Hydrogen and deuterium total neutron cross sections in the MeV region

Total neutron cross sections, using a continuous-energy source of neutrons, were measured for hydrogen and deuterium. The neutron energy range covered was from less than 1 MeV, to about 30 MeV. No structure is observed for either isotope. The precision of the cross-section magnitudes appears to be within 1 % over much of the measured energy interval.     

The neutron total and capture cross sections of 92, 94Zr

The neutron total and capture cross sections of^92,94Zr have been measured at the 80 and 40 m flight stations, respectively, on the Oak Ridge Electron Linear Accelerator (ORELA). Resonance analysis of the total cross sections gave values of s, $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ strength functions. Strong intermediate structure was observed in the $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ cross section of ⁹²Zr. Significant single particle transitions identified in the p-wave capture cross section indicate the importance of the valence process for both nuclei. It is noted that the intermediate structure in the $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ total cross section leads to enhanced valence effects in the capture cross section. The effects of non statistical E1 transitions following particle-hole annihilation in the compound states were not observed in either the ⁹²Zr or ⁹⁴Zr capture cross sections as they had been in that for ⁹⁰Zr.     

Rising total cross sections

As two hadrons pass one another the vacuum between them becomes polarised. It is shown that quark-loop contributions to the vacuum polarisation account for most, if not all, of the rise of the total cross section with energy.     

Upper bound on total cross sections

It is shown, under certain assumptions, that if the Nth derivative of the absorptive part of an elastic scattering amplitude exists in the interval t ₁t0, then, the total cross section has the asymptotic upper bound      

Measurement of the fast neutron scattering and total cross sections of141Pr

The differential elastic neutron scattering cross sections of¹⁴¹Pr were measured at the incident neutron energies of 1.2, 1.7 and 1.9 MeV in the angular range between 25 and 150 degrees. At 1.7 MeV the differential inelastic neutron scattering cross sections corresponding toQ=?1122 keV, and at 1.9 MeV the ones corresponding toQ=?1122, andQ=?1295 keV were also determined. In a transmission experiment, the total cross section was measured between 0.50 and 2.42 MeV. The total and differential cross sections were calculated using the nuclear optical model. The calculated results were compared with the experimental data.     

165Ho fast neutron cross sections

Total neutron cross sections of¹⁶⁵ Ho were measured from 0.1 to 1.5 MeV with resolutions of ? 2.5 keV. The observed total cross sections varied slowly with energy and displayed no significant structure. Differential neutron elastic and inelastic scattering cross sections were determined at intervals of ?50keV from 0.3 to 1.5 MeV. The inelastic excitation of states in¹⁶⁵Ho at; 98, 214, 371, 460, 517, 586, 712, 824, 995, 1104 and 1143 keV was positively observed with probably identification of several additional states. The observed excited structure and the respective cross sections were correlated with known single-particle and collective states and with excited structure postulated from systematics. The measured cross sections were compared with calculated values based upon spherical and deformed optical-potentials, and compound-nuclear processes. Total cross sections were best described by a spherical potential while the differential elastic angular distributions were better represented by deformed-potential calculations. Resonance interference effects were found small and, at the energies of the present experiments, the contribution of direct processes was not large.     

Diffraction dissociation in nuclei; Application to nuclear total cross sections

We demonstrate that (i) calculations of the inelastic shadowing effect in nuclear total cross sections done to lowest order in the inelastic couplings are invalid at Fermilab energies; (ii) a recent estimate of this effect to all orders by Gribov is still too large by at least a factor six.     

Heavy-ion total reaction cross sections

A one-parameter expression has been found which predicts with a smaller χ² than previous expressions, the total reaction cross sections for a large number of heavy-ion systems covering a wide energy range. The expression uses an interaction radius which is a sum of the equivalent uniform matter radii of the interacting nuclei plus and energy-dependent term.     

Influence of nuclear excitations on absorption cross sections

From the mean free path in excited nuclear matter a temperature dependent optical model is derived. With its help the approximation of inverse cross sections by ground state absorption cross sections is studied.     

Universality tests for total cross sections

Starting directly from data we test the universality of the decomposition of total cross-sections in an asymptotically dominant term, the Pomeron, and a non dominant one, the Reggeon. Without assuming Regge pole model behaviour or additive quark model relations we show that data are compatible with both models. Support is not found for models predicting asymptotical equality of total cross-sections.     

Determination of nuclear spectroscopic factors from data on differential cross sections for elastic neutron scattering on light nuclei

The values of the coupling constants (spectroscopic factors) dpn, ¹²C¹¹Cn and ¹⁴N¹³Nn have been derived by means of the extrapolation of differential cross section data to the corresponding poles. Some general questions concerning the application of this method to light nuclei are considered.     

Optical phase shifts from low-energy neutron cross sections

The Lorentz-weighted average of the S-matrix introduced by G.E. Brown is used in the Feshbach theory of the generalized optical potential to show that the average many-body S-matrix for elastic scattering is exactly equal to the two-body S-matrix of an optical potential. However, the optical potential S-matrix must be evaluated at the complex energy $\text{E}\text{= E + iI,}\text{where}\text{I}$ is the half-width of the lorentzian. The resulting equation for the optical phase shifts (OPS) δ_c, exp $\text{[2iδ}{}_{\mathrm{c}}\text{(}\text{E}\text{)] = 〈S}{}_{\mathrm{cc}}\text{(E)〉}$, holds even when the level spacing D forces the use of an averaging half-width I > D which is comparable to the energy E, providing that the OPS are also evaluated at the complex $\text{E}$ instead of being approximated by their values on the real energy axis at E. An appendix discusses briefly the conditions on a potential necessary for the result obtained by Brown that $\text{〈S}{}_{\mathrm{cc}}\text{(E)〉 = S}{}_{\mathrm{cc}}\text{(}\text{E}\text{)}$ when Lorentz-weighted averaging is used.     

Constraints on the asymptotic behaviour of total cross sections

We derive constraints on the asymptotic behaviour of total cross sections which follow from dispersion relations and measured real parts of the forward scattering amplitudes. For πN and pp scattering, these constraints are calculated using recent results from FNAL and Serpukhov. The relation to other methods is discussed.     

Measurement of cross sections for 14 MeV neutron capture

Activation cross sections for neutron capture have been measured at an energy of 14.6 ± 0.2 MeV relative to $\text{σ(}{}^{27}\text{Al}\text{(}\text{n}\text{,α)}{}^{24}\text{Na}\text{) = 114.2}\text{mb}\text{± 1.2\%}$ for the nuclei ³⁷Cl, ¹⁴K, ⁵⁰Ti, ⁵¹V, ⁵⁵Mn, ⁷¹Ga, ⁸⁷Rb, ⁸⁹Y, ¹²⁷I, ¹³⁰Te, ¹³⁸Ba, ¹³⁹La, ¹⁴²Ce, ¹⁸⁶W, ¹⁹⁸Pt,¹⁹⁷Au. Gamma-ray spectra of the product nuclei were measured with a Ge(Li) detector. Special attention was paid to taking into account all possible sources of error, especially contributions of lower energy neutrons. It seems to be shown that consistent results can be obtained for the cross sections for 14 MeV neutron capture if one properly takes into account the influence of lower energy neutrons even in cases where the relevant correction is large. In particular results from activation measurements agree well with results obtained by the method of integrated γ-spectra.     

Pionization effects in proton-nucleus total cross sections

A simple unitary model for meson production effects in proton-nucleus scattering was used earlier to estimate the pionization corrections to the proton-deuteron total cross section. This model is here used to study the corresponding effects in heavy nuclei using a generalization of the optical limit. An increase in the total cross sections at the upper limit of NAL energies of roughly 20% is found.     

Role of the nuclear surface in the formation of total cross sections for heavy-ion reactions

Within the Glauber-Sitenko approach, a procedure for calculating cross sections for intermediate-energy heavy-ion reactions is developed by using the analytic form of the eikonal phase for the symmetrized Woods-Saxon potential. The differential and total cross sections obtained on this basis comply well with the results derived by numerically solving the wave equation. A clear and instructive model of the phase is constructed, which makes it possible to separate, in total reaction cross sections, the contributions of the internal and the peripheral region of interaction. It is found that the nuclear surface plays an important role in the formation of reaction cross sections, and the effect of the Coulomb field on these cross sections is investigated. The origin of a continuous ambiguity in optical potentials is revealed in interpreting total cross sections.     

Alignment effects in deuteron total cross sections

The alignment dependence of the total cross section of deuterium is a purely multiple scattering phenomenon. An estimate of this for pion scattering using Glauber theory shows that the most important contribution is associated with the deuteron D-state (typically 1%) with corrections coming from the double spin flip. Measurements of the proton total cross section with an aligned deuteron beam should also yield other interesting information on the wave function of the deuteron D-state.