The Study of α Emission Induced by 46.7MeV/u 12C on 58Ni、115In and 197Au

The energy spectra and angular distribution of α particles emitted from ¹²C induced reactions with ⁵⁸Ni,¹¹⁵In and ¹⁹⁷Au have been measured.Three moving sources of emitting α particle are clearly seen from invariant cross section distribution in velocity coordinates.The experimental data were analyzed by using three moving sources.Extracted parameters of the source with half-beam velocity are in agreement with the systematic values from Fermi Gas Model.The energy spectra and the extracted parameters for various targets are discussed.The low energy peak in energy spectra is possibly from the emitted α particle from equilibrium system after pre-equilibrium emission of target-like products.The energetic α particles are mainly from projectile fragmentation and projectile-like fragmentation.     

Complex Fragments Emitted in Reactions of 46．7MeV/u 12C on 197Au,115In and 58Ni

Energy spectra of complex fragments emitted in the reactions of 46.7MeV/u ¹²C with different targets ¹⁹⁷Au,¹¹⁵In and ⁵⁸Ni have been measured by telescopes,consisting of a gis ionization counter followed by a position Sensitive semiconductor detector.Tha most probable kinematical energies.E_p of complex fragments and temperature parameters of long－live intermediate systems have been deduced by complex fragment ernergy spectra.The experimental values of E_p are lower than the calculated ones by E=V_coul+2T.The experimental values of complex fragment yields can be reproduced by simple A.Friedman statistical evaporation model satisfactorily.     

Study on the formation of the composite system of 238U+238U

Strongly damped reactions of ²³⁸U+²³⁸U, at E_cm= 680—1880 MeV have been studied based on the improved quantum molecular dynamics model. We find that at a certain energy region the entrance channel potential is weakly repulsive and the dissipation is very strong after touching configuration, these two effects make the time delay of re-separation for colliding system. The single particle potential well of the transiently formed composite system has Coulomb barrier about 15—20 MeV high at the surface, which makes the excited unbound protons being still embedded in the potential well and moving in a common mono-single particle potential for a period of time and thus restrains from quick decay of the composite system.     

β-Delayed Proton Decays of 140Tb and 141Dy as Well as the Spin and Parity of 143Dy

¹⁴⁰Tb and ¹⁴¹Dy were produced via fusion evaporation in the reaction ⁴⁰Ca+¹⁰⁶Cd. Their β-delayed proton decays were studied by means of “p-γ” coincidence in combination with a He-jet tape transport system, including half-lives, proton energy spectra, γ-transitions following the proton emissions, and the branching ratios to the low-lying states in the grand-daughter nuclei. The ground-state spins and parities of 140Tb and 141Dy were extracted as 7^± and 9/2^±, respectively, by fitting the experimental data with a statistical model calculation. The configuration-constrained nuclear potential energy surfaces (NPES) of ¹⁴⁰Tb and ¹⁴¹Dy were calculated by using the Woods-Saxon Strutinsky method, which indicate the ground-state spins and parities of ¹⁴⁰Tb and ¹⁴¹Dy to be 7⁺and 9/2^－, respectively. In addition, the configuration-constrained NPES of ¹⁴³Dy was also calculated by using the same method. From the NPES a 1/2⁺ ground state and a 11/2^－ isomer with the excitation energy of 198keV were found. The calculated results are consistent with our experimental data on the decay of ¹⁴³Dy reported in Eur. Phys. J., 2003, A16: 347—351.     

Cross section of reaction 181Ta(p,nγ)181W and the influence of the spin cut-off parameter on the cross section

In this work, the program Cindy was modified to calculate the formation cross section of each energy level of residual nucleus ¹⁸¹W resulting from the reaction ¹⁸¹Ta(p,nγ)¹⁸¹W. The concerned cross sections calculated at proton energy E_p=4.5-8.5 MeV agreed well with experimental results. The influence of the spin cut-off parameter in the energy level density model on the cross section was studied. The obtained results show that the influence of spin cut-off is obvious for lower energy levels.     

6.8MeV/A—5.1MeV/A 14N+59Co, 51V发射α粒子的研究

用ΔE-E半导体望远镜测量了6.8MeV/A—5.1MeV/A的¹⁴N轰击⁵⁹Co和⁵¹V产生的α粒子, 得到了发射α粒子, 得到了发射α粒子的能谱、角分布和E-θ平面上的d²σ/dΩdE等高图, 区分了直接机制α及复合核蒸发α粒子, 并对直接机制α粒子的来源作了讨论.     

(EC/β+) Decay of 130Nd and 140Tb

Isotopes,¹³⁰Nd and ¹⁴⁰Tb were produced using enriched targets ⁹⁶Ru and ¹⁰⁶Cd, respectively,bombarded by ³⁶Ar ion beam. The two nuclides were identified and studied by a He-jet tape transport system in combination with "X-γ" and "γ-γ" coincidence measure- ments. The half-life of ¹³⁰Nd was determined to be (13±2)s. The EC/β⁺ decay scheme of 130Nd was proposed for the first time, and the spins and parties of the ground-state and observed low-lying states in the daughter nucleus ¹³⁰Pr were speculated tentatively. The previous simple EC/β⁺ decay scheme of ¹⁴⁰Tb was revised, and the spin-parity of its groundstate was assigned to be 7⁺.     

β-Delayed Proton Decays of 133Sm and 149Yb

¹³³Sm was produced via fusion evaporation in the reaction ⁴⁰Ca+⁹⁶Ru. Its β-delayed proton decay was studied by means of “p-γ” coincidence in combination with a He-jet tape transport system, including half-lives, proton energy spectra, γ-transitions following the proton emissions, and the branching ratios to the low-lying states in the grand-daughter nuclei. The possible spins and parities of ¹³³Sm were extracted by fitting the experimental data with a statistical model calculation. The configuration-constrained nuclear potential energy surfaces of ¹³³Sm were calculated by using the Woods-Saxon Strutinsky method. Comparing the experimental and calculated results, the spins and parities of ¹³³Sm were assigned to be 5/2⁺ and 1/2^－, which is reconciled with our published simple (EC+β⁺) decay scheme of ¹³³Sm in 2001. In addition, our experimental data on the beta-delayed proton decay of ¹⁴⁹Yb reported in Eur. Phys. J., 2001, A12: 1—4 was also analyzed by using the same method. The spin and parity of ¹⁴⁹Yb was assigned to be 1/2^－.     

Franck--Condon factors and r-Centroids for the A 1∑+u-X1∑+g Band System of 107,109Ag2: Comparison of the Observed and Calculated Absorption Band Strengths

Franck-Condon factors and r-centrolds for the, A^1 ∑^＋ u-X^1∑^＋ 9 band system of ^107,109Ag2 are computed using Morse and Rydberg-Klein-Rees potentials for both lower and upper electronic states. The differences between the two sets of results are typically in the third decimal place for transitions involving vibrational levels with ν＇ and ν＂ up to about 15. Somewhat larger deviations appear for higher vibrational levels, but both sets of results follow the same pattern, which is to match well with the relative absorption band strength distribution in our experimental spectrum. The relative absorption band strengths are calculated by assuming that the electronic transition moment has only a weak dependence on the internuclear distance r. Good agreement between our measured and calculated absorption band strength ratios is found, which provides an excellent test of the calculated Franck- Condon factors and relative absorption band strengths. The r-centrold value for the （ν＇ = 0, ν＂ = 0） band is found to be approximately equal to the average value of r＇ and r＇＇e , indicating that the potentials of both states are not significantly aaharmonic around their minimum regions.     

Mixing of two-quasineutron and two-quasiproton Kπ=6+ configurations in the vicinity of 174Yb

In the framework of the projected shell model, we investigate the competition between the two-quasineutron and two-quasiproton K^π=6⁺ states in the ytterbium isotopes and N =104 isotones adjacent to ¹⁷⁴Yb. The ¹⁷⁴Yb results are compared with the experimental data.The K^π =6⁺ isomer observed in ¹⁷⁴ Yb is assigned as an admixture of the ν7/2^-[514] ν5/2^-[512] and π7/2⁺ [404]π5/2⁺ [402] intrinsic structure, which explains the experimental |g K-g R | value. Similar mixing would appear in ¹⁷⁴ Yb, ¹⁷⁶ Hf,and ¹⁷⁸ W. The low-lying K^π=6⁺ states are also predicted in ^170-178 Yb.     

(EC+β+) Decay of 130Pm and 128Pr

¹³⁰Pm and ¹²⁸ Pr were produced by irradiation of ⁹⁶Ru with 171MeV ³⁶Ar beam,and a He-jet recoil tape transport system transported radioactivities to shielded reigon. Based on X-γ-t and γ-γ-t coincidence measurements ,the (EC+β⁺)decay scheme of ¹³⁰Pm was proposed for the first time and the (EC+β⁺)decay scheme of ¹²⁸Pr was revised.     

Theoretical investigation of the structure of 19N

We have employed the shell model and Skyrme-Hartree-Fock methods to investigate the structure of the neutron-rich nucleus ¹⁹N. The level scheme of ¹⁹N from the shell-model calculation with the WBT interaction is displayed. The potential-energy-surface calculation with the SGII interaction implies that ¹⁹N should be a deformed nucleus. The theoretical β-decay half life of ¹⁹N reproduces well the available experimental data.     

Effect of Pentaquark Θ+ on the Equation of State of Nuclear Matter

Assuming Θ⁺ interacts with nucleon or Θ⁺ by exchanging isoscalar mesons σ and ω, the equation of state of {p,n,Θ⁺} 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 Θ⁺ 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, Θ⁺ might be bound in the nuclear matter.     

Configuration of the valence neutrons of 17B

The reaction cross section of ¹⁷B on ¹²C target at (43.7±2.4)MeV/u has been measured at the Radioactive Ion Beam Line in Lanzhou (RIBLL). The root-mean-square matter radius (R_rms) was deduced to be (2.92±0.10)fm, while the R_rms of the core and the valence neutron distribution are 2.28fm and 5.98fm respectively. Assuming a ``core plus 2n' structure in ¹⁷B, the mixed configuration of (2s_1/2) and (1d_5/2) of the valence neutrons is studied and the     

790 MeV 136Xe轰击56Fe靶时产生的丰中子同位素54Ti,56V,57V,58Cr

用790MeV¹³⁶Xe轰击⁵⁶Fe靶,测量了类靶碎片的质量数和原子序数。探测且鉴定了四个丰中子同位素⁵⁴Ti,⁵⁶V,⁵⁷V,⁵⁸Cr。同时提供了⁵⁵Ti,⁵⁸V,⁵⁹Cr存在的可能性。使用西德重离子研究中心的磁谱仪和磁分析一起进行了飞行时间和ΔE-E测量,同位素鉴定是可靠的。     

(EC+β+) Decay of 133Sm and 1.1s Isomer of 133Pr

By irradiation of an enriched target of ⁹⁶Ru with ⁴⁰Ca and using a helium-jet fast tape transport system in combination with X-γ and γ-γ coincidence measurements,the very neutron deficient isotope ¹³³Sm was produced and studied. A simple(EC+β⁺) decay scheme of Sm is proposed for the first time. A by product ¹³³Pr was produced simultaneously because of the ^98－102Ru contents of the ruthenium target. The half-life of an 11/2^－ low-lying isomeric state in ¹³³Pr has been measured to be (1.1±0.2)s. Using single-particle model,the reduced transition probabilities of the 11/2^－ isomers in ^{131,133,135,137}Pr are extracted from their experimental half-lives and compared with the Weisskopf estimate.     

Study on Stiffness of the Symmetry Energy at High Densities by π－/π+ Ratio

using the isospin–and momentum–dependent transport model, for three different symmetry energies, we have calculated the π^–/π⁺ ratio as a function of time and tranverse–momentum in central 132sn+124 sn collision at e_beam/A=400mev. the results show that the π^–/π⁺ ratios is very sensitive to the stiffness of the symmetry energy. thus we can probe the stiffness of the symmetry energy at high densities by using the π–/π+ ratio at different time or transverse momentum more accurately than before. comparing experimental data with the calculations will reveal crucial information about the stiffness of the symmetry energy more accurately.hadronic transport model, symmetry energy, π–/π+ ratio     

80.6MeV 16O轰击27Al反应的弛豫过程的研究

从80.6MeV ¹⁶O+²⁷Al出射类弹碎片的测量实验结果导出了角分布衰减系数、电荷分布及电荷分布的一次矩和二次矩随TKEL的变化. 对该反应中的弛豫过程进行了分析. 并讨论了势能面对电荷分布的一次矩和二次矩的影响.     

Half-Life and the Nuclear Matrix Element of the 2νββ Decay in 76Ge

We apply the shell-model wave functions of ⁷⁶Ge to calculate the nuclear matrix elements and the half-life of the 2νββ decay of ⁷⁶Ge. Our result is comparable to the recent observed 2νββ decay half-life of ⁷⁶Ge. Furthermore it provides the upper limit of the effective neutrino mass is about 0.4eV with the recent experimental data of the 0νββ decay half-life.     

Level Schemes in Neutron-Rich 141Xe、152Ce、153Nd and 160Sm Nuclei

The level schemes of neutron-rich nuclei,¹⁴¹Xe、¹⁵²Ce、¹⁵³Nd and ¹⁶⁰Sm have been established for the first time through measuring the prompt γ-rays from spontaneous fission of ²⁵²Cf.The highest spin state is up to 16⁺.The collective band structures in these neutron-rich nuclei are discussed.