40Ca和208Pb快中子辐射俘获过程研究

对快中子引起的核反应作预平衡修正,即考虑直接–半直接俘获作为统计平衡前1激子态和3激子态的γ发射过程,5个及5个以上激子态的粒子(中子、质子及α粒子等)及γ发射过程用达到统计平衡的复合核过程描述,在中子入射能量3MeV至20MeV能区对⁴⁰Ca和²⁰⁸Pb的辐射俘获截面进行了理论计算并与实验结果作了比较,得到了较好符合的结果.同时,对统计平衡前后γ发射对(n,γ)截面的贡献及直接俘获、半直接俘获和两者的相干项的特性进行了讨论     

Radial Expansion Flow in Reactions of 40Ca+58Fe and 40Ca+58Ni

By means of using an isospin-dependent Boltzmann-Langevin equation which includes isospin-dependent symmetry energy, Coulomb energy, isospin-dependent nucleon-nucleon cross sections, Pauli blocking, and initialization, the radial expansion flow of reaction systems ⁴⁰Ca+⁵⁸Ni and ⁴⁰Ca+⁵⁸Fe at 53, 100, 150, and 200 MeV/u in the central collisions were studied. It has shown that the more neutron rich system exhibits smaller radial expansion flow. It was found that the neutron rich system had smaller threshold energy which may provide a new method to determine the isospin dependent nuclear equation of state from calculated result and linear fitting result.     

Theoretical Calculations and Analysis of n+208Pb Reaction for Intermediate Energy Neutron

Based on experimental data of total, nonelastic, elastic cross section and elastic scattering angular distributions for n+Pb reactions, a set of neutron optical model potential parameters is obtained in the region of incident neutron energy from 1—300 MeV. The cross sections, angular distributions and energy spectra are calculated and analyzed by optical model, distorted wave Born approximation theory, Hauser-Feshbach theory, exciton model and cascade mechanism inside nuclear. The results indicate that the cross sections can be given for n+ ²⁰⁸Pb reactions which are all in good agreement with experimental data.     

THE FINE STRUCTURE OF 208Pb 1+ STATES

The energy levels and transition probabilities B（M1） of the ²⁰⁸Pb 1⁺ states are calculated using the matrix diagonalized method in which the （1p 1h） configurations are coupled to collective octupole phonons. Calculated results show that the fine structure of the ²⁰⁸Pb giant magnectic resonance depends rather strongly on the phononparticle coupling constant.     

208Pb平均振幅或形变参数系统研究及中子直接非弹性散射截面计算

对２０８Ｐｂ的低激发态分立能级属性和相关平均振幅或形变参数进行了系统研究,利用扭曲波波恩近似方法系统计算了１２个分立能级的中子直接非弹性散射截面． The amplitudes or form factors of the low discrete levels of 208 Pb are investigated systematically, the neutron direct inelastic scattering cross sections from 12 levels on 208 Pb are calculated.     

Surface Diffuseness Anomaly in 16O+208Pb Quasi-elastic Scattering at Backward Angle

The quasi-elastic scattering excitation function of the doubly magic ^16O＋^208 Pb system at a backward angle is measured at sub-barrier energies with high precision. The diffuseness parameters extracted from both the singlechannel and the coupled-channels calculations give almost the same value a = 0.76 ± 0.04 fro. The results show that the coupling effect is negligible for the spherical system. The obtained value is smaller than the extracted value from the fusion excitation function, but larger than the value of a -- 0.63 fm, which is from the systematic analysis of elastic scattering data.     

SINGLE-PARTICLE AND SINGLE-HOLE ENERGIES IN THE 40Ca REGION

The single particle (SP) energies of ⁴¹Ca and the single hole energies of ³⁹Ca are calculated with eigenvalue equation derived from SP Green's function.The matrix element of M-3Y force is adopted as the equivalent of G-matrix element.Two particle one hole (2plh) and two hole one particle (2hlp) multiple scattering (MS) correlation were studied.The results show the 2hlp MS correlation is more important than the 2plh MS correlation.     

A STUDY OF THE ISOSCALAR GIANT RESONANCE IN 40Ca

The strength functions of the isoscalar giant resonance monopole resonance and giant quardropole resonance in ⁴⁰Ca are calculated by coupling the 1p-1h states to 2p-2h states. The results can explain the recent experimental data.     

EFFECT OF MULTIPOLE VIBRATION ON M1 TRANSITION OF 1+ STATES IN 208Pb

In this paper, the generate coordinator method (GCM) is applied to study the effect of multipole vibration on M1 transition of 1⁺ states in ²⁰⁸Pb. The calculation shows that coupling between 3^－ collective state and (1p1h) gives much more effect than the coupling effect of 2⁺ state with (1p1h).     

Study on Deformation and Shape Coexistence for 188Pb

The deformation and shape coexistence in ¹⁸⁸Pb have been investigated in terms of the Projected Shell Model. Comparing the experimental data with the calculated results, it is shown that three shape configurations of sphere (Z=82 shell closure), oblate (two particle-two hole in proton h_9/2 orbital) and prolate (multi-particle-hole)coexist each other in the low-lying excited states and the prolate band exhibits a mixture between two kinds of multi-particle-hole configurations, which means that the neutron i_13/2 alignment happens gradually in this case. The mixing is discussed and the mixing coefficients are given. The oblate band structure is predicted and the 2⁺ prolate state is estimated to be in the energy range of 804—80keV.     

Probability Distribution and Entropy of Nonequilibrium State for 208Pb Nuclei Under Different Excited Energies

The probability distribution and the entropy of ²⁰⁸Pb nuclei under different excited energies are calculated.Comparison is made between the probability distributions and the entropies with time for different excited energies.The result shows that our previous calculation is reasonable.     

Delta Excitation Calculation Studies in Compressed Finite Spherical Nucleus 40Ca

With an oscillator basis, the nuclear Hamiltonian is defined in a no core model space. It consists of an effective nucleon nucleon interaction obtained with Brueckner theory from the Reid soft core interaction, a Coulomb potential, nucleon delta transition potentials, and delta delta interaction terms. By performing spherical Hartree Fock (SHF) calculations with the realistic baryon Hamiltonian, the ground state properties of 40Ca are studied. For an estimate of how the delta degree of freedom is excited, SHF calculations are performed with a radial constraint to compress the nucleus. The delta degree of freedom is gradually populated as the nucleus is compressed. The number of Δ’s is decreased by increasing model space. Large amount of the compressive energy is delivered to create massive Δ in the nucleus. There is a significant reduction in the static compression modulus for RSC static compressions which is reduced by including the Δ excitations. The static compression modulus is decreased significantly by en larging the nucleon model space. The results suggest that inclusion of the delta in the nuclear dynamics could head to a significant softening of the nuclear equation of state.     

Dynamic Model Study of Fusion Reactions for 40,48Ca+90,96Zr

Based on the Improved Quantum Molecular Dynamics Model the fusion reactions of ^40,48Ca+^90,96Zr are studied by making a more rigorous treatment of the initial condition. The study shows that:(1) the calculated fusion cross sections for all four reactions of ^40,48Ca+^90,96Zr are in good agreement with experiment data; (2) the sub-barrier fusion for the neutron-rich reaction ⁴⁰Ca+⁹⁶Zr is ubstantially enhanced as compared with the other three reactions. In order to understand the reason why the sub-barrier fusion of the neutron-rich reaction ⁴⁰Ca+⁹⁶Zr is enhanced as compared with the non-neutron-rich reaction ⁴⁰Ca+⁹⁶Zr and that of the neutron-rich reaction ⁴⁸Ca+⁹⁶Zr is not enhanced, the further investigations are carried out, those are: the dynamic fusion barriers for four reactions, the relation between dynamic fusion barrier and nucleon transfer and the relation between nucleon transfer and corresponding reaction Q value. It has been found that positive Q value leads to the strong nucleon transfer which reduces the dynamic fusion barrier and enhances the sub-barrier fusion cross section.     

12C快中子辐射俘获反应中的共振现象

主要研究中子辐射俘获反应中的共振现象,利用DSD模型计算激发能量在5—25MeV能区的¹²C(n,γ0)反应截面与E_n=9MeV时的角分布.所考虑的反应机制包括复合核俘获、直接和半直接俘获、复弹性和非弹性散射道的辐射俘获.计算表明,矮共振的峰值在激发能量为13MeV处;巨共振的峰值位置在激发能量21MeV处.计算结果与实验符合较好.     

Time-Odd Component and its Influence on the Properties of 41Ca

The triaxial deformed Relativistic Mean Field (RMF) model including the time-odd component is developed. The magnetic potential and baryon current in ⁴¹Ca and their influence on the magnetic moment, single particle level splitting for time reversal states and other properties are investigated in triaxial deformed RMF model with the spatial-component of vector meson fields by using PK1 effective interaction, which includes the self-coupling of σ and ω meson fields as well as the microscopic correction for the center of mass.     

Identification of 208Hg

This paper describes in detail the procedure used in identifing the new neutronrich isotope ²⁰⁸Hg and measuring its half-life. The idetification included two-step chemical separations. The first step was the collection of Hg element products from the irradiated target with a high efficiency and good element selectivity, which was realized by means of an off-line melt Ph target device. The second step was to extract periodically the growing T1 element from the collected Hg sample. In the γspectra of the extracted T1 samples a 2614.6keV γ activity with a half-life of 3min was observed, which may only be assigned to the daughter ²⁰⁸T1 of ²⁰⁸Hg β^－ decay.     

Control of a Cloud of Laser-Cooled 40Ca+ in a Linear Ion Trap

A cloud of laser-cooled ^40Ca^＋ is successfully trapped and manipulated under well control in our home-built linear ion trap, which is designed and constructed solely for studying quantum information processing. By exploring the variation of the ion cloud with respect to the trap parameters, we have optimized the trapping condition and obtained very good fluorescence spectra. We observe the dynamics of the ion cloud, and estimate the temperature of the ion cloud to be of the order of milli-Kelvin.     

11B快中子非弹性散射的理论计算

本文采用直接作用模型和扭曲波玻恩近似（ＤＷＢＡ）理论,计算了１１Ｂ的２．１４ＭｅＶ激发态在入射中子能量为７:５４～２０．０ＭｅＶ的非弹性散射的积分截面和角分布,计算结果与评价的实验值进行了比较,符合较好．对实验上所缺乏的数据作出了理论预期值． BY using the direct reaction mode and the DWBA theory, We calculate the integrated sections and angular distributions of inelastic neutron scattering of 11B(n, n )11B 2. 14MeV excited state in energy range from 7. 54MeV to 20. 0MeV. The calculated results are comparaed with the experimental values, and a good agreement has been obtained. The theory values are given for absent experimental data.     

Cross Section Calculations for Proton-Induced Reaction on 208Pb with Intermediate Energy up to GeV by Using Quantum Molecular Dynamics

The spallation neutron source induced by high energy protron nucleus interaction is an important link for acceralator driven system. The quantum molecular dynamics (QMD) model is applied to analize the high energy proton induced reactions on ²⁰⁸Pb. The QMD simulations of the double differential cross section of ²⁰⁸Pb (p,xn) reactions with incident energies of 590,800 and 1500MeV are in good agreement with the experimental data,and the results of QMD calculations are better than that of HETC and LAHET.     

A Limit of Neutrinoless Double Beta Decay of 48Ca

A search for the neutrinoless double beta decay of ⁴⁸Ca is carried out in a coal mine which is located 512m underground near Beijing.Large scintillation crystals of natural CaF₂ were used as both the detector and the double beta decay source.Result obtained after a total of 7588.5 hours of data taking gives 1.1×10²² years (68%C.L.) as the lower limit of the half-life of the neutrinoless double beta decay of ⁶⁸Ca.