By using the rigorous spectral representation of relativistic random phase approximation, the low-lying excitation of finite nuclei and its longitudinal response function for quasielastic electron scattering are calculated in the σ-ω model of quantum hadrodynamics. It is shown that the reproduction of the correct order of the 1- and 3- excitation states of 16O is due to the contribution of the exchange vertex. There is no significant influence of the retardation effect on the low-lying excitation states. In contrast, the retardation effect plays an important role in the electron scattering process of nuclei. The theoretical longitudinal responses of 12C and 40Ca, including the contributions of the exchange vertex and the retardation effect, are suppressed and reproduce the experimental data better than the results excluding them. 相似文献
The reaction cross section, together with the one-, two- and three neutron removal cross sections, of 17C with the energy of 79A MeV on carbon target were measured using the radioactive beam line RIPS of RIKEN. The reaction cross section and the one-neutron removal cross section were analyzed within the frame of Glauber model. Both the analyses favor the dominant configuration of a 16C core (2+) plus a d5/2 valence neutron for 17C. The work for the neutron-rich carbon isotope on the reaction cross section σR and the interaction cross section σI on 12C target are summarized.相似文献
We have measured the reaction cross section σR of 17C on the carbon target at the intermediate energy of 97A MeV by using transmission method.finite-range Glauber model has been employed to investigate the density distribution of 17C by fitting the present result and the previous result of interaction cross section σI.By contrast with the result from the analysis of σI,a tail in the neutron density distribution of 17C is found necessary to interpret the present result.Considering the configuration of the valence neutron,a dominant 1d5/2(77±21%)occupancy is found,which is in agreement with results of momentum distribution measurements. 相似文献
The quenching factors of one-neutron spectroscopic factors,which are ratios of theoretical to experimental one-neutron removal cross sections,are studied for the carbon isotopes ~(15-19)C,with ~(12)C and ~9Be targets within incident energies from around 50 to 900 MeV/nucleon.The resulting values of quenching factors do not show strong energy dependence within such an energy range.The average values of the these quenching factors agree well with the systematics in [J.A.Tostevin and A.Gade,Phys.Rev.C,90 057602(2014)],which was established for a large set of radioactive nuclei with different masses below 305 MeV/nucleon. 相似文献
Transparent and flexible carbon doped ZnO (C:ZnO) field emission device was successfully fabricated on an arylite substrate. Excellent adhesion of deposited C:ZnO on the flexible substrate was achieved with low sputtering power and Ar flow rate. In the fabricated device, nanostructured C:ZnO and as‐deposited thin films were used as field emitter and phosphor screen, respectively. The C:ZnO thin film showed a transparency of about 80% at 550 nm wavelength and average sheet resistance of 1.96 kΩ/□. The C:ZnO phosphor screen emitted red light during the field emission measurement, correlating the dominant cathodoluminescence peak at 646 nm. Thus, a promising transparent and flexible field emission display can be realized with C:ZnO based material.
Transparent and flexible C:ZnO film phosphor screen (anode) and nanocone emitters (cathode) for field emission device. 相似文献
Fourier transform infrared spectroscopy has been applied to the study of cyclohexane adsorbed on Al2O3 and Pt/Al2O3 surfaces. Earlier studies of benzene on these same materials have also been extended to include benzene adsorbed on a Pt/Al2O3 surface which contains structured carbon residues. The data provide indirect evidence for the formation of a carbon residue on Pt/Al2O3 which retains the six-membered cyclic structure of the parent adsorbates. The carbon residue can be formed upon vacuum heating of the parent C6 ring molecules chemiorbed on Pt/Al2O3. There is spectroscopic evidence that cyclohexane dehydrogenates on Pt/Al2O3 at 300 K to form two different chemisorbed species; a π-bonded benzene and a dissociated σ-bonded benzene. These two chemisorbed species have CH stretching vibrations centered at 3030 and 2947 cm?1, respectively. Benzene added to a clean catalyst surface forms only a π-bonded benzene. However, benzene added to Pt/Al2O3 with ordered carbon residues forms both π- and σ-bonded benzenes. The addition of H2 at 300 K to any of the π- or σ-bonded benzenes or to the carbon residue results in the formation of cyclohexane physisorbed on the catalyst. The absence of CH3 groups upon hydrogenation suggests the lack of CC bond breaking during adsorption or hydrogenation. Simultaneous infrared and thermal desorption studies on chemisorbed deuterated benzene (from C6D12) indicate that the a-bonded species exchange H from the surface OH groups of the alumina support more readily than does the π-bonded benzene. In addition to hydrogen exchange with the support, thermal desorption experiments indicate the oxidation of a portion of the chemisorbed hydrocarbons and/or carbon residue by oxygen from the alumina support. Therefore, the support is capable of playing a direct role in reactions occurring on the catalyst surface. 相似文献
The experimental (n,2n) cross sections around 14 MeV have been collected, analyzed, and evaluated. Data were taken from 124 nuclei for A=19–209 up to the end of 1983. Relation between σn, 2n and (N-Z)/A has been studied. No neutron shell effect is found. The cross sections for some nuclei have been calculated by using a statistical theory. The good agreement with the experimental σn, 2n at 14 MeV has been obtained in terms of a single set of fitting parameters. 相似文献
Relativistic Hartree equations for spherical nuclei have been derived from a relativistic quark model of the structure of bound nucleons which interact through the (self-consistent) exchange of scalar (σ) and vector (ω and ϱ) mesons. The coupling constants and the mass of the σ-meson are determined from the properties of symmetric nuclear matter and the rms charge radius in 40Ca. Calculated properties of static, closed-shell nuclei from 16O to 208Pb are compared with experimental data and with results of Quantum Hadrodynamics (QHD). The dependence of the results on the nucleon size and the quark mass is investigated. Several possible extensions of the model are also discussed. 相似文献
We have calculated cross sections for pion electroproduction from nuclei near threshold, including the distortion of the pion wave function by the pion-nucleus optical potential. Distortion effects near threshold are found to be significant, changing the ratio σπ-/σπ+ for production of 10 MeV pions from 16O by nearly fifty percent. 相似文献
Cross section of the thermal neutrons is considered in the framework of the statistical approach to the complicated nuclei. The probability distribution ?(z = σ/σ*) to have given cross section σ (determined by fluctuations of resonance positions and widths), where σ* is the cross section for the model of equidistant resonances with the same width, has been calculated. The last quantity can be represented in terms of the neutron strength function for given nuclei. The probability distribution ?(z) is universal for all nuclei. 相似文献
ABSTRACTA computational study of the complexes formed by F2C=CFZH2 (Z?=?P, As, and Sb) and F2C=CFPF2 with two Lewis bases (NH3 and NMe3) has been carried out. In general, two minima complexes are found, one with a σ-hole pnicogen bond and the other one with a π-hole tetrel bond in most complexes but two σ-hole pnicogen bonded complexes are obtained for F2C=CFZH2 and NH3. They have similar stability though F2C=CFSbH2 engages in a much stronger σ-hole pnicogen bond with NMe3. The –PF2 substitution makes the π-hole on the terminal carbon form a tetrel bond with NH3. A heavier –ZH2 group engages in a stronger σ-hole pnicogen bond but results in a weaker π-hole tetrel bond. Other than electrostatic interaction, the stability of both complexes is attributed to the charge transfer from the N lone pair into the C–Z/H–Z anti-bonding orbital in the pnicogen bond and the C=C anti-bonding orbital in the tetrel bond.The σ-hole pnicogen bonded and π-hole tetrel bonded complexes between F2C=CFZH2 (Z = P, As, and Sb) and two Lewis bases (NH3 and NMe3) have been compared. The results indicate that both interactions can compete, dependent on the nature of the N base. 相似文献
We use perturbative QCD to calculate the cross sections σLT for the diffractive production of open charm (cc) from longitudinally and transversely polarised photons (of virtuality Q2) incident at high energy (√S) on a proton target. We study both the Q2 and M2 dependence of the cross sections, where M is the invariant mass of the cc pair. Surprisingly, the result for σT, as well as for σL, is perturbatively stable. We estimate higher-order corrections and find a sizeable enhancement of the cross sections. The cross sections depend on the square of the gluon density g(x, K2), and we show that the observation of open charm at the HERA electron-proton collider can act as a sensitive probe of the gluon distribution for x = (Q2 + M2)/s and scale K2 = (M2c + )(1 + Q2/M2) where the average quark transverse momentum squared 〈k2t~ (M2c . As compared to diffractive J/#x03C8; production, open charm has the advantage that it is independent of the non-perturbative ambiguities arising from the J/#x03C8; wave function. We estimate the fraction of diffractive events that arise from cc¯ production. 相似文献
The nucleation rate was measured by directly counting the number of nuclei, which were developed while an isotactic polypropylene melt was flowing under shear in a thin film. The nucleation rate was enhanced with an increased rate of shear, e.g., by a factor of 10 larger at the rate of shear of 14 s?1 compared with the quiescent state, at 134°C. The ratio of the shear‐enhanced nucleation rate to the nucleation rate in the quiescent state was larger at a higher temperature of crystallization, i.e., about 10 times at 134°C to 590 times at 140°C. The increase of the nucleation rate under shear flow was explained by a reduction of the lateral and end (fold) surface free energies; the product σs2 σe decreased to 3.2×10?7 for the sheared melt, from 6.0×10?7 (J m?2)3 for the isotropic state. The free energy reduction was caused by transition of the nucleus formation mode from three‐dimensional folded chain nuclei to two‐dimensional bundle nuclei, in which chains lie down on the glass substrate, aligning parallel to the flow direction. 相似文献
Yield curves of the reactions16O (γ, x)11C,16O (γ, x)13N and12C(γ, t) have been measured relative to12C(γ, n)11C with bremsstrahlung. The cross section σ[16O(γ, x)11C] has a shape similar to σ[16O(γ, t)] and shows a broad maximum near 38 MeV. Differences between σ[16O(γ, x)13N] and σ[16O(γ, t)] point to a reaction mechanism via quadrupole absorption in16O. The yield of12C(γ, t) exceeds the16O(γ,t) yield by a factor of two. 相似文献
The experimental data of the neutron total cross section σt,nonelastic cross section σnon and elastic scattering angular distribution σel(θ) for ten target nuclei ranging from 12C to 238U with incident energies En=20—1000MeV were used to optimize the relativistic phenomenological optical potential (RPOP) through automatic search of the best parameters by computer.In addition,a relativistic microscopic optical potential (RMOP) based on Walecka model were also used to analyze the same data and compare with the RPOP. Through comparison between these two kinds of relativistic optical potential hints in improving both the RMOP and RPOP is indicated. 相似文献