Neutron (PF2)-P-3 superfluidity in neutron matter and the effect of microscopic three-body force

The neutron (PF2)-P-3 pairing gap in pure neutron matter has been studied by using the Brueckner-Hartree-Fock( BHF) approach and the BCS theory. We have concentrated our attention on investigating the three-body force effect on the neutron superfluidity in the (PF2)-P-3 channel. The calculated results indicate that the three-body force enhances remarkably the (PF2)-P-3 superfluidity in neutron matter. When adopting the BHF single-particle spectrum, the three-body force turns out to increase the maximum value of the pairing gap from about 0.22 MeV to about 0.5 MeV.

Probing the high density behavior of the symmetry energy by using the free neutron-proton ratio

Based on the isospin- and momentum-dependent transport model IBUU04, the transverse momentum distributions of the free neutron-proton ratio in the Sn-132+(124) Sn reaction system at mid-central collisions with beam energies of 400/A MeV, 600/A MeV and 800/A MeV are studied by using two different symmetry energies. It is found that the free neutron-proton ratio as a function of the transverse momentum at the mid-rapidity is very sensitive to the density dependency of the symmetry energy especially at incident energies around 400/AMeV.

Nuclear potential and fusion cross sections for synthesizing super-heavy elements in di-nuclear systems

A double folding method with simplified Skyreme-type nucleon-nucleon interaction is used to calculate the nuclear interaction potential between two nuclei. The calculation is performed in tip-to-tip orientation of the two nuclei if they are deformed. Based on this methods, the potential energy surfaces, the fusion probabilities and the evaporation residue cross sections for some cold fusion reactions leading to super-heavy elements within di-nuclear system model are evaluated. It is indicated that after the improvement, the exponential decreasing systematics of the fusion probability with increasing charge number of projectile on the Pb based target become better and the evaporation residue cross sections are in better agreement with the experimental data.

The neutron/proton ratio of squeezed-out nucleons and the high density behavior of the nuclear symmetry energy

Within a transport model it is shown that the neutron/proton ratio of squeezed-out nucleons perpendicular to the reaction plane, especially at high transverse momenta, in heavy-ion reactions induced by high energy neutron-rich nuclei can be a useful tool for studying the high density behavior of the nuclear symmetry energy.

Proton and neutron S-1(0) superfluidity in asymmetric nuclear matter

The proton and neutron S-1(0), pairing gaps and their isospin dependence in isospin asymmetric nuclear matter have been studied by the isospin dependent Brueckner-Hartree-Fock approach and the BCS theory. We have focused on investigating and discussing the effect of three-body force. The calculated results indicate that as the isospin asymmetry increases, the density range of the S-1(0) neutron superfluidity is narrowed slightly and the maximum value of the neutron pairing gap increases 9 while the density domain for the proton superfluidity enlarges rapidly and the peak value of the proton gap decreases remarkably. The three-body force turns out to affect only weakly the neutron S-1(0) superfluidity and its isospin dependence, i. e., it leads to a small reduction of the neutron S-1(0) paring gap. However, the three-body force not only reduces largely the strength of the proton S-1(0) gaps at high densities in highly asymmetric nuclear matter but also suppresses strongly the density domain for the proton S-1(0) superfluidity phase.

Study of the LED based light calibration system for neutron wall detector

The light calibration system is one of the key components of Neutron Wall detector. It is used to calibrate the electronics and to monitor the long-term stability of the detector modules. With the detaile investigations, a calibration system with high-power LED (3W) driven by the fast pulses has been carried out. It is also tested together with the detector module of the Neutron Wall and the result of the preliminary calibration demonstrates that it fulfills the needs. It's a new design proposal to the light calibration system of the fast scintillator detector.

Isospin dependence of S-1(0) proton and neutron superfluidity in asymmetric nuclear matter

We investigate the S-1(0) neutron and proton superfluidity in isospin-asymmetric nuclear matter. We have concentrated on the isospin dependence of the pairing gaps and the effect of a microscopic three-body force. It is found that as the isospin asymmetry goes higher, the neutron S-1(0) superfluid phase shrinks gradually to a smaller density domain, whereas the proton one extends rapidly to a much wider density domain. The three-body force turns out to weaken the neutron S-1(0) superfluidity slightly, but it suppresses strongly the proton S-1(0) superfluidity at high densities in nuclear matter with large isospin asymmetry.

Isotopic dependence of production cross sections of superheavy nuclei in hot fusion reactions

The dinuclear system model has been further developed by introducing the barrier distribution function method in the process of heavy-ion capture and fusion to synthesize superheavy nuclei. The capture of two colliding nuclei, formation and de-excitation process of compound nucleus are decribed by using empirical coupled channel model, solving master equation numerically and statistical evaporation model, respectively. Within the framework of the dinuclear system model, the fusion-evaporation excitation functions of the systems Ca-48(Am-243, 3n-5n) (288-286)115 and Ca-48(Cm-248, 3n-5n)(293-291)116 are calculated, which are used for synthesizing new superheavy nuclei at Dubna in recent years. Isotopic dependence of production cross sections with double magic nucleus Ca-48 bombarding actinide targets U, Np, Pu, Am, Cm to synthesize superheavy nuclei with charged numbers Z=112-116 is analyzed systematically. Based on these analysis, the optimal projectile-target combination and the optimal excitation energy are proposed. It is shown that shell correction energy and neutron separation energy will play an important role on the isotopic dependence of production cross sections of superheavy nuclei.

Isospin effect in the nuclear reaction induced by neutron-halo nuclei

We study the average property of the isospin effect of reaction induced by halo-neutron nuclei He-8 and He-10 in the intermediate energy heavy ion collisions using the isospin-dependent quantum molecular dynamics model (IQMD). This study is based on the extended neutron density distribution for the halo-neutron nuclei, which includes the average property of the isospin effect-of reaction mechanism and loose inner structure. The extended neutron density distribution brings an important isospin. effect into the average property of reaction mechanism because the interaction potential and nucleon-nucleon(N-N) cross section in IQMD model depend sensitively on the density distribution of colliding system. In order to see clearly the average properties of reaction mechanism induced by halo-neutron nuclei we also compare the results for the neutron-halo colliding systems with those for the corresponding stable colliding systems under the same incident channel condition. We found that the extended density distribution for the neutron-halo projectile brings an important isospin effect to the reaction mechanism, which leads to the decrease of nuclear stopping R, yet induces obvious increase of the neutron-proton ratio of nucleon emissions and isospin fractionation ratio for all beam energies studied in this work, compared to the corresponding stable colliding system. In this case, nuclear stopping, the neutron-proton ratio of nucleon emissions and isospin fractionation ratio induced by halo-neutron nuclei can be used as possible probes for studying the average property of the isospin effect of reaction mechanism and extracting the information of symmetry potential and in-medium N-N cross section by the neutron-halo nuclei in heavy ion collisions.

Probing the symmetrical potential in nuclear reaction iinduced by neutron-halo nuclei

In terms of the isospin-dependent quantum molecular dynamics model (IQMD), important isospin effect in the halo-neutron nucleus induced reaction mechanism is. investigated, and consequently, the symmetrical potential form is extracted in the intermediate energy heavy ion collision. Because the interactive potential and in-medium nucleon-nucleon (N-N) cross section in the IQMD model sensitively depend on the density distribution of the colliding system, this type of study is much more based on the extended density distribution with a looser inner nuclear structure of the halo-neutron nucleus. Such a density distribution includes averaged characteristics of the isospin effect of the reaction mechanism and the looser inner nuclear structure. In order to understand clearly the isospin effect of the halo-neutron nucleus induced reaction mechanism, the effects caused by the neutron-halo nucleus and by the stable nucleus with the same mass are compared under the same condition of the incident channel. It is found that in the concerned beam energy region, the ratio of the emitted neutrons and protons and the ratio of the isospin fractionations in the neutron-halo nucleus case are considerably larger than those in the stable nucleus case. Therefore, the information of the symmetry potential in the heavy ion collision can be extracted through such a procedure.

Measurement of neutron-removal cross section of neutron-rich nucleus He-8 by using the transmission method

The neutron-rich nucleus He-8 is selected by RIBLL from the breakup of 50MeV/u C-13 on be target at HIRFL. The 2n-removal and 4n-removal cross section of He-8 was measured by using the transmission method. The point that He-4 is He-8 core can be reduced from the experiment data via the Ogawa's theory.

Double neutron-proton differential transverse flow as a probe for the high density behavior of the nuclear symmetry energy

The double neutron-proton differential transverse flow taken from two reaction systems using different isotopes of the same element is studied at incident beam energies of 400 and 800 MeV/nucleon within the framework of an isospin- and momentum-dependent hadronic transport model IBUU04. The double differential flow is found to retain about the same sensitivity to the density dependence of the nuclear symmetry energy as the single differential flow in the more neutron-rich reaction. Because the double differential flow reduces significantly both the systematic errors and the influence of the Coulomb force, it is thus more effective probe for the high-density behavior of the nuclear symmetry energy.

Improved BCS-type pairing for the relativistic mean-field theory

A density-dependent delta interaction (DDDI) is proposed in the formalism of BCS-type pairing correlations for exotic nuclei whose Fermi surfaces are close to the threshold of the unbound state. It provides the possibility to pick up those states whose wave functions are concentrated in the nuclear region by making the pairing matrix elements state dependent. On this basis, the energy level distributions, occupations, and ground-state properties are self-consistently studied in the RMF theory with deformation. Calculations are performed for the Sr isotopic chain. A good description of the total energy per nucleon, deformations, two-neutron separation energies and isotope shift from the proton drip line to the neutron drip line is found. Especially, by comparing the single-particle structure from the DDDI pairing interaction with that from the constant pairing interaction for a very neutron-rich nucleus it is demonstrated that the DDDI pairing method improves the treatment of the pairing in the continuum.

Phase transition to color-flavor-locked matter and condensation of Goldstone bosons in neutron star matter

Deconfinement phase transition and condensation of Goldstone bosons in neutron star matter are investigated in a chiral hadronic model (also referred as to the FST model) for the hadronic phase (HP) and in the color-flavor-locked (CFL) quark model for the deconfined quark phase. It is shown that the hadronic-CFL mixed phase (MP) exists in the center of neutron stars with a small bag constant, while the CFL quark matter cannot appear in neutron stars when a large bag constant is taken. Color superconductivity softens the equation of state (EOS) and decreases the maximum mass of neutron stars compared with the unpaired quark matter. The K-0 condensation in the CFL phase has no remarkable contribution to the EOS and properties of neutron star matter. The EOS and the properties of neutron star matter are sensitive to the bag constant B, the strange quark mass m(s) and the color superconducting gap Delta. Increasing B and m(s) or decreasing Delta can stiffen the EOS which results in the larger maximum masses of neutron stars.

Probing the high density behavior of the symmetry energy by using the neutron-proton differential flow

Based on the isospin- and momentum-dependent transport model IBUU04, we investigated the neutron-proton differential flow in the (132) Sn + (124) Sn mid-central collisions at beam energies of 400MeV/A, 600MeV/A and 800MeV/A by adopting two different symmetry energies. It was found that the neutron-proton differential flow as a function of rapidity is very sensitive to the density dependence of symmetry energy, especially at incident energies around 400MeV/A