Microstructure and Mechanical Properties of Ti3SiC2 Irradiated by Carbon Ions

Thanks to its noteworthy mechanical properties, excellent damage tolerance and good thermal stability, the Ti3SiC2 ternary compound has attracted great concern and has been considered as a potential structural component material for the 4th generation of reactors （e.g., gas fast nuclear reactors） and future fusion reactors. The outstanding properties are due to the nanolameIlar structure which imparts characteristics of both metals and ceramics to this material In our work, Ti3SiC2 samples have been irradiated by C^＋ ions with a high fluence of 1.78 × 10^17 ions/cm^2 at a range of temperatures from 120℃～850℃. Subsequently, series of characterization techniques including synchrotron irradiation x-ray diffraction, scanning electron microscopy and nano-indentation are carried out to understand the changes of microstructure and mechanical properties. The composition exhibits high damage tolerant properties and a high recovery rate through the analysis, especially at high temperature. The minimum damage to an irradiated sample appears around 350℃ in the temperature range 120℃-550℃. At a high irradiation temperature, a significant reduction in the damage can be achieved and an almost complete lack of damage compared with an un-irradiated sample is revealed at the temperature of 850℃.     

Neutronic calculations for CANDU thorium systems using Monte Carlo techniques

In this paper,we have investigated the prospects of exploiting the rich world thorium reserves using Canada Deuterium Uranium(CANDU)reactors.The analysis is performed using the Monte Carlo MCNP code in order to understand how much time the reactor is in criticality conduction.Four different fuel compositions have been selected for analysis.We have obtained the infinite multiplication factor,k∞,under full power operation of the reactor over 8 years.The neutronic flux distribution in the full core reactor has already been investigated.     

Neutronic calculations for CANDU thorium systems using Monte Carlo techniques

In this paper, we have investigated the prospects of exploiting the rich world thorium reserves using Canada Deuterium Uranium （CANDU） reactors. The analysis is performed using the Monte Carlo MCNP code in order to understand how much time the reactor is in criticality conduction. Four different fuel compositions have been selected for analysis. We have obtained the infinite multiplication factor, k∞, under full power operation of the reactor over 8 years. The neutronic flux distribution in the full core reactor has already been investigated.     

Nuclear structure around ~(80)Zr

Recent years have witnessed intense activity concerning the study of nuclei with equal numbers of neutrons and protons (N = Z). Exotic properties have been exhibited in the N = Z nuclei, especially in those with atomic masses around 80. In the present paper, the projected shell model(PSM)together with a relativistic Hartree-Bogoliubov (RHB) theory is used to study the nuclear structure near the N = Z line in the mass A ≈ 80 region. For three Zr isotopes 80,82,84Zr, the projected potential energy surfaces an...     

Progress of the 87Rb Fountain Clock

A fountain atomic clock based on cold 87Rb atoms has been in operation in our laboratory for several months. We therefore report the design of the rubidium fountain clock including its physical package, optical system and daily operation. Ramsey fringes have been attained with the signal to noise ratio of about 100.     

Three-body Effect on Equation of State of Spin-polarized Nuclear Matter

The equation of state (EOS) of spin-polarized nuclear matter has been investigated within the spin-dependent; Brueckner-Hartree-Fock framework by adopting the realistic nucleon-nucleon interaction supplemented with a microscopic three-body force. The three-body force effects have been studied and stressed with a special attention. The calculated results are given in Fig.1. It is seen that; in the Brueckner-Hartree-Fock framework the predicted energy per particle of spin-polarized nuclear matter versus the neutron and proton spin-polarization parameters fulfills a quadratic law in the whole range of spin-polarization. The related physical quantities such as spin the Landau parameters Go in spin channel and G′0 in spin-isospin channel, have been also calculated.     

Cross Sections of Barium Isotopes in Interaction of 60 MeV／u ^18O with Natural Uranium

The reactions induced by heavy ions lower than 10 MeV/u have been studied widely. Their reaction mechanism has been also understood in more detail. The contribution to the reaction cross sections in the low energy reactions comes mainly from complex nuclei and deep inelastic process. Early studies mainly focused on the nuclear collisions of low and high energies. In the recent years, great attention has been paid on the intermediate energy heavy ion collisions. Among them measurements of the cross sections and recoiling properties for the target fragmentation products have been applied widely to study the mechanism of the nuclear reactions induced by the intermediate energy heavy ions. But there are a few papers on raodioehemieal studies in the intermediate energy region up to now.     

Equation of State of Spin-polarized Neutron Matter and Three-body Effect

Within the spin-dependent Brueckner-Hartree-Fock (BHF) framework, the equation of state of the spinpolarized neutron matter has been investigated by adopting the realistic nucleon-nucleon interaction supplemented with a microscopic three-body force. The three-body force has been turn out to be crucial for reproducing the empirical saturation properties of nuclear matter in a non-relativistic microscopic approach[2] such as BHF. The related physical quantities such as spin-symmetry energy, magnetic susceptibility, have been extracted. The three-body force effects have been studied and discussed with a special attention. It is found that in the whole range of spin-polarization, the cnergy per particle of spin-polarized neutron matter fulfills a quadratic relation versus the spin-polarization parameter. The calculated spin-symmetry energies as a function of densityare shown in Fig.l, where the solid curve is obtained by using the AVis two-body force plus the three-body force and the dashed curve is the result by adopting the pure AVis two-body force.     

Lower Hybrid Wave Absorption in a Quasi-stationary Reversed Shear Mode of Operation in HL-2A

To demonstrate the viability of steady-state tokamak operation in a high performance regime, which is one of the key physics issues for a viable economic fusion reactor, the quasi-stationary reversed shear (RS) mode of operation in the HL-2A tokamak have been modeled with the TRANSP code. In order to sustain the RS operation towards steady-state, off-axis current drive with lowerhybrid (LH) wave at 2.45 GHz is used to control the current profile.     

Nuclear Level Density with Non-zero Angular Momentum

The statistical properties of interacting fermions have been studied for various angular momentum with the inclusion of pairing interaction. The dependence of the critical temperature on angular momentum for several nuclei, have been studied. The yrast energy as a function of angular momentum for 28Si and 24 Mg nuclei have been calculated up to 60.0 MeV of excitation energy. The computed limiting angular momenta are compared with the experimental results for ^26Al produced by ^12C＋ 14N reaction. The relevant nuclear level densities for non-zero angular momentum have been computed for ^44Ti and ^136 Ba nuclei. The results are compared with their corresponding values obtained from the approximate formulas.     

Configuration with Low Central Magnetic Shear Formed in Pellet Injection Discharge on HL-2A

Control and optimization of the plasma current profile is a key point in enhancing the plasma performance. Although several tools have been identified to modify transport directly, the effect of the current profile on transport is large and remains an important transport control feature. In the tokamak experiments it is demonstrated that the configuration with flat q-profile in the central plasma region is beneficial to improve plasma confinement. Discharges with internal transport barrier （ITB） have been established with low magnetic shear （so called optimized shear operation mode） in JET and ASDEX Upgrade.     

Nuclear structure around ~(80)Zr

Recent years have witnessed intense activity concerning the study of nuclei with equal numbers of neutrons and protons (N = Z). Exotic properties have been exhibited in the N = Z nuclei, especially in those with atomic masses around 80. In the present paper, the projected shell model(PSM)together with a relativistic Hartree-Bogoliubov (RHB) theory is used to study the nuclear structure near the N = Z line in the mass A ≈ 80 region. For three Zr isotopes 80,82,84Zr, the projected potential energy surfaces and ground state bands are calculated. It is shown that shape coexistence occurs in all of these nuclei. Moreover, we find that the residual neutron-proton interaction strongly affects the ground state band of 80Zr; however, it slightly modifies those of 82Zr and 84Zr.     

Production of Silicon and Chlorine Ion Beams

We did some preliminary tests on LECR3 to produce Silicon and Chlorine ion beams in October 2003. Some good results have been achieved. Some useful conclusions have been drawn from those experiments. And afterwards, we also provided the HIRFL accelerator with the ^35Cl^12 ion beam for the nuclear physics experiments.     

Experimental Study on Flashlamp Pumped Nd3+∶KGd(WO4)2 Laser

The lasing properties of Nd∶KGW crystal in free-running mode with different transmission of the output couplers are reported.The best results have been obtained with the output coupler of 24% transmission.The slope efficiency is 1.0% and the extrapolated energy threshold is 0.54 J.A comparative experiment of Nd∶KGW and Nd∶YAG laser crystals has been cavried out under identical experimental conditions in both free-running and Q-switched modes.The much higher efficiency and the lower threshold for Nd∶KGW (Nd: 2.2 at.-%) compared to Nd∶YAG (Nd: 1.1 at.-%) at 1.064 μm are demonstrated in both operation mode.     

Isospin effect of the in-medium nucleon-nucleon cross section in excited nuclear reactions

Using relativistic mean field theory, the neutron and the proton density distribution of 56Ni nuclei could be obtained in the ground state and the excited state. Based on the framework of the quantum molecular dynamics model, the 56Ni nuclei have been simulated in ground state and in the neutron or proton excited state. We then used the three different states of 56Ni to collide with the 56Ni in the ground state. To discuss the evolution of the nuclear stopping in different reactions, two kinds of different excited nuclear reactions were studied at different reaction energies and at different impact parameters. Studies have shown that the nuclear stopping of an excited nuclear reaction is sensitive to the isospin-dependent in-medium nucleon-nucleon cross section, compared with the response value of the ground state nuclear reaction. So, it is better for the excited nuclei to extract the isospin dependence of nucleon-nucleon cross section information.     

Influence of breakup on elastic and α-production channels in the ~6Li+~(116)Sn reaction

The effects of breakup reactions on elastic and α-production channels for the ~6Li+~(116)Sn system have been investigated at energies below and near the Coulomb barrier. The angular distributions of α-particle production differential cross sections have been obtained at several projectile energies between 22 and 40 MeV. The measured breakup α-particle differential cross sections and elastic scattering angular distributions have been compared with the predictions of continuum-discretized coupled channels(CDCC) calculations. The influence of breakup coupling has also been investigated by extracting dynamic polarization potentials(DPP) from the CDCC calculations. From the predictions of CDCC calculations the relative importance of the nuclear, Coulomb, and total breakup contributions have also been investigated. The nuclear breakup couplings are observed to play an important role in comparison to the Coulomb breakup for the direct breakup mechanisms associated in the reaction of ~6Li projectile with ~(116)Sn target nuclei. The influence of strong nuclear breakup coupling exhibits suppression in the Coulomb-nuclear interference peak. The direct breakup cross sections from the CDCC calculations under-predict the measured α-particle differential cross sections at all energies. This suggests that the measured α particles may also have contributions from other possible breakup reaction channels.     

New empirical formula for(γ, n) reaction cross section near GDR peak for elements with Z ≥ 60

A new empirical formula has been developed that describes the(7,n) nuclear reaction cross sections for isotopes with Z ≥ 60.The results were supported by calculations using TALYS-1.6 and EMPIRE-3.2.2 nuclear modular codes.The energy region for incident photon energy has been selected near the giant dipole resonance(GDR) peak energy.The evaluated empirical data were compared with available data in the experimental data library EXFOR.The data produced using TALYS-1.6 and EMPIRE-3.2.2 are in good agreement with experimental data.We have tested and presented the reproducibility of the present new empirical formula.We observe the reproducibility of the new empirical formula near the GDR peak energy is in good agreement with the experimental data and shows a remarkable dependency on key nuclei properties:the neutron,proton and atomic number of the nuclei.The behavior of nuclei near the GDR peak energy and the dependency of the GDR peak on the isotopic nature are predicted.An effort has been made to explain the deformation of the GDR peak in(γ,n) nuclear reaction cross sections for some isotopes,which could not be reproduced with TALYS-1.6 and EMPIRE-3.2.2.The evaluated data have been presented for the isotopes ~(180)W,~(183)W,~(202)Pb,~(203)Pb,~(204)Pb,~(205)Pb,~(231)Pa,~(232)U,~(237)U and ~(239)Pu,for which there are no previous measurements.     

Nuclear structure around 80Zr

Recent years have witnessed intense activity concerning the study of nuclei with equal numbers of neutrons and protons （N = Z）. Exotic properties have been exhibited in the N = Z nuclei, especially in those with atomic masses around 80. In the present paper, the projected shell model（PSM）together with a relativistic Hartree-Bogoliubov （RHB） theory is used to study the nuclear structure near the N = Z line in the mass A ≈ 80 region. For three Zr isotopes 80,82,84Zr, the projected potential energy surfaces and ground state bands are calculated. It is shown that shape coexistence occurs in all of these nuclei. Moreover, we find that the residual neutron-proton interaction strongly affects the ground state band of 80Zr; however, it slightly modifies those of 82Zr and 84Zr.     

Neutral Beam Injection Experiments in the HL-1M Tokamak

Neutral beam injection (NBI) experiments have been carried out with two operation modes of a bucket ion source in the HL-1M tokamak. During the first mode, more than 30% rise in ion temperature above the Ohmic level is routinely achleved after NBI power about 0.5 MW is injected. Ion temperature only increases 20-30% for the second operation mode, which is often limited by current termination. The heating effects of the NBI have been analysed experimentally and theoretically. The performance of the NBI system is well described.     

The atomic structure and the properties of ununbium (<Emphasis Type="Italic">Z</Emphasis> = 112) and Mercury (<Emphasis Type="Italic">Z</Emphasis> = 80)

A super heavy element Uub (Z = 112) has been studied theoretically in conjunction with rela-tivistic effects and the effects of electron correlations. The atomic structure and the oscillator strengths of low-lying levels have been calculated, and the ground states have also been determined for the singly and doubly charged ions. The influence of relativity and correlation effects to the atomic properties of such a super heavy element has been investigated in detail. The results have been compared with the properties of an element Hg. Two energy levels at wave numbers 64470 and 94392 are suggested to be of good candidates for experimental observations.