2006 Vol. 30, No. S2
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For the last two decades, dramatic progress has been made in China for the investigation of the nuclear structure and related fields. A brief review is given and the main focus will be on shell structure, rotation and vibration, pairing and superconductivity, high spin physics, superdeformed rotational nucleus, exotic nuclei with extreme isospin, superheavy nucleus, etc.
The Reflection Asymmetric Shell Model has been generated to include the triaxial degree of freedom. The signature inversion and chiral and wobbling band structures can be described by the present model as results of some nuclei having intrinsic mean fields with spontaneously broken rotational symmetry. As a application of the theory, the triaxial rotation, a fundamental question in nuclear structure, has been investigated by examining the signature inversion and chirality phenomena in nuclei. The signature inversion phenomenon is interpreted as the change of the dynamic cranking axis in triaxially deformed nuclei. An other goal is to provide a new understanding of the nature of the doublet bands in 134Pr.
The ground-state properties of odd-Z superheavy nuclei (Z=117 and Z=119) have been systematically studied in the framework of the relativistic mean-field model (RMF). The calculated binding energy, α decay energy, quadrupole deformation are compared with those from Skyrme-Hartree-Fock model (SHF). It is found that the binding energies given by two models agree well, while the quadrupole deformations show a certain degree of model dependence.
Based on analysis for the idea and features of the Monte Carlo method, we propose the simulating algorithms for the stochastic equations of two kinds describing nuclear fusion and fission dynamics: the master equation and the Langevin equation. The calculated results for three examples are in agreement with the experimental data.
We discuss briefly the phases of nuclear single particle motion and collective motion. Meanwhile we review the status of the research on the phase structure of the vibration, axially symmetric rotation and $\upgamma$-soft rotation of the collective motion and the shape phase transition induced by nucleon number and angular momentum. In addition we depict simply the nuclear liquid gas phase transition as well as the deconfinement and chiral phase transition of strong interacting matter.
In this paper we present a brief discussion on regular structures of many-body systems generated from random two-body interactions. In particular, we discuss the famous problem of spin zero ground state dominance, regularities of energy centroids and collectivity in the presence of random interactions.
Pairing correlation strongly influences various nuclear properties, including the binding energy, low-lying excited spectrum, and angular momentum alignment of a rotational band etc. The systematically observed large fluctuation in odd-even differences of moments of inertia and their nonadditivity can't be accounted for by the traditional BCS method for treating nuclear pairing correlations, instead, can be explained satisfactorily by the Particle-number conserving method, in which blocking effect is treated strictly.
The magnetic moments of nuclei near double closed-shell with A=133, 207, 209 are calculated within spherical and triaxial deformed relativistic mean field theory. The relativistic effect and core polarization effect on nuclear magnetic moment have been examined. The observed large discrepancy between Schmidt values and experimental data for 133Sb and 209Bi can be reduced significantly with the consideration of time-odd magnetic potential in triaxial deformed RMF theory.
Some common used rotational spectrum formulas are reviewed and compared. Analyses for the experimentally observed normally deformed and superdeformed rotational bands now available show that the two-parameter ab and three-parameter abc formulas are the best compared with the other formulas with the same number parameters, and may be conveniently used by experimentalists.
By comparing the values of some quantities obtained in the SD pair truncated shell model and the dynamical symmetries of the interacting boson model(IBM), we identify the nuclear shape phases in the shell model. We study the dependence of the nuclear shape phases on the monopole-pair, quadrupole-pair and quadrupole-quadrupole interaction strength, respectively, in the shell model. We also investigate the vibrational to γ-soft rotational phase transition in the shell model. The obtained results coincide with those obtained in the IBM very well.
The ground-state properties of light odd-odd mirror nuclei 12N and 12B have been investigated within the time-odd triaxial relativistic mean-field theory. The influences of spatial-component of vector meson fields on the ground-state properties, especially the single-particle energies have been analyzed.
The exactly solvable Nilsson mean-field plus nearest-orbit pairing model is applied to describe nuclei in actinide and rare-earth regions. Binding energies, pairing excitation energies, even-odd mass differences, and moment of inertia of low-lying excitation states for even-even nuclei of 226—234Th, 230—239U, 236—243Pu, 160—170Er, 166—176Yb, 172—180Hf are calculated in both proton-proton and neutron-neutron pairing and proton-proton pairing excitation frozen cases, and compared with the corresponding experimental data.
We calculate the single-particle resonances in a spherical Woods-Saxon potential using real stabilization method. The box discretization method is used to find positive energy states of the Woods-Saxon potential. The discretized positive energy is stabilized against the box size when a resonance condition is met. The phase shifts are calculated by using the wave functions thus obtained. The resonance parameters could be calculated through fitting the energies and phase shifts in resonance region to the Wigner formula.
The E-Gamma Over Spin (E-GOS) analysis method is applied to study the shape evolution of yrast-bands in A～150 nuclei.The results show that the vibration and the rotation coexist in this region. There is a critical point and the nuclear structure changes notably at this critical point. It is found that these nuclei in A～150 region are in the transition from U(5) to SU(3) dynamical symmetry.
A method for calculation of Gamow-Teller transition is developed in the framework of the Projected Shell Model (PSM). The shell model wavefunction is the superposition of the angular-momentum-projected multi-quasiparticle configurations. Calculation of transition matrix elements in the PSM is briefly discussed. Our first example indicates that, while experimentally known Gamow-Teller transition rates from the ground state of the parent nucleus are reproduced, stronger transitions from some low-lying excited states are predicted to occur, which may considerably enhance the total decay rates once these nuclei are exposed to hot stellar environments.
With pairing correlations and microscopic center-of-mass correction considered, new parameter sets for the Lagrangian density in the relativistic mean field (RMF) theory, NLLN with nonlinear σ- and ω-meson self-coupling and DDLN with the density-dependent meson-nucleon coupling are proposed for light nuclei. They are able to provide an excellent description for the properties of the Z≤8 nuclei in and far from the valley of β stability. The neutron drip line nucleus 26O for Oxygen isotopes is obtained in new parameter sets. In addition new magic number N=16 in 24O can be well explained in new frame.
Pseudospin symmetry and spin symmetry in the relativistic square well are investigated systematically by solving the Dirac equation with scalar and vector potentials and are found to be a good approximation in realistic nuclei such as 208Pb. The pseudospin breaking and spin breaking are shown in correlation with nuclear mean field. The square well radius plays an important role in the splittings of energy and wavefunction. The dependence of splittings with quantum numbers is also analyzed.
Static and dynamic quadrupole (Q) moments of C and Ne isotopes are investigated by using Skyrme Hartree-Fock and shell model wave functions. We point out that the deformation of C isotopes have a strong isotope dependence as a manifestation of nuclear Jahn-Teller effect. It is shown at the same time that the Q moments and the magnetic moments of the odd C isotopes depend clearly on assigned configurations, and their experimental data will be useful to determine the spin-parities and the deformations of the ground states of these nuclei. Electric quadrupole (E2) transitions in even C and Ne isotopes are also studied by using the polarization charges obtained by the particle-vibration coupling model for shell model wave functions.
The ground-state properties and high-spin spectra of the light even-even Rn-Th nuclei have been systematically investigated using the cranking shell model in a multidimentional deformation space, including β2, β3, β4 and β5 degrees of freedom. Calculations reproduce well the experimental values of the moment of inertia. The investigation of the structures shows that, with increasing neutron number, the ground-state shapes of these nuclei evolve from nearly spherical(N≈130), through well-developed octupole (N≈136) to well-deformed quadrupole (N≥140) shapes. Cranking calculations display that the nuclei investigated are very octupole soft and will restore to reflection-symmetric shapes at high spin.
The configuration-dependent cranked Nilsson-Strutinsky approach has been used to investigate rotational structures of neutron deficient isotopes 125,127,129Ce. Signature splitting and deformation of yrast bands have been discussed. Shape coexistence may exist in 127,129Ce. The signature splitting of yrast bands for Ce isotopes is strongly dependent on occupied orbitals because of slight triaxial deformation.
The mass differences of mirror nuclei have been calculated using the Skyrme-Hartree-Fock model. The deviation of these masses differences from the corresponding experimental results is a longstanding problem and has been studied intensively. In this paper we studied this anomaly systematically. The calculations show that significant changes in the evolution pattern occur around the magic numbers. After the Skyrme force parameters are adjusted to reflect this shell effect, we found that this anomaly is significantly reduced. This shows that the anomaly is dependent on shell closure.
The clustering phenomenon in heavy nuclei is discussed in this paper within the relativistic mean field (RMF) approach. The clusters can be observed in experiments are obtained through the calculated nucleon binding energy distributions according to the RMF theory after the atomic nucleus is divided into two parts, instead of the usual method of analysis to the calculated nucleon density distributions because of the stronger spin-orbit couple in heavy nuclei. The results indicate that the RMF theory is well suited for the study of clustering in heavy nuclei.
We study the features of nuclear shape phase transition in the framework of interacting boson model(IBM). By comparing the critical behaviors in the U(5)-O(6) and U(5)-SU(3) transitional regions with the increasing of the total boson number, we find out that the B(E2) ratios B(E241→21)/B(E2};21→01),B(E2;02→21)/B(E2;21→01) and so on can be taken as the effective order parameters to distinguish between the first and second phase transition.
Shell-model-like approach(SLAP) is adopted to treat the pairing correlations in relativistic mean field theory (MFT). The ground state properties of C isotopes are studied and the obtained results are compared with available data.
With the relativistic boundary condition, single proton resonant states in spherical nuclei are studied by an analytic continuation in the coupling constant (ACCC) method within the framework of the self-consistent relativistic mean field (RMF) theory. In this scheme, the energies, widths and the wave functions for proton resonant states in 120Sn are analyzed to discuss the probability of the existence of pseudospin symmetry in the resonant states, which is consistent with that in the bound states, where the splittings of energies and widths, as well as the behavior of the wave function between pseudospin doublets are found in correlation with the quantum numbers of single particle states.
Configuration-constrained calculations of potential-energy surfaces have been performed to study the shape of the Kπ=7－ isomer in 130Ce. The calculated excitation energy agrees well with the experimental data. The resulting deformation indicates that this isomer has a prolate shape as large as that of the ground state. However, the potential-energy surface of the isomeric state is remarkably soft on the γ degree of freedom, which would be an indication of the K mixing.
A caculation that had been done in low rotation frequency is carried out in 175Hf in higher rotation frequency by TRS method. A second local minimun that was not found in low rotation frequency is found in the total potential energy surface. Futhermore, the mechanism of the local minimun is analysed and a comparison of energy is made between two different rotation frequencies.
The superdeformed or highly deformed band terminations in 38K, 36Ar, 32,34S and 35Cl have been studied by the configuration dependent cranked Nilsson-Strutinsky approach. Some possible superdeformed band terminations were predicted, such as the π(d5/2)－2(f7/2)2⊙ν(d5/2)－2(f7/2)2([22,22]) configuration in 32S with deformation about ε2=0.61 and γ≈0° at spin I=0－10, especially the superdeformed band terminates at I=19 and about ε2=0.39 (with ε2=0.50 when I≤9) in 38K, and all of them are favorable for observation. The tendency of these bands in energy with spin increasing favors the band termination, so superdeformed bands terminating would be smooth. The calculated superdeformed band is in good agreement with observed one in 36Ar confirms that the calculated results are reliable.
We have perfomed calculations for the six rotational bands in 178Hf which have been found experimentally by using triaxial projected shell model (TPSM). The γ band can be well reproduced with γ=22°. By using the same γ value, the present calculations predict a γ-band built on 178m2Hf(16+) state, and its band head (I=14+)lies about 900keV above the 178m2Hf(16+) state. This 14+ state should be rather easily excited from the 16+ isomeric state because of the same intrinsic configuration of these two states. It is hope that the 14+ state could have more probable chance to decay into the ground state band than that from the 178m2Hf(16+) state, and then to realize the de-excitation of the isomeric state.
Based on a particle and a hole plus triaxial rotor model, treating the pairing correlations with BCS theory, we develop two quasiparticles plus triaxial rotor model to study the chiral bands. In this paper, fixing the proton as a pure h11/2 particle, we investigate the influence of the neutron fermi surface on the excitation energies and electromagnetic transition probabilities of doublet bands.
We used the shell model to investigate the β decays of the neutron-rich nucleus 18N. The reduced transition strengths B(GT) of Gamow-Teller β decays in 18N are calculated with the different interactions in the psd shell space; the results are compared and dicussed. A series of consistent results with the recent experimental data are found in this shell space, which seems to show that the observed properties of 18N and 18O are mainly produced in psd shell space. In addition, a B(GT) value is predicted around 9.5MeV in our calculation. These will be useful in the future experiment.
270Hs is predicted theoretically as a double magic nucleus. The formation cross sections of 266—270Hs with different projectile-target combinations are calculated using a two-parameter Smoluchowski equation. The optimal projectile-target combination and bombarding energy for the formation of superheavy nuclei 266—270Hs are suggested. The half-lives of α decay for superheavy nuclei 266—270Hs are predicted.
The shapes of light Krypton isotopes have been investigated using cranking Woods-Saxon model. The calculated results show that nuclei 70,72Kr have oblate ground states and coexisting low-lying prolate states, while nuclei 74,76Kr have prolate ground states and coexisting low-lying oblate states. In addition, the cranking calculations of 72Kr display that the ground-state shape of 72Kr changes from oblate to prolate as ω increases.
The cross sections of elastic scattering of pion on 24Mg and 32S are calculated on the basis of the independent α-particle cluster model in the frame of the Glauber multiple scattering theory. The calculated results are in good agreement with the experimental data.
The status of HI-13 tandem accelerator and its upgrading program BRIF and the future plan BRIF-II are briefly described. The in-beam gamma-ray spectroscopy of nuclear structure based on recent and its perspectives on the future equipments has been presented.
The history of experimental study on β-delayed proton decays in the rare-earth region was simply reviewed. The physical results of the β-delayed proton decays obtained at IMP, Lanzhou over the last 10 years were summarized, mainly including the first observation of 9 new β-delayed proton precursors along the odd-Z proton drip line and the new data for 2 waiting-point nuclei in the rp-process. The results were compared and discussed with different nuclear model calculations. Finally, the perspective in near future was briefly introduced.
The differential cross-sections for elastic scattering of 17F and 17O on 208Pb have been measured at Radioactive Ion Beam Line at Lanzhou (RIBLL). The variation of the logarithms of differential cross-sections with the square of scattering angles, viz. angular dispersion plot, shows clearly that there exists a turning point in the range of small scattering angles (6°—20°) for 17F due to its exotic structure, while no turning point was observed for 17O. The experimental results have been compared with previous data of other groups. Systematical analysis on the available data seems to conclude that there is an exotic behavior of elastic scattering angular dispersion of weakly bound nuclei with halo or skin structure as compared with that of the stable nuclei. Therefore the fact that the turning point of the elastic scattering angular dispersion plot appears at small angle for weakly bound nuclei can be used as a new probe to investigate the halo and skin phenomenon.
Through heavy-ion nuclear reactions and in-beam γ-ray spectroscopy technique, the high spin states of odd A 137La and odd-odd 138Pr nuclei which are located near the N=82 closed shell on A=135 region, have been studied. The 130Te(11B,4n) and 128Te(14N,4n) reactions were used to populate the level states for 137La and 138Pr respectively. The level schemes of these two nuclei have been extended. In 137La, four collective bands have been newly identified. Among them, the near-yrast band is with weak prolate deformation, and another one belongs to a oblate band. In 138Pr，six collective bands have been observed. The yrast band is with weak prolate deformation also, and all the other five bands, two of which are newly identified by the present work, are assigned as the oblate bands. The characteristics for these collective bands, such as the signature inversion, the configuration origination etc. have been discussed.
The nuclear moment measurement methods of the time differential perturbed angular distribution, transient magnetic field-ion implantation perturbed angular distribution and β-ray detected nuclear magnetic resonance and nuclear quadrupole resonance and their applications in nuclear structure studies are described briefly. As examples, the nuclear moment measurements and their nuclear structure studies for the 43Sc(19/2－,3.1232MeV,0.45μs) isomeric state,84,86Zr and 83Y high spin states,17F(I=5/2+,T1/2=64.49s),12B and 12N mirror nuclei are given.
High spin states of odd-odd nucleus 158Tm have been studied by using 144Nd(19F,5n) reaction at beam energies of 108 and 112MeV. Two new bands are identified. And their possible configurations and spin/parity assignments are discussed. Furthermore, experimental B(M1)/B(E2) values are obtained for the πh11/2⊙νi13/2 band and compared with calculations based on geometric model.
Through measuring high-fold prompt γ-ray coincidence events following the spontaneous fission of 252Cf with the Gammasphere detector array, new level scheme in the very neutron-rich 112Ru nucleus has been established.The ground-state band and the one-phonon γ-vibrational band have been confirmed and extended with spin up to 16h and 15h, respectively. The other two side bands, one proposed as two-phonon γ-vibrational band and another proposed as two-quasiparticle band, have been identified for the first time. From cranked shell model calculations, 112Ru nucleus may have triaxial deformation with parameters β2～0.27, γ～－29° and the band crossing in the yrast band is due to the alignment of two h11/2 neutrons. The characteristics for the quasiparticle band and γ-vibrational bands have also been discussed.
High-spin states of 152Gd have been studied via the 148Nd(9Be, 5n)152Gd fusion-evaporation reaction. The ground-state band, octupole band and β band have been extended up to spins 20+, 21－ and 16+, respectively. A possible aligned two quasi-neutron band, was observed for the first time. The kinematic behaviors of the ground-state bands and yrast bands in 152,154Gd indicate that the shape of 152Gd may change with the increasing of rotational frequency, which are consistent with the theoretical calculations using Cranked Woods-Saxon-Strutinsky methods. The first band crossing observed in 152Gd can be ascribed to the alignment of a pair of i13/2neutrons.
The high spin states of 155Tm have been populated via heavy-ion fusion evaporation reaction 142Nd(19F, 6n)155Tm. From the γ-γ coincidence analysis, a new level scheme of 155Tm was established, and the high spin states of 155Tm was discussed by systemic comparision.
The present experiment was carried out at HI-13 tandem accelerator of the China Institute of Atomic Energy in Beijing. High spin states in 52Mn and 54Mn, were populated via 12C+48Ti fusion evaporation reactions at beam energy of 60MeV. Gamma-gamma coincidence experiment was performed with an array consisting of fourteen Compton suppressed HPGe-BGO spectrometers. Level scheme of 52Mn and 54Mn has been established in this experiment, In order to understand the insight structure of the high spin states of 52Mn observed in present work, we have performed OXBASH shell model calculations, the results agree with the experimental results.
High spin states in 106Ag have been studied using the 100Mo(11B,5n)106Ag reaction at a beam energy of 60MeV at HI-13 tandem accelerator in China Institute of Atomic Energy. The γ-γ coincidences were measured using 15 HPGe detectors with Compton suppressed shield. By analyzing the γ-γ coincidence and their DCO ratios, new level scheme of 106Ag has been presented. 26 new γ were found compared with previous level scheme. Experimental evidences for chiral doublet bands built on πg9/2⊙υh11/2 configuration in 106Ag are briefly discussed. But 2h difference in alignments is too large to interpret as chiral doublet bands.
The criteria for chiral doublet bands obtained by assuming one proton (neutron) particle and one neutron (proton) hole sitting in a corresponding high-j shell coupled to a triaxial rotor with γ=30° have been summarized. Two representative cases in A～100 odd-odd nuclei, nearly degenerate ΔI=1 doublet bands in 104Rh and 106Rh are checked against these chiral criteria. It is shown that 106Rh possesses better chiral geometry than 104Rh, although the energy near degeneracy is achieved in 104Rh in comparison with the constant energy separation of doublet bands in 106Rh.
High-spin band structures in neutron-rich 105Mo nucleus have been investigated by measuring prompt γ-rays emitted by the spontaneous fission fragments of 252Cf with the Gammasphere detector array. The yrast band has been confirmed and updated. The other three new collective bands are observed and they are proposed as the single-neutron excitation bands built on the 3/2+, 1/2+ and 5/2+ Nilsson orbitals, respectively. The characters of these bands are discussed.
The systematics of signature inversion of the πg9/2⊙υh11/2 configuration bands in Ag, Rh and Tc isotopes is studied. The inversion point shifts toward the lower spin with neutron number increasing for isotopes and shifts toward the higher spin with proton number increasing for isotones. This systematic feature of signature inversion in A～100 mass region is well explained by the competition between the p-n residual interaction and the Coriolis force.
The γ rays following the β+/EC decay of 176,178Ir nuclei have been investigated using in-beam γ-ray experiment. In addition, with the aid of a helium-jet recoil fast tape transport system, the β+/EC decay of 176Ir was further studied, the new γ rays were proved and a low-spin isomer was proposed in 176Ir. The isomeric state was analysized according to the systematics in neighboring nuclei.
The halo or skin structure of excited states in odd nuclei near the stability line is studied in terms of the spherical nonlinear relativity mean field theory calculation, considering nucleus as a spherical core plus a valence nucleon outside it. The tail of density distributions of excited states with exotic structure are presented for medium-heavy nuclei. The ratio (Rvc) of valence nucleon rms radii to that of nuclear core are deduced. Together with the separation energy (Sn(p)), the ratio (Rvc) constitutes a correlation, in which the exotic nuclei excited states distribution presents a strap structure. It implied the effects of centrifugal barrier and the shell structure.
The neutron asymptotic normalization coefficients (ANCs) for the virtual decay 27Mg→26Mg+n are determined from the angular distributions of the 26Mg(d,p)27Mg reaction leading to the ground, first and second excited states of 27Mg respectively, based on distorted wave Born approximation analysis (DWBA). According to charge symmetry of mirror nuclei, we extract the proton ANC and spectroscopic factor for 27P ground state and the proton widths of the first and second excited states of 27P. The rms radius of valence proton is then derived. Our result indicates that the 27P ground state has a proton halo structure.
We measured the reaction cross sections(σR) and parallel momentum distributions(P//) of 23Al and it's neighboring nuclei at RIKEN-RIPS. An enhanced σR of 23Al is observed, which is consistent with the previous experimental result. And the P// of fragment from the projectile breakup nuclei have been obtained at the same time.We discuss our experimental data under the Few-Body Glauber Model. The P// of 23Al shows the ground state of the valence proton is a d-wave, which is consistent with the recent measurement of 23Al's g factor. To explain the experimental σR and P// of 23Al at the same time, we suggest an enlarged core of 23Al.
The neutron-rich target-like isotope 236Th was produced in 238U-2p multinucleon transfer reaction between a 60MeV/u 18O beam and nature 238U targets. The thorium activities were radiochemically separated from the mixture of uranium and reaction products. The isotope 236Th was identified by 642.2keV, 687.6keV and 229.6keV characteristic γ-rays. The production cross section of 236Th has been determined to be 250±50μb.
14N of 78.6MeV/u was used as primary beam to bombard on Be target to produce RIB 12N of 34.9MeV/u on RIBLL (Radioactive Ion Beam Line in Lanzhou). The total reaction cross section of 12N on Si target was measured by directly break-up reaction. And the calculation with micro Glauber model is consistent with the experimental results. It is found that inside 12N, compared with its neutron density, the proton density distribution has a larger diffusion.
The entrance-channel effects and dynamical mechanisms on the fusion reaction of 74Ge+74Ge and 48Ti+100Mo are studied with the microscopic transport model-Improved Quantum Molecular Model(ImQMD). The time evolution of the〈r2〉1/2 and β of the compound nuclei are analyzed, and these results show that the lager deformation of the compound nuclei are more easily produced for the mass symmetry reaction system 74Ge+74Ge than that for the mass asymmetry reaction system 48Ti+100Mo. The final results on the larger deformed compound nuclei are determined by this dynamical process.
A four-parameter correlation measurement, including two semiconductors and a liquid scintillator as well as a 60% HPGe detector, was employed to measure the correlations of neutron multiplicity and γ yield with the fission parameters, such as fragment mass number A* and total kinetic energy TKE of fragments. Because it is the first time that the absolute γ yield for the selected fragment is determined, so the angular momentum excitation of fragments can be investigated using the correlations of γ multiplicity with the neutron yield as well as with A* and TKE. The results show that there is the complex correlation between the angular momentum excitation and the fragment deformation. The measured data can not be explained on the basis of the bending and wriggling excitation modes, but it could be understood partly by the assumption that there exists the positive correlation between the angular momentum excitation of fragments and the excitation energy of fission nuclei at the scission.
A setup aiming to measure the resonance scattering reactions with radioactive ion beams in inverse kinematics is installed on the secondary beam line at HI-13 TANDEM laboratory. The setup consists of a beam-monitoring time of flight system, and a ΔE-E telescope based on large-area Double-Sided Silicon Strip Detector (DSSSD). The thick-target method for excitation function of proton resonance scattering is checked with a 57.0MeV 17F secondary beam on a 7.66mg/cm2 thick (CH2)n target.
The properties optimization process and testing results for β-delayed neutron detection array were stated in this paper. The amplitude and time resolution of the prototype modules wrapped with several different reflective materials have been tested with 60Co source and cosmic rays. The properties of several coupling materials between scintillator and light guide have been studied and compared. The LED light fibre calibration monitoring system was introduced to monitor the long-term working status of neutron detection array and optimize electronics. All of those are the groundwork of the in-beam β-delayed neutron emission experiments.
Search for low-spin signature inversion in the πi13/2⊙νi13/2 bands in odd-odd 182,184,186Au has been conducted through the standard in-beam γ-spectroscopy techniques via the 152Sm(35Cl,5n)182Au, 172Yb(19F,5n)186Au, and 159Tb(29Si,4n)184Au reactions, respectively. The πi13/2⊙νi13/2 bands in these three nuclei have been identified and extended up to high-spin states. In particular, the inter-band connection between the πi13/2⊙νi13/2 band and the ground-state band in 184Au has been established, leading to a firm spin-and-parity assignment for the πi13/2⊙νi13/2 band. The low-spin signature inversion is found in the πi13/2⊙νi13/2 bands according to our spin-assignment and the signature crossing observed at high-spin states.
Excited states in 188,190Tl have been studied experimentally by means of in-beam γ spectroscopy techniques, and resulted in the identification of a strongly coupled band based on the πh9/2⊙νi13/2 configuration with oblate deformation. The oblate band in doubly odd Tl nuclei shows low-spin signature inversion. It is the first experimental observation of low-spin signature inversion for a band associated with the oblate πh9/2⊙νi13/2 configuration.
Nuclear structure information plays an extremely important role in studies of the evolution and explosion of stars and the cosmic synthesis of the elements. Properties of nuclear ground states (e.g., masses, lifetimes, decay branches) and low-lying resonances (excitation energies, spins, parities, decay widths, spectroscopic factors), especially on unstable nuclei, can quantitatively and qualitatively change predictions of astrophysical simulations. The location of the particle driplines and shell structure far from stability also strongly influence our astrophysical predictions. A number of examples of the dramatic impact that new nuclear structure information has on simulations of nova explosions, X-ray bursts, and core collapse supernovae are given. Some of these are results of recent measurements with radioactive 18F, 82Ge, and 84Se beams at ORNL's Holifield Radioactive Ion Beam Facility. A new suite of software tools to help determine the astrophysical impact of nuclear physics studies will also be presented.
The status of the isoscaling analysis has been simply reviewed and the corresponding information on the extraction of the symmetry energy is discussed. We discuss the secondary decay effect on isoscaling parameter, the excitation energy and density dependences of the symmetry energy.
In this paper we calculated some properties of nuclear matter using the quark-meson coupling model (QMC) with self-interactions,and obtained the density-dependent coupling constant between nucleon and scalar meson. Then we analyzed the contribution of nucleon structure to the properties of nuclear matter by introducing the variation of the coupling constant into VDD and SDD. Numerical results suggest that the influence of the nucleon struture on the properties of nuclear matter is obvious.
The clustering phenomenon in light stable nuclei is studied within the shell- model-like approach in relativistic mean field theory. The result reproduces α-clustering phenomenon in light stable nuclei by calculating 8Be, 12C, 16O, 20Ne. Comparison of our result with RMF calculation indicates that the pairing correlation could change the properties of clear ground state and lead to different α-clustering structure.
In the framework of the relativistic mean field theory nuclear matter including Δ isobars is investigated.The numerical results indicate that no matter what parameter set is chosen,there exist abnormal states.The high temperature is critical factor for abnormal states.The critical temperature that abnormal state begins to appear is Tc=127MeV.When T≥165MeV the normal state will disappear and only abnormal state survives.The influence of abnormal state on the EoS of nuclear matter is also discussed.
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 239Pa on the universe age estimation is simply mentioned.
Anisotropic flows (v2 and v4) of light nuclear clusters are studied by Isospin-Dependent Quantum Molecular Dynamics model for the system of 86Kr+124Sn at 25MeV/A and large impact parameters. Number-of-nucleon scaling of the elliptic flow (v2) is demonstrated for the light fragments up to A=4, and the ratio of v4/v22 shows a constant value of 1/2. It can be understood by the coalescence mechanism in nucleonic degree of freedom for the cluster formation.
Latest progress of 1keV—200MeV A>24 nucleon phenomenological local and non-local spherical optical potentials are briefly introduced.
We study the α(p,p')ηα reaction theoretically and analyse the mechanism of N*(1535) excitation in the projectile and target nucleus. The cross section, invariant mass spectrum of ηN, and angular distribution of η are given numerically at Tp=2.8GeV. The implications of our results to experiments at CSR in Lanzhou are discussed.
Some experimental data in p-Be collisions at 19GeV/c with the E864/E941 spectrometer at the Alternating Gradient Synchrotron(AGS) has been analyzed. The invariant mass distribution of leading Λ and Δ++ in p-Be collisions at 19GeV/c is presented with a new iterative algorithm through studying distribution of the pairs of proton and pion.
Bulk viscosity of interacting strange quark matter is calculated in the light of ms dependent reaction rate of u+s←→d+u, and the extra terms come from the interaction between quarks and theomodynamic consistency are included. We find that the results were larger than previously assumed. The application to the damping time of the interacting strange quark matter shows that although the bulk viscosity becomes larger, the previous conclusion about the observation of the existence of strange stars is unchanged.
In the framework of the relativistic mean field theory(RMFT),the condensations of K－ and K0 in neutron star matter are studied. We find that K－ and K0 condensations can both occur,even in the case that the neutron star matter includes baryon octet and Δ resonances.Also we investigate how hyperons and K condensations influence each other. K0 condensations depress K－ condensations and make Δ resonances appear easily. In the high density region, the system may consist of many kinds of baryons, whose number densities are becomming identical. And ultimately K0-rich matter is formed in the core. The equation of state including K condensations becomes softer resulting in a smaller maximum mass of neutron star.
The MeV photon beam will be produced by Shanghai Laser Electron γ Source which is being proposed. Based on it, a series of nuclear astrophysics experiments can be carried on and the reaction rates of these reactions can be determined accurately. In this paper, the reaction rates of the key reaction 12C(α,γ)16O are calculated according to experiments data and theoretical results, and the mean value and statistical error of these calculated rates are evaluated. The new set of parameters of reaction rate formula are obtained though fitting above results. The reaction rate and its error at T9=0.2 in which 12C(α,γ)16O occurred are extracted, and the screening effects of reaction rate are discussed.
Upon application of the mass-density-dependent quark model with thermodynamic self-consistency, we investigate the bulk properties of hybrid stars and calculate the particle fraction and equation of state(EOS) for hybrid star matter. Numerical results indicate that the pressure extra term deriving from self-consistently thermodynamical treatment can soften the EOS, put off the appearence of phase transition and decrease the maximum mass for a hybrid star from 2.4M⊙(without pressure extra term) to 1.8M⊙ with corresponding radius from 15km to 12km. Similar to the Nambu-Jona-Lasinio(NJL) model, this model is suitable for describing the massive hybrid stars.
The radioactive ion beams produced on the secondary beam facility of Beijing tandem accelerator have been used in the experimental studies of nuclear structure and nuclear astrophysics. The results for the nuclear structure studies are introduced briefly in the present paper.
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.
Based on the isospin and momentum dependent MDI interaction constrained by the isospin diffusion data in heavy-ion collisions, we study the temperature dependence of the nuclear matter symmetry energy and symmetry free energy. Using the resulting density and temperature dependent symmetry energy, the isotopic scaling data in heavy-ion collisions is then discussed.
Irradiation facility for single-event effects (SEEs) experiments of space-borne microelectronic devices has been established at Beijing HI-13 tandem accelerator. Mono-energetic and uniformly-distributed accelerated beams over the certain area were obtained at the focal plane in Q3D magnetic spectrometer, and these beams have been extensively used in SEE ground testing. In order to study the mechanism pertinent to SEEs, a heavy-ion microbeam irradiation test system has been developed utilizing a pinhole aperture to define the accelerator beam to microbeam. The performance of the irradiation system was tested by microbeam strike on a plastic track detector. The microbeam with the spot size of about 2.3μm×3.5μm has been achieved by a micro-collimator with an opening area of about 2μm×3μm.
The structure of Ξ*Ω(0,1/2) is studied in the extended chiral SU(3) quark cluster model in which vector meson exchange are included using the resonating group method. It is shown that the system is still a deeply bound state.
The isoscaling behavior in projectile fragmentation has been systematically investigated by a modified statistical abrasion-ablation (SAA) model. The reduced isoscaling parameters are found to decrease with the excitation energy per nucleon and have no significant dependence on the size of reaction systems. Assuming a Fermi-gas behavior, the excitation energy dependence of the symmetry energy coefficients are tentatively extracted from α and β which looks consistent with the experimental data.
A combined dynamical and statistical model has been applied to simulate the fission process of 112Sn+112Sn and 116Sn+116Sn. The mass distribution of the fission fragments is given by the Gaussian probability sampling. The isoscaling behavior has been observed from yield ratio of the fission fragments and the isoscaling parameter α and β have been extracted. It seems that the isoscaling parameters are sensitive to the width of fission probability and the beam energy as well as the deduce friction parameter.
Isoscaling roles have been studied for two isospin similar system by isospin dependent quantum molecular dynamical model (IQMD) and statistical sequential decay model GEMINI. For the light fragments, isoscaling parameter α increases with the reaction time, the heavy fragment presents decreasing with reaction time. α of the light fragment keeps flat, but α of the intermediate and heavy fragments is dependent on the fragment size, increases with the fragment size. Statistical sequential decay will increase isoscaling parameter α slightly, but does not change the roles in light and heavy fragments.
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