Probing the high density behavior of the symmetry energy by using proton elliptic flow

Based on the isospin- and momentum-dependent transport model IBUU04, we calculated the reaction of the Sn-132+Sn-124 systems in semi-central collisions at beam energies of 400/A MeV, 600/A MeV and 800/A MeV by adopting two different density dependent symmetry energies. It was found that the proton differential elliptic flow as a function of transverse momentum is quite sensitive to the density dependence of symmetry energy, especially for the considered beam energy range. Therefore the proton differential elliptic flow may be considered as a robust probe for investigating the high density behavior of symmetry energy in intermediate energy heavy ion collisions.

Optimization of the HIRFL-CSR cluster target

A new gas delivery system is designed and installed for HIRFL-CSR cluster target. The original blocked nozzle is replaced by a new one with the throat diameter of 0.12mm. New test of hydrogen and argon gases are performed. The stable jets can be obtained for these two operation gases. The attenuation of the jet caused by the collision with residual gas is studied. The maximum achievable H-2 target density is 1.75x10(13) atoms/cm(3) with a target thickness of 6.3x10(12) atoms/cm(2) for HIRFL-CSR cluster target. The running stability of the cluster source is tested both for hydrogen and argon. The operation parameters for obtaining hydrogen jet are optimized. The results of long time running for H-2 and Ar cluster jets look promising. The jet intensity has no essential change during the test for H-2 and Ar.

First results of SECRAL at 18GHz for intense beam production of highly charged ions

A Superconducting ECR ion source with Advanced design in Lanzhou (SECRAL) was successfully built to produce intense beams of highly charged ions for Heavy Ion Research Facility in Lanzhou (HIRFL). The ion source has been optimized to be operated at 28GHz for its maximum performance. The superconducting magnet confinement configuration of the ion source consists of three axial solenoid coils and six sextupole coils with a cold iron structure as field booster and clamping. For 28GHz operation, the magnet assembly can produce peak mirror fields on axis 3.6T at injection, 2.2T at extraction and a radial sextupole field of 2.0T at plasma chamber wall. A unique feature of SECRAL is that the three axial solenoid coils are located inside of the sextupole bore in order to reduce the interaction forces between the sextupole coils and the solenoid coils. During the ongoing commissioning phase at 18GHz with a stainless steel chamber, tests with various gases and some metals have been conducted with microwave power less than 3.2kW and it turned out the performance is very promising. Some record ion beam intensities have been produced, for instance, 810e mu A of O7+, 505e mu A of Xe20+, 306e mu A of Xe27+, 21e mu A of Xe34+, 2.4e mu A of Xe38+ and so on. To reach better results for highly charged ion beams, further modifications such as an aluminium chamber with better cooling, higher microwave power and a movable extraction system will be done, and also emittance measurements are being prepared.

Research on metallic ion beam production at IMP

Since 1998, many experiments for metallic ion production have been done on LECR2 (Lanzhou ECR ion source NO.2), LECR3 (Lanzhou ECR ion source NO.3) and SECRAL (Superconductiong ECR ion source Advanced design in Lanzhou) at Institute of Modern Physics. The very heavy metallic ion beams such as those of uranium were also produced by the plasma sputtering method, and supplied for HIRFL (Heavy Ion Research Facility in Lanzhou) accelerators successfully. During the test, 11.5e mu AU(28+), 9e mu AU(24+) were obtained. Some ion beams of the metal having lower melting temperature such as Ni and Mg ion beams were produced by oven method on LECR3 too. The consumption rate was controlled to be lower for Mg-26 ion beams production, and the minimum consumption was about 0.3mg per hour. In this paper, the main experimental results are given. Some discussions are made for some experimental phenomena and results, and some conclusions are drawn.

Capability verification of the beam delivery system in the superficially-placed tumor therapy terminal at HIRFL

The passive beam delivery system in the superficially-placed tumor therapy terminal at Heavy Ion Researc h Facility in Lanzhou (HIRFL), which includes two orthogonal dipole magnets as scanning system, a motor-driven energy degrader as range-shifter, series of ridge filters as range modulator and a multileaf collimator, is introduced in detail. The capacities of its important components and the whole system have been verified experimentally. The tests of the ridge filter for extending Bragg peak and the range shifter for energy adjustment show both work well. To examine the passive beam delivery system, a beam shaping experiment were carried out, simulating a three-dimensional (3D) conformal irradiation to a tumor. The encouraging experimental result confirms that 3D layer-stacking conformal irradiation can be performed by means of the passive system. The validation of the beam delivery system establishes a substantial basis for upcoming clinical trial for superficially-placed tumors with heavy ions in the therapy terminal at HIRFL.

Construction and test of Wien-filter combined with RIBLL

A recoil separator Wien-filter which was developed for the Radioactive Ion Beam Line in Lanzhou (RIBLL) as an extension is described. It consists of 2 quadruple triplets and a standard Wien-filter. It was designed for study of the fusion-evaporation reactions. The overall design, background suppression, the transmission efficiency, the angular acceptance and the momentum acceptance have been described. All the performances fulfil the designed requirements. Based on the test results, with some modifications the investigations of the nuclei with Z <= 110 and the drip-line nuclei in the medium-heavy mass region can be carried out with this facility.

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.

Restoration of the signals from multi-hit three-layer delay-line anode position-sensitive detector

Multi-hit 3-layer delay-line anode (Hexanode) has an increased ability to detect multi-hit events in a collision experiment. Coupled with a pair of micro-channel plates, it can provide position information of the particles even if the particles arrive at the same time or within small time dwell. But it suffers from some ambiguous outputs and signal losses due to timing order and triggering thresholds etc. We have developed a signal reconstruction program to correct those events. After the program correction, the dead time only exists when 2 paxticles arrive at the same time and the same position within a much smaller range. With the combination of Hexanode and the program, the experimental efficiencies will be greatly improved in near threshold double ionization on He collisions.

Pa-239 may influence astrophysics study

The estimation method of the universe age using the nuclear cosmochronology by the heavy chronometers is essentialized. The influence of the novel long half-life of Pa-239 on the universe age estimation is simply mentioned.

Experimental study of the high-voltage breakdown and simulations for the RFQ cooler and buncher RFQ1L

The RFQ cooler and buncher RFQ1L is one of the key parts of the being-built super-heavy nuclide research spectrometer. In order to understand the high-voltage breakdown phenomenon, the voltages between electrodes have been measured. In addition, more extensive simulations have been performed for better understanding and optimizing the RFQ1L work points.

Effect of pentaquark Theta(+) on the equation of state of nuclear matter

Assuming Theta(+) interacts with nucleon or Theta(+) by exchanging isoscalar mesons sigma and omega, the equation of state of {p, n, Theta(+)} and possible metastable state are studied in the framwork of the density dependent relativistic hadron field theory(DDRH). The ratio of the proton isospin to the neutron isospin with different baryon densities and the effect of the Theta(+) component on the binding energy per baryon of the system are also discussed. It is shown that when the binding energy per baryon of the system takes the maximal value, Theta(+) might be bound in the nuclear matter.

Measurement of neutron flow with the external target experimental device on CSR

With the construction of the neutron detection wall at the external target position on Heavy Ion Research Facility in Lanzhou-Cooling Storage Ring (HIRFL-CSR), it will be possible to detect high energy neutron. A BUU model is applied to simulate the flow in both symmetric (Ni+Ni, Pb+Pb) and asymmetric(Pb+Ni) systems. It is shown that at above several hundreds MeV/u, the flow signals are very obvious and depend clearly on the centrality of the collisions. Based on the products in the forward angle less than 20 degrees, the simulation also reveals that the determination of the reaction plane and the selection of the impact parameter, both of which are essential in the flow measurement, are well implemented. The double event and its influence on the determination of the neutron flow are also simulated.

DBHF approach and thermodynamic consistency for nuclear matter calculations

Within the framework of Dirac Brueckner-Hartree-Fock (DBHF) approach, we calculate the energy per nucleon, the pressure, the nucleon self-energy, and the single-nucleon energy in the nuclear matter by adopting two different covariant representations for T-matrix. We mainly investigate the influence of different covariant representations on the satisfiable extent of the Hugenholtz-Van Hove (HVH) theorem in the nuclear medium in the framework of DBHF. By adopting the two different covariant representations of T-matrix, the predicted nucleon self-energy shows a quite different momentum and density dependence. Different covariant representations affect remarkably the satisfiable extent of the HVH theorem. By adopting the complete pseudo-vector representation of the T-matrix, HVH theorem is largely violated, which is in agreement with the result in the non-relativistic Brueckner-Hartree-Fock approach and reflects the importance of ground state correlations for single nucleon properties in nuclear medium, whereas by using the pseudoscalar representation, the ground state correlation cannot be shown. It indicates that the complete pseudo-vector presentation is more feasible than the pseudo-scalar one.

Production cross sections of superheavy nuclei based on dinuclear system model

The barrier distribution function method is introduced in the dinuclear system model in the calculation of the transmission probability, which is the first stage in the synthesis of superheavy nuclei. Dynamical deformation and averaging collision orientations are considered in the calculation of the fusion probability by solving master equation numerically. Survival probability with respect to xn evaporation channel (x = 1-5) in the de-excitation process of the thermal compound nucleus is calculated, in which the level density of the Fermi-gas model is used. Production cross sections of a series of superheavy nuclei formed in the reactions taken magic and deformed nuclei as target in Ca-48 induced reactions are studied systematically. The calculated results are in good agreement with available experimental data. Isotopic dependence of the production cross sections in the reactions Ca-48 + Pu is analyzed.

Signature inversion in pi h(9/2) circle times nu i(13/2) oblate band of Tl-188

High-spin Level structure of Tl-188 has been studied via Gd-157 (Cl-35,4n) fusion-evaporation reaction at beam energy of 170MeV. A rotational band built on the pi h(9/2) circle times nu i(13/2) configuration with oblate deformation has been established. Spin values have been proposed to the pi h(9/2) circle times nu i(13/2) oblate band based on the similarities between the oblate band of Tl-188 and those in odd-odd Tl190-200. With the spin assignments, the low-spin signature inversion has been revealed for the pi h(9/2) circle times nu i(13/2) oblate band of Tl-188. The low-spin signature inversion can be interpreted qualitatively in the framework of the quasi-particles plus rotor model including a J dependent p-n residual interaction.