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Ross, T. J.

Publications and source records attributed to Ross, T. J..

Neutron elastic and inelastic scattering differential cross sections on carbon

Elastic and inelastic neutron scattering angular distributions were measured on natural carbon samples to confirm existing experimental data and evaluations in the fast neutron region and to guide improvements in resonance parameters, where needed. Sixty-four (n,n') differential cross section measurements were performed at 45 incident neutron energies between 0.5 and 8.0 MeV. Experimental angle-integrated elastic scattering cross sections are consistent with ENDF/B-VIII.0 values with the exception of the region from 3.2 to 4.0 MeV where our results are ~3% higher. In the 3.4 to 3.6 MeV region our differential cross sections are slightly lower at forward angles and somewhat higher at backward angles than the ENDF/B-VIII.0 calculations; however, our results are consistent with measured data from other research groups. The first- through fourth-order elastic scattering Legendre coefficients from fits to these experimental data are consistent with ENDF/B-VIII.0 values across this range of incident neutron energies. Inelastic scattering cross sections were measured at 12 incident neutron energies between 5.6 and 7.8 MeV. Angle-integrated cross sections agree well with the 1978 Perey and ENDF/B-VIII.0 values; however, the angular-distribution shapes deviate somewhat from the ENDF/B-VIII.0 calculations. These data will allow refinement of the resonance parameter description in this difficult energy region.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

Photo response of 164 Dy

Background: Little data is available for the pygmy dipole resonance (PDR) in axially deformed nuclei. Photon-scattering experiments are complicated by high level densities in the PDR region and the small energy difference of transitions to the ground state and to excited states. Purpose: In this work, we report on an experimental study of the low-energy dipole strength distribution of the well-deformed nucleus 164 Dy between 4.0–7.7 MeV. Methods: The low-lying photoresponse of 164 Dy has been investigated using the method of nuclear resonance fluorescence using a quasimonochromatic linearly polarized $\textit{γ}$-ray beam in the energy range of 4.0–7.7 MeV in steps of 0.2 MeV. Results: For excitation energies between 4 MeV and 5 MeV, sufficiently low level densities allow for the identification of individual states, including level energies, reduced transition widths and branching ratios. Energy-averaged mean decay branching ratios, mean population ratios and partial absorption cross sections were determined above 5 MeV up to the neutron-separation threshold at 7.7 MeV. A Lorentzian-shaped enhancement of the partial photo absorption cross section followed by decays back to the ground-state band is found at 6.10(5) MeV with a width of 0.77(23) MeV. A comparison with results from complementary measurements is performed using the framework of the statistical model. Conclusions: The experimental results for the mean population ratios deviate systematically from the statistical model simulation by 30(6)%. However, they are in agreement within one standard deviation of the simulation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Δ$\textit{K}=0 \textit{M}1$ Excitation Strength of the Well-Deformed Nucleus 164 Dy from $\textit{K}$ Mixing

We report the size of a Δ$\textit{K}=0 \textit{M}1$ excitation strength has been determined for the first time in a predominantly axially deformed even-even nucleus. It has been obtained from the observation of a rare $\textit{K}$-mixing situation between two close-lying $J^π = 1^+$ states of the nucleus 164 Dy with components characterized by intrinsic projection quantum numbers $\textit{K}$ = 0 and $\textit{K}$ = 1. Nuclear resonance fluorescence induced by quasimonochromatic linearly polarized γ-ray beams provided evidence for $\textit{K}$ mixing of the 1 + states at 3159.1(3) and 3173.6(3) keV in excitation energy from their γ-decay branching ratios into the ground-state band. The Δ$\textit{K}$ = 0 transition strength of $B(M1; 0^+_1 → 1^+_{K=0}) = 0.008(1)μ^2_N$ was inferred from a mixing analysis of their $\textit{M}$1 transition rates into the ground-state band. It is in agreement with predictions from the quasiparticle phonon nuclear model. This determination represents first experimental information on the $\textit{M}$1 excitation strength of a nuclear quantum state with a negative $\mathcal{R}$-symmetry quantum number.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗