D.E. Bainum

Neutron elastic scattering on T = 0 nuclei☆

Abstract Neutron elastic scattering on Si, S and Ca has been measured at 11, 20 and 26 MeV using the Ohio University 11 MeV Tandem Van de Graaff. A time-of-flight technique was used and the angular distributions covered an angular range from 15° through 155°. The measured cross sections were corrected for dead time, source anisotropy, detector efficiency, finite geometry, neutron flux attenuation and multiple scattering. Individual as well as global fits to the data using an optical-model search code are presented. The comparison of the optical-model analysis to the neutron and proton elastic scattering data in the case of 40 Ca, allows an empirical determination of the Coulomb correction term which may be parametrized as 0.46 Z/A 1 3 . It is also shown that the elastic scattering and inelastic scattering to the first 2 + states in 28 Si and 32 S may be fitted using the same optical-model parameters obtained for 40 Ca using the coupled-channel formalism.

Isospin effects in nucleon inelastic scattering from single-closed-shell nuclei: (I). The N = 50 isotones

Accurate measurements of elastic- and inelastic-scattering differential cross sections are obtained over a wide angular range for 11 MeV neutrons incident on 88Sr, 90Zr and 92Mo. The absolute cross sections are accurate to better than 5%. The parameters of complex optical potentials were extracted from the elastic-scattering data and applied via the collective model to the description of the cross sections of the first 2+ state of each isotope. Deformation parameters βnn′ (and lengths) δ = βR) were obtained for the quadrupole excitations and compared with similar parameters obtained from (p, p′) data on the same nuclei. The results clearly indicate that βnn′ > βpp′ for the N = 50 isotones, in good agreement with the theoretical predictions of Madsen, Brown and Anderson. The values of βnn′ and βpp′ are used to extract the isoscalar and isovector deformation parameters β0 and β1.

Neutron scattering from 208Pb

Elastic scattering of 7, 9, 11, 20 and 26 MeV neutrons from 208Pb has been measured with the Ohio University Tandem Van de Graaff accelerator. Standard pulsed beam time-of-flight techniques were employed. Measurements of the incident flux at 0° were used to normalize the differential cross sections. The measured cross sections were corrected for dead time, detector efficiency, flux attenuation, multiple scattering, finite geometry, neutron source anisotropy and compound elastic contribution. Relative uncertainties are estimated to be between 5%–10% and the uncertainty in the normalization is estimated to be less than 5 %. The data were used to obtain neutron optical potential parameters. A comparison with proton optical parameters is presented, and the (p, n) quasi-elastic cross section is calculated and compared with available data. Deformation parameters for the 3− state (Q = −2.615 MeV) and 5ā (Q = −3.198 MeV) in 208Pb were obtained at incident energies of 11 and 26 MeV.

Neutron elastic scattering from 116,118,120,122,124Sn

Abstract Accurate measurements of neutron differential elastic cross sections have been obtained from even isotopes of Sn. Data are presented for the elastic scattering of 11 MeV neutrons from 116, 118, 120, 122, 124Sn, the elastic scattering for 24 MeV neutrons from 116, 118, 124Sn and the neutron total cross section from 118, 120, 122, 124Sn in the energy ranges 5.0–10.6 MeV and 20.0–26.0 MeV. The elastic scattering data are analyzed in terms of an empirical optical-model potential. The obtained optical-potential parameters are analyzed in terms of energy and isospin dependence and compared with those obtained from proton elastic scattering on even Sn isotopes.

Neutron elastic scattering from 92, 96, 98, 100Mo between En = 7 and MeV☆

Abstract Elastic scattering of 7, 9, 11, 20 and 26 MeV neutrons from 92, 96, 98, 100Mo has been measured using the Ohio University time-of-flight facility. The measured yields were normalized with respect to the incident flux at 0°, to obtain absolute differential cross sections. These values were corrected for dead time, detector efficiency, flux attenuation, multiple scattering, finite geometry, neutron source anisotropy and compound elastic contributions. Relative uncertainties are estimated to be between 5%–10%, and the uncertainty in the normalization is estimated to be less than 5%. The data were used to obtain neutron optical model potential parameters. The energy and isospin dependence of the potential depths is presented. Coupled channel calculations are presented and compared with standard optical model calculations.

Comparison of the 12C(p, n)12N and 12C(p, p′) reactions at Ep = 62 and 120 MeV☆

Abstract Measured 12 C(p, p′) and 12 C(p, n) 12 N reaction cross-section angular distributions leading to isobaric analog states are compared at 62 and 120 MeV bombarding energies. It is shown that the (p, p′) differential cross section is one-half the (p, n) differential cross section to the analog state. This relation and these reactions are demonstrated to be very useful for the determination of the detection efficiency of large volume neutron detectors at intermediate energies.

Energy levels in 98Tc from the 98Mo(p, n)98Tc and 97Mo(3He, d)98Tc reactions☆

Abstract Low-lying states in 98Tc have been studied via the 98Mo(p, n)98Tc and 98Mo(p, nγ)98Tc reactions for proton energies between 2.4 and 4.2 MeV. The γ-ray decay schemes are reported. Additional information was obtained from the study of the 97Mo(3He, d)98Tc reaction at E 3 He = 19 and 23 MeV . Proton transfer l-values and spin assignments are discussed.

Neutron inelastic scattering to octupole states in single-closed-shell nuclei☆

Abstract Differential cross sections for the excitation of the first octupole-vibrational state in the closed- neutron-shell nuclides 88 Sr and 90 Zr and in the closed-proton shell-nuclei 116, 118, 120, 124 Sn by 11 MeV neutrons are presented. The distorted-wave Born approximation is used to obtain deformation lengths, σ(3 − ), for each state. Results are compared with earlier measurements of inelastic proton scattering to the same states. Although limited resolution in the neutron time- of-flight spectrometer complicates the interpretation of the Sn data, the overall conclusion that σ nn′ (3 − ) ≈ σ pp′ (3 − ) is supported by all of the measurements.