Search Results (88 total)

Charge-changing and fragment production cross sections at 0^° have been obtained for interactions of 290, 400, and 650 MeV/nucleon ⁴⁰Ar beams, 650 and 1000 MeV/nucleon ³⁵Cl beams, and a 1000 MeV/nucleon ⁴⁸Ti beam. Targets of C, CH₂, Al, Cu, Sn, and Pb were used. Using standard analysis methods, we obtained fragment cross sections for charges as low as 8 for Cl and Ar beams and as low as 10 for the Ti beam. Using data obtained with small-acceptance detectors, we report fragment production cross sections for charges as low as 5, corrected for acceptance using a simple model of fragment angular distributions. With the lower-charged fragment cross sections, we can compare the data to predictions from several models (including NUCFRG2, EPAX2, and PHITS) in a region largely unexplored in earlier work. As found in earlier work with other beams, NUCFRG2 and PHITS predictions agree reasonably well with the data for charge-changing cross sections, but these models do not accurately predict the fragment production cross sections. The cross sections for the lightest fragments demonstrate the inadequacy of several models in which the cross sections fall monotonically with the charge of the fragment. PHITS, despite its not agreeing particularly well with the fragment production cross sections on average, nonetheless qualitatively reproduces some significant features of the data that are missing from the other models.

Cross sections and analyzing powers for proton elastic scattering from ^{116,118,120,122,124}Sn at 295 MeV have been measured for a momentum transfer of up to about 3.5 fm^-1 to deduce systematic changes of the neutron density distribution. We tuned the relativistic Love-Franey interaction to explain the proton elastic scattering of a nucleus whose density distribution is well known. Then, we applied this interaction to deduce the neutron density distributions of tin isotopes. The result of our analysis shows the clear systematic behavior of a gradual increase in the neutron skin thickness of tin isotopes with mass number.

The strength distributions of the giant monopole resonance (GMR) have been measured in the even-A Sn isotopes (A=112–124) with inelastic scattering of 400-MeV α particles in the angular range 0°–8.5°. We find that the experimentally observed GMR energies of the Sn isotopes are lower than the values predicted by theoretical calculations that reproduce the GMR energies in ²⁰⁸Pb and ⁹⁰Zr very well. From the GMR data, a value of K_τ=-550±100  MeV is obtained for the asymmetry term in the nuclear incompressibility.

Charge-changing and fragment production cross sections at 0° have been obtained for interactions of 290 and 400 MeV/nucleon carbon beams with C, CH₂, Al, Cu, Sn, and Pb targets. These beams are relevant to cancer therapy, space radiation, and the production of radioactive beams. We compare these results against previously published results using C and CH₂ targets at similar beam energies. Because of ambiguities arising from the presence of multiple fragments on many events, the previous publications reported only cross sections for B and Be fragments. In this work, we have extracted cross sections for all fragment species, using data obtained at three distinct values of angular acceptance, supplemented by data taken with the detector stack placed off the beam axis. A simulation of the experiment with the particle and heavy ion transport system (PHITS) Monte Carlo model shows fair agreement with the data obtained with the large-acceptance detectors, but agreement is poor at small acceptance. The measured cross sections are also compared with the predictions of the one-dimensional cross section models EPAX2 and NUCFRG2; the latter is presently used in NASA's space radiation transport calculations. Though PHITS and NUCFRG2 reproduce the charge-changing cross sections with reasonable accuracy, none of the models is able to accurately predict the fragment cross sections for all fragment species and target materials.

The invariant mass spectra of ϕ→K⁺K^- are measured in 12 GeV p+A reactions in order to search for the in-medium modification of ϕ mesons. The observed K⁺K^- spectra are well reproduced by the relativistic Breit-Wigner function with a combinatorial background shape in three βγ regions between 1.0 and 3.5. The nuclear mass number dependence of the yields of the K⁺K^- decay channel is compared to the simultaneously measured e⁺e^- decay channel for carbon and copper targets. We parameterize the production yields as σ(A)=σ₀A^α and obtain α_ϕ→K⁺K^--α_ϕ→e⁺e^- to be 0.14±0.12. Limits are obtained for the partial decay widths of the ϕ mesons in nuclear matter.

We observed the electric-field-induced insulator-to-metal (IM) transition in YBa₂Cu₃O_7−δ∕Pr_1−xCa_xMnO₃ (PCMO,x=0.5)∕SrRuO₃ ramp-type junctions with a small area of ∼6 μm² using an external series resistor from 150 Ω to 2 MΩ. As a result, it was revealed that the resistance of the junctions immediately after the transition was on a comparable order to the external series resistance. Therefore, the smaller the external series resistance is, the smaller the resistance of the PCMO film immediately after the IM transition will be. The parasitic resistance in the junction works as a series resistance to the PCMO film. We achieved the minimum resistivity of ∼10⁻¹ Ω cm by reducing the parasitic resistance in the junctions without an external series resistor. The present results indicate that the intrinsic resistivity, as realized in the magnetic-field- and x-ray- and photon-irradiation-induced IM transitions, can also be achieved in the electric-field-induced IM transition if we succeed in sufficiently diminishing the parasitic resistance.

Invariant mass spectra of e⁺e^- pairs have been measured in 12 GeV p+A reactions to detect possible in-medium modification of vector mesons. Copper and carbon targets are used to study the nuclear-size dependence of e⁺e^- invariant mass distributions. A significant excess on the low-mass side of the ϕ meson peak is observed in the low βγ(=β/sqrt[1-β²]) region of ϕ mesons (βγ<1.25) with copper targets. However, in the high βγ region (βγ>1.25), spectral shapes of ϕ mesons are well described by the Breit-Wigner shape when experimental effects are considered. Thus, in addition to our earlier publications on ρ/ω modification, this study has experimentally verified vector meson mass modification at normal nuclear density.

We report resistivity, Hall effect, Nernst effect, and magnetoresistance measurements on T^′-phase La_1.85Y_0.15CuO_4−δ (LYCO) films prepared by pulsed laser deposition under different oxygen conditions. Our results show that superconductivity in LYCO originates from an oxygen-doped Mott-like insulator and not from a weakly correlated, half-filled band metal as proposed previously.

We have measured deexcitation x rays emitted from the resonant coherently excited 2¹P₁ state of heliumlike Fe²⁴⁺ ions of 423  MeV/amu, planar channeling through a Si crystal. Large anisotropy in the angular distribution of deexcitation x-ray emission is observed: the x-ray emission in the direction parallel to the channeling plane is favored by a factor of 2 compared to the perpendicular direction. This anisotropy originates from the direction of the periodic crystal field, which populates specific m states in resonant coherent excitation and aligns the excited states.

We have observed resonant coherent excitation (RCE) of H-like Ar¹⁷⁺ ions traveling through a 1  μm-thick Si crystal at an energy of 391  MeV/u in the nonchanneling condition. A three-dimensional periodic array of atomic planes induces RCE of the nonchanneling ions. The high energy heavy ions together with the thin crystal allow us to observe this new RCE through the measurements of the charge-state distribution of the emerging ions. The observed resonances are much narrower than those of planar-channeling ions due to the absence of the large Stark shift caused by the planar potential.

The inclusive production of ω and ϕ mesons is studied in the backward region of the interaction of 12 GeV protons with polyethylene, carbon, and copper targets. The mesons are measured in e⁺e^- decay channels. The production cross sections of the mesons are presented as functions of rapidity y and transverse momentum p_T. The nuclear mass number dependences (A dependences) are found to be A^{0.710±0.021(stat)±0.037(syst)} for ω mesons and A^{0.937±0.049(stat)±0.018(syst)} for ϕ mesons in the region of 0.9<y<1.7 and p_T<0.75 GeV/c.

The invariant mass spectra of e⁺e^- pairs produced in 12 GeV proton-induced nuclear reactions are measured at the KEK Proton Synchrotron. On the low-mass side of the ω meson peak, a significant enhancement over the known hadronic sources has been observed. The mass spectra, including the excess, are well reproduced by a model that takes into account the density dependence of the vector meson mass modification, as theoretically predicted.

Secondary neutron-production cross sections have been measured from interactions of 290 MeV/nucleon C and 600 MeV/nucleon Ne in a target composed of simulated Martian regolith and polyethylene, and from 400 MeV/nucleon Ne interactions in wall material from the International Space Station. The data were measured between 5° and 80° in the laboratory. We report the double-differential cross sections, angular distributions, and total neutron-production cross sections from all three systems. The spectra from all three systems exhibit behavior previously reported in other heavy-ion neutron-production experiments, namely, a peak at forward angles near the energy corresponding to the beam velocity, with the remaining spectra generated by pre-equilibrium and equilibrium processes. The double-differential cross sections are fitted with a moving-source parametrization. Also reported are the data without corrections for neutron flux attenuation in the target and other intervening materials and for neutron production in nontarget materials near the target position. These uncorrected spectra are compared with SHIELD-HIT and PHITS transport model calculations. The transport model calculations reproduce the spectral shapes well but, on average, underestimate the magnitudes of the cross sections.

For magnetic alloy (MA) loaded rf accelerating cavity, we have developed an indirect cooling system, which is effective for retaining its shunt impedance by cooling only one side of the MA cores. Because of its low-Q high-permeability property, MA cores are suitable for constructing untuned broadband accelerating systems. Since these same cores are made of wound thin tape, the key to establishing an untuned broadband cavity with effective indirect cooling method is to suppress the reduction of core impedance when attaching metallic cooling plates to the core and keeping a good thermal contact between them. We have employed indium bonding to thermally connect both cores and cooling plates. Both cooling and endurance tests have demonstrated its successful results.

We have studied the various conditions and limitations for achieving compact fixed-field alternating-gradient (FFAG) accelerators to be widely used in heavy-ion cancer therapy. For the case of a normal-conducting FFAG accelerator, our linear calculation indicates 12-cell radial sectors with a field index of 10.5 as a suitable configuration. We found that its ring circumference can be as small as 70 m and that triple-cascade rings are needed to accelerate a carbon beam from 40  keV/u to 400  MeV/u. In this paper, we report a systematic analysis based on a linear optical model, a comparison of various types of FFAG, and a design example with some technical concerns. An important result is that viable radial-sector designs are possible with circumference factor C significantly lower than the value 4.45 previously quoted.

The systematic behavior of the isoscalar giant dipole resonance (ISGDR) in ⁹⁰Zr, ¹¹⁶Sn, ¹⁴⁴Sm, and ²⁰⁸Pb is studied with inelastic α scattering at E_α=386  MeV. Multipole-decomposition analysis is applied to extract the excitation strengths of giant resonances from the (α,α^′) differential cross sections at θ_lab=0.64°–13.5°. The bimodal structure of the ISGDR is discussed and compared with recent theoretical results from Hartree‐Fock+random‐phase‐approximation calculations.

Background-free inelastic scattering spectra have been obtained for five Sm isotopes with 386-MeV α particles at forward angles (including 0°) to investigate the effect of deformation on the compressional-mode giant resonances. The strength distributions for the L≤3 isoscalar giant resonances have been extracted via a multipole decomposition analysis using angular distributions calculated in the framework of the density-dependent single-folding model. We observed a splitting of the giant monopole resonance because of its mixing with the giant quadrupole resonance. For the isoscalar giant dipole resonance, the observed effects of deformation are different for the low- and high-excitation-energy components. Evidence has been obtained for the theoretically predicted mixing between the isoscalar giant dipole resonance and the high energy octupole resonance.

We present a joint experimental and theoretical study of convoy-electron emission resulting from highly-charged-ion transport through carbon foils at moderately relativistic speeds. Energy spectra of electrons ejected at 0° have been measured for 390 MeV/u hydrogen-like Ar¹⁷⁺ ions and 460 MeV/u (β=v/c=0.74,γ=1.49) Fe²⁵⁺ (1s), Fe²⁴⁺ (1s²), and Fe²³⁺ (1s²2s) incident on carbon foils with thicknesses from 25 to 8700 μg/cm². Due to this unprecedented wide range of thicknesses, the sequential excitation and ionization of initially deeply bound electrons to highly excited states and continuum states can be followed in considerable detail. The analysis of the spectra is aided by simulations based on the classical transport theory which has been extended to relativistic energies and to multielectron projectiles. The motion of the projectile electron inside the solid target is calculated taking into account the Coulomb potential of the projectile ion and the multiple stochastic collisions with target cores and target electrons. Different phases of the convoy-electron emissions can be disentangled: direct ejection to the continuum, the transient buildup of an excited-state wave packet followed by ionization, and postionization modification of the continuum spectrum. We find good agreement between experiment and simulation for the evolution of charge states and the emission spectrum.

A behavior of a two-qubit system coupled by the electric capacitance has been studied quantum mechanically. We found that the interaction is essentially the same as the one for the dipole-dipole interaction; i.e., qubit-qubit coupling of the NMR quantum gate. Therefore, a quantum gate could be constructed by the same operation sequence for the NMR device if the coupling is small enough. The result gives an information to the effort of development of the devices assuming capacitive coupling between qubits.

Total charge-changing cross sections and cross sections for the production of B and Be fragments were directly measured for reactions induced by ∼110–250 MeV/nucleon ¹²C ions in C, CH₂, and H₂O targets. Etched track detector (CR-3) was used, together with an automatic track measuring system and a track matching algorithm, to count and to identify the primary and secondary particles. A comparison of the present data and of previously measured cross sections with model predictions is carried out. For the total charge-changing cross section, a model developed at NASA gives the best agreement with the present results (about 3% on the average). However, for the production of fragments, the results of models deviate on average for all systems studied by 9–58 % from the data presented in this work for Z=5 and by 5–47 % for Z=4. The model known as NUCFRG2 is the most reliable in giving the closest values for fragmentation cross sections, 9 and 5% for B and Be fragments, respectively, for the systems studied in this work.

We discuss the renormalization of a Becchi-Rouet-Stora-Tyutin (BRST) and anti-BRST invariant composite operator of mass dimension 2 in Yang-Mills theory with general BRST and anti-BRST invariant gauge-fixing terms of Lorentz type. The interest of this study stems from a recent claim that the nonvanishing vacuum condensate of the composite operator in question can be an origin of mass gap and quark confinement in any manifestly covariant gauge, as proposed by one of the authors. First, we obtain the renormalization group flow of the Yang-Mills theory. Next, we show the multiplicative renormalizability of the composite operator and that the BRST and anti-BRST invariance of the bare composite operator is preserved under the renormalization. Third, we perform the operator product expansion of the gluon and ghost propagators and obtain the Wilson coefficient corresponding to the vacuum condensate of mass dimension 2. Finally, we discuss the connection of this work with previous works and argue the physical implications of the obtained results.

We have measured the double-differential cross sections for neutron production from C, Ne, and Ar projectiles at E/A=290–600 MeV on C, Cu, and Pb targets. Neutron energies were measured at laboratory angles between 5° and 80°. The measured neutron spectra have three components. At forward angles, a prominent peak originating from the projectile-fragmentation process was observed. The velocity of neutrons corresponding to the peak was about the same as that of the projectile. In addition to the peak, two components of Maxwellian-shape distributions corresponding to the preequilibrium and equilibrium processes were observed. By fitting with a moving-source model having three components, the neutron spectra were fairly well described. The parameters obtained for each component are consistent with a picture of the projectile fragmentation, preequilibrium, and equilibrium processes. By integrating the fitted functions with respect to the neutron energies and solid angles, the angular distributions and total cross sections for the neutron production were determined. The neutron spectra, angular distributions, and total cross sections were compared with those calculated by the quantum molecular dynamics and heavy-ion codes. We found that neither of the codes could reproduce the measured cross sections for all combinations of the projectiles and targets.

Charge-changing and fragment production cross sections have been obtained for interactions of a 600 MeV/nucleon neon beam in H, C, Al, Cu, Sn, Ta, and Pb targets. The H target results were obtained using a polyethylene target and subtracting the cross sections obtained with the carbon target. At 600 MeV/nucleon, the angular distributions of the fragments are strongly forward peaked, and consequently the spectra seen in the detectors with the largest angular acceptance—corresponding to a forward cone with half angle 7°—show obvious fragment peaks only for charges 5 through 9. No clear peaks are seen below charge 5 in the large-acceptance detectors, but spectra from detectors subtending smaller angular acceptances show peaks for all fragment species, and additional identifiable peaks from events with between two and four fragments in coincidence. Production cross sections for all fragment species are reported here and, where possible, compared to earlier measurements and to the predictions of three model calculations (Nucfrg2, Qmsfrg, and an empirical parametrization that is tuned for higher-mass beams). The cross sections for fragments of charge 5 and below have not been previously reported. Also, the charge-changing cross sections are compared to earlier measurements and to Nucfrg2 and the Bradt-Peters model.

We measured the invariant mass spectra of electron-positron pairs in the target rapidity region of 12-GeV p+A reactions. We have observed a significant difference in the mass spectra below the ω meson between p+C and p+Cu interactions. This difference indicates that the spectral shape of mesons is modified at normal nuclear-matter density.