Search

A program of systematic measurement and analysis of differential cross sections and vector analyzing powers for (n,n), (p,n) and (p,p) reactions at energies below 16 MeV for a wide range of target nuclei is underway at Triangle Universities Nuclear Laboratory.

The analyzing power Ay(θ) for 12C(n↘,n0,1)12C has been measure between 9 and 16.8 MeV incident neutron energy using the polarization transfer reaction 2H(d↘,n↘)3He. The pulsed and polarized deuteron beam of the TUNL polarized ion source was used in conjunction with conventional neutron time‐of‐flight detection techniques. The data are intended to test reaction models and to enable multiple scattering corrections to be determined for previously obtained high precision n‐p scattering data.

The use of the newly developed pulsed polarized deuteron beam for obtaining (d,n) analyzing power data was investigated. Results are given for the 2H(d,n)3He reaction between 5.5 and 11.5 MeV.

The various theoretical and experimental results for comparisons between the polarization and analyzing power in (p,n) reactions are summarized. Such differences are due to isospin symmetry breaking by the Coulomb interaction and have been observed in selected cases.

The transverse polarization transfer coefficient Ky′(0°) has been measured for the 15N(p↘,n↘)15O reaction from 12.5 to 16.5 MeV using a novel technique. The observed values lie between +0.2 and −0.2 except for one point of +0.4 at 14 MeV.

Cross sections and analyzing powers have been measured for 58N(n,n) and 208Pb(n,n) at 10 MeV. Multiple‐scattering corrections are discussed. Comparisons are made to optical‐model calculations for 58Ni and to earlier data for 208Pb.

Lane model analyses of (p,p), (n,n), and (p,n) data, especially analyzing powers, can provide new constraints on the nuclear symmetry potential. Previous work on the symmetry spin‐orbit potential is reviewed, and future directions of study are outlined.

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.

Analyzing powers have been measured between 9 and 15 MeV for neutron scattering to the ground and 2.43‐MeV (5/2−) states of 9Be. The Ay(θ) data vary smoothly with energy. Results at 10 MeV are compared to a Lane optical‐model prediction and coupled‐channel predictions.

Techniques for (p,n) analyzing power measurements using recoil spectrum stripping and neutron time‐of‐flight have been developed. Results are discussed in terms of the 9Be(p,n0)9B reaction.

The average neutron polarization of the reaction 2H(d↘,n↘)3He has been measured in about 3° steps up to θ=20°(lab) in order to investigate the suitability of the reaction as a source of polarized neutrons for cases where the scatterer is close to the 2H target. It is shown that the ‘‘effective’’ neutron polarization (average polarization when the spin is flipped at the polarized ion source) is constant for angles between 0° and 10°.

Polarized neutrons have been scattered from 54Fe and 65Cu at 10 MeV. Analyzing powers and cross sections have been fitted with an optical model. The spin‐orbit term has a well depth of about 6 MeV, a radius parameter of 1.1 fm, and a diffuseness of 0.5 to 0.6 fm. The need for an imaginary spin‐orbit term is indicated. A need is shown for a volume absorptive term in addition to the usual surface term.

Neutron time‐of‐flight techniques have been used to measure analyzing powers for the reactions 9Be(p,n)9B, 11B(p,no)11C, 13C(p,no)13N, and 15N(p,no)15O between 7 and 17 MeV. The results show systematic behavior similar to that of Lane model predictions.

Analyzing powers have been measured for the 11B(p,no)11C reaction at 8.56 MeV and for the 13C(p,no)13N reaction at 6.88 and 8.00 MeV. Comparisons are made to earlier measurements of the polarization, and differences are discussed in terms of current theoretical results.