119159473
Equation of state for neutron stars in SU(3) flavor symmetry
Using several relativistic mean field models (such as GM1, GM3, NL3, TM1, FSUGold and IU-FSU) as well as the quark-meson coupling model, we calculate the particle fractions, the equation of state, the maximum mass and radius of a neutron star within relativistic Hartree approximation. In determining the couplings of the isoscalar, vector mesons to the octet baryons, we examine the extension of SU(6) spin-flavor symmetry to SU(3) flavor symmetry. Furthermore, we consider the strange ($\sigma^{\ast}$ and $\phi$) mesons, and study how they affect the equation of state. We find that the equation of state in SU(3) symmetry can sustain a neutron star with mass of $(1.8 \sim 2.1) M_{\odot}$ even if hyperons exist inside the core. In addition, the strange vector ($\phi$) meson and the variation of baryon structure in matter also play important roles in supporting a massive neutron star.
119162077
The quark-meson coupling model and chiral symmetry
We extend the quark‐meson coupling (QMC) model to incorporate chiral symmetry. The relationship between the QMC model and chiral perturbation theory is also discussed. The nuclear central potential is modified by the effect of internal structure of the nucleon.
121131573
New Scaling Phenomena in Nuclear Structure Functions
We consider the nuclear mass-number (A) dependence of the nuclear structure functions. We restrict ourselves to a two-component model, in which we assume the existence of an exotic component other than the normal nucleon component in nuclei. We find that there exist scaling phenomena and that the structure function of the exotic component should be independent of A. We also show that the A dependence of the nuclear structure function can be attributed to that of the surface-to-volume ratio which is incorporated in the probability of finding the exotic component in the nucleus.
10938062
Composite nucleons in scalar and vector mean fields.
We emphasize that the composite structure of the nucleon may play quite an important role in nuclear physics. It is shown that the momentum-dependent repulsive force of second order in the scalar field, which plays an important role in Dirac phenomenology, can be found in the quark-meson coupling (QMC) model, and that the properties of nuclear matter are well described through the quark-scalar density in a nucleon and a self-consistency condition for the scalar field. The difference between theories of pointlike nucleons and composite ones may be seen in the change of the {omega}-meson mass in nuclear matter if the composite nature of the nucleon suppresses contributions from nucleon-antinucleon pair creation.
119311709
A new molecular dynamics calculation and its application to the spectra of light and strange baryons
A new approach based on antisymmetrized molecular dynamics is proposed to correctly take account of the many-body correlations. We applied it to the spectra of low-lying, light and strange baryons. The inclusion of the quark–quark correlation is important to predict the precise spectra, and the semi- relativistic kinematics is also vital to correct the level ordering. The baryon spectra calculated by the present method is as precise as the Faddeev calculation.
15022310
A Deformable Bag Model of Hadrons. I
As a generalization of the MIT spherical bag model, we construct the spheroidal bag model of hadron with an arbitrary eccentricity. This generalization is made by slightly modifying the MIT linear boundary condition: The linear boundary condition is examined in detail. Our model always satisfies two necessary requirements of the MIT bag model --i. e., n-j=O, no quark colour flux leaves the bag, and ijq =0, the scalar density of quark should vanish on the bag surface-- and it reduces to the MIT spherical bag model in the limit of zero-eccentricity. Lagrangian formalism of our model is briefly described. The eigenfrequencies of a single massless quark confined in this spheroidal bag are numer­ ically calculated. We obtain the level-splitting of the excited quark orbits, which is just analogous to the well-known Nilsson's splitting of single particle orbits in deformed nuclei. By using the numerical results of the lowest orbit, the effect of the bag-deformation on the mass of low-lying hadrons is estimated. It is found that, although the spherical bag is stable, tbe quark bag is extremely soft against the quadrupole deformation. Brief discussions are added on the mechanisms which make the spherical bag more stable.
92855588
Study of Radionuclides Induced in Low-activation Concrete Using the 12-GeV Proton Synchrotron Accelerator at KEK
Low-activation concrete made of limestone aggregates was irradiated by secondary particles in the beam-line tunnel of the 12-GeV proton synchrotron accelerator at KEK (12GeV-PS), and the radioactive concentrations induced in the concrete were measured using a Ge detector system. Although various radionuclides, such as 22Na, 24Na, 54Mn, 56Mn, 60Co and l52Eu, were induced in the low-activation concrete, those concentrations were below those induced in ordinary concrete made of non-limestone aggregates. Among the induced radionuclides, reducing the 24Na concentration is especially important for preventing the radiation exposures of radiation workers during the maintenance of an accelerator. In order to estimate the 24Na concentration induced in shielding concrete, chemical reagents such as NaHC03, MgO, A1203, Si02 and CaC03 were irradiated at several locations in the beam-line tunnel of the 12GeV-PS, and the 24Na concentrations induced in those chemical reagents were measured. Although the MgO concentration in limestone varies widely from 0.4% to 10% in each mine, the experimental results concluded that low-activation concrete made of limestone aggregates is useful for preventing the radiation exposure of workers as shielding concrete in a particle accelerator facility because the 24Na concentration induced in Mg is below that in Na. It was also confirmed that concentrations of long-lived radionuclides, such as 60Co and 152Eu, induced in the low-activation concrete were lower than those induced in ordinary concrete.
137446914
Hydrogen Absorption in Electropolishing of Niobium
Electropolishing process had been considered to cause hydrogen absorption that could result in hydrogen Q‐disease in niobium superconducting RF cavities. Recently, however, we found that hydrogen Q‐disease did not always occur in a L‐band niobium RF cavity treated by continuous electropolishing (EP) only. We consider mechanical grinding as a very powerful method to eliminate surface defects. Therefore, our surface treatment process is a combination of mechanical grinding and EP. We developed a simple and fast mechanical grinding method, centrifugal barrel polishing method (CBP), as the pre‐treatment for the EP. We applied a combination of CBP and EP to a L‐band niobium cavity and found the result showing a heavy hydrogen Q‐disease. We found out that hydrogen absorption occurred during the CBP, and the absorbed hydrogen came from the water used during the CBP. Hence, we replaced the water by a liquid without hydrogen as its component. As the result, we successfully prevented hydrogen absorption in the CBP....
55249742
Activities on Superconducting Cavities at TOSHIBA
Abstructs R&D activities on superconducting cavities at TOSHIBA are presented. Two L-band single-cell niobium cavities and an L-band three-cell structure were fabricated in our company and measured at KEK. The maximum field gradient of Eacc,max>30MV/m in both single-cell cavities and Eacc,max =18MV/m in the three-cell structure were attained respectively. An optimization study on the annealing temperature for the hydrogen Q-disease is reported. R&D of hydroforming to fabricate seamless cavities is also presented.
33048374
Beam operation with crab cavities at KEKB
KEKB has been operating with crab cavities for the first time in the world. This paper represents beam operation with the crab crossing.
97830649
Detailed spatial measurements and Monte Carlo analysis of the transportation phenomena of thermal and epithermal neutrons from the 12-GeV proton transport line to an access maze
Abstract In order to investigate the neutron transportation from a beam-line tunnel to an access maze at a 12-GeV proton accelerator, we measured the spatial distribution of thermal and epithermal neutrons by using the Au activation method in detail. Gold foils were placed at about 70 positions in the maze in the case of the insertion (or extraction) of a copper target of 1 mm thickness into (or from) the beam axis in front of the maze. After the end of accelerator operation, relative activities of the Au foils were simultaneously measured by using an imaging plate technique and the radioactivity of one reference foil was also measured with a HPGe detector to convert to the absolute activities of all foils. It was found that the neutrons reach to the depth of the maze in the case of the insertion of the copper target. This result reflects higher proportion of high-energy particles from the copper target to that from other beam loss points and high-energy particles become the successive source of low-energy neutrons. Furthermore, it was found that several circumstances such as door walls and electric wire cables obviously affect the absorption effect of thermal neutrons. The reaction rates obtained in this study were also used for the benchmark of the Monte Carlo simulation code, MARS15 (version of February 2008). The results of the MARS15 calculations precisely reproduced experimental results and significant effects of the electric wire cables and door walls.