Halo or skin in the excited states of some light mirror nuclei

The properties of three pairs of mirror nuclei ¹³N- ¹³C, ¹⁵N- ¹⁵O and ²¹Na- ²¹Ne (these mirror nuclei are all made of a good inert core plus an unpaired valence nucleon) are investigated by using the nonlinear relativistic mean-field (RMF) theory. It is found that the calculated binding energies with two different parameter sets are very close to the experimental ones for both the ground states and the excited states except for the large deformed nuclei. The calculations show that the 2s_1/2 excited states of ¹⁵N and of ²¹Na are both weakly bound with a proton halo and a proton skin (or a pigmy proton skin), respectively. In addition, the 1d_5/2 excited state of ¹³C and the 2s_1/2 excited state of ¹⁵O are also weakly bound with a neutron skin, respectively. The ratio of the valence nucleon radius to matter radius is deduced and it can be regarded as an additional criterion for the existence of exotic structure. The unbound 2s_1/2 and 1d_5/2 excited states of ¹³N are also discussed.     

Halo nuclei studied by relativistic mean-field approach

Density distributions of light neutron-rich nuclei are studied by using the relativistic mean-field approach. The effective interaction which parameterizes the recent Dirac-Brueckner-Hartree-Fock calculations of nuclear matter is used. The results are discussed and compared with the experimental observations with special reference to theneutron halo in the drip-line nuclei.     

晕核和推广的Glauber理论

简要介绍了中子晕和质子晕研究的最新实验进展,同时,讨论了近年来发展的同位旋,能量有关的具有晕核结构的Glauber理论及它在描述晕核与核散射时的重要性.The development of new experiments for neutron (or proton) halo is briefly described, while the isospin and energy dependence of Glauber theory and its importance in describing halo nuclei-nucleus scattering are discussed.     

Spectra of Halo Nuclei

Based on the self-similar-structure shell model a size resonance model, which includes the size resonance of halo neutron orbit and the correlation size resonance of core surface, is proposed. In terms of the size resonance model the excited spectra and the soft dipole resonances for ¹¹Be and ¹¹li are reproduced.     

Effects of neutron skin on the excitation of isovector modes of neutron-rich nuclei

The existence of a neutron skin in neutron-rich nuclei is discussed in connection with the excitation of isovector dipole and quadrupole giant modes via isoscalar nuclear probes. In the case of large neutron excess, important contributions are obtained from the nuclear excitation, which may even become predominant according to proper kinematical conditions. At variance with the usual situation encountered in inelastic processes, constructive interference can be found between nuclear and Coulomb contributions.     

Exploring nuclear symmetry energy with isospin dependence in neutron skin thickness of nuclei

We propose an alternative way to constrain the density dependence of the symmetry energy from the neutron skin thickness of nuclei which shows a linear relation to both the isospin asymmetry and the nuclear charge with a form of Z^2/3. The relation of the neutron skin thickness to the nuclear charge and isospin asymmetry is systematically studied with the data from antiprotonic atom measurement, and with the extended Thomas-Fermi approach incorporating the Skyrme energy density functional. An obviously linear relationship between the slope parameter L of the nuclear symmetry energy and the isospin asymmetry dependent parameter of the neutron skin thickness can be found, by adopting 70 Skyrme interactions in the calculations. Combining the available experimental data, the constraint of -20 MeV L 82 MeV on the slope parameter of the symmetry energy is obtained. The Skyrme interactions satisfying the constraint are selected.     

质子晕研究的新进展

介绍了质子晕研究在理论和实验方面的最新进展 ,着重讨论了 2 s1 d壳的晕核结构和不同理论模型预示2 6～28P和2 7～ 2 9S中质子晕的存在 ,最近的实验证实了 2 6～ 2 8P核存在一个质子晕.最后简要讨论了质子晕形成的条件. The new progress of proton halo researches in theory and experiment was introduced. Especially the structure of halo nuclei having 2s1d shell and the different models predicting the existence of proton halos in 26～28 P, 27～29 S were discussed. A recent experiment proving the existence of one proton halo in 26～28 P was reviewed and finally the conditions forming proton halo were discussed briefly.     

Long-Range Effective Potential in Halo Nuclei

A way to derive the long range effective potential and the corresponding eigenequation for halo nuclei¹¹ Ll, ¹⁴Be and ¹⁷B is presented by using the equivalent two body method for a three body system. The results agree with both Efimov' s conclusions and experimental data for halo nuclei.     

Proton Elastic Scattering from 14Be and Halo Effects

The elastic scattering ofp-14Be system at Elab = 200 MeV is evaluated within the relativistic impulse approximation. We discuss the effects of the halo neutrons on the three observables of the elastic scattering system,such as differential cross section dσ/dΩ, analyzing power Ay and spin rotation Q. The results of the three observables of the elastic scattering of p-14Be system are compared with those of p-12C and p-16O systems at the same energy as Elab = 200 MeV. We have found that in the small angular region the Ay and Q, as well as dσ/dΩ, are quite sensitive to the nucleon density distributions on the surface of the target nucleus and offer some unique behaviors of halo nuclei.     

Significance of Deuteron Breakup in Halo Transfer

 We discuss the quasi-adiabatic approximations to the three-body wave-function in breakup processes and clarify the assumptions underlying the model. This suggests alternative approximation schemes. Using different theoretical three-body models, calculated angular distributions of differential cross sections for the ¹¹Be(p,d) reaction are presented, for which new preliminary data have been reported at 35 MeV. We show that calculations are sensitive to the inclusion of deuteron breakup and to the breakup model used, particularly if absolute spectroscopic information on the 0⁺ and 2^{+ 10}Be core-state parentages is deduced. There is also considerable sensitivity to the model employed in calculations of the relative cross sections of the two states. Received January 19, 1999; revised April 16, 1999; accepted for publication February 28, 2000     

Efimov Effect in 2-Neutron Halo Nuclei

We provide a brief overview of our theoretical investigations, carried out in recent years, to study Efimov effect in 2-n halo nuclei. The calculations provide the evidence for the occurrence of at least two Efimov states in ²⁰C. These states disappear one by one as the two-body binding energy is increased and show up as asymmetric resonances in the elastic scattering cross section of n–¹⁹C system. The asymmetric nature of the resonances is explained by invoking the mechanism of Fano resonance.     

用QMD模型研究晕核 11 Be+208Pb的熔合机制

通过用QMD模型研究晕核^11Be ^208Pb的近垒熔合反应,发现晕核引起的熔合反应中,并存着两种相互竞争的机制：一方面当入射晕核^11Be靠近靶核时,由于^11Be是弱束缚体系,与靶核的相互作用可使其很容易破裂或少数核子被靶核俘获形成核子转移反应,从而对于熔合表现出压制;另一方面当^11Be的少数中子进入靶核并与靶核相互作用而使得靶核有些激发,而使局部半径增大,导致熔合势垒降低,熔合截面增强。用QMD模型计算出的熔合截面与实验值基本符合,垒附近表现出增强效应。     

超高能核作用中的晕事例

观测能量大于10¹⁵eV的γ族事例,在乳胶室中往往形成晕,给进一步观测超高能核作用的特征带来许多不便.目前只能给出一些粗糙的量来描述晕事例.然而晕事例的内部还有精细的结构,能提供更多的信息.作者对超高能族事例尽可能作逐个簇射测量,并用测量晕的方法进行重复测量,进行比较.并就某些特例作了分析与讨论.     

Halo structure of (14)Be

The two-neutron halo nucleus (14)Be has been investigated in a kinematically complete measurement of the fragments ((12)Be and neutrons) produced in dissociation at 35 MeV/nucleon on C and Pb targets. Two-neutron removal cross sections, neutron angular distributions, and invariant mass spectra were measured, and the contributions from electromagnetic dissociation (EMD) were deduced. Comparison with three-body model calculations suggests that the halo wave function contains a large nu(2s(1/2))(2) admixture. The EMD invariant mass spectrum exhibited enhanced strength near threshold consistent with a nonresonant soft-dipole excitation.     

Entstehung und Eigenschaften des Halo bei Pinch-Plasmen

In pinch discharges a second plasma regime called halo^1,2 outside the central plasma column^1-4 has been observed. This surrounding plasma was investigated in the experiments with the 5.4 m long compression coil in the ISARI linear theta pinch because there it appears highly pronounced. The development of the discharge was observed side-on (stereoscopic) with image converters and a streak camera. It appears possible to resolve the space-time behaviour of the plasma, especially in the dynamic phase of the discharge where the halo shows a filament like structure, by using high-speed color reversal film (streak camera). Furthermore, the smear pictures show that after 6–8 μsec the halo region is frozen into the external magnetic field, that is from this time the halo is characterized by a high electrical conductivity. The boundary layer of the halo follows a magnetic flux tube. The parameters of the halo, such as electron densityn _e (< 10¹⁵ cm^?3), atomic temperatureT _a , and ion temperatureT _i (< 15 eV), were determined spectroscopically as a function of time and location from the broadening of the deuterium Balmer lines. The absolutely measured line intensities do not allow direct calculation of the electron temperature since the excited levels of the investigated Balmer lines are mainly populated from the ground level. By numerical solution of a system of rate equations describing the change of the levels a region for the electron temperature 5<T _e <10eV can be specified. Different mechanisms, such as photoionization, ionization by electron impact in a time varying magnetic field, ionizing collisions of high velocity neutral atoms with neutral gas at rest, transport processes in the plasma across the magnetic field, instabilities which may cause the development of the halo, are discussed by means of the experimental results. It is concluded that the halo region is caused by flute instabilities.