K. Murphy

Comparisons of vector analyzing-power data and calculations for neutron-deuteron elastic scattering from 10 to 14 MeV

High-accuracy analyzing-powerAy(θ) data forn-d elastic scattering at 12 MeV have been measured using the polarized-neutron facilities at the Triangle Universities Nuclear Laboratory (TUNL). The present data have been combined with our previousn-d measurements at 10, 12, and 14.1 MeV to form the highest-accuracyAy(θ) data set forn-d elastic scattering below 20 MeV. These data are compared to recent Faddeev-based neutron-deuteron (n-d) calculations which use the Paris and Bonn equivalent separable potentials PEST and BEST, as well as Doleschalls representation of theP- andD-wave nucleon-nucleon interactions. None of these models adequately describe the data in the angular region around the maximum ofAy(θ). Possible reasons for the discrepancies are discussed. The sensitivity of the present Faddeev-based calculations to various angular momentum components of the nucleon-nucleon interaction are examined.

Analyzing power and differential cross section at 9.9, 11.9 and 13.9 MeV for Ca(n, n)Ca

Abstract The analyzing power and differential cross section for elastic neutron scattering from calcium have been measured at 9.9, 11.9 and 13.9 MeV using the 2 H(d, n) 3 He source reaction and neutron time-of-flight (t.o.f.) techniques to detect the scattered neutrons. Polarized neutron beams were produced via the polarization transfer reaction 2 H( d , n ) 3 He at θ = 0°. The data have been corrected for finite geometry and multiple scattering effects. None of the global neutron-nucleus optical model parameter sets usually referred to in the literature reproduces the present cross-section and analyzing power data. Individual as well as energy-averaged fits of the data resulting from new optical model searches are presented. It is shown that the quoted uncertainties of a recent empirical determination of the real part Δ V c of the Coulomb correction term are probably underestimated. Our imaginary Coulomb correction term Δ W c agrees quite well with both a very recent empirical determination and theoretical studies. Although the quality of the fits to the data can be improved by adding l -dependent potentials to the general optical potential, no definite conclusions can be drawn from the present data as to whether or not l -dependent potentials are important in neutron-calcium scattering in the energy range investigated. The data have also been analyzed using a Fourier-Bessel series description of the real central optical potential. Comparing the X 2 values, the experimental data are better reproduced by the Fourier-Bessel method than by our Woods-Saxon optical model analyses. The Fourier-Bessel potentials obtained show strong deviations from the standard Woods-Saxon shape but are in good agreement with calculations using the nuclear structure approach.

Cross-section measurement and Lane model analysis for the 9Be(p,n)9B reaction

Abstract Neutron time-of-flight techniques were used to measure the 9 Be(p, n 0 ) 9 B cross section from 0° to 160°(lab) at 10 energies between 8.15 and 15.68 MeV. The data are combined with previous results below 30 MeV in a Legendre coefficient analysis to evaluate the differential and integral behavior of the 9 Be(p,n) and 9 Be(p, n 0 ) 9 B cross sections. A coupled-channels Lane analysis of cross sections and analyzing powers for (p,n) quasi-elastic scattering and (p, p) and (n, n) elastic scattering is presented and compared to previous single-channel models.

The 15N(p, n)15O reaction below 9.3 MeV

Abstract In connection with studies of differences between the polarization and analyzing power observables for the 15 N(p, n) 15 O reaction, differential cross sections at ten proton energies between 5.5 and 9.3 MeV were measured using time-of-flight techniques. These new measurements allowed all previous data to be evaluated through use of the extensive total cross sections measured by Barnett in a study of the mass-16 system. Although some previous data were clearly discrepant, a simple renormalization of Barnetts measurements results in consistency of most of the data.

The analyzing power for the 2H(d, n)3Heg.s. reaction from 5.5 to 11.5 MeV

Abstract The analyzing power A y ( θ ) for the 2 H(d, n) 3 He g.s. , reaction was measured from 0° to about 150° (c.m.) at 5.5, 7.0, 8.5, 10.0 and 11.5 MeV. The experiment was conducted with a newly developed pulsing and bunching system for the polarized deuteron beam and used standard time-of-flight neutron detection. The present results disagree in some angular regions with measurements of the same observable reported recently by a Zurich group who detected the 3 He particles, but agree with the limited angular distribution measured at 10 MeV by Hilscher and Liers, who also detected 3 He particles. The present results are reported in terms of associated Legendre polynomial expansions of the product σ ( θ ) A y ( θ ).

Measurements of σ(θ) and Ay(θ) for the 9Be(p, n)9B reaction and lane model analysis for the 9Be + nucleon system

Abstract Differential cross sections at 16.44 and 17.57 MeV and analyzing powers at 8.0, 9.1, 11.1, 13.5 and 15.0 MeV have been measured for the 9 Be(p, n 0 ) 9 B reaction and combined with previous measurements for 9 Be(p, p 0 ) 9 Be, 9 Be(p, n 0 ) 9 B and 9 Be(n, n 0 ) 9 Be to form the first model-complete data base for a Lane model analysis. Energy dependences of the model parameters (including Coulomb corrections) have been handled in a consistent manner. The real central part of the isovector Lane model potential exhibits no surface peaking for this nucleus. Strong evidence is found for a complex spin-orbit part of the isovector potential describing nucleon scattering from 9 Be.

The analyzing power for neutron scattering from 9Be at 9 to 17 MeV

Abstract Time-of-flight techniques were used to measure the analyzing power for the scattering of neutrons from 9 Be at energies from 9 to 17 MeV. Because of the high nuclear density of beryllium, particular attention was paid to finite-geometry and multiple-scattering effects. For representing the data, an unusual method of Legendre-coefficient analysis was used to establish the smooth energy dependence of both the cross section σ(θ) and the analyzing power A y ( θ ). Spherical optical-model calculations were able to describe the σ(θ) and A y ( θ ) data simultaneously, but only after the introduction of an imaginary spin-orbit potential W s.o. ( r ). The geometry of the W s.o. ( r ) term was found to be the same as that of the surface-peaked imaginary central potential. Coupledchannels calculations using a quadrupole-deformed rotational model built on the 3 2 − ground state were able to describe inelastic scattering to the 5 2 − and 7 2 − excited states, but also required a W s . o . r potential.

The analyzing power Ay[(θ) for 12C(n, n0,1)12C between 8.9 and] 14.9 MeV neutron energy

Abstract The analyzing power A y ( θ ) for 12 C(n,n) 12 C elastic scattering and for inelastic scattering to the first excited state ( J π = 2 + , Q = −4.44 MeV) of 12 C was measured in the energy range from 8.9 to 14.9 MeV in 1 MeV steps. A pulsed polarized neutron beam was produced via the su2rmH( d , n ) 3 He polarization transfer reaction. Monte Carlo simulations were used to correct the data for finite geometry and multiple scattering effects. The A y data, together with published crosssection data, were analyzed in the framework of the spherical optical model and in the coupled-channels formalism. A good description of the data has been achieved.

Neutron-deuteron elastic scattering and breakup reactions below 20 MeV

Abstract In this paper we review the results of a series of high-accuracy measurements on the neutron-deuteron (n-d) scattering system at incident neutron energies below 20 MeV. These measurements were designed to: 1) provide data of sufficient accuracy to be used to refine the parametrization of the nucleon-nucleon force, 2) to test the reaction dynamics in the “rigorous” calculations of three-nucleon (3N) breakup reactions, and 3) identify 3N scattering observables that are specifically sensitive to three-nucleon forces and/or off-shell effects. At TUNL we have measured vector analyzing powers Ay (θ) for n-d elastic scattering and the breakup reaction to an accuracy better than ± 0.005 and ± 0.020, respectively. Recent results on items 1) and 2) will be presented. Also, results of cross-section measurements for n-d and p-d breakup will be compared to a “rigorous” 3N calculation.

The analyzing power for elastic scattering of 9.9, 11.9 and 13.9 MeV neutrons from Ca

Using the polarization transfer reaction 2H(d↘,n↘)3He at 0° as a source of polarized neutrons, the analyzing power in elastic neutron scattering from Ca has been measured. Optical‐model predictions based on global analyses differ appreciably from our present data. Preliminary optical‐model studies indicate a lower strength and a much smaller diffuseness of the spin‐orbit potential than usually assumed.