Ne. The possible nuclear structure of ²³Al is also discussed.

We have demonstrated for the first time the production of highly polarized short-pulse positrons with a finite energy spread in accordance with a new scheme that consists of two-quantum processes, such as inverse Compton scattering and electron-positron pair creation. Using a circularly polarized laser beam of 532 nm scattered off a high-quality, 1.28 GeV electron beam, we have obtained polarized positrons with an intensity of 2×10⁴ e⁺/bunch. The magnitude of positron polarization has been determined to be 73±15(stat)±19(syst)% by means of a newly designed positron polarimeter.

In order to understand the dynamical properties of a neural network, it is important to characterize the relation between spike trains of two neurons in the network. In this study, we show that in some neuron pairs in inferior temporal cortices of macaque monkeys, spike trains of a pair are described by a two-dimensional Poisson process whose means are modulated by a common two-state Markov process. The common two-state Markov process describes a correlated state transition between firing and nonfiring states of the constituent neurons of the pair.

A detailed study of torsional oscillator experiments under steady rotation up to 6.28 rad∕sec is reported for a ⁴He superfluid monolayer film formed in 1-μm-pore-diameter porous glass. We discovered a new dissipation peak, whose height changes in proportion to the angular speed. The new peak appears at a temperature lower than the vortex pair unbinding peak observed in the static state. A model of three-dimensional (3D) coreless vortices (“pore vortices”) is proposed to explain this additional peak in terms of 2D vortex pair dynamics in the presence of a flow field caused by 3D vortices. The new peak originates from dissipation close to the pore vortex lines, where a large superfluid velocity shifts the vortex pair unbinding dissipation to lower temperature. This explanation is consistent with the observation of nonlinear effects at high oscillation amplitudes.

The reaction cross section (σ_R) for the neutron-rich nucleus ¹⁷B on a carbon target has been measured at an energy of 77A  MeV by the transmission method. An enhancement of σ_R at intermediate energy compared to that at high energy was observed. The density distribution of ¹⁷B was deduced through the energy dependence of σ_R using a finite-range Glauber-type calculation under an optical-limit approximation as well as a few-body approach. The existence of a long neutron tail in ¹⁷B was demonstrated. The fraction of the wave function with the valence two-neutron configuration of (2s_1∕2)_J=0² or (1d_5∕2)_J=0² was found to be 50±10% based on a finite-range few-body Glauber-type calculation.

For high luminosity in electron-positron linear colliders, it is essential to generate low vertical emittance beams. We report on the smallest vertical emittance achieved in single-bunch-mode operation of the Accelerator Test Facility, which satisfies the requirement of the x-band linear collider. The emittances were measured with a laser-wire beam-profile monitor installed in the damping ring. The bunch length and the momentum spread of the beam were also recorded under the same conditions. The smallest vertical rms emittance measured at low intensity is 4 pm at a beam energy of 1.3 GeV, which corresponds to the normalized emittance of 1.0×1.0^-8   m. It increases by a factor of 1.5 for a bunch intensity of 10¹⁰ electrons. The measured data agreed to the calculation of intrabeam scattering within much better than a factor of 2.

We have developed a polarimetry of ultrashort pulse γ rays based on the fact that γ rays penetrating in the forward direction through a magnetized iron carry information on the helicity of the original γ rays. Polarized, short-pulse γ rays of (1.1±0.2)×10⁶/bunch with a time duration of 31 ps and a maximum energy of 55.9 MeV were produced via Compton scattering of a circularly polarized laser beam of 532 nm off an electron beam of 1.28 GeV. The first demonstration of asymmetry measurements of short-pulse γ rays was conducted using longitudinally magnetized iron of 15 cm length. It is found that the γ-ray intensity is in good agreement with the simulated value of 1.0×10⁶. Varying the degree of laser polarization, the asymmetry for 100% laser polarization was derived to be (1.29±0.12)%, which is also consistent with the expected value of 1.3%.

Based on the requirements from a conceptual design of a polarized positron beam for future linear colliders, we constructed a special collision system with a short focal length of 150 mm of the laser beams so as to produce γ rays through inverse Compton scattering. In order to achieve efficient laser-electron collisions, we created a special optics to produce very small e^--beam sizes of σ_ex0=7.6   μm and σ_ey0=5.4   μm in the horizontal and vertical directions at the collision point. Using laser light with a wavelength of 532 nm and an e^- beam of 1.28 GeV, provided from the ATF-damping ring at KEK, we generated 2×10⁵ γ rays with a time duration of 26 ps in rms, leading to a peak brightness of 1.7×10¹⁸/(mrad² mm² 0.1%bandwidth s) near to the maximum energy of 56 MeV.

The two-neutron removal cross section ( σ_-2n) and the longitudinal momentum distribution of ¹⁵B fragments from the breakup of ¹⁷B on ⁹Be were measured at 70A MeV. The distribution in the projectile rest frame is characterized by a FWHM of 80±10 MeV/c for ¹⁵B. The σ_-2n is found to be 0.22±0.05 b. A Glauber–type analysis of the data provides clear evidence of a two-neutron halo structure in ¹⁷B.

Electron beams with the lowest, normalized transverse emittance recorded so far were produced and confirmed in single-bunch-mode operation of the Accelerator Test Facility at KEK. We established a tuning method of the damping ring which achieves a small vertical dispersion and small x-y orbit coupling. The vertical emittance was less than 1% of the horizontal emittance. At the zero-intensity limit, the vertical normalized emittance was less than 2.8×10^-8 rad m at beam energy 1.3 GeV. At high intensity, strong effects of intrabeam scattering were observed, which had been expected in view of the extremely high particle density due to the small transverse emittance.

The axial charge in the weak nucleon axial vector current has been precisely determined by measuring the alignment correlation terms in the β-ray angular distributions of the purely spin aligned mirror pair nuclei ¹²B(I^π=1⁺,T_1/2=20.2 ms) and ¹²N(I^π=1⁺,T_1/2=11.0 ms). The axial charge was determined to be y=4.96±0.09 (stat.)±0.05 (syst.) at a 90% confidence level. The previously obtained data in the year 1996 was reanalyzed to be added to the present result. The combined result is y=4.90±0.10 at a 90% confidence level. The axial charge is enhanced as much as (72±4)% from the impulse approximation model calculated value y_IA=2.85. Calculations using the impulse approximation with the soft-π contribution y_th=4.15 explain the data quite well but not completely. If we introduce the in-medium mass renormalization the unexplained part of the experimental result corresponds to an in nuclear-medium nucleon mass reduction of (16±4)% at a 90% confidence level relative to the free nucleon mass, at the place where the decaying nucleon resides.

The G-parity irregular induced tensor form factor in the weak nucleon axial vector current has been precisely determined by measuring the alignment correlation terms in the β-ray angular distributions of the purely spin aligned mirror pair ¹²B(I^π=1⁺, T_1/2=20.2 ms) and ¹²N(I^π=1⁺, T_1/2=11.0 ms) in order to place a new limit on the applicability of the G-parity conservation law. The coefficient of the induced tensor term was determined to be 2Mf_T/f_A=-0.21±0.09 (stat.) ±0.07 (syst.)±0.05 (theory) at a 90% confidence level. The previously obtained data in the year 1996 was reanalyzed to be added to the present result. The combined result is 2Mf_T/f_A=-0.15±0.12±0.05 (theory) at a 90% confidence level. The obtained induced tensor coefficient is vanishingly small and is consistent with the theoretical prediction based on QCD in the framework of which the induced tensor form factor is proportional to the mass difference between up and down quarks. Also we set constraints on the Kubodera-Delorme-Rho parameters from the present result together with the results of correlation-type experiments in the mass A=8 and 20 systems as ζ=-(0.12±0.14)×10^-3 MeV^-1 and λ=+(0.30±0.88)×10^-3 in the 1σ level.

The nuclear magnetic dipole moment μ and electric quadrupole moment Q of the β-emitting ¹⁶N(I^π  =  2^-,T_1/2  =  7.13  s) nucleus have been determined for the first time by detecting its β-NMR in a MgO crystal and β-NQR (nuclear quadrupole resonance) in a TiO ₂ crystal to be |μ|  =  (1.9859±0.0011)μ_N and |Q|  =  (17.9±1.7)  mb, respectively. Although the prediction of μ given by the Hartree-Fock calculation agrees well with the experiment, an abnormally small effective charge for neutrons is required to account for the experimental Q.

The axial charge of the weak nucleon axial vector current extracted from the anisotropic β-ray angular distributions of spin aligned ¹²B and ¹²N was accounted for mainly in terms of the impulse value y_IA and the soft pion exchange effect term y_exch. The experimental value, y  =  4.66±0.06(stat)±0.13(syst), was enhanced by 63% from the impulse value y_IA  =  2.85 which includes the core polarization effect. The experimental excess of 0.54 over the theoretical value y_IA+y_exch  =  4.12 is accounted for by the in-medium mass reduction from the free nucleon value, if there is such an effect, of about (12±4)% for the nucleons decaying in the A  =  12 triad.

The angular distributions of β rays from spin aligned ¹²B and ¹²N were precisely remeasured using a further refined spin-manipulation technique. Our old data have also been recorrected for precisely determined systematic corrections. A nonzero G-parity violating induced tensor form factor f_T has been concluded as 2Mf_T/f_A  =  +0.22±0.05(stat)±0.15(syst)±0.05(theor.). In this result the asymmetry in the axial charges due to the binding-energy difference of the transforming nucleons is taken into account.

In the aim of providing a theoretical basis for conventional calculation, the translational invariance of both the density temperature Green’s function and the current temperature Green’s function is proved for an interacting electron gas in a uniform magnetic field. The proof is based on the previously proposed nonperturbative canonical method [Phys. Rev. B 50, 18 640 (1994)].

The quadrupole moment of the ⁸B (I^π=2⁺, T_1/2=769 msec) nucleus was measured as ‖Q(⁸B)‖=68.3±2.1 mb by use of modified β-NMR. This value is twice as large as the prediction of the Cohen-Kurath shell model. It is found by subtracting the contribution of deeply bound neutrons that the protons in ⁸B carry more than 90% of the observed moment. The anomalous value is accounted for fairly well by the proton halo due to the loosely bound valence configuration. This is the first experimental evidence for the existence of a proton halo covering a neutron core.