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.     

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.     

β-delayed fission of 228Ac

The basic process of an exotic decay mode namely β-delayed fission is simply introduced. The progress status of the study in the world is essentialized. The observation of β-delayed fission of ²²⁸Ac is reported. The radium was radiochemically separated from natural thorium. Thin Ra sources in which ²²⁸Ac was got through ²²⁸Ra →β^－228Ac were prepared for observing fission fragments from β-delayed fission of ²²⁸Ac. They exposed to the mica fission track detectors, and measured by an HPGe γ-ray detector. The β-delayed fission events of ²²⁸Ac were observed and its β-delayed fission probability was found to be (5±2)×10^－12.     

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.     

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.     

Shape evolution and test of the critical-point symmetry X(5) in 176Os

The lifetimes of excited states in the yrast band of ¹⁷⁶Os have been measured up to I=20h level using the Doppler shift attenuation method. The high-spin states of ¹⁷⁶Os were populated via fusion evaporation reaction ¹⁵²Sm(²⁸Si, 4n)¹⁷⁶Os at a beam energy of 140 MeV. The results support an X(5) structure for ¹⁷⁶Os at low spin. This structure disappears at high spin and shows a symmetry rotor character. The shape change of ¹⁷⁶Os is similar to that of ¹⁷⁸Os.     

A formula used to subtract the effect of gamma-ray of the others to that of measured reaction in measurement of cross section of nuclear reaction and its application

According to the regulation of growing and decay of artificial radioactive nuclide, a formula used to subtract the effect of characteristic γ-ray of the others to that of measured reaction was deduced. And then the cross sections of ¹²⁰Te (n,2n)^119mTe reaction induced by neutrons around 14~MeV were measured by activation relative to the ⁹³Nb (n, 2n) ^92mNb. In the process of the cross sections measured to be calculated, it was subtracted that the effect of characteristic γ-ray of ¹²⁶Te (n, p) ¹²⁶Sb to that of measured ¹²⁰Te (n, 2n) ^119mTe reaction using the formula deduced. The experimental results were (689±37) and (750±41) mb at the neutron energies of (13.5±0.3) and (14.6±0.3)MeV, respectively. Measurements were carried out by γ-detection using a coaxial HPGe detector. As samples, spectroscopically pure tellurium powder has been used. The fast neutrons were produced by the T(d, n)⁴He reaction. The neutron energies in these measurements were determined by the method of cross-section ratios between ⁹⁰Zr (n, 2n) ^89m+gZr and ⁹³Nb (n, 2n) ^92mNb reactions.     

Prompt neutron multiplicity distribution for ~（235）U（n,f） at incident energies up to 20 MeV

For the n+²³⁵U fission reaction, the total excitation energy partition of the fission fragments, the average neutron kinetic energy <ε>(A) and the total average energies E_γ(A) removed by γ rays as a function of fission fragment mass are given at incident energies up to 20 MeV. The prompt neutron multiplicity as a function of the fragment mass, ν(A), for neutron-induced fission of ²³⁵U at different incident neutron energies is calculated. The calculated results are checked with the total average prompt neutron multiplicities ν and compared with the experimental and evaluated data. Some prompt neutron and γ emission mechanisms are discussed.     

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.     

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     

High spin band structure in 139Nd

High-spin states in ¹³⁹Nd nucleus have been reinvestigated with the reaction ¹²⁸Te (¹⁶O, 5n) at a beam energy of 90 MeV. The level scheme has been expanded with spin up to 47/2 h. At the low spin states, the yrast collective structure built on the νh_{11 / 2}^－1 multiplet shows a transitional shape with γ≈32° according to calculations of the triaxial rotor-plus-particle model. Three collective oblate bands with γ~－60° at the high spin states were identified for the first time. A band crossing is observed around hω~0.4 MeV in one oblate band based on the 25/2^－ level.     

Dependence of the cross sections for Ir isotopes on the values of Qgg in the heavy ion collision

¹⁹⁷Au were irradiated with 47 MeV/u ¹²C ions. Iridium was produced via the multinucleon transfer reactions in bombardments of ¹⁹⁷Au with ¹²C. and was separated radiochemically from Au and the mixture of the reaction products. The γ radioactivities of Ir isotopes were measured by using a HPGe detector. The production cross sections of Ir isotopes were determined from activities of Ir isotopes at the end of bombardment and the other relative data. It has been found that the cross sections for neutron-rich isotopes of iridium show an exponential dependence on the values of Q_gg. Our experimental results also demonstrate lack of correlation between the cross sections and Q_gg in the case of neutron-deficient isotopes of iridium. The fact can be explained from that neutron-rich isotopes of iridium were produced in the deep inelastic transfer reactions.     

g-factors measurement of magnetic rotation band in 85Zr

The magnetic-rotational band in ⁸⁵Zr was populated by the fusion-evaporation reaction ⁶⁰Ni(²⁸Si, 2pn)⁸⁵Zr with a 98 MeV Si beam from the HI-13 tandem accelerator at China Institute of Atomic Energy. The g-factors of the high spin states of this magnetic rotation band in ⁸⁵Zr were measured by the TMF-IMPAD method for the first time. The measured g-factors decrease with the increasing of spin. It implies that the valence neutron alignment is more rapid than that of the valence proton, which leads to a decrease of g-factors along the band.     

Calculation of astrophysical reaction rate of 82Ge(n,γ)83Ge

The neutron capture reaction on a neutron-rich near closed-shell nucleus ⁸²Ge may play an important role in the r-process following the fallout from nuclear statistical equilibrium in core-collapse supernovae. By carrying out a DWBA analysis for the experimental angular distribution of ⁸²Ge(d, p)⁸³Ge reaction we obtain the single particle spectroscopic factors, S_2,5/2 and S_0,1/2 for the ground and first excited states of ⁸³Ge=⁸²Ge⊙n, respectively. And then these spectroscopic factors are used to calculate the direct capture cross sections for the ⁸²Ge(n, γ)⁸³Ge reaction at energies of astrophysical interest. The optical potential for neutron scattering on unstable nucleus ⁸²Ge is not known experimentally. We employed a real folding potential which was calculated by using the proper ⁸²Ge density distribution and an effective nucleon-nucleon force DDM3Y. The neutron capture reactions on neutron-rich closed-shell nuclei are expected to be dominated by the direct capture to bound states. We will show that the direct capture rates on these nuclei are sensitive to the structure of the low-lying states.     

Level structure of 159Lu

The high-spin states of ¹⁵⁹Lu were populated by fusion-evaporation reaction ¹⁴⁴Sm (¹⁹F, 4n) with beam energy 106 MeV. A new level scheme was established, which consists of the yrast band with negative parity, the octupole vibration band based on the states and quasipartical band with positive parity. The high spin states of ¹⁵⁹Lu were discussed by systemic characteristics.     

Prompt fission neutron spectra of n+235U above the (n,nf) fission threshold

Calculations of prompt fission neutron spectra (PFNS) from the ²³⁵U(n, f) reaction were performed with a semi-empirical method for E_n=7.0 and 14.7 MeV neutron energies. The total PFNS were obtained as a superposition of (n,xnf) pre-fission neutron spectra and post-fission spectra of neutrons which were evaporated from fission fragments, and these two kinds of spectra were taken as an expression of the evaporation spectrum. The contributions of (n,xnf) fission neutron spectra on the calculated PFNS were discussed. The results show that emission of one or two neutrons in the (n,nf) or (n,2nf) reactions influences the PFNS shape, and the neutron spectra of the (n,xnf) fission-channel are soft compared with the neutron spectra of the (n,f) fission channel. In addition, analysis of the multiple-chance fission component showed that second-chance fission dominates the PFNS with an incident neutron energy of 14.7 MeV whereas first-chance fission dominates the 7 MeV case.     

Study of charmonium(-like) states via ISR at Belle

The cross sections for e⁺e－→π⁺π^－J/ψ, π⁺π^－ψ(2S), K⁺K^－J/ψ, DD, D⁰D^－+π⁺+c.c., D^*D+c.c., and D^*D^* are measured using data sample collected on or near the Υ(4S) resonance with the Belle detector at KEKB. A peak near 4.25GeV/c², corresponding to the so called Y(4260), is observed in π⁺π^－J/ψ final state. In addition, there is another cluster of events at around 4.05GeV/c². Two resonant structures are observed in the π⁺π^－ψ(2S) invariant mass distribution, one at 4361±9±9MeV/c² with a width of 74±15±10MeV/c², and another at 4664±11±5MeV/c² with a width of 48±15± 3MeV/c². The rich structures observed in all these final states indicate that our understanding of the vector charmonium states above the open charm threshold is still poor, let alone the other possible dynamics such as charmonium hybrids or final state re-scattering and so on.     

∧c^＊ in a coupled-channel baryon-meson scattering

Possible structures and properties of some excited states of Λ_c⁺ dynamically generated in the coupled-channel P-wave meson-baryon scattering are studied by solving the Bethe-Salpeter(BS) equation in the framework of the Chiral Unitary Approach. It is shown that both Λ_c⁺(2765) and Λ_c⁺(2940) could be generated dynamically and could be compound states with multi-configuration molecular-like structures. The couplings of the generated states to various reaction channels are also calculated. Moreover, two highly excited states, Λ_c⁺(3024) and Λ_c⁺(3134), are predicted.     

Structure of high spin states in 112In

The high spin states of ¹¹²In have been populated via the ¹¹⁰Pd(⁷Li,5n)¹¹²In reaction with a beam energy of 50 MeV. By analyzing the γ-γ coincidence relations and DCO ratios of γ transitions,A new level scheme of ¹¹²In including seventy-four new gamma transitions and six new bands up to the excitation energy of 6.8 MeV has been presented.     

Reinvestigation of the high spin states in ^（161）Er and enhanced E1 transitions in the N=93 isotones

High-spin states in ¹⁶¹Er have been studied experimentally using the ¹⁵⁰Nd(¹⁶O, 5n) reaction at a beam energy of 86 MeV. The relatively enhanced E1 transitions between the 5/2⁺[642] and 3/2^-[521] bands are observed in ¹⁶¹Er, and the B(E1) values are extracted experimentally. The systematics of the R(E1) values in the N=93 isotones are presented. It is found that the strength of the E1 transitions obviously exhibits angular momentum dependence, and the occurrence of the relatively enhanced E1 transitions could be attributed to octupole softness.