[en] We present measurements of n–d analyzing power, $A_y(\mathrm{\theta <!--\; ??\; -->})$, at E_n = 21.0 MeV. The experiment produces neutrons via the ²H($\stackrel{\to <!--\; ???\; -->}{d}$, $\stackrel{\to <!--\; ???\; -->}{n}$)³He reaction and uses a deuterated liquid-scintillator center detector and six pairs of liquid-scintillator neutron side detectors. Elastic neutron scattering events are identified by using time-of-flight techniques and by setting a gate in the center-detector pulse-height spectrum. Beam polarization is monitored by using a high-pressure helium gas scintillator. The n–d $A_y(\mathrm{\theta <!--\; ??\; -->})$ data at 21.0 MeV show a significant discrepancy with the results of rigorous three-body calculations and are consistent with data taken previously by us at 19.0 and 22.5 MeV. We review the overall energy dependence of the three-nucleon analyzing power puzzle in neutron–deuteron elastic scattering, using the best data available. We find that the relative difference between calculations and data is nearly constant at 25% up to E_n = 22.5 MeV. (paper)

[en] We present new corrections for the polarization-dependent efficiency (PDE), which introduces a false asymmetry into measurements of n-p analyzing power A_y(θ) caused by double scattering in the neutron side detectors. To accomplish this, we created a new database of ¹²C(n-vector,n) A_y(θ) by using a combination of fits to data, phase-shift analysis, and R-matrix analysis. Our recorrection for PDE of previously reported n-p A_y(θ) data at 7.6 and 12.0 MeV and new data at 7.6 MeV indicate that we have achieved a superior representation of ¹²C(n-vector,n). Our results continue to suggest a possible charge dependence of the pion-nucleon coupling constant.

[en] Measurements of neutron-deuteron (n-d) analyzing power A_y(θ) at E_n=19.0 MeV are reported at 16 angles from θ_c.m.=46.7 to 152.0 deg. The objective of the experiment is to better characterize the discrepancies between n-d data and the predictions of three-nucleon calculations for neutron energies above 16.0 MeV. The experiment used a shielded neutron source, which produced polarized neutrons via the ²H(d-vector,n-vector)³He reaction, a deuterated liquid scintillator center detector (CD) and liquid-scintillator neutron side detectors. A coincidence between the CD and the side detectors isolated the elastic-scattering events. The CD pulse height spectrum associated with each side detector was sorted by using pulse-shape discrimination, time-of-flight techniques, and by removing accidental coincidences. A Monte Carlo computer simulation of the experiment accounted for effects due to finite geometry, multiple scattering, and CD edge effects. The resulting high-precision data (with absolute uncertainties ranging from 0.0022 to 0.0132) have a somewhat lower discrepancy with the predictions of three-body calculations, as compared to those found at lower energies.

[en] Differential scattering cross-section data have been measured at 43 angles from 11 deg. to 160 deg. for 37-MeV neutrons incident on ²⁰⁹Bi. The primary motivation for the measurements is to address the scarcity of neutron scattering data above 30 MeV and to improve the accuracy of optical-model predictions at medium neutron energies. The high-statistics measurements were conducted at the China Institute of Atomic Energy using the ³H(d,n)⁴He reaction as the neutron source, a pulsed deuteron beam, and time-of-flight (TOF) techniques. Within the resolution of the TOF spectrometer, the measurements included inelastic scattering components. The sum of elastic and inelastic scattering cross sections was computed in joint optical-model and distorted-wave Born approximation calculations under the assumption of the weak particle-core coupling. The results challenge predictions from well-established spherical optical potentials. Good agreement between data and calculations is achieved at 37 MeV provided that the balance between surface and volume absorption in a recent successful model [A. J. Koning and J. P. Delaroche, Nucl. Phys. A 713, 231 (2003)] is modified, thus suggesting the need for global optical-model improvements at medium neutron energies.

[en] Data for σ(θ) and A_y(θ) previously obtained at the Triangle Universities Nuclear Laboratory for ¹²⁰Sn(n, n) are combined with other measurements of σ(θ) and A_y(θ) to create an elastic-scattering database from 9.9 to 24 MeV. In addition, relatively recent high-accuracy measurements of the neutron total cross section σ_T for Sn from 5 to 80 MeV are combined with earlier σ_T data to form a detailed σ_T database from 0.24 to 80 MeV. All of these data are analysed in the framework of a dispersive optical model (DOM). The DOM is extended to negative energies to investigate properties of single-particle and single-hole bound states. The DOM also is used in calculations of compound-nucleus contributions to σ(θ), so that DOM predictions can be compared to σ(θ) measurements. Excellent agreement is obtained for the entire set of scattering data from 0.4 to 24 MeV, and for σ_T values from 0.05 to 80 MeV. Calculations of bound-state quantities are compared to values derived from experiment for energies down to -15 MeV. Reasonable agreement for the binding energies is achieved, while the predicted spectroscopic factors disagree somewhat with the values found in stripping and pickup experiments. Finally, the DOM is modified to investigate two features (volume absorption that is asymmetric about the Fermi energy and zero absorption in the vicinity of the Fermi energy) that have been ignored in many DOM models. These modifications have little effect on the agreement of the calculations with the scattering data or with the bound-state quantities