121120033
Yields and isomeric ratio of xenon and krypton isotopes from thermal neutron fission of /sup 235/U
The experimental cumulative yields of /sup 85/Kr/sup m/, /sup 87/Kr, /sup 88/Kr, /sup 133/Xe/sup g/, /sup 135/Xe/sup m/, and /sup 135/Xe/sup g/ and the independent isomeric yield of /sup 133/Xe/sup m/ in the thermal neutron fission of /sup 235/U have been measured by the gas chromatographic method. The independent yields of /sup 133/Xe/sup g/, /sup 135/Xe/sup m/, and /sup 135/Xe/sup g/ were deduced with the aid of /sup 133/I and /sup 135/I data. The isomeric yield ratios of /sup 133/Xe and /sup 135/Xe have been computed and compared with theoretical values since they have the same high spin state J = 11/2/sup -/ and low spin ground state J = 3/2/sup +/. The influence of the shell effect on the fission isomeric yield ratio is discussed. From the measured independent yield of Xe isotopes plus the reported data, the Xe-isotopic distribution curve has been constructed. The curve is compared with the isotopic distribution curves of Xe isotopes formed in 11.5 GeV proton interactions with /sup 238/U and Cs isotopes formed in 24 GeV proton interactions with /sup 238/U. Upon fitting the yield curves we find that only those products with N/Z> or =1.48 fit a curve typical of a binarymore » fission process.« less
52103890
A past capture event at Sagittarius A* inferred from the fluorescent X-ray emission of Sagittarius B clouds
The fluorescent X-ray emission from neutral iron in the molecular clouds [Sagittarius (Sgr) B] indicates that the clouds are being irradiated by an external X-ray source. The source is probably associated with the Galactic central black hole (Sgr A*), which triggered a bright outburst 100 yr ago. We suggest that such an outburst could be due to a partial capture of a star by Sgr A*, during which a jet was generated. Using constraints from the observed flux and the time variability (∼10 yr) of the Sgr B fluorescent emission, we find that the shock produced by the interaction of the jet with the dense interstellar medium represents a plausible candidate for the X-ray source emission.
119022638
A statistical classification of the unassociated gamma-ray sources in the second Fermi Large Area Telescope Catalog
With the assistance of the identified/associated sources in the second Fermi Large Area Telescope (LAT) catalog, we analyze and resolve the spatial distribution and the distributions of the gamma-ray spectral and variability indices of the remaining 575 unassociated Fermi LAT sources. Consequently, it is suggested that the unassociated sources could statistically consist of Galactic supernova remnants/pulsar wind nebulae, BL Lacertae objects, flat spectrum radio quasars and other types of active galaxies with fractions of 25%, 29%, 41% and 5%, respectively.
120879129
Effect of a strong magnetic field on the surface electric field of strange stars
We made a detailed study of the properties of the electron layer near the quark surface of strange stars with strong (${\sim}10^{14}{-}10^{17}$ G) magnetic fields. The electrostatic potential and the electric field at the quark surface were calculated as functions of the magnetic field intensity of bare strange stars. Using an ultrastrong ($B\geq 2.5\times10^{16}$ G) magnetic field, we found that the distribution of electrons becomes an exponential function of radial distance, which is quite different in a magnetic field-free case. We also calculated the variation in gap width between the strange core and the normal nuclear crust for strange stars, which is due to magnetic field effect.
41248825
Yield and recoil properties of iodine isotopes from the interaction of 240 MeV 12C with 238U.
The independent yields, recoil properties, and forward-to-backward ratios (F/B) of iodine isotopes from the interaction of 240 MeV /sup 12/C with /sup 238/U have been measured radiochemically by the thick-target/thick-catcher method. The isotopic yield distribution curve has been constructed and is found to consist of two overlapping Gaussians, peaking at A = 126.5 and 133.8 with width parameters of 2.29 and 2.04 mass units, respectively. All the measured iodine isotopes had ranges of 7.7 +- 0.4 mg/cm/sup 2/. The neutron-deficient products have F/B of 1.76 +- 0.14, but the neutron-excessive products have F/B of only 1.09 +- 0.06. The yield curve was analyzed with the liquid drop model and the recoil curve was analyzed by the standard two-step vector model; the results show that the neutron-deficient products are formed from nonequilibrium processes and the neutron-excessive products are formed from the normal low-energy fission process.
119289155
HIGH-ENERGY GAMMA-RAY AFTERGLOWS FROM LOW-LUMINOSITY GAMMA-RAY BURSTS
The observations of gamma-ray bursts (GRBs) such as 980425, 031203 and 060218, with luminosities much lower than those of other classic bursts, lead to the definition of a new class of GRBs—LL-GRBs. The nature of the outflow responsible for them is not yet clear. Two scenarios have been suggested: one is the conventional relativistic outflow with initial Lorentz factor of order of Γ0 10 and the other is a trans-relativistic outflow with Γ0 1-2. Here, we compare the high-energy gamma-ray afterglow emission from these two different models, taking into account both synchrotron self-inverse Compton (SSC) scattering and the external inverse Compton scattering due to photons from the cooling supernova or hypernova envelope (SNIC). We find that the conventional relativistic outflow model predicts a relatively high gamma-ray flux from SSC at early times (<104 s for typical parameters) with a rapidly decaying light curve, while in the trans-relativistic outflow model, one would expect a much flatter light curve of high-energy gamma-ray emission at early times, which could be dominated by both the SSC emission and the SNIC emission, depending on the properties of the underlying supernova and the shock parameter e and B . The Fermi Gamma-ray Space Telescope should be able to distinguish between the two models in the future.
117386269
N phi states in a chiral quark model
The structures of N{phi} states with spin-parity J{sup p}=3/2{sup -} and J{sup p}=1/2{sup -} are dynamically studied in both the chiral SU(3) quark model and the extended chiral SU(3) quark model by solving a resonating group method (RGM) equation. The model parameters are taken from our previous work, which gave a satisfactory description of the energies of the baryon ground states, the binding energy of the deuteron, the nucleon-nucleon (NN) scattering phase shifts, and the hyperon-nucleon (YN) cross sections. The channel coupling of N{phi} and {lambda}K{sup *} is considered, and the effect of the tensor force which results in the mixing of S and D waves is also investigated. The results show that the N{phi} state has an attractive interaction, and in the extended chiral SU(3) quark model such an attraction plus the channel coupling effect can consequently make for an N{phi} quasi-bound state with several MeV binding energy.
115699498
A study of nucleon-nucleon spin-orbit force in quark model
Abstract Spin-orbit interactions between two quarks due to the one-gluon exchange, confinement potential, σ-exchange of the chiral field and two-gluon exchange are considered in our calculation. As a consequence, the spin-orbit energy splitting of the 1P state in the baryon spectrum and the 3 P 2 phase shifts of NN scattering can unifiedly be explained.
120385473
Three-dimensional charge dispersion curves from interactions of 11--29 GeV protons with uranium
Experimental nuclear charge dispersion curves from interactions of 11--29 Gev protons with /sup 238/U have been used in the construction of three-dimensional charge dispersion curves. They show the yield variation with mass number A. Neutron-deficient products are distributed over the entire mass range with a peak at A near 87, while the yield of neutron-excessive products is distributed only in the relatively narrow mass region between A=70 and A=150 and has a maximum around A=115. An isobaric yield curve has been obtained by summing up each of the charge dispersion curves and shows a peak, rather than the flat top, in the mass region A=80 to 140 reported previously. The mass yield curves of neutron-excessive and neutron-deficient products are obtained by a decomposition of the charge dispersion curve with two Gaussians, and the mechanism of formation is suggested.
119329935
THE SHORT RANGE MECHANISM OF N-N INTERACTION IN THE EXTENDED CHIRAL SU(3) QUARK MODEL
We give the comparisons between the chiral SU(3) quark model and the extended chiral SU(3) quark model. The results show that the phase shifts of NN scattering are very similar. However, the short range mechanisms of nucleon-nucleon interaction are totally different. In the chiral SU(3) quark model, the short range interaction is dominantly from OGE, and in the extended chiral SU(3) quark model, it is dominantly from vector meson exchanges.
18533521
Deltaron dibaryon structure in chiral SU(3) quark model
We discuss the structure of Deltaron dibaryon in the chiral SU(3) quark model. The energy of Deltaron is obtained by considering the coupling of the $\Delta\Delta$ and $CC$ (hidden color) channels. The effects of various parameters on the Deltaron mass are also studied. It is shown that the mass of Deltaron is lower than the mass of $\Delta\Delta$ but higher than the mass of $\Delta N \pi$.