Analysis of inelastic scattering of3He on14C at 37.9 MeV

The analogue of the 0⁺ ground state in¹¹⁸Sn has been observed in the compound nucleus¹¹⁸Sb through¹¹⁷Sn(p,nγ)¹¹⁷Sb reaction. The neutron decays of this analogue resonance have been studied from the deexcitingγ-rays of the residual nucleus¹¹⁷Sb. From off resonance excitation functions, spin assignments have been made to states in¹¹⁷Sb, on the basis of Hauser-Feshbach formalism. The resonance parameters of the isobaric analogue resonance have been determined, including the total, proton and neutron decay widths.     

The structure of low-lying states of 60Co

Studies of the neutron stripping reaction ⁵⁹Co(d, p)⁶⁰Co and the proton pickup reaction ⁶¹Ni(d, ³He)⁶⁰Co have been combined to determine the structure of the low-lying states of ⁶⁰Co. A DWBA analysis established values of the transferred orbital angular momentum and spectroscopic factors. In addition L-values were inferred for a number of ⁵⁸Fe(³He, p)⁶⁰Co transitions. The data are qualitatively consistent with a weak coupling picture.     

Microscopic and macroscopic aspects of 135 MeV proton scattering from 16O

Differential cross sections have been measured for the scattering of 135 MeV protons from ¹⁶O and data from the transitions to 13 states (up to 19.5 MeV excitation) have been analysed using microscopic and macroscopic nuclear reaction models. Extensive collective model calculations have been made of the transitions to all natural-parity states. The deformation parameters for the 4p4h rotational band are in good agreement with theoretical models. The inelastic scattering data from the excitation of the negative-parity states have also been analysed in the distorted-wave approximation using microscopic (shell and RPA) models of nuclear structure and with density-dependent two-nucleon t-matrices. For positive-parity states, we report the first shell-model calculation using the complete 2?ω basis space and find that the triplet of 2p2h states (4⁺, 2⁺, 0⁺) around 11 MeV excitation is quite well described by this model, as may be a 1⁺ state which is observed for the first time by proton scattering from ¹⁶O.     

Spatial periphery of lithium and beryllium isotopes

The spatial structure of the periphery of lithium and beryllium isotopes is studied by means of charge-exchange reactions and the (t, p) and (d, p) reactions on their nuclei. It is shown that the 0⁺ isobaric-analog state of ⁶Li at 3.56 MeV has a halo structure formed by a proton and a neutron, that there is virtually no manifestation of a neutron halo in the ground state of the ⁹Li nucleus, and that the ¹¹Li nucleus has a Borromean halo structure that two neutrons form with respect to the ⁹Li core and which manifests itself in cigar and dineutron configurations. The ¹⁰Be nucleus has a substantial two-neutron periphery in either configuration both in the ground and in the 2⁺ excited state at 3.37MeV.     

0+ analogue state in 118Sb from 117Sn(p,nγ) reaction

The analogue of the 0⁺ ground state in ¹¹⁸Sn has been observed in the compound nucleus ¹¹⁸Sb through ¹¹⁷Sn(p,n γ) ¹¹⁷Sb reaction. The neutron decays of this analogue resonance have been studied from the deexciting γ-rays of the residual nucleus ¹¹⁷Sb. From off resonance excitation functions, spin assignments have been made to states in ¹¹⁷Sb, on the basis of Hauser-Feshbach formalism. The resonance parameters of the isobaric analogue resonance have been determined, including the total, proton and neutron decay widths.     

Proton occupation numbers for Ca

The (d, ³He) proton pickup reaction on ⁴⁴Ca has been studied at a deuteron energy of Ed = 19.0 MeV using the Minnesota MP Tandem Van de Graaff. Differential cross sections were measured at forward angles and spectroscopic factors were extracted in the usual fashion for the transitions to five states of ⁴³K. The results are compared with previous proton pickup and stripping reactions on the even Ca isotopes. Only about half of the sd hole state excitation strength observed in the stripping reactions could be found in the pickup from the fp orbitals if the data are analyzed by standard distorted wave calculations. This discrepancy can be removed by using bound state potential radii which are slightly larger for sd orbitals than for fp orbitals.     

Parameters of the <Superscript>64,66,68,70</Superscript>Zn single-particle structure

Populations and energies of neutron subshells in ^{64, 66, 68, 70}Zn and proton subshells in ^{64, 66, 68}Zn are found from the joint evaluation of the data on stripping and pickup reactions and data on spins and parities of nuclear states. The analysis of the thus obtained parameters made it possible to find population features of the nucleon subshells in the nuclei mentioned. A relation between these features and the available data on the first excited 2⁺ states and deformations in this region of nuclei is shown.     

Spatial periphery of lithium isotopes

The spatial structure of lithium isotopes is studied with the aid of the charge-exchange and (t, p) reactions on lithium nuclei. It is shown that an excited isobaric-analog state of ⁶Li (0⁺, 3.56MeV) has a halo structure formed by a proton and a neutron, that, in the ⁹Li nucleus, there is virtually no neutron halo, and that ¹¹Li is a Borromean nucleus formed by a ⁹Li core and a two-neutron halo manifesting itself in cigar-like and dineutron configurations.     

Invariant Mass Spectroscopy of 23O via the (p, p′) Reaction in Inverse Kinematics

The neutron-rich oxygen isotope ²³O has been investigated via proton inelastic scattering on a liquid hydrogen target at 63.5 MeV/nucleon. The invariant mass method in inverse kinematics was employed to reconstruct the energy spectrum. A sharp resonance state was observed at 42(5) keV above the neutron threshold. A comparison of the differential cross section leading to this state with a microscopic DWBA calculation allowed a J ^π assignment of 5/2⁺ for this state.     

Investigation of high spin states in23Na and23Mg and the12C+12C resonance atE c.m.=19.3 MeV

The resonance in the¹²C+¹²C system atE _c.m.=19.3 MeV has been studied in the neutron and proton decay channels. From(p, γ), (n, p) and (n, γ) coincidence measurements high spin states could be localized inA=23 nuclei, in²³Mg up to possibly 21/2⁺. These states were resonantly populated. The present data favorJ ^π=17/2⁺ for the 9.61 MeV state in²³Mg and therefore also for the probable parent state at 9.81 MeV in²³Na. AJ ^π=12⁺ assignment to the resonance is supported and evidence was found that the resonant excitation of the lowest 15/2⁺ and 17/2⁺ states in mass 23 nuclei is caused by a change of the intrinsic structure of the Yrast levels aroundJ ^π=15/2⁺ towards larger deformation.     

近垒重离子熔合反应中的中子转移效应(英文)

近势垒及其以下能区重离子熔合反应中的中子转移耦合道效应是一个复杂且有争议的问题。简要介绍了近年来在中国原子能科学研究院的HI-13串列加速器上,基于静电偏转板装置完成的32S+90,94,96Zr,18O+74Ge和18O+58Ni等几个典型体系的熔合反应研究情况,并结合耦合道理论对实验数据进行了分析。选取反应体系时同时关注了正Q值的中子拾取和削裂道。另外,基于完全耦合道理论计算,提出了一种能够定量提取熔合反应中中子转移效应的自洽方法。这些研究进一步证实了垒下重离子熔合反应中的中子转移效应,同时指出了其复杂性。需要进一步的实验和理论研究来澄清相关核反应机制。The effect of neutron transfers on near-and sub-Coulomb-barrier fusion of heavy-ions is still a complicated and controversial problem. This paper reviews the recent experimental results of the fusion excitation functions of several typical systems, which have been measured by using an electrostatic deflector setup at the HI-13 tandem accelerator of CIAE. Both the neutron pickup and stripping effects were studied. Moreover, a self-consistent method to reliably isolate the transfer effect quantitatively based on the coupledchannels calculation is proposed. These studies give a further support for the neutron transfer effect on sub-barrier fusion of heavy-ions and its complexity. Further experimental and theoretical studies are needed for clarifying the relevant reaction mechanisms.     

Microscopic structure of nuclei from scattering through isobaric analogue resonances

Microscopic nuclear structure information that can be reached by proton scattering through isobaric analogue resonances (IAR) is discussed, mainly within the framework of weak-coupling. The concept of isospin for unbound states is examined. A critical evaluation of the methods for extracting nuclear structure information from the experimental results (such as excitation functions, angular distributions, etc.) is given. The mass regions that are studied in detail are the Pb-region and the N = 82 neutron single-closed shell nuclei. Attention is given to the comparison between weak-coupling calculations and experimental results supporting this concept in many nuclei. Level schemes as well as proton partial decay widths and angular distributions have been calculated and compared with the existing data concerning the proton decay of IAR. The concept of generalized neutron particle-hole (GNPH) state is introduced and its occurence extensively discussed within the Pb-region and N = 82 nuclei.     

Low lying states of 96Tc

The ⁹⁶Mo(p, n) and ⁹⁶Mo(p, nγ) reactions have been studied for proton energies between 3.8 and 5.5 MeV. Energy levels in ⁹⁶Tc up to 632 keV excitation energy have been determined. Possible spin and parity assignments are given for several levels based on the neutron enhancement and angular distributions observed on and off resonance of the $\text{5}\text{2}{}^{\mathrm{>+}}$ isobaric analog state in ⁹⁷Tc, as well as the observed γ-yields. The first excited state reported at 34 keV was found to be a close doublet only 0.8 keV apart. The observation of this doublet in the (p, n) reaction was used to determine the ground state Q-value Q = ? 3.760±0.010 MeV.     

The Zr(d,n)Nb and Zr(d,n)Nb reactions

The (d, n) reaction on ⁹⁰Zr and ⁹⁶Zr has been studied at 12 MeV deuteron bombarding energy using the neutron time-of-flight technique with an overall neutron time resolution of 1.9 ns. Angular distributions of neutron groups leading to states in ⁹¹Nb and ⁹⁷Nb were measured in the angular range between 15° and 60°. The measured cross sections were analyzed in the framework of the distorted-wave theory of stripping reactions to deduce l-values and proton spectroscopic factors of states in the residual nuclei. The results are compared with the corresponding data available from (³He, d) studies. The fractionation of the single-particle proton states and their centroid energies are determined.     

Spin-flip probability in the inelastic scattering of 16.9 MeV neutrons from 12C

The neutron spin-flip probability S(θ) for inelastic scattering of unpolarized 16.9 MeV neutrons to the 4.44 MeV state of ¹²C has been determined by measuring the absolute directional correlation between the scattered neutrons and the subsequent E2 deexcitation γ- radiation emitted perpendicular to the scattering plane. Time-of-flight techniques with carbon recoil detection in a plastic scintillator were used to separate elastically and inelastically scattered neutrons. The neutron spin-flip data were found to be in close agreement with 20.0 MeV proton spin-flip results. Comparison of the measurement is made with the predictions of a microscopic antisymmetrized distorted wave calculation in which the direct reaction mechanism is supplemented by a two step resonance contribution. This theoretical analysis reveals the presence of a strong quadrupole resonance at 20.5 MeV excitation in ¹²C. The results are also influenced to a lesser extent by the E1 giant dipole resonance.     

Sequential emission of neutrons in the reaction16O+64Ni at 7.5–12 MeV per nucleon

Neutron energy and angular distributions have been studied in coincidence with projectilelike fragments (PF) for quasielastic and deeply inelastic collisions of¹⁶O on⁶⁴Ni at 7.5–12 MeV/u bombarding energy. The neutron yield can be explained assuming only two isotropically emitting sources:i) sequential emission from fully accelerated PF andii) evaporation from fully accelerated targetlike fragments (TF). ForZ=6 andZ=8 ejectiles known excited states in¹³C and¹⁷O could be identified. For oxygen, this suggests a direct excitation process,n pickup from the target. No significant evidence for preequilibrium neutron emission was found even at the highest bombarding energy. The TF temperatures and neutron multiplicities are consistent with the assumption that thermal equilibrium was reached during the binary reaction.     

Study of the165Ho(γ,n)164Ho reaction

The spectrum of neutrons following photo-excitation of¹⁶⁵Ho with 8,999 keVγ-rays has been observed. The data indicate a neutron separation energy of 7,987 (2) keV. Eleven excited states are identified, with excitation energies generally in good agreement with those observed in the neutron pickup reaction. Significant discrepancies between observed and theoretical branching are noted.     

Direct processes in the6Li(α, d)8Be reaction

The angular distributions of deuterons from the ⁶Li(α, d)⁸Be reaction corresponding to the 0⁺ ground state and the 2.9 MeV (2⁺) state in⁸Be have been measured at E_α = 17.3, 23.3 and 25.1 MeV. The excitation functions for this reaction have been measured at seven emission angles in the region from 12 up to 25 MeV. The experimental angular distributions are compared with theoretical predictions obtained using DWBA stripping calculations and the plane wave approximation (PWA) for various direct processes. It is shown that the experimental angular distributions can be described throughout the angular region using the simple mechanisms associated with the break-up of the ⁶Li target nuc clusters and heavy-particle stripping. The interference of these processes is taken into account.     

Structure of the 1<Emphasis Type="Italic">d</Emphasis>2<Emphasis Type="Italic">s</Emphasis> Shell from the Data on Single-Nucleon-Transfer Reactions

For the stable silicon isotopes ²⁸Si and ³⁰Si, the energies and occupancies of single-particle states of the 1d2s shell are determined by analyzing the combined data for the nucleon stripping and pickup reactions. From the results of analysis and the available experimental data, the variation of the 1d2s proton-shell structure with increasing neutron number for the silicon isotopes with A = 26–34 is discussed.