β-delayed neutron decay of 21N

The β-delayed neutron and γ spectra of neutron-rich nucleus ²¹N using β-γ and β-n coincidence measurements were presented in this paper. Thirteen new neutron groups ranging from 0.28 MeV to 4.98 MeV and with a total branching ratio 88.7±4.2% were observed. One γ transition among the excited states of ²¹O, and four γ transitions among the excited states of ²⁰O were identified in the β decay chain of ²¹N. The ungated half-life of 83.8±2.1 ms was also determined for ²¹N.     

The β Decay of 21N

The β-delayed neutron and γ energy spectra taken from the decay of neutron-rich nucleus ²¹N were measured by using the β-γ and β-n coincidence detection method. Thirteen new neutron groups ranging from 0.28MeV to 4.98MeV and with a total branching ratio of 88.7±4.2% were observed andpresented. One γ transition with an energy of 1222keV emitted from the excited state of ²¹O, and four γ transitions with energies of 1674, 2397, 2780, and 3175keV emitted from the excited states of ²⁰O were identified in the β decay chain of ²¹N. The β decay half-life for ²¹N is determined to be 82.9±1.9ms. The uncertainty of half-life is much smaller than the previous result.     

The neutron halo structure of 17B studied with the relativistic Hartree-Bogoliubov theory

The properties of neutron-rich boron isotopes are studied in the relativistic continuum Hartree-Bogoliubov theory in coordinate space with NL-SH, PK1 and TM2 effective interactions. Pairing corrections are taken into account by a density dependent force of zero range. The binding energies calculated for these nuclei agree with the experimental data quite well. The neutron-rich nucleus ¹⁷B has been predicted to have a two-neutron halo structure in its ground state. The halo structure of ¹⁷B is reproduced in a self-consistent way, and this halo is shown to be formed by the valence neutron level 2_s1/2.     

Configuration of the valence neutrons of 17B

The reaction cross section of ¹⁷B on ¹²C target at (43.7±2.4)MeV/u has been measured at the Radioactive Ion Beam Line in Lanzhou (RIBLL). The root-mean-square matter radius (R_rms) was deduced to be (2.92±0.10)fm, while the R_rms of the core and the valence neutron distribution are 2.28fm and 5.98fm respectively. Assuming a ``core plus 2n' structure in ¹⁷B, the mixed configuration of (2s_1/2) and (1d_5/2) of the valence neutrons is studied and the     

Study of Borromean halo nuclei by the neutron wall with simulation

The model of three-body Borromean halo nuclei breakup was described by using standard phase space distributions and the Monte Carlo simulation method was established to resolve the detection problem of two neutrons produced from breakup reaction on the neutron wall detector. For ⁶He case,overall resolution σE_k for the Gaussian part of the detector response and the detection efficiency including solid angle acceptance with regard to the excitation energy E_k are obtained by the simulation of two neutrons from ⁶He breakup into the neutron wall. The effects of the algorithm on the angular and energy correlations of the fragments are briefly discussed.     

Isospin and mixed symmetry structure in 24Mg

The interacting boson model with isospin (IBM-3) has been used to study the isospin excitation states and electromagnetic transitions for ²⁴Mg nucleus. The mixed symmetry states at low spin are also analyzed. The theoretical calculations are in agreement with experimental data. The present calculations indicate that the 3₁⁺ state is the lowest mixed symmetry state.     

Cross section of reaction 181Ta(p,nγ)181W and the influence of the spin cut-off parameter on the cross section

In this work, the program Cindy was modified to calculate the formation cross section of each energy level of residual nucleus ¹⁸¹W resulting from the reaction ¹⁸¹Ta(p,nγ)¹⁸¹W. The concerned cross sections calculated at proton energy E_p=4.5-8.5 MeV agreed well with experimental results. The influence of the spin cut-off parameter in the energy level density model on the cross section was studied. The obtained results show that the influence of spin cut-off is obvious for lower energy levels.     

Calculation of prompt fission neutron spectra for 235U(n,f)

The prompt fission neutron spectra for the neutron-induced fission of ²³⁵U at E_n < 5 MeV are calculated using nuclear evaporation theory with a semi-empirical model, in which the nonconstant and constant temperatures related to the Fermi gas model are taken into account. The calculated prompt fission neutron spectra reproduce the experimental data well. For the n(thermal)+²³⁵U reaction, the average nuclear temperature of the fission fragment, and the probability distribution of the nuclear temperature, are discussed and compared with the Los Alamos model. The energy carried away by γ rays emitted from each fragment is also obtained and the results are in good agreement with the existing experimental data.     

Quantitative conditions for the formation of p-wave neutron halos

With the experimental binding energies and configurations, the root-mean-square radii of p-wave valence neutron distributions for nuclei up to the second p-shell have been calculated in the framework of the single-particle potential model. By analyzing the relations between the radii and the binding energies, the scaling laws of p-wave valence neutron distributions are obtained. The quantitative conditions for the formation of p-wave neutron halos are deduced from these scaling laws. Based on the investigation on the probability of finding the valence nucleon outside the range of the interaction potential, a 2p_3/2 halo state in ⁴⁷S is anticipated for the first time. These obtained results might provide reference for searching for p-wave neutron halos in nuclei up to the second p-shell.     

New high spin level scheme of 87Sr

High spin states of the odd-A ⁸⁷Sr were populated by the fusion-evaporation reaction ⁸²Se(⁹Be, 4n) ⁸⁷Sr at a beam energy of 46 MeV. Excited levels of ⁸⁷Sr have been extended up to an excitation energy of 7.4 MeV at spin 31/2ħ. The coupling of a g_9/2 neutron hole to the yrast states of the ⁸⁸Sr core can account for the low-lying states in ⁸⁷Sr. The structure of the higher spin states is discussed by analogy with those of the neighboring odd-A N=49 isotones and possible configurations are proposed.     

Electromagnetic transition properties and isospin excitation in the cross-conjugate nuclei 44Ti and 52Fe

The interacting boson model with isospin (IBM-3) is applied to study the band structure and electromagnetic transition properties of the low-lying states in the cross-conjugate nuclei ⁴⁴Ti and ⁵²Fe. The isospin excitation states with T=0, 1 and 2 are identified and compared with available data. The E2 and M1 matrix elements for the low-lying states have been investigated. According to this study, the 2₃⁺ state is the lowest mixed symmetry state in the cross-conjugate nuclei ⁴⁴Ti and ⁵²Fe. The excitation energy of the second 0₂⁺ and 2₂⁺ states with T=0 in the nucleus ⁵²Fe are identified. The agreement between the model calculations and data is reasonably good.     

Fore-aft asymmetry of the 2H(n,γ)3H at very low energies

We have used the recent effective field theory (EFT) which is constructed from two-and three-nucleon interactions, using minimal substitution in the momentum dependence of these interactions. We present the calculations of the fore-aft asymmetry of γ-rays in the reaction ²H(n,γ)³H which are based on EFT up to next-to-next-to leading order (N²LO). The results are compared with the recently reported calculations and measurements of the fore-aft asymmetry of γ-rays from neutron-deuteron radiative capture. The calculated fore-aft asymmetry of the nd radiative capture process above deuteron breakup threshold is in good agreement with the available experimental data up to 20 MeV.     

Theoretical investigation of the structure of 19N

We have employed the shell model and Skyrme-Hartree-Fock methods to investigate the structure of the neutron-rich nucleus ¹⁹N. The level scheme of ¹⁹N from the shell-model calculation with the WBT interaction is displayed. The potential-energy-surface calculation with the SGII interaction implies that ¹⁹N should be a deformed nucleus. The theoretical β-decay half life of ¹⁹N reproduces well the available experimental data.     

Triaxial deformation in 104Rh of the chiral doublet bands

Triaxial relativistic mean field (RMF) approaches are used to study the properties of ¹⁰⁴Rh. The existence of multiple chiral doublets is suggested for ¹⁰⁴Rh based on the triaxial deformations and their corresponding proton and neutron configurations.     

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.     

A new probe of neutron skin thickness

The correlation between neutron-to-proton yield ratio (R_np) and neutron skin thickness (δ_np) in neutron-rich projectile induced reactions is investigated within the framework of the Isospin-Dependent Quantum Molecular Dynamics (IQMD) model. The density distribution of the Droplet model is embedded in the initialization of the neutron and proton densities in the present IQMD model. By adjusting the diffuseness parameter of neutron density in the Droplet model for the projectile, the relationship between the neutron skin thickness and the corresponding R_np is obtained. The results show strong linear correlation between R_np and δ_np for neutron-rich Ca and Ni isotopes. It is suggested that R_np may be used as an experimental observable to extract δ_np for neutron-rich nuclei, which is very interesting in the study of the nuclear structure of exotic nuclei, the equation of state (EOS) of asymmetric nuclear matter and neutron-rich matter in astrophysics, etc.     

Uncertainty study of DS-(D-)→γlν (l=e,μ) decays determined by wave function

Wave function is important for determining decay constants f_DS^- and f_D^-. Using the 5 types of D meson wave functions in the heavy quark limit, we studied the uncertainties of radiative pure-leptonic decays of D_S^-(D^-) mesons. The branching ratios are (1.025390—1.706812) × 10^-5 and (0.953498—1.576725) × 10^-6 for D_S^- and D^- decays, respectively, which are sensitive to the type of wave function.     

Pure annihilation type decays B0→Ds- K2+ and Bs→Da2 in perturbative QCD approach

We calculate the branching ratios of pure annihilation type decays B⁰→D_s^- K₂^*+ and B_s→Da₂ using the perturbative QCD approach based on k_T factorization. The branching ratios are predicted to be (60.6_{-16.5-10.4-2.1}^{+17.3+4.3+3.2} )× 10^-6 for B⁰→D_s^- K₂^*+, (1.1_-0.4-0.2-0.1^+0.4+0.1+0.1)×10^-6 for B_s→D⁰a₂⁰ and (2.3_-0.8-0.4-0.1^+0.8+0.2+0.1)×10^-6 for B_s→D^-a₂⁺. They are large enough to be measured in the ongoing experiment. Due to the shortage of contributions from penguin operators, there are no direct CP asymmetries for these decays in the Standard Model. We also derive simple relations among these decay channels to reduce theoretical uncertainties for the experiments to test the accuracy of theory and search of new physics signal.     

Nuclear uncertainties in the s-process simulation

The heavy elements in the Universe are formed during the s- and r-processes mainly in AGB stars and supernovae, respectively. Simulation of s- and r-nucleosynthesis critically depends on the neutron capture and weak decay rates for all the nuclei on the reaction chain. The present work analyzes systematically the neutron capture rates (cross sections) for the s-process nuclei, including ～3000 rates on ～200 nuclei. The network calculations for the constant temperature s-process have been performed using the different data sets selected as the nuclear inputs to investigate the uncertainties in the predicted s-abundances. We show that the available cross sections of neutron capture on many s-process nuclei still carry large uncertainties, which lead to low accuracy in the determination of s-process isotope abundances. We analyze the neutron capture cross section data for the same unique isobar nucleus accorded by year from previous work. Such an analysis indicates that the s-process has been studied for more than fifty years and there exist two research stages around 1976 and 2002, respectively. The needs and opportunities for future experiments and theoretical tools are highlighted to remove the existing shortcomings in the neutron capture rates.     

Rotational properties in even-even superheavy 254-258Rf nuclei based on total-Routhian-surface calculations

High-spin yrast structures of even-even superheavy nuclei ^254-258Rf are investigated by means of total-Routhian-surface approach in three-dimensional (β₂, γ, β₄) space. The behavior in the moments of inertia of ²⁵⁶Rf is well reproduced by our calculations, which is attributed to the j_15/2 neutron rotation-alignment. The competition between the rotationally aligned i_13/2 proton and j_15/2 neutron may occur to a large extent in ²⁵⁶Rf. High-spin predictions are also made for its neighboring isotopes ^254,258Rf, showing that the alignment of the j_15/2 neutron pair is more favored than that of the i_13/2 proton pair.