Absorption effects in halo-nucleus core or nucleon stripping reactions

Inclusive halo-nucleus core or nucleon stripping reactions are considered on the basis of a potential three-body model using the eikonal and adiabatic approximations. Clear analytical expressions for the cross sections of these reactions are obtained, and numerical calculations for ¹¹Be halo nucleus are performed. Constituent absorption by the target nucleus substantially influences the integral and differential (with respect to longitudinal momentum) nucleon stripping cross section. It is demonstrated that the differential core stripping cross section contains more complete information on the unperturbed wave function of the halo nucleus.     

Longitudinal momentum distributions in stripping reactions with halo nuclei

Differential cross sections and longitudinal momentum distributions of observed particles are calculated for stripping reactions that result from diffractive interaction between halo nuclei and targets. The applicability of different analytic methods of calculation is considered. The advantages of an improved approximation of small target radius are demonstrated for valent halo nucleon absorption radii of 2–4 fm in describing momentum distributions in particular.     

On some approximations in the theory of halo nucleus reactions

The halo nucleus nucleon stripping reaction on a light target is studied using the diffraction theory of reactions with weakly bound nuclei. An improved version of the approximation of a small target’s radius (compared to the size of a halo nucleus) is formulated. Simple analytical expressions for the differential cross section and the longitudinal momentum distribution of observed particles that allow us to calculate them with good accuracy are obtained.     

Scaling property in one-nucleon removal reactions induced by exotic nuclei

Assuming a core plus valence nucleon structure, one-nucleon removal reaction is investigated within the framework of few-body Glauber theory. Fermi-type distribution is used for the core density, while the wavefunction of the valence nucleon is calculated by solving the single particle eigeuvalue problem of the SchrSdinger equation with the Woods-Saxon potential. The parallel momentum distribution (P//) of the fragments is calculated for isotopes with 3 < Z < 18. A remarkable scaling property is observed from the dependence of the dimensionless quantity R2v/R2c on the full width at half maximum of the parallel momentum distribution (FWHMp//). R2v/R2c is a measure of the exotic extent of the nuclear halo. Based on the obtained scaling law, FWHMp// can be used as an experimental observable to extract R2v/R2c and measure the exoticextent for the nuclear halo.     

Inclusive stripping reaction in the theory of deuteron-nucleus diffraction interaction and the spectator model

The applicability of the spectator model to reactions with weakly bound nuclei is considered by the example of the inclusive proton stripping reaction at deuteron-nucleus diffraction interaction. Analytical methods are used to calculate the integral and differential (with respect to the neutron longitudinal momenta) stripping cross sections. An actual relation is obtained for the effective potentials describing the absorption of each nucleon by the target nucleus in different configuration space regions, which contribute to the stripping cross section.     

Transverse momentum spectra of the produced hadrons at SPS energy and a random walk model

The transverse momentum spectra of the produced hadrons have been compared to a model, which is based on the assumption that a nucleus–nucleus collision is a superposition of isotropically decaying thermal sources at a given freeze-out temperature. The freeze-out temperature in nucleus–nucleus collisions is fixed from the inverse slope of the transverse momentum spectra of hadrons in nucleon–nucleon collision. The successive collisions in thessss nuclear reactions leads to gain in transverse momentum, as the nucleons propagate in the nucleus following a random walk pattern. The average transverse rapidity shift per collision is determined from the nucleon–nucleus collision data. Using this information, we obtain parameter-free result for the transverse momentum distribution of produced hadrons in nucleus–nucleus collisions. It is observed that such a model is able to explain the transverse mass spectra of the produced pions at SPS energies. However, it fails to satisfactorily explain the transverse mass spectra of kaons and protons. This indicates the presence of collective effect which cannot be accounted for, by the initial state collision broadening of transverse momentum of produced hadrons, the basis of random walk model.     

One-neutron knockout from individual single-particle states of 11Be

The structure of the halo nucleus 11Be has been studied using the reaction 9Be(11Be,10Be+gamma)X at 60 MeV/nucleon. The ground state structure of 11Be is determined by comparing the experimental cross sections to a calculation combining spectroscopic factors from the shell model with l-dependent single-particle cross sections obtained in an eikonal model. This experiment shows the dominant 1s single-particle character of the 11Be ground state and indicates a small contribution of 0d admixture in the wave function. After correction for the approximately 22% intensity to excited levels, a clean and precise distribution of parallel momentum for knockout from the 1s halo wave function is obtained for the first time.     

Momentum Distribution of a Fragment and Nucleon Removal Cross Section in the Reaction of Halo Nuclei

Recently the research on the halo structure of drip-line nuclei has shown some interesting properties of the existence of one or more halo nucleons. In the framework of few-body Glauber model, the momentum distribution of a fragment and nucleon removal cross section in the reaction of halo nuclei is presented and extended to nuclei having more than one halo nucleons. The reaction mechanism is treated with and without taking account of the final-state interaction. The wave function of removal halo nucleons in the continuum state is modified by imposing an orthogonal condition to the bound state. An analytical expression of the longitudinal momentum distribution of the fragment is derived when the bound state wave function of halo nucleons is taken as a Gaussian-type function. This is useful in the further investigation on the structure of halo nuclei.     

Momentum Distribution of a Fragment and Nucleon Removal Cross Section in the Reaction of Halo Nuclei

Recently the research on the halo structure of drip-line nuclei has shown some interesting properties of the existence of one or more halo nucleons. In the framework of few-body Glauber model, the momentum distribution of a fragment and nucleon removal cross section in the reaction of halo nuclei is presented and extended to nuclei having more than one halo nucleons. The reaction mechanism is treated with and without taking account of the final-state interaction. The wave function of removal halo nucleons in the continuum state is modified by imposing an orthogonal condition to the bound state. An analytical expression of the longitudinal momentum distribution of the fragment is derived when the bound state wave function of halo nucleons is taken as a Gaussian-type function. This is useful in the further investigation on the structure of halo nuclei.     

Theory of deuteron stripping on doubly even nuclei

Using the method of quantum Green functions we derive a rigorous formula for the deuteron stripping on a doubly even nucleus. Starting from this formula we discuss the distorted-wave Born approximation, some additional assumptions usually made in numerical calculations and the high-energy case. In addition to this we show that the formfactor can be calculated using a model for the nucleon self energy.     

Effects of the HMT on Nucleon Collective Flows within BUU Transport Model

Within the framework of a semiclassical Boltzmann-Uehling-Uhlenbeck(BUU) transport model,the high momentum tail(HMT) effects of nucleon momentum distribution in the nucleus on the nucleon collective Bows are studied in semicentral Au+Au collisions.The HMT due to the isospin-dependent short-range correlations causes a smaller value of the collective Bows.We Bnd that the HMT effects on the nucleon collective Bows are remarkable at beam energy of 300 MeV/nucleon and become weak as the incident beam energy increases.The results indicate that for the collective Bow studies at intermediate energies,the HMT of nucleon momentum distribution in nucleus should be taken into account in transport models.     

On three particle stripping reactions

The formalism for the coupled-channel analysis of stripping reactions of complex nuclear projectiles by nuclei is presented. The general adiabatic approximation is developed. The indirect transitions that are considered are those which arise via intermediate rotational excitations of the target and product nuclei, i.e. the adiabatic approximation for rotational bands is used. At the same time the generalized DWBA procedure is considered for the intrinsic states. Also the antisymmetrization problem is solved. A new method for the calculation of the matrix elements of the (α,n) stripping reaction with finite range effective forces is developed. The method is based on an expansion of the radial functions which describe the relative motion in terms of harmonic oscillator wave functions multiplied by a Gauss one. Effective forces of Gauss type are assumed between the outgoing neutron and each captured nucleon     

伴有靶核核心激发的氘核削裂反应

本文研究了在氘核削裂反应中伴随有靶核核心激发的情况。在这种情况下,假定由于核子-核子剩余相互作用,靶核的组态除了通常壳模型组态外,还混杂有核心激发的组态。同样,剩余核的组态主要是某一种核心激发的组态,但也还混杂有别种组态。在这假定下,给出了所考虑的反应过程的微分截面表示式。它表明,反应截面主要由靶核的组态混合所贡献。一般说来,组态的混合程度不大,故可预期截面数值是较小的。公式还表明,反应角分布的特征峯是由核心在激发后留下来的空穴态的轨道角动量量子数所决定的。这二点结论与这类反应的实验结果是一致的。运用这公式具体估计了六个反应事例的核谱因子,在实验误差内,理论值和从实验的估计值大致相合。     

用中子晕弹核探寻同位旋非对称核物质状态方程

总结和评述了用中子晕弹核探寻同位旋非对称核物质状态方程。 在具有同位旋和动量依赖的同位旋相关量子分子动力学框架内, 采用对比中子晕弹核和相等质量稳定弹核在完全相同入射道条件下物理观测量的差别, 来突出中子晕核明显的同位旋效应和加强物理观测量对于同位旋的灵敏性, 从而提取核物质状态方程。 例如, 与稳定弹核碰撞系统相比, 中子晕弹核明显提高了发射核子的中子\|质子比和增加了它对于对称势的灵敏性, 这两点特征非常有利于提取对称势。 同样, 由于中子晕弹核碰撞系统在低能区（E<60 MeV）由于内部松散结构减弱了核子碰撞力度和动量耗散, 与稳定核碰撞系统相比, 明显提高了原子核阻止; 而在高能区由于两体碰撞同位旋效应的增加, 从而明显提高了原子核阻止。 利用这些特征可以提取核子\|核子碰撞截面的介质效应和同位旋依赖性。 Based on the isospin and momentum dependent quantum molecular dynamics, we use the comparison for the differences between observables in the reactions induced by the halo\|neutron projectile and stable projectile with the same mass under complete same incident channel condition to protrude the isospin effect of halo\|neutron projectile and strengthen the sensitivity of observable on the isospin for extracting the information for the equation of state. For example, the halo\|neutron projectile increases the emitted neutron\|proton ratio and then enhances its sensitivity on the symmetrical potential. Two points above are more favorable than the normal neutron\|rich and neutron\|poor projectiles for extracting the symmetry potential. We also found that the neutron\|halo projectile induces the decrease of nuclear stopping in lower beam energy region and the increase in higher beam energy region, compared to corresponding same mass stable projectile under the same incident channel condition, so that we can use these properties to extract the information for the medium effect and isospin effect of in\|medium nucleon\|nucleon cross section.     

Three-body model for stripping nuclear reactions

A three-body model for the deuteron stripping nuclear reactions is presented. A set of three integral equations is obtained for the wave functions of the three-body problem by introducing a decomposition into angular momentum states into the Lippmann-Schwinger equation. Simple two-particle interactions with separable potentials are used. These separable potentials reduce the three-body problem to the solution of coupled sets of one-dimensional Fredholm integral equations. The angular distributions for²⁸Si(d,p)²⁹Si and⁴⁰Ca(d, p)⁴¹Ca stripping reactions are calculated. From the extracted spectroscopic factors, good agreement with the experimental measurements is obtained.     

Transparency to vector polarization transfer in deuteron stripping reactions

For certain deuteron polarizations, when the spin transfer is pure $\text{s =}\text{1}\text{2}$, it is shown that deuteron stripping reactions are transparent to vector polarization transfer and the outgoing nucleon polarization independent of scattering angle and deuteron energy. With $\text{s =}\text{3}\text{2}$ contributions there is still considerable transparency at the stripping main peak in DWBA calculations.     

Nuclear Halo-Like Phenomena and Short-Range Nuclear Correlation

Based on Glauber Multiple Scattering Theory, high-energy proton elastic scattering on halo-like nucleus ^13C is studied in a single nucleon wave function with low angular momentum configurations. A great agreement with experimental data is obtained and the theoretical prediction clearly shows that 13U has a neutron halo-like structure.Then, the origin and nature of nuclear halo phenomena are explained in terms of nuclear short-range correlations. Our conclnsion shows ttiat the origin of nuclear halo-like phenomena originates from short range nuclear correlation.     

One-neutron stripping reactions of <Superscript>11</Superscript>Be and <Superscript>19</Superscript>C on light target

We have calculated the one-neutron absorption cross-section and the longitudinal momentum distribution of the core fragment coming out from the breakup of ¹¹Be and ¹⁹C on ⁹Be target at 63 MeV/A and 88 MeV/A beam energies respectively. The reaction mechanism is treated within the framework of the eikonal approximation. The effective range of the nuclear interaction between the core and the valence neutron within the projectile has been determined by comparing the predicted stripping cross-section with the recently measured one. The effective range for ¹⁹C has been found to be smaller than that for ¹¹Be. It qualitatively indicates that ¹⁹C is slightly more halo than ¹¹Be. The smaller width, predicted as well as measured, of the LMD of ¹⁸C than ¹⁰Be also strengthens this fact. The experimental data concerning the LMD of core fragments have been well represented.