Wei Huiling

The Symmetry Energy from the Neutron-Rich Nucleus Produced in the Intermediate-Energy 40,48Ca and 58,64Ni Projectile Fragmentation

In the framework of a modified Fisher model, using the isobaric yield ratio method, we investigate the fragments produced in the 140 A MeV 40,48Ca+9Be and 58,64Ni+9Be projectile fragmentation reactions. Using different approximation methods, asym/T (the ratio of symmetry-energy coefficient to temperature) of symmetric and neutron-rich fragments are extracted. It is found that asym/T of fragments depend on the reference nucleus and the neutron excess of fragments. The asym/T of the isobar decreases when the neutron-excess of the isobar increases, while for a fragment with the same neutron-excess, asym/T increases as the mass of the fragment increases but saturate when the mass of the fragment becomes larger.

Isospin dependence of projectile-like fragment production at intermediate energies

The cross sections of fragments produced in 140 A MeV Ca + Be and Ni + Be reactions are calculated by the statistical abration-ablation(SAA) model and compared to the experimental results measured at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. The fragment isotopic and isotonic cross section distributions of Ca and Ca, Ni and Ni, Ca and Ni, and Ca and Ni are compared and the isospin dependence of the projectile fragmentation is studied. It is found that the isospin dependence decreases and disappears in the central collisions. The shapes of the fragment isotopic and isotonic cross section distributions are found to be very similar for symmetric projectile nuclei. The shapes of the fragment isotopic and isotonic distributions of different asymmetric projectiles produced in peripheral reactions are found very similar. The similarity of the distributions are related to the similar proton and neutron density distributions inside the nucleus in framework of the SAA model.

Residue Coulomb interaction among isobars and its influence in symmetry energy of neutron-rich fragment

The residue Coulomb interaction (RCI), which affects the result of symmetry-energy coefficient of neutronrich nucleus in isobaric yield ratio (IYR) method, is difficult to be determined. Four RCI approximations are investigated: (i) The M1-RCI adopting the a(c)/T (the ratio of Coulomb energy coefficient to temperature) determined from the IYR of mirror-nucleus fragments; (ii) The M2-RCI by fitting the difference between IYRs; (iii) The M3-RCI adopting the standard Coulomb energy at a temperature T = 2 MeV; and (iv) Neglecting the RCI among isobars. The M1-, M2- and M3-RCI are no larger than 0.4. In particular, the M2-RCI is very close to zero. The effects of RCI in a(sym)/T of fragment are also studied. The M1- and M4-a(sym)/T are found to be the lower and upper limitations of a(sym)/T, respectively. The M2-a(sym)/T overlaps the M4-a(sym)/T, which indicates that the M2-RCI is negligible in the IYR method, and the RCI among the three isobars can be neglected. The relative consistent low values of M3-a(sym)/T (7.5 +/- 2.5) are found in very neutron-rich isobars.

Surface and Volume Symmetry Energy Coefficients of a Neutron-Rich Nucleus

Using an isobaric method, the symmetry-energy coefficient (a(sym)) of a neutron-rich nucleus is obtained from experimental binding energies. The shell effects are shown in a(sym)*/A equivalent to 4a(sym)/A of nuclei. A (sub) magic neutron magic number N = 40 is suggested in a very neutron-rich nucleus, and a(sym)*/A of a nucleus is found to decrease when its mass increases. The a(sym)*/A of a very neutron-rich nucleus with large mass saturates. The volume-symmetry coefficients (b(v)) and surface-symmetry coefficients (b(s)) of a neutron-rich nucleus are extracted from a(sym)*/A by a correlation a(sym)*/A = b(v)/A - b(s)/A (4/3). It is found that b(v) and b(s) decrease when the nucleus becomes more neutron-rich, and tend to saturate in the very neutron-rich nucleus. A linear correlation between b(v) and b(s) is obtained in nuclei with different neutron-excess I, and b(v) of I > 7 nuclei is found to coincide with the results of infinite nuclear matter a(sym) = 32 +/- 4 MeV, and b(s)/b(v) of the nucleus is found to coincide with the results of the finite-range liquid-drop model results.

Disappearance of isospin effect in projectile fragmentation at intermediate energy

The 140 MeV/u 40,48Ca+9Be and 58,64Ni+9Be reactions are simulated by the statistical abrasion ablation model, and the simulation results are compared to the National Superconducting Cyclotron Laboratory (NSCL) experimental data. By comparing the fragment isotopic distributions of 40,48Ca and 58,64Ni, we study the isospin effect in the projectile fragmentation induced by the neutron-rich nuclei at intermediate energy experimentally and theoretically. It is found that the isospin effect in projectile fragmentation decreases and even disappears as the violence of the collision increases.

Probing Temperature from Intermediate Mass Fragment by Isobaric Yield Ratio in Heavy-Ion Collisions

A probe to extract the temperature (TIYR) from intermediate-mass fragment has been proposed using the isobaric yield ratio (IYR) difference based on the modified Fisher model. By analyzing the isobaric cross section in the measured 140A MeV 40,48Ca+9Be reactions, the TIYR can well fit the IYR difference for the large mass fragments. Because of the fragments are produced in different colliding regions, it is also suggested to select the fragments according to different mechanisms when using TIYR.

Research on charge-transport properties of TTF–TTP derivatives and organic interfaces

The electronic and charge transport properties of four derivative groups containing nineteen different tetrathiafulvalene (TTF) and tetrathiapentalene (TTP) derivative compounds were theoretically investigated by density functional theory (DFT) based on the Marcus–Hush theory. In particular, we have considered TTF or TTP systems where some hydrogen atoms are substituted with methoxy or halogen moieties since it is well known that these electron-withdrawing groups are used to reduce the energies of frontier orbitals (HOMO and LUMO) and to increase the stability of the TTF derivative. A comparative analysis of the crystal structures reveals that the face-to-face layer structure and the herringbone structure with slip-stacks of the dimers exhibit higher charge transfer values compared with the disordered structures, and that the face-to-face π–π interaction and S–S interactions are favorable for molecular stacking and charge transport behavior. The computed values of the transfer integrals show that variation in calculated transfer integral values is likely along specific directions corresponding to the π–π stacking degree of the molecules. The interface charge conduction mechanism between two different molecule crystals is investigated, and we find there are high-conducting interfaces and low resistances of about 10–50 kΩ. Furthermore, the calculated data demonstrate that the TTF derivatives should be candidates for high-performance organic materials with high mobility values and good stability, and that the predicted highest hole and electron mobility values are 1.821 cm2 V−1 s−1 and 1.709 cm2 V−1 s−1, respectively, at 300 K. The high mobility combined with simple processing make TTF derivatives promising candidate materials for electronic devices where low cost and flexibility are required.

Empirical Scaling Laws of Neutral Beam Injection Power in HL-2A Tokamak

We present an experimental method to obtain neutral beam injection (NBI) power scaling laws with operating parameters of the NBI system on HL-2A, including the beam divergence angle, the beam power transmission efficiency, the neutralization efficiency and so on. With the empirical scaling laws, the estimating power can be obtained in every shot of experiment on time, therefore the important parameters such as the energy confinement time can be obtained precisely. The simulation results by the tokamak simulation code (TSC) show that the evolution of the plasma parameters is in good agreement with the experimental results by using the NBI power from the empirical scaling law.

Theoretical study of the charge transport mechanism in π-stacked systems of organic semiconductor crystals

In this study, the orientational dependence of the charge transport mechanism and some important factors related to crystal structure are systematically investigated by quantum chemical methods. Organic semiconductors with small reorganization energies and large transfer integrals originating from their π-stacking crystal structures show excellent charge transport properties. The reorganization energy from the geometrical relaxation occurs during the charge transfer process. The transfer integral of a molecular crystal should be attributed to multiple stacking parameters. A semi-classical simulation model to calculate the anisotropic mobility of a crystalline molecule is extended from one to three dimensions. As we predicted, the anisotropic mobility calculated from our model is improved by considering the contribution from every direction in space, rather than just one plane. This theoretical study determines the importance of tuning the molecular geometry and calculation accuracy for high-performance organic semiconductor materials.

Reexamination of the neutron skin thickness using neutron removal cross sections

The neutron removal cross section [{sigma}{sub -N}(Z)] is defined for the projectile-like fragment isotopes and extended to the lower Z isotopes in the projectile fragmentation reaction. The cross sections of fragments in 1 A GeV even {sup 42-52}Ca+{sup 12}C projectile fragmentation reactions are calculated using the statistical abrasion-ablation model. The correlations between {sigma}{sub -N}(Z) of different fragment isotopes and neutron skin thickness (S{sub n}) for finite neutron-rich nuclei are revisited. Good linear {sigma}{sub -N}(Z)-S{sub n} correlations are observed in fragment isotopes, and it is suggested that {sigma}{sub -N}(Z) be used as an observable to determine S{sub n} of neutron-rich nucleus in addition to {sigma}{sub -N} for isotopes of the projectile nucleus.