E. Ramström

The 54,56Fe(n, p)54,56Mn reactions at En = 97 MeV

Abstract Double-differential cross sections of the 54,56Fe(n, p) reactions have been measured at 97 MeV in the angular range 0–30° for excitation energies up to 40 MeV. The spectra have been decomposed into different multipolarities by a technique based on the use of sample angular distributions calculated within the distorted-wave Born approximation. From the identified Gamow-Teller strength, Sβ+ values were obtained for 54Fe and 56Fe. Comparisons with available shell-model calculations of the GT strength were made. The results are important for models of supernova explosions since electron-capture rates, which are proportional to Sβ+, in 1f2p-shell nuclei affect the dynamics of the star. At higher excitation energies, the spectra are dominated by L = 1 strength in broad distributions with a maximum at about 12 MeV. Microscopic calculations based on the random-phase approximation were performed and compared with the experimental data.

Microscopic and conventional optical model analysis of neutron elastic scattering at 21.6 MeV over a wide mass range

Abstract Differential fast neutron elastic scattering angular distributions have been measured at 21.6 MeV for the natural elements Mg, Al, Si, S, Ca, Cr, Fe, Co, Ni, Y, Ce, Pb r (radiogenic lead) and Bi by employing pulsed beam time-of-flight techniques. The energy resolution was about 0.5 MeV (FWHM) throughout the measurements. The experimental data have been analysed in terms of a standard phenomenological spherical optical model. Potential depths and geometrical parameters were determined from individual best fits to the data. Volume integrals of the real and imaginary parts of the potential were calculated using these parameters. A similar technique was utilized to calculate root mean square radii of the real potential, from which radii of point matter distributions were obtained for comparison with α-particle scattering data at 166 MeV and with charge distribution radii from electron scattering. Microscopic folding models for the optical potential according to Jeukenne, Lejeune and Mahaux, Brieva and Rook, and Yamaguchi et al . have been tested by calculating angular distributions, volume integrals and root mean square radii for the real and imaginary potential parts. The results of these calculations are compared with those of the phenomenological analyses. The microscopic potentials have also been intercompared by studying introduced normalizing parameters of the real and imaginary potential parts as well as isovector and isoscalar contributions to the volume integrals.

THE C-12(N,P)B-12 REACTION AT E(N)=98 MEV

Double-differential cross sections of the C-12(n, p) reaction have been measured at 98 MeV in the angular range 0-degrees-33-degrees for excitation energies up to 35 MeV. The spectra have been analysed in terms of multipole components, using peak fitting and decomposition techniques. The data have been compared with cross sections obtained in the distorted-wave Born approximation, using matrix elements from shell-model calculations. The unit cross section and the related strength of the spin-isospin part of the nucleon-nucleon interaction were determined from the extracted Gamow-Teller strength. Cross sections and fractions of strength exhausted by dipole and higher-multipole transitions were extracted and compared with data available in the literature.

Neutron elastic and inelastic scattering from Mg, Si, S, Ca, Cr, Fe and Ni AT En = 21.6 MeV

Abstract The Studsvik high-resolution, low-background time-of-flight facility has been used to measure differential neutron elastic and inelastic scattering cross sections for Mg, Si, S, Ca, Cr, Fe and Ni at the neutron energy 21.6 MeV. The results have been analysed in terms of collective rotational, vibrational or rotation-vibrational models using the coupled-channels formalism. Optical model potential depths and geometrical parameters as well as nuclear deformation parameters were determined from fits to the measured data.

Coupling of valence particles/holes to 68,70Ni studied via measurements of the B(E2) strength in 67,69,70Ni and 71Cu

Coupling of valence particles/holes to 68,70Ni studied via measurements of the B(E2) strength in 67,69,70Ni and 71Cu.

Neutron elastic and inelastic scattering from beryllium, nitrogen and oxygen at En = 21.6 MeV

The Studsvik high-resolution, low-background time-of-flight facility has been used to measure differential neutron-scattering cross sections for 9Be, 14N and 16O at the neutron energy 21.6 MeV. Angular distributions in the range 10°–160° have been measured for elastic scattering, and also for inelastic scattering from some low-lying levels in the three nuclei. The results for elastic scattering have been treated in terms of a phenomenological spherical optical model, while inelastic-scattering cross sections for 14N and 16O were calculated using the distorted-wave Born approximation. The coupled-channels formalism for rotational and vibrational nuclei was also used in the analysis of scattering from 9Be and 16O, respectively. Potential parameters and deformations from these calculations are given in the paper.

Isomeric and two-quasiparticle states in the neutron-excess odd-odd nucleus 134Sb

Detailed theoretical calculations of the properties of the neutron-excess odd-odd nucleus 134Sb are performed by using different theoretical approaches. A comprehensive comparison with the recent experimental data is performed; this comparison suggests the presence of isomeric states among the low-lying levels of this nucleus. These states are the twins of the corresponding levels of the odd-odd nucleus 210Bi that is situated near the stability line. The obtained results manifest the similarity of nuclear structure in the region of the “remote” doubly magic nucleus 132Sn and in the region of the classical stable doubly magic nucleus 208Pb.

Neutron elastic and inelastic scattering from carbon in the energy range 16.5–22.0 MeV

Abstract The Studsvik high-resolution, low-background time-of-flight facility has been used to obtain a comprehensive set of differential neutron-scattering cross sections for carbon at the neutron energies 16.5, 17.6, 18.7, 19.8, 20.9, 21.6 and 22.0 MeV. Angular distributions in the range 10–160° have been measured for elastic scattering, and also for inelastic scattering from the levels at 4.44, 7.65 and 9.64 MeV. Angle-integrated cross sections have been determined by fitting Legendre polynomial expansions to the differential data. The results have been treated in terms of a phenomenological spherical optical model. Potential depths and geometrical parameters were determined from fits to the elastic-scattering data, while deformation parameters were obtained from inelastic scattering using the distorted-wave Born approximation. Elastic and inelastic angular distributions were also calculated with the coupled-channels formal-

SCATTERING EFFECTS IN NEUTRON DIAGNOSIS OF DT TOKAMAK PLASMAS

The scattered background flux accompanying observation of fusion plasma neutrons is a limiting factor in high accuracy neutron diagnostics such as will be required on ITER. The factors determining the shape and magnitude of the scattered neutron spectrum have been investigated in terms of the possibilities for calculating and measuring the spectrum, and to determine the dependence on the nuclide composition of the plasma vessel and changes in the plasma condition.

The Pb-208(n,p)Tl-208 reaction at E-n=97 MeV

Abstract Double-differential cross sections of the 208 Pb(n,p) reaction have been measured at 97 MeV in the angular range 0°–30° for excitation energies up to 40 MeV. The experimental proton spectra have been compared with calculated spectra obtained with a statistical multistep direct reaction theory, in which charge exchange and inelastic response functions are described microscopically in the quasiparticle random phase approximation. The direct parts of the spectra have also been distributed on different multipole components by using a decomposition technique, based on sample angular distributions calculated within the distorted-wave Born approximation.