Proton Halo or Skin in the Excited States of Light Nuclei

Properties of nuclei 13,15,N and 9B are investigated in the relativistic mean-field theory with NLz and NL3 force parameters.The calculated binding energies are very close to the experimental ones.The calculations show that the first excited state (1p1/2) in 9B,the first excited state (2s1/2)in 13 N and the second excited state(2s1/2) in 15N are weakly bound .In particular,for 13N and 15N,the proton density distributions in the two above excited states have a long tail and the rms radii of the last proton are greatly larger compared with their respective matter radii.It is predicted that a proton halo exists in the first excited state of 13N and in the second excited state of 15N,respectively.It also indicates that the first excited state in 9B is a proton skin state.     

Neutron halos in the excited states for N=127 isotones

Properties of the ground states and the excited states of N=127 isotones are investigated by using the nonlinear relativistic mean field theory with the interactions PK1. By analyzing the rms of proton and neutron, the single particle energies of valence nucleon and the density distributions of neutron, proton and the last neutron, it can be found that there exists a neutron halo in the excited states of 3d5/2, 4s1/2 and 3d3/2 in 209Pb. It is also predicted that there exists a neutron halo in the excited states of 3d5/2, 4s1/2 and 3d3/2 in 207Hg, 208Tl, 210Bi and 211Po.     

Neutron halos in the excited states for N=127 isotones

Properties of the ground states and the excited states of N=127 isotones are investigated by using the nonlinear relativistic mean field theory with the interactions PK1. By analyzing the rms of proton and neutron, the single particle energies of valence nucleon and the density distributions of neutron, proton and the last neutron, it can be found that there exists a neutron halo in the excited states of 3d5/2, 4s1/2 and 3d3/2 in ²⁰⁹Pb. It is also predicted that there exists a neutron halo in the excited states of 3d5/2, 4s1/2 and 3d3/2 in ²⁰⁷Hg, ²⁰⁸Tl, ²¹⁰Bi and ²¹¹Po.     

Density effect of the neutron halo nucleus induced reactions in intermediate energy heavy ion collisions

Using an isospin-dependent quantum molecular dynamics (IQMD) model, we study the 15C induced reactions from 30-120 MeV/nucleon systematically. Here the valence neutron of 15C is assigned at both 1d5/2 and 2s1/2 states respectively in order to study the density effect of reaction mechanism. It is believed that the existent neutron halo structure at the 2s1/2 state of 15C will affect the light particle emission evidently. In our calculation, the different density distributions of 15C at two states are calculated by relativistic mean field (RMF) model and introduced in the initiation of IQMD model, respectively. It is found that some observables such as emission fragmentation multiplicity, emission neutron/proton ratio and emission neutrons’ kinetic energy spectrum are sensitive to the initial density distribution.     

Theoretical Analysis of the Exotic Structure of ^17F

The first excited state and the ground state of ^17F are studied with the asymptotic normalization coefficient method. The results show that the probabilities of the last proton being out of the binding-potential in both the states are P = 59.71% and P = 27.61%, respectively. This means that the last nucleon in both the states of ^17F is far-extended beyond the range of nuclear force, especially in the first excited state. This result is also verified by the calculation of the density distributions of the last proton in ^17F. It is quantitatively confirmed that the first excited state of^1TF is a nuclear halo state and its ground state is a proton skin state.     

N=127同中子核素激发态的RMF理论研究

在球形相对论平均场模型下,采用PK1和NL3相互作用, 对N=127同中子核素的基态和低激发态进行了研究,获得了价核子的激发能及中子、 质子和最后一个中子的密度分布, 指出209Pb的3d_5/2,4s_1/2和3d_3/2激发态可能存在一个中子晕结构,207Hg,208Tl,210Bi和211Po的3d5/2,4s_1/2及3d_3/2激发态也可能存在一个中子晕结构。Properties of the ground state and the excited states in N=127 isotones are investigated with relativistic mean field theory with　 the interactions PK1 and　 NL3. By analyzing the rms of proton and neutron, the single particle levels of valence nucleon and the density distributions of neutron, proton and the last neutron, it can be found that there exists a neutron halo in the excited states of 3d_5/2,4s_1/2 and 3d_3/2. It is also predicted that there exists 　a neutron halo in the excited states of 3d_5/2,4s_1/2 and 3d_3/2 in 207Hg,208Tl,210Bi and 211Po.     

Density effect of the neutron halo nucleus induced reactions in intermediate energy heavy ion collisions

Using an isospin-dependent quantum molecular dynamics (IQMD) model, we study the ¹⁵C induced reactions from 30—120 MeV/nucleon systematically. Here the valence neutron of ¹⁵C is assigned at both 1d 5/2 and 2s 1/2 states respectively in order to study the density effect of reaction mechanism. It is believed that the existent neutron halo structure at the 2s 1/2 state of ¹⁵C will affect the light particle emission evidently. In our calculation, the different density distributions of ¹⁵C at two states are calculated by relativistic mean field (RMF) model and introduced in the initiation of IQMD model, respectively. It is found that some observables such as emission fragmentation multiplicity, emission neutron/proton ratio and emission neutrons' kinetic energy spectrum are sensitive to the initial density distribution.     

Structures of ^17F and ^17O, ^17Ne and ^17N in the Ground State and the First Excited State

The structures of two couples of mirror nuclei ^17F and ^17O, ^17Ne and ^17N in the ground state and in the first excited state are investigated using the relativistic mean-field approach. Two-proton halo in ^17Ne in the first excited state and in the ground state and two-neutron halo in ^17N in the first excited state are suggested.Meanwhile, one-proton halo in ^17F in the first excited state and one-neutron halo in ^17O in the first excited state are also suggested. The skin structure appears in ^17F and ^17N in the ground state.     

Isospin effect of the in-medium nucleon-nucleon cross section in excited nuclear reactions

Using relativistic mean field theory, the neutron and the proton density distribution of 56Ni nuclei could be obtained in the ground state and the excited state. Based on the framework of the quantum molecular dynamics model, the 56Ni nuclei have been simulated in ground state and in the neutron or proton excited state. We then used the three different states of 56Ni to collide with the 56Ni in the ground state. To discuss the evolution of the nuclear stopping in different reactions, two kinds of different excited nuclear reactions were studied at different reaction energies and at different impact parameters. Studies have shown that the nuclear stopping of an excited nuclear reaction is sensitive to the isospin-dependent in-medium nucleon-nucleon cross section, compared with the response value of the ground state nuclear reaction. So, it is better for the excited nuclei to extract the isospin dependence of nucleon-nucleon cross section information.     

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.     

Proton halo in the <Superscript>13</Superscript>N nucleus

We demonstrate that the radii of excited nuclear states can be estimated using the (³He, t) charge-exchange reaction and relying on the modified diffraction model. The radius of the N excited state with an excitation energy of E*=2.73 MeV, which lies in a continuous spectrum, is determined. The radius of this state proves to be close to that of the mirror 3.09-MeV state of the ¹³С nucleus, which possesses a neutron halo but lies in a discrete spectrum. Thereby, we demonstrate that the 2.37-MeV state of the ¹³N nucleus has a proton halo. The analysis is based on published measurements of differential cross sections for relevant reactions.     

13N的一个可能的类晕的质子2p态

假设¹³N是单粒子的2p态的结构,用Glauber多重散射理论计算了1GeV的质子在¹³N上弹性散射的微分截面,研究了¹³N的类晕结构.与¹³C的情况不同,虽然目前还没有关于p-¹³N弹性散射微分截面的实验材料与我们的理论结果相比较,但是这个理论结果可以作为对未来的实验测量工作的一个指导,特别是对兰州近代物理研究所的晕核实验研究工作有参考和指导价值.参照先前我们对¹³C晕核结构的理论预言和进而的实验证实,本文的计算结果清楚地表明:¹³N可能存在着一个类晕的质子皮结构.因此,实验上测量p-¹³N弹性散射的微分截面就是当前需要马上进行的一个实验研究工作.     

Two-body and three-body halo nuclei

We have extracted the nuclear asymptotic normalization coefficients (ANC) for the virtual transitions B→A+N via some transfer reactions and the radioactive nuclear beam experiments. With these coefficients, root-mean-square (rms) radii for the valence particle in some possible halo nuclei have been calculated. The values of rms radii extracted with ANC approach are nearly model-independent, hence are a good quantity for the investigation of nuclear halo. In addition, we have also calculated the rms radii for the two valence neutrons in some three-body systems in terms of the relationship between the radii of valence particle, core nucleus and nuclear matter. With two conditions for nuclear halo formation, we have examined these extracted rms radii. The results show that 11Be(1/2+, g.s), 12B(1-, 2.621 MeV), 13C(1/2+, 3.089 MeV), 14C(0-, 6.903 MeV), 14C(1-, 6.094 MeV), 15C(1/2+, g.s) and 19C(1/2+, g.s) with the valence particle in the 2s ground or excited state are the neutron halo nuclei, whereas 17F(1/2+, 0.495 MeV) and 21Na(1/2+, 2.423 MeV) are the proton halo nuclei in the excited state. For three-body systems, except the well-established two-neutron halo nuclei 6He and 11Li, 14Be and 17B might be the two-neutron halo nuclei as well.     

天然丰度的N-磷酰化氨基酸的15N NMR 研究

采用¹⁵N-¹H的2D HSQC、HMBC实验方法,测定了天然丰度的N-磷酰化氨基酸样品在溶液中的¹⁵N化学位移δ_N及偶合常数J_N-P,J_N-H. 实验表明：对于¹⁵N天然丰度样品,这是一种快速有效的实验方法. 研究发现：N-酰化后的氨基酸,其δ_N以及与氮原子直接相连的质子¹H的化学位移均发生十分明显的高场位移,而偶合常数¹J_N-P,¹J_N-H的变化与化合物构型相关联 .     

Use of (<Superscript>3</Superscript>He, <Emphasis Type="Italic">t</Emphasis>) charge-exchange reactions in determining radii of excited states of nuclei

A method for determining the radii of excited states of nuclei by means of (³He, t) charge-exchange reactions was proposed. Two versions of a comparison of differential cross sections for (³He, t) reactions were considered. The first relies on a comparison with cross sections for inelastic-scattering processes leading to the formation of isobaric analog states, while the second involves (³He, t) reactions leading to the production of the ground state. The two versions in question yield similar results and make it possible to determine the radius of the first excited state of the ¹³N nucleus. This state has the excitation energy of E* = 2.37 MeV, lying above the proton-emission threshold. The resulting radius proved to be enhanced in relation to the ground state and is close to the radius of the 3.09-MeV isobaric analog state of the ¹³С nucleus, which has a neutron halo. This permitted drawing the conclusion that the ¹³N nucleus in the 2.37-MeV state has a proton halo. The possibility of revealing a proton halo in other states of light nuclei is considered.     

Radii of the bound states in 16N from the asymptotic normalization coefficients

The asymptotic normalization coefficients (ANCs) of the virtual decay ¹⁶N→¹⁵N+n are extracted from the ¹⁵N(⁷Li, ⁶Li)¹⁶N reaction populating the ground and first three excited states in ¹⁶N. The root-mean-square (rms) radii of the valence neutron in these four low-lying ¹⁶N states are then derived by using the ANCs. The probabilities of the valence neutron staying out of the core potentials are found to be 31%±8%, 58%±12%, 32%±8%, and 60%±12%. The present results support the conclusion that a one-neutron halo may be formed in the ¹⁶N first and third excited states, while the ground and second excited states do not have a one-neutron halo structure. However, the core excitation effect has a strong influence on the one-neutron halo structure of the ground and first excited states in ¹⁶N.