Relations between the differential cross sections for diffractive processes of nucleon stripping and halo-nucleus core stripping

A comparative analysis of the nucleon stripping and core stripping reactions induced by a halo nucleus is presented on the basis of certain models for diffractive processes. It follows from calculations for the halo nucleus 11Be that the transverse momentum distribution of nucleons for core stripping (as the longitudinal momentum distribution) is less distorted by absorption in a target than the distribution of core fragments for nucleon stripping. The obtained relations between the cross sections for the stripping reactions simplify interpretation of the calculation results.     

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.     

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.     

The influence of ambiguities in the pion production operator on (p, π+) cross sections

Various aspects of the pionic stripping mechanism for (p, π⁺) reactions are studied in a momentum-space DWBA framework. A Foldy-Wouthuysen nonrelativistic reduction of a pseudoscalar field theory leads to several ambiguities in the pion production operator H′. The extent to which these ambiguities are reflected in the (p, π⁺) differential cross section is studied, for the particular case of 185 MeV protons incident on ¹²C. The results indicate that the O(1/m³) terms (m is the nucleon mass) in the production operator have as important an effect on the differential cross section as the O(1/m²) nucleon recoil term. The freedom of carrying out a further unitary transformation on H′ is found to have a substantially larger effect on the cross section than does the uncertainty associated with the relativistic transformation properties in the external nucleonnucleus potential. The size of these several effects suggests that the DWBA pionic stripping theory in its present form cannot serve as a sensitive probe of nuclear structure. Our results indicate the need for a more consistent relativistic theory of (p, π⁺) reactions.     

恒星能量下核子俘获反应率的晕核效应

恒星能量下俘获截面很难直接测量。¹⁰Be（n，γ）¹¹Be俘获反应涉及到非均匀宇宙大爆炸核合成，无直接测量实验截面数据。利用转移反应¹⁰Be（d，p）¹¹Be的渐近归一化系数（ANC）方法，计算了¹⁰Be（n，γ）¹¹Be俘获反应截面和反应率。¹¹Be是中子晕核。研究表明，在恒星能量下俘获到晕态的截面和反应率显著增大。     

Electron scattering on two-neutron halo nuclei: The case of 6He

The formalism to describe electron scattering reactions on two-neutron halo nuclei is developed. The halo nucleus is described as a three-body system (core +n + n), and the wave function is obtained by solving the Faddeev equations in coordinate space. We discuss elastic and quasielastic scattering using the impulse approximation to describe the reaction mechanism. We apply the method to investigate the case of electron scattering on ⁶He. Spectral functions, response functions, and differential cross sections are calculated for both neutron knockout and α knockout by the electron.     

Elastic scattering of protons from 9Li in inverse kinematics within diffraction theory

The differential cross section for elastic scattering of protons from the ⁹Li nucleus has been calculated within the framework of the Glauber multiple scattering theory. The calculations were carried out with two versions of cluster wave functions for the nucleus obtained within the α-t-2n and ⁷Li-n-n three-body models with realistic potentials of intercluster interactions. The differential cross section was calculated at E = 700 and 60 MeV/nucleon. A comparison with the experimental data allows the conclusion that the wave function in the ⁷Li-n-n model describes the cross section better than in the α-t-2n model.     

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.     

Effect of nuclear-reaction mechanisms on the population of excited nuclear states and isomeric ratios

Experimental data on the cross sections for channels of fusion and transfer reactions induced by beams of radioactive halo nuclei and clustered and stable loosely bound nuclei were analyzed, and the results of this analysis were summarized. The interplay of the excitation of single-particle states in reaction-product nuclei and direct reaction channels was established for transfer reactions. Respective experiments were performed in stable (⁶Li) and radioactive (⁶Не) beams of the DRIBs accelerator complex at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, and in deuteron and ³Не beams of the U-120M cyclotron at the Nuclear Physics Institute, Academy Sciences of Czech Republic (?e? and Prague, Czech Republic). Data on subbarrier and near-barrier fusion reactions involving clustered and loosely bound light nuclei (⁶Li and ³He) can be described quite reliably within simple evaporation models with allowance for different reaction Q-values and couple channels. In reactions involving halo nuclei, their structure manifests itself most strongly in the region of energies below the Coulomb barrier. Neutron transfer occurs with a high probability in the interactions of all loosely bound nuclei with light and heavy stable nuclei at positive Q-values. The cross sections for such reactions and the respective isomeric ratios differ drastically for nucleon stripping and nucleon pickup mechanisms. This is due to the difference in the population probabilities for excited single-particle states.     

Transfer and fusion reactions of unstable nuclei

The transfer and fusion reactions are studied for reactions between a stable and an unstable nucleus with neutron skin, taking as examples the reactions ^16,28O+⁴⁰Ca. The two-dimensional time-dependent Hartree-Fock method is used. It is shown that, in such reactions, the nucleon transfer is enhanced enormously for both protons and neutrons. The neutron skin does not enhance the fusion cross section contrary to the usual expectation.     

Scattering of deuterons by nuclei with breakup effects

The deuteron direct-breakup reaction is explicitly incorporated into the d + nucleus formulation of model K which is a simplified version of the microscopic resonating-group method. By employing the same nucleon-nucleon potential as that used in the corresponding nucleon + nucleus system and by adopting an imaginary potential with a single adjustable parameter to crudely represent other reactions not explicitly included in the formulation, it is shown that a good agreement between calculated and experimental differential cross sections can be obtained for deuteron scattering by a wide variety of target nuclei, ranging from ²⁸Si to ²⁰⁸Pb. In addition, the results also indicate that the deuteron breakup reaction is a significant, but not dominant, reaction in the d + nucleus system. To make model K into a truly microscopic model without any phenomenological imaginary potential, one must further explicitly include the (d, p) and (d, n) one-nucleon-transfer or stripping reactions into the model-K formulation.     

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。     

Breakup Reactions of Drip-Line Nuclei Near N = 20, 28

The one-neutron removal cross section from ²⁹Ne, ^33,35,37Mg, and ^39,41Si on a Pb target have been measured at around 240 MeV/nucleon at the RIBF (RI-Beam Factory) at RIKEN. This main goal of the experiment was to extract the inclusive Coulomb breakup cross sections in order to probe possible halo structures through their enhanced low-energy E1 strengths - so-called soft E1 excitations. The results showed significant enhancement of the one-neutron removal Coulomb breakup cross section for ³⁷Mg. This in turn provides evidence for the existence of halo structure in ³⁷Mg.     

Pion and eta photoproduction in nuclei

We calculate the quasifree photoproduction of pions and eta mesons on nuclei from¹²C to²⁰⁸Pb. Assuming that for the quasifree process the cross sections forπ/η photoproduction on a nucleon in medium are — besides a lowering due to Pauli blocking — identical to those on a free nucleon, we use these as an input. The produced mesons or resonances then propagate through the nucleus where they can undergo several scattering and absorption processes. This final state interaction, which leads to a lowering of the initial meson yield up to 70%, we simulate in a coupled channel Boltzmann-Uehling-Uhlenbeck transport model. It allows us to study in detail the influence of Fermi motion, Pauli blocking and of the additional decay channels for nucleon resonances in medium on the photoproduction cross section. The calculated total and differential cross sections are compared to experimental data and the influence of the different medium effects on the cross sections is discussed in detail.     

Application of the diffraction theory to proton scattering by the 15C nucleus in inverse kinematics

The calculation of the amplitude of proton elastic scattering by unstable neutron-rich nucleus ¹⁵C within the Glauber diffraction theory with the ¹⁵C nucleus wave function in the multiparticle shell model is presented. In optical limit approximation (single scattering), the differential cross section of proton elastic scattering is calculated at energies of 0.2, 0.6, and 1 GeV/nucleon. For an energy of 0.2 GeV/nucleon, the contribution of double scattering, determining the differential cross section at angles exceeding 20° is taken into account. Original Russian Text ? E.T. Ibraeva, A.M. Zhusupov, O. Imambekov, G. Nurbakova, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 6, pp. 892–897.     

核反应总截面和奇异结构研究

本总结了晕和皮等奇异核子结构研究的现状,介绍了发现晕和皮现象的实验证据。然后集中介绍了利用奇异核反应总截面的实验测量和理论模型,从中提取奇异核物质半径,核内核子分布以及介质中的核子－核子碰撞截面等重要信息,我们将特别强调通过实验测量和理论模型之间的联系来研究奇异结构性质。     

Production cross sections of multiply charged fragments in heavy ion interactions at 150–200 MeV/nucleon

A total of 1720 ¹⁶O-emulsion nucleus interactions at 150–200 MeV/nucleon have been investigated. Production cross sections of multiply charged projectile fragments are given. It is found that the cross section for the production of N, C, B and Be projectile fragments in ¹⁶O-nucleus interactions is similar at 0.2 and 2 GeV/nucleon. The fragmentation cross sections for Li and He are larger at 0.2 than at 2 GeV/nucleon.     

Increasing p-p and p-nucleus cross sections

p-Nucleus cross sections are calculated assuming that total p-p cross sections increase with energy. The dependence on the nucleon structure in b-space is examined and it is found that p-nucleus cross sections grow very rapidly with A if the increasing p-p cross section is attributed to an expanding nucleon halo.     

Optical model description of the elastic scattering of 6He from a polarized proton target at 71 MeV/nucleon

The vector analyzing power and differential cross section for the elastic scattering of ⁶He nucleus from polarized protons at 71 MeV/nucleon have been analyzed using the optical model potentials. Different versions of the nuclear potential are constructed using phenomenological potentials and semimicroscopic potentials based upon four different versions of 6He density and three effective nucleon-nucleon interactions. The effects of density dependence and the sensitivity of the cross sections for interactions have been investigated.     

Nucleon transfer reactions to rotational states induced by206, 208Pb projectiles

In a systematic study of nucleon transfer reactions accompanied by Coulomb excitation we have bombarded¹⁵²Sm,¹⁶⁰Gd and²³²Th with^{206, 208}pb beams at incident energies close to the Coulomb barrier. Particle-gamma coincidence techniques were used to identify excited states of reaction products populated through inelastic scattering and in nucleon transfer reactions. One-neutron stripping and pick-up reactions on¹⁵²Sm were observed leading to known states of the rotation alignedi _13/2-bands in¹⁵³Sm and¹⁵¹Sm. In the¹⁶⁰Gd+^{206, 208}Pb systems no significant population of low lying states of product nuclei was found in the nucleon-transfer channels. Large cross sections were observed for one- and two-neutron pick-up from²³²Th at an incident energy of 6.4 MeV/u. Around the grazing angle they are of the same order of magnitude as the cross section measured for inelastic scattering. The results are analyzed in the framework of semiclassical models.