F.D. Brooks

Polarization in neutron-proton scattering at 16.4 and 21.6 MeV

Abstract The polarization in neutron-proton scattering was studied using polarized neutron beams obtained from the 3 H(d, n) reaction, scattering these beams in monocrystalline anthracene scintillators and observing the asymmetry of the associated recoil protons. The technique used is a new one which utilizes the direction dependence of the scintillation properties in order to determine the left-right asymmetry of the proton recoils within the scintillation crystal. The measurements led to polarization values at neutron c.m. scattering angles from 90° to 150° at 16.4 MeV and from 50° to 170° at 21.6 MeV, in 20° steps in both cases. The Δ LS P and Δ LS D spin-orbit splitting phase parameters derived from the measurements are: 0.52°±0.06° and 0.02°±0.05° respectively at 16.4 MeV; and 0.93°±0.04° and 0.11°±0.02° respectively at 21.6 MeV. The data are compared with the predictions of the Yale-Buffalo and Livermore phase parameter fits.

Neutron capture cross sections of Cr, Mn, Ni, Nb, Ag, In, Sb and Au in the 8 to 120 keV region

Abstract Moxon-Rae detectors were used to measure ratios of the radiative capture cross section of elemental Cr, Mn, Ni, Nb, Ag, Sb and Au to that of In for neutrons of energy 8 to 120 keV. Relative capture cross sections of In for 8 to 30 keV neutrons were also measured. These were converted to absolute cross sections by using the In capture cross sections determined by Gibbons et al . The data were analysed to determine p-wave strength functions for Nb, Ag, Sb and Au, and average radiation widths for Cr, Mn and Ni.

Angular distribution of neutrons from 2H(γ, n)1H at Eγ = 2.75 MeV

Abstract The angular distribution of neutrons from deuteron photodisintegration by 2.75 MeV gamma rays was measured at six laboratory angles between 30° and 135°. The dipole cross section ratio derived from the measurements, σ m σ e = 0.290±0.021 , is consistent with theoretical calculations which include contributions from meson-exchange currents and isobar configurations.

Differential cross section for n-p radiative capture at En = 63.4 MeV

Abstract The angular distribution of photons from n-p radiative capture of 63.4 MeV neutrons has been measured. Data taken at eight n- γ laboratory angles (45°–150°) were transformed to deuteron photodisintegration cross sections at the equivalent laboratory energy, E γ = 33.9 MeV, and analysed in combination with independent measurements of the 0° and 180° cross sections. Legendre polynomial coefficients obtained from the analysis are consistent with values reported from global fits and deviate marginally from predictions based on the Bonn and Paris potentials.

Analyzing power in neutron-proton scattering at 21.6 MeV

Abstract The analyzing power in neutron-proton elastic scattering at 21.6 MeV was measured using polarized neutrons from the 3H(d, n )4He reaction. The results agree with recent measurements and with revised earlier data in the vicinity of 22 MeV. The combined data give ΔPLLS = (0.847 ±0.019)° and ΔDLS = (0.100±0.008)° and are consistent with predictions made from the Paris potential.

Excitation of the analogue dipole state in 28Al via the reaction 28Si(n, p) 28Al

Abstract Cross sections and proton spectra have been measured at lab angles θ = 0° (15°) 60° for the reaction 28 Si(n, p) 28 Al at 21.6 MeV incident energy. The spectra show enhancements which correspond both in position and in magnitude with the excitation of the analogue of the giant dipole state in 28 Si.

Inelastic scattering of neutrons to the 59 keV level of 127I

Abstract The excitation of the 59 keV level of 127I by neutron inelastic scattering was studied using a small NaI scintillation crystal as both target and detector. Measurements were carried out in the incident neutron energy range 50–500 keV, and the neutron flux incident on the crystal was monitored with a 6Li loaded glass scintillator. The cross sections obtained are compared with those calculated from Hauser-Feshbach theory.

Neutron-proton bremsstrahlung at 4.8 MeV

The differential cross section for neutron-proton bremsstrahlung has been measured at an incident energy of 4.8 MeV and outgoing nucleon angles of θn = 35°, θp = 25°. An upper limit of was obtained. The experimental method was unusual in that the hydrogen target was a stilbene scintillation crystal, which also served as recoil proton detector, and the bremsstrahlung photon was detected in addition to the two nucleons. A theoretical estimate of the cross section corresponding to that measured in this experiment was made using an on-shell approximation and gave a result of 89 μb · sr−2. The measured upper limit exceeds this and other theoretical predictions but nevertheless represents a marked improvement over previous measurements of n-p bremsstrahlung at energies below 100 MeV.

Polarization in n-d Scattering at 16.4 and 21.6 MeV

A comparison of the polarization asymmetries observed in n-d and p-d elastic scattering provides a test of the charge symmetry of nuclear forces. Discrepancies have been observed between the p-d and n-d polarizations measured at incident energies near to 22 MeV 1−3) and 35 MeV 1,4) respectively. However Morris et al. 5) have recently measured P at incident neutron energies of 16.8 and 21.1 MeV and have obtained results in good agreement with the p-d polarization data. The present work has been motivated by the need for further n-d data in this region.