R. C. Byrd

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.

Comparison of analyzing power and polarization in the reaction 3H(p, n)3He: (II). New polarization results below 4 MeV

Abstract The polarization P y for the 3 H(p, n) 3 He reaction was measured for energies between 2 and 4 MeV. Special care was given to minimizing the effects of background and to interpreting the experimental spectra. The new values for P y are significantly higher than previous values, and comparison to the available data for the analyzing power A y for the same reaction now shows that in this energy range P y and A y are equal within experimental uncertainties. This equality negates earlier conclusions that sizeable differences existed between these observables. In particular, our new results demonstrate that in this reaction the effects of charge symmetry breaking on differences between these observables must be small.

The analyzing power Aγ(θ) for the elastic scattering of 12 MeV neutrons from deuterons

Abstract The analyzing power Aγ(θ) was obtained at 10° intervals between 30° (lab) to 120° (lab) for 2H(n, n)2H at 12.0 MeV. The polarized neutron beam employed in the measurement was obtained by using neutrons emitted at 0° from the polarization transfer reaction 2 H ( d , n ) 3 He . The accuracy in the Aγ(θ) values that was achieved ranged from ± 0.006 to ± 0.013. Comparison of the data to Aγ(θ) results obtained at 12 MeV for the charge symmetric reaction 2H(p, p)2H shows that the two Aγ(θ) distributions are equal to within the above accuracy.

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.

Self-Consistent Application of the Lane Model

The Lane model has been an appealing and successful technique for coupling the (p, p), (n, n), and (p,n) channels in a single calculation. However, detailed description has been more difficult with the additional constraints of fitting either all three channels or the (p, n) analyzing power. In our attempts to examine the ability of the Lane model to describe a complete set of data using a new search code, we find that consistent application of the model leads us to choose an approach which we believe to be more fundamental than those usually employed in similar calculations. In this paper we will review the more significant aspects and applications of the Lane model and indicate the developments which led us to our resent position. We include an application of the model to the Be(N,N) system, for which a fairly complete set of data has been obtained at our laboratory.

Polarization Observables in (p,n) Reactions

In (p, n) reactions, three parameters have been measured that involve polarized incident proton beams, polarized outgoing neutron beams, or both. The present paper will review the data that have been obtained and the conclusions that have been based on that data. The discussion will be limited to experiments blow 30 MeV and therefore will ignore some of the earliest work, that is, the measurements performed at the Rutherford Laboratory with 30 to 200 MeV polarized proton beams. With the advent of polarized proton beams at the Indiana cyclotron, one would expect that this intermediate energy range soon will be active again.