Neutron scattering from 208Pb

Elastic scattering of 7, 9, 11, 20 and 26 MeV neutrons from ²⁰⁸Pb has been measured with the Ohio University Tandem Van de Graaff accelerator. Standard pulsed beam time-of-flight techniques were employed. Measurements of the incident flux at 0° were used to normalize the differential cross sections. The measured cross sections were corrected for dead time, detector efficiency, flux attenuation, multiple scattering, finite geometry, neutron source anisotropy and compound elastic contribution. Relative uncertainties are estimated to be between 5%–10% and the uncertainty in the normalization is estimated to be less than 5 %. The data were used to obtain neutron optical potential parameters. A comparison with proton optical parameters is presented, and the (p, n) quasi-elastic cross section is calculated and compared with available data. Deformation parameters for the 3^? state (Q = ?2.615 MeV) and 5ā (Q = ?3.198 MeV) in ²⁰⁸Pb were obtained at incident energies of 11 and 26 MeV.     

A model independent technique to determine relative proton strengths of isobaric analog states

The proton ($\text{p}$) decay of the isobaric analog state (IAS) of ²⁰⁸Pb has been observed in coincidence with the IAS neutron from the (p, n) reaction of ²⁰⁸Pb. Such a technique allows an accurate model-independent determination of the relative widths of the $\text{p}$ decay to the first three states of ²⁰⁷Pb, and, in principle, a much more accurate determination of the relative widths than either resonance or non-coincidence $\text{p}$-measurements.     

The 208Pb(n,p)208Tl reaction at En = 97 MeV

Double-differential cross sections of the ²⁰⁸Pb(n,p) reaction have been measured at 97 MeV in the angular range 0°–30° for excitation energies up to 40 MeV. The experimental proton spectra have been compared with calculated spectra obtained with a statistical multistep direct reaction theory, in which charge exchange and inelastic response functions are described microscopically in the quasiparticle random phase approximation. The direct parts of the spectra have also been distributed on different multipole components by using a decomposition technique, based on sample angular distributions calculated within the distorted-wave Born approximation.     

Cross sections and reaction mechanisms of (p,pxn) reactions on 208Pb in the 24–52 MeV range

The cross sections for the reactions ²⁰⁸Pb(p, pn)^207mPb, ²⁰⁸Pb(p, p2n)^206mPb have been measured for 24, 28, 36, 44 and 52 MeV incident protons. The experimental results are shown to be consistent with the clean knockout mechanism for the (p, pn) reaction and with knockout of one neutron followed by evaporation of another for the (p, p2n) reaction. We deduce a theoretical formula for the cross section for these reactions.     

The single-particle characteristics of Pb isotopes near the drip lines calculated within the dispersive optical model

The neutron and proton dispersive optical potential for the ²⁰⁸Pb nucleus has been determined for the energy region from–70 to +60 MeV and used to calculate the differential elastic scattering, the total interaction and reaction cross sections, as well as the single-particle characteristics, the neutron and charge densities, rms radii, and the thickness of the nucleus skin. The calculated results are in good agreement with the experimental data. The proton dispersive optical model potential for the spherical and close to spherical Pb isotopes within the neutron and proton drip lines has been obtained by a similar method. The calculation predicts a trend towards the growth of the proton particle-hole gap, which corresponds to Z = 82 shell closure as Z approaches the proton drip line.     

Scattemng of 14.1 MeV neutrons from 209Bi

Differential cross sections for the elastic and inelastic scattering of 14.1 MeV neutrons from ²⁰⁹Bi have been measured with a time-of-flight system which had an energy resolution of 650 keV. For elastic scattering from ²⁰⁹Bi, an optical-model analysis gave the best-fit potential parameters. The absolute cross sections for excitation of collective (2.66 and 4.36 MeV) states are reproduced by the results of distorted-wave calculations under the assumption of a core (²⁰⁸Pb) excitation model using deformation parameters obtained from (p, p') reactions.     

Proton-hole states in Bi From the Po (t, α) reaction

The ²¹⁰Po(t, α)²⁰⁹Bi reaction has been studied at 20 MeV triton energy with an overall resolution of 20 keV FWHM. Absolute cross sections were established by a comparison of the (t, α) intensities to elastic triton scattering. The three lowest single-proton states in ²⁰⁹Bi were observed and spectroscopic factors were extracted from the measured cross sections by DWBA analysis. Starting at 2.43 MeV, six levels were strongly excited. These states have large 2p-1h proton components. The spectroscopic factors were extracted by a comparison of ²¹⁰Po(t, α) cross sections to ²⁰⁸Pb(t, α)²⁰⁷T1 single-proton-hole cross sections measured previously at the same bombarding energy. The observed states and their properties were analyzed within the framework of the particle- (or hole) vibration coupling model. Surface vibrational states in ²⁰⁸Pb coupled to single protons as well as the proton pair addition modes (states in ²¹⁰Po) coupled to a proton-hole were included in the analysis.     

Neutron scattering from 26Mg

Elastic and inelastic cross sections have been measured for 24 MeV neutrons incident on ²⁶Mg using the time-of-flight technique. These cross sections and existing proton data were analyzed in terms of a Lane-consistent optical potential. Distorted-wave and coupled-channel calculations are presented. Deformation parameters for the first 2⁺ state (1.81 MeV) and the second 2⁺ state (2.94 MeV) derived from both the (n, n') and (p, p') data are used to obtain the ratio of neutron and proton transition matrix elements M_n(E2) and M_p(E2) for these states. Comparison of results for $\text{M}{}_{\mathrm{<mtext>n</mtext>}}\text{(}\text{E}\text{2)}\text{M}{}_{\mathrm{<mtext>p</mtext>}}\text{(}\text{E}\text{2)}$ with those obtained from pion work, from electromagnetic (EM) rates and theoretical evaluations are presented.     

Fusion cross sections for 10,11B+12C at sub-Coulomb energies

Total fusion cross sections for the ¹⁰B + ¹²C and ¹¹B + ¹²C reactions have been determined over a 5 MeV (c.m.) energy range extending to ≈ 3 MeV below the Coulomb barrier. Absolute γ-ray yields for specific transitions in the de-excitation of the heavy products following compound nucleus decay were measured using a Ge(Li) detector. Statistical model calculations of the decay modes of the compound nucleus have been used to deduce, from the γ-ray data, cross sections for single proton, neutron and α-particle emission, and to determine total cross sections for compound nucleus formation. No evidence has been found for sub-Coulomb resonances in either reaction. The total reaction cross sections are compared with optical model calculations using different parameter sets and the observed trend in the very low energy cross sections is discussed relative to other reactions in the same mass region.     

Quantum molecular dynamics approach to estimate spallation yield from<Emphasis Type="Italic">p</Emphasis> +<Superscript>208</Superscript>Pb reaction at 800 MeV

The spallation yield of neutrons and other mass fragments produced in 800 MeV proton induced reaction on²⁰⁸Pb have been calculated in the framework of quantum molecular dynamics (QMD) model. The energy spectra and angular distribution have been calculated. Also, multiplicity distributions of the emitted neutrons and kinetic energy carried away by them have been estimated and compared with the available experimental data. The agreement is satisfactory. A major contribution to the neutron emission comes from statistical decay of the fragments. For mass and charge distributions of spallation products the QMD process gives rise to target-like and projectile-like fragments only.     

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.     

Two-neutron pickup strengths on the even lead isotopes the transition from single-particle to “collective”

The (p, t) reaction on ²⁰⁸Pb, ²⁰⁶Pb, and ²⁰⁴Pb has been studied with 35 MeV protons. It is observed that the L = 0 ground-state cross section rapidly increases as one changes targets from ²⁰⁸Pb to ²⁰⁶Pb to ²⁰⁴Pb while the cross section for other natural-parity transitions decreases. The observed cross sections are compared with predictions of the shell model and the pairing-vibration model. Both models are seen to describe some features of the data.     

Charge-changing cross sections of the neutron-rich isotopes8,9,11Li

Total charge-changing cross sections have been measured for⁸Li on C and Pb targets, for⁹Li on C, Al, Cu, Sn and Pb targets, as well as for¹¹Li on C, Sn and Pb targets at about 80 MeV/nucleon. These data are compared to measured total reaction cross sections and Glauber-type calculations using Hartree-Fock density distributions. These comparisons allow to draw conclusions on the proton density distribution of the neutronrich lithium isotopes. The results show that even for the most exotic nucleus¹¹Li the proton distribution is only very weakly influenced by the long tail in the neutron density distribution already established in several experiments.     

Untersuchung von57Co mit der Reaktion57Fe(p,n)57Co

A neutron time-of-flight investigation of the⁵⁷Fe(p, n)⁵⁷Co reaction performed at bombarding energies of 4.9, 5.6 and 6.2 MeV results in new energy levels of⁵⁷Co. In addition, gamma spectra andn-γ-coincidence spectra were taken to complete the decay scheme of⁵⁷Co up to an excitation energy of 4 MeV.     

Measurement of double-differential (n,xp) cross sections of natural nickel in 14.6 MeV neutron energy

The energy spectra and angular distributions of proton emission in the reaction of ^natNi(n,xp) at neutron energy 14.6 MeV have been measured by the USTC multitelescope system. The double-differential cross sections of 16 reaction angles from 25° to 164.5° have been obtained in this measurement. The statistical error can be reduced because of the thicktarget used. The angular distributions show a slightly energy-dependent forward-backward asymmetry. The angle-integrated proton spectrum is compared with ENDF/B-VI evaluation and Grimes' result. The total p-emission cross section is in fair agreement with prediction and evaluation.     

Theoretical Calculations and Analysis of n+208Pb Reaction for Intermediate Energy Neutron

Based on experimental data of total, nonelastic, elastic cross section and elastic scattering angular distributions for n+Pb reactions, a set of neutron optical model potential parameters is obtained in the region of incident neutron energy from 1—300 MeV. The cross sections, angular distributions and energy spectra are calculated and analyzed by optical model, distorted wave Born approximation theory, Hauser-Feshbach theory, exciton model and cascade mechanism inside nuclear. The results indicate that the cross sections can be given for n+ ²⁰⁸Pb reactions which are all in good agreement with experimental data.     

p+~(58)Ni反应中集体态及转移机制的影响

在p+58Ni反应的理论计算中考虑了集体态和转移反应机制,利用大型程序MEND计算了Ein≤200MeV能区6种轻粒子(n,p,α,d,t及3He)出射的能谱和双微分截面。计算结果与实验数据基本一致;与以前的工作相比,解释了能谱和双微分截面中出现的尖峰,并减小了单粒子态密度修正因子ccg1(v)。     

Angular distributions of photoprotons from 208Pb

Angular distributions of photoprotons following the (e, e′p) reaction in ²⁰⁸Pb have been measured at incident energies of 25.0 MeV and 40.0 MeV. The proton energy distributions were measured at several angles and the angular distributions were obtained for several proton energy ranges. Proton groups at around 11.0 MeV and 15.3 MeV are separated for the angular distributions and the results show almost isotropic distributions, which indicate that these proton groups are emitted through IAR. The angular distributions for other slowly varying parts of the proton spectra proved strongly asymmetrical, indicative of interference between E1 and E2 transition.     

Investigation of states in17F by the15N(3He,n)17F reaction

The absolute differential cross sections for several levels in the¹⁵N(³He,n)¹⁷F reaction were measured at laboratory scattering angles from 0 to 140 degrees using neutron time-of-flight techniques. Angular distributions were obtained at effective helion bombarding energies of 3.8 and 4.8 MeV. A new state was identified at 5.18 ±0.02 MeV excitation energy which is probably the analogue of the 5.217 MeV state in¹⁷O. Spectroscopic factors were obtained for the low-lying states using distorted wave method calculations.     

Angular correlations from 6Li break-up near the Coulomb barrier of 118Sn and 208Pb

Absolute coincidence cross sections for three-particle final states have been measured inplane in the ⁶Li + ¹¹⁸Sn and ⁶Li +²⁰⁸Pb reactions at incident energies of 22.2 and 23.0 MeV, respectively. Most strongly populated is the α + d branch, proceeding sequentially through the first excited state (E_x = 2.18 MeV, J^π = 3⁺) of ⁶Li. The angular distributions are fitted by DWBA calculations including Coulomb interaction in the excitation of the projectile. The main competing reaction channels above and at the Coulomb barrier (¹¹⁸Sn: E/E_c ≈ 1.3; ²⁰⁸Pb: E/E_c ≈ 0.9) are: neutron transfer (⁶Li, αp) and the non-sequential α + d break-up of ⁶Li. The latter spectra are consistent with a quasi-free break-up mechanism. No ³He or tritons have been found in the coincidence spectra, as well as no evidence for a three-particle dissociation of ⁶Li into α + p + n.