R. W. Bauer

Justification of a Simple Ramsauer Model for Neutron Total Cross Sections

The simple nuclear Ramsauer model has been used successfully to fit neutron total cross sections for more than four decades but has not been widely used because the foundations of the model seem so unrealistic. A diffraction model calculation with the inclusion of refraction and optical model calculations are shown to validate the use of this simple nuclear Ramsauer model for neutron total cross sections in the neutron energy region of 6 to 60 MeV. This model yields a simple formula for parameterizing the energy dependence of the neutron total cross section.

Dependence of neutron total cross sections on energy for 100 ≤ En ≤ 500 MeV and mass number for 7 ≤ A ≤ 238

Abstract Two recent measurement programs have yielded an extensive body of neutron total cross-section data for a number of targets at energies up to 500 MeV. Recently, it has been shown that the simple Ramsauer model provides a good description of the data up to 120 MeV. The parameterization developed in this energy region did not do as well above this energy. The data in the region 100 ≤ En ≤ 500 MeV are examined, and it is concluded that a simple parameterization can describe the data well. The applicability of the Glauber model is tested in the energy region above 150 MeV.

A New Method for Estimating Neutron Reaction Cross Sections Based on Wick’s Limit

Wick’s limit is an inequality that relates the zero‐degree differential elastic scattering cross section to the total cross section. The deviation of Wick’s limit from an exact equality is small over a wide range of incident energies and target masses. Under these circumstances we show that Wick’s limit can be used to correlate the uncertainties in the two terms of the reaction (nonelastic) cross section expressed as the difference between the total and angle‐integrated elastic cross sections. When suitable elastic angular distributions are available, we show that the reaction cross section may be obtained with small errors (typically 1.5–3%). Examples are shown for 208Pb, 54–56Fe, 232Th, and 238U.

Modeling of High Precision Neutron Nonelastic Cross Sections

Abstract A new method has been applied to the determination of neutron nonelastic cross sections for iron 56Fe and lead 208Pb for energies between 5 and 26 MeV. These data have estimated errors of only a few percent and do not suffer from the ambiguities encountered in earlier nonelastic data. We attempt to fit these high-precision data using both a semiclassical single phase shift model (nuclear Ramsauer model) as well as a recent global optical model that well reproduces a wide body of neutron scattering observables. At the 5% uncertainty level, both models produce satisfactory fits. However, neither model gives satisfactory fits to these new precise data. We conclude that fitting precise data, i.e., data with errors of ~2% or less, may require a nuclear mass dependence of radii that reflects structure effects such as shell closures.

Comparison of Ramsauer and Optical Model Neutron Angular Distributions

Abstract In a recent paper it has been shown that the nuclear Ramsauer model does not do well in representing details of the angular distribution of neutron elastic scattering for incident energies of <60 MeV for 208Pb. In this paper, we show that the default angular bin dispersion most widely used in Monte Carlo transport codes is such that the observed differences in angular shapes are on too fine of a scale to affect transport calculations. The effect of increasing the number of Monte Carlo angle bins is studied to determine the dispersion necessary for calculations to be sensitive to the observed discrepancies in angular distributions. We also show that transport calculations are sensitive to differences in the elastic-scattering cross section given by recent fits of 208Pb data compared with older fits.

Yrast superdeformed band in {sup 194}Pb: J{sup {pi}} and E{sub x}

The yrast superdeformed band in {sup 194}Pb has been populated using the {sup 174}Yb({sup 25}Mg,5n){sup 194}Pb reaction at E{sub beam}=130 MeV. Decay {gamma} rays were detected using the GAMMASPHERE array at the 88-Inch Cyclotron. Twelve {gamma}-ray transitions have been observed directly linking three members of the {sup 194}Pb yrast superdeformed band to low-lying normal deformed levels. Anisotropy measurements indicate that these linking decays include E1, M1, and mixed M1/E2 multipolarities. The radiative widths deduced are very inhibited, typically B(E1){approximately}10{sup {minus}8} Weisskopf units (W.u.) and B(M1){approximately}10{sup {minus}5} W.u. Without recourse to {ital a priori} assumptions J{sup {pi}}=6{sup +} and E{sub x}=4878.4(3) keV have been unambiguously assigned to the lowest-lying observed superdeformed state (the state populated by the 170-keV intraband transition). The intensity of the observed primaries accounts for 21(2){percent} of the superdeformed band population. {copyright} {ital 1997} {ital The American Physical Society}

Yrast superdeformed band in Pb-194: Jpi and Ex

The yrast superdeformed band in {sup 194}Pb has been populated using the {sup 174}Yb({sup 25}Mg,5n){sup 194}Pb reaction at E{sub beam}=130 MeV. Decay {gamma} rays were detected using the GAMMASPHERE array at the 88-Inch Cyclotron. Twelve {gamma}-ray transitions have been observed directly linking three members of the {sup 194}Pb yrast superdeformed band to low-lying normal deformed levels. Anisotropy measurements indicate that these linking decays include E1, M1, and mixed M1/E2 multipolarities. The radiative widths deduced are very inhibited, typically B(E1){approximately}10{sup {minus}8} Weisskopf units (W.u.) and B(M1){approximately}10{sup {minus}5} W.u. Without recourse to {ital a priori} assumptions J{sup {pi}}=6{sup +} and E{sub x}=4878.4(3) keV have been unambiguously assigned to the lowest-lying observed superdeformed state (the state populated by the 170-keV intraband transition). The intensity of the observed primaries accounts for 21(2){percent} of the superdeformed band population. {copyright} {ital 1997} {ital The American Physical Society}