Neutron-proton transfer reactions leading toT=1 particle-hole states of56Co

Zero range DWBA analysis for two-particle (neutron and proton) transfer reactions is carried out, using simple shell model structure wave functions for⁵⁴Fe,⁵⁶Co and⁵⁸Ni, with⁵⁶Ni inert core. In this structure calculation, a microscopic set of two-body interaction matrix elements derived from the non-local separable potential of Tabakin are employed. These matrix elements include in the perturbation theory two corrections (i) the second-order Börn term and (ii) the appropriate core excitations. Unlike the situation in many two-particle transfer reactions, the fragmentation of the reaction strengths to the excited states with respect to the lowest states of same spin and parity in the above transfer processes is satisfactorily borne out from this analysis.     

Interfering proton and neutron transfer in the reaction C(N, N)C

Elastic scattering and one-nucleon transfer reactions induced by ¹⁶O have been investigated in the energy region 45–60 MeV on targets of ²⁶Mg, ²⁷Al, ³⁰Si and ⁴⁸Ca. Angular distributions were measured in the angular range 4°–40°. Optical model parameters were derived from the elastic scattering data and the transfer reaction data were analysed using both no-recoil and full-recoil DWBA codes. In the case of proton transfer reactions on ⁴⁸Ca, good agreement was obtained between the data and the DWBA calculations while the data for the lighter targets could not be satisfactorily reproduced. The oscillatory pattern of the angular distributions is discussed in terms of the three-parameter model of Kahana, and it is found that the model qualitatively explains the observed transition from smooth to oscillatory angular distributions.     

Determination of the neutron electric form factor from the reaction 3 He(e,e'n) at medium momentum transfer

The electric form factor of the neutron G_En has been determined in double polarized exclusive ³ He(e,e'n) scattering in quasi–elastic kinematics by measuring asymmetries A _⊥, A _∥ of the cross section with respect to helicity reversal of the electron, with the nuclear spin being oriented perpendicular to the momentum transfer q in case of A_⊥ and parallel in case of A_∥. The experiment was performed at the 855 MeV c. w. microtron MAMI at Mainz. The degree of polarization of the electron beam and of the gaseous ³ He target were each about 50%. Scattered electrons and neutrons were detected in coincidence by detector arrays covering large solid angles. Quasi–elastic scattering events were reconstructed from the measured electron scattering angles ϑ_e, φ_e and the neutron momentum vector p _n ^′ in the plane wave impulse approximation. We obtain the result <G _En>_{(0.27 < Q2c2/GeV2 < 0.5)}= 0.0334 ± 0.0033_stat± 0.0028_syst which is averaged over the indicated range of Q ², the squared momentum transfer. This G _En value is significantly smaller than measured from the D(e,e'n) reaction under similar kinematical conditions. To what extent final state interactions in ³He quench the G _En result is subject of calculations currently in progress elsewhere. Received: 29 April 1999     

Observation of the reaction products formed in the interaction of 3.65 A GeV O ions with thick copper target at wide angles

Experiments have been carried out to study the ‘heavy fragments’ emitted at wide angles in the interaction of 3.65 A GeV ¹⁶O ions with a thick Cu target, using a stack of CR-39 track detectors. Diametric distribution in a stack registering ¹⁶O-beam halo are compared with diameters observed in a stack placed downstream at an angle of 25°. There is a strong indication that the heavy fragments are scattered at large angles.     

Calculation of the wide-angle neutron spectra from the ~9Be(d,xn) reaction in a thick beryllium target

The multi-layer computing model is developed to calculate wide-angle neutron spectra, in the range from0° to 180° with a 5° step, produced by bombarding a thick beryllium target with deuterons. The double-differential cross-sections(DDCSs) for the ~9 Be(d, xn) reaction are calculated using the TALYS-1.8 code. They are in agreement with the experimental data, and are much better than the PHITS-JQMD/GEM results at 15°, 30°, 45° and 60° neutron emission angles for deuteron energy of 10.0 MeV. In the TALYS-1.8 code, neutron contributions from direct reactions(break-up, stripping and knock-out reactions) are controlled by adjustable parameters, which describe the basic characteristics of typical direct reactions and control the relative intensity and the position of the ridgy hillock at the tail of DDCSs. It is found that the typical calculated wide-angle neutron spectra for different neutron emission angles and neutron angular distributions agree quite well with the experimental data for 13.5 MeV deuterons. The multi-layer computing model can reproduce the experimental data reasonably well by optimizing the adjustable parameters in the TALYS-1.8 code. Given the good agreement with the experimental data, the multi-layer computing model could provide better predictions of wide-angle neutron energy spectra, neutron angular distributions and neutron yields for the ~9 Be(d, xn) reaction neutron source.     

The radial distribution of the 1f72 neutron in 41Ca from the 40Ca(13C, 12C)41Ca reaction

The reaction ⁴⁰Ca(¹³C, ¹²C)⁴¹Ca leading to the ground and low-lying $\text{3}\text{2}$^? levels has been studied at bombarding energies of 18.5 and 19.0 MeV, close to the Coulomb barrier. The cross sections have been analysed using the DWBA with previously measured calibrations to obtain the rms radii of 1f_{$\text{7}\text{2}$} and 2p_{$\text{3}\text{2}$} orbits in the ⁴¹Ca levels. The rms radius of the 1f_{$\text{7}\text{2}$} point neutron orbit in the ground state relative to the ⁴⁰Ca core was determined to be 3.89 ± 0.12 fm. This is compared with various theoretical predictions based on Hartree-Fock theory. The 1f_{$\text{7}\text{2}$} orbit radius gives the point neutron excess size to a good approximation for comparison with the value of 3.45 fm deduced from Coulomb energy differences. The consistency of the results with ⁴⁰Ca(t, d)⁴¹Ca experiments using a (t/d), zero-range normalization of 3.26 × 10⁴ MeV² · fm³ is demonstrated, and trends in neutron size parameters through the Ca isotopes are discussed.     

Levels of 188os populated in the 189Os(d,t)188Os reaction and in the decay of 41h 188Ir

The 0 level structure of ¹⁸⁸Os has been investigated by the ¹⁸⁹Os(d, t)¹⁸⁸Os reaction using a broad range magnetic spectrograph, and the properties of the ¹⁸⁸Os levels populated in the decay of ¹⁸⁸Ir have been re-examined. The (d, t) results yield new information about the location of two-neutron excitations in ¹⁸⁸Os involving the $\text{3}\text{2}$[512] orbital. Since the ¹⁸⁸Os ground state contains admixtures of both $\text{K =}\text{3}\text{2}\text{and}\text{K =}\text{1}\text{2}$ character, cross-section formulae for single-neutron transfer from a target state which is not pure in K are considered, and it is found that rather small $\text{K =}\text{1}\text{2}$ admixtures in the ¹⁸⁹Os ground state give rise to striking interference effects, which are manifested in the experimental (d, t) cross sections into the members of the ¹⁸⁸Os ground state band. The consequences of the mixed character of the target state on the (d, t) population of members of the K^π = 2⁺ γ-vibration and of higher-lying two-quasiparticle bands are also discussed.     

SU(6)破缺效应对核子形状因子的贡献

最近杰斐逊实验室测量了中子的两个弹性电磁形状因子之比GEn/GMn,它反映了中子内部的电磁分布并能帮助理解中子的内部结构.传统的相对论组分夸克模型在解释质子的两种电磁形状因子之比GEp/GMp是很成功的,但在解释中子的该比值时计算值比实验值要低.为了解释这种现象,我们在相对论组分夸克模型框架下计算考察了SU(6)破缺效应的贡献.发现考虑该破缺效应后的计算结果同实验符合有明显改善.     

基于准弹性中子散射谱分析水化硅酸钙(C-S-H)中受限水的动态

研究水化硅酸钙(C-S-H)中受限水动态的一种重要手段是准弹性中子散射(quasi-elastic neutron scattering, QENS)实验. C-S-H样品的QENS谱数据可通过跳跃扩散和转动扩散模型进行分析拟合, 进而导出C-S-H样品微纳孔中水动态的相关物理参数: 不动水指数C、转动扩散系数D_r、均方位移< u² >、自扩散系数D_t及平均停留时间τ₀. 本文对水与水泥质量比为30%的C-S-H样品, 测量温度为230-280 K的QENS谱进行了分析, 得到的拟合参数可定量描述C-S-H样品内不同尺度的微纳孔中受限水随温度变化的动态过程. 转动扩散系数D_r随散射矢量Q的变化可知, Q值较大时, 水分子的转动对QENS谱影响较大. 均方位移 < u² > 随Q值的不同而变化, 其拟合值可区分C-S-H样品中的不动水、强受限水和受限水. 在Q较小时, D_t 和τ₀ 的拟合值随温度而变化, 并分别在230和240 K突然增大, 由此揭示温度为230-240 K 时, C-S-H 样品中受限水分子的动态特性发生了转变.     

The astrophysical S-factor of the reaction 7Be (p, γ)8B in the direct capture model

The astrophysical S-factor for the reaction ⁷Be(p, γ)⁸B up to an energy of 2 MeV (c.m.) and the capture cross section of ⁷Li(n,γ)⁸Li up to 1 MeV (c.m.) are calculated using the Direct Capture model (DC). Both calculations are in good agreement with experimental data.     

Role of cross-shell excitations in the reaction 54Fe($$ \vec d $$, p)55Fe

The reaction ⁵⁴Fe(, p)⁵⁵Fe was studied at the Munich Q3D spectrograph with a 14MeV polarized deuteron beam. Excitation energies, angular distributions and analyzing powers were measured for 39 states up to 4.5MeV excitation energy. Spin and parity assignments were made and spectroscopic factors deduced by comparison to DWBA calculations. The results were compared to predictions by large-scale shell model calculations in the full pf -shell and it was found that reasonable agreement for energies and spectroscopic factors below 2.5MeV could only be obtained if up to 6 particles were allowed to be excited from the f _7/2 orbital into p _3/2 , f _5/2 , and p _1/2 orbitals across the N = 28 gap. For levels above 2.5MeV the experimental strength distribution was found to be significantly more fragmented than predicted by the shell model calculations.     

A study of the proton resonant property in 22Mg by elastic scattering of 21Na + p and its astrophysical implication in the 18Ne(α, p)21Na reaction rate

Proton resonances in ²²Mg have been investigated by the resonant elastic scattering of ²¹ Na + p . The ²¹Na beam with a mean energy of 4.00 MeV/nucleon was separated by the CNS radioactive-ion-beam separator (CRIB) and bombarded a thick ( CH_{2 n} target. The energy spectra of recoiled protons were measured at scattering angles of θ_c.m. ≈ 172^° , 146^° , respectively. Several excited states observed before have been confirmed including two states (at 6.616, 6.796 MeV) observed at TRIUMF. A new state at 7.06 MeV has been observed, and another new one at 7.28 MeV is tentatively identified due to its low statistics. The proton resonant parameters were deduced from an R -matrix analysis of the differential cross-section data with a SAMMY-M6-BETA code. The astrophysical implication for the ¹⁸ Ne(α, p)²¹ Na reaction has been briefly discussed.     

Analysis of prompt fission neutron spectrum and multiplicity for 237Np（n,f） in the frame of multi-modal Los Alamos model

The improved version of Los Alamos model with the multi-modal fission approach is used to analyse the prompt fission neutron spectrum and multiplicity for the neutron-induced fission of 237Np. The spectra of neutrons emitted from fragments for the three most dominant fission modes (standard Ⅰ, standard Ⅱ and superlong) are calculated separately and the total spectrum is synthesized. The multi-modal parameters contained in the spectrum model are determined on the basis of experimental data of fission fragment mass distributions. The calculated total prompt fission neutron spectrum and multiplicity are better agreement with the experimental data than those obtained from the conventional treatment of the Los Alamos model.     

Analysis of alpha-cluster transfer in O + C and C + O at energies near Coulomb barrier

The aim of this work is to track the phenomenon of α-cluster transfer mechanism at low energies 1.25, 1.5 and 1.75 MeV/n, close to the Coulomb barrier energy for ¹²C(¹⁶O, ¹²C)¹⁶O and ¹⁶O(¹²C, ¹⁶O)¹²C nuclear systems. The measurements of the angular distribution show a significant increase in the differential cross section at large angles due to alpha-transfer mechanism. The optical model code SPI-GENOA could be used effectively for fitting the experimental data with the theoretical predictions nearly up to angle 90°, where the differential cross section decreases steadily with increasing the scattering angle. For the second hemisphere, at angles greater than 100°, there is a large increase in cross section due to the contribution of α-transfer mechanism, and the Distorted Wave Born Approximation (DWBA) method could be used effectively for fitting the experimental data with the theoretical predictions at this region using (DWUCK5) code.