Weak neutral-current effects in electron-scattering coincidence experiments

Using a recently developed helicity analysis of electron-scattering coincidence experiments, we derive general expressions for the asymmetry in the coincidence cross section with polarized incident electrons. The asymmetry cross section is expressed in terms of the helicity components of the electromagnetic and weak neutral currents in the center-of-momentum frame. The asymmetry arises from an interference between the electromagnetic and weak neutral currents and from parity admixtures in the nuclear wave functions. In the limit of heavy, static nuclei, connection can be made to the usual multipole matrix elements of the electromagnetic and weak interactions. Some simple examples are discussed for the case where the reaction proceeds through a single intermediate resonance.     

The theory of electron-scattering coincidence experiments

A general expression for the electron-scattering coincidence cross section for the reaction A₁(e, e′ X) A₂ with a nuclear target is derived in the one-photon exchange approximation. The result is exact to lowest order in α, the fine-structure constant. It is expressed in terms of four kinematic factors involving the electron scattering variables in the laboratory frame, and four combinations of transition matrix elements of the nuclear current operator expressed in the center-of-momentum (COM) frame. The nuclear matrix elements are decomposed into transition amplitudes of definite angular momentum using a helicity analysis. General expressions for the angular distribution of particle X in the COM frame are then derived. The analysis is independent of the detailed structure of the nucleus and particle X and depends only on general symmetry considerations and the existence of a local electromagnetic current operator for the hadronic target. A unitary transformation from the helicity basis for the final particle X and A₂ to an LS coupling basis is relevant if X is massive and a finite number of total angular momenta J are involved in the reaction. Tables of angular correlation coefficients are given for the case where the initial nucleus A₁ has J₁^π = 0⁺. They constitute one of the most useful results of this paper.Connection is made in the “static limit,” and with the assumption that the reaction proceeds through a finite number of Breit-Wigner resonances with a corresponding factorization of the electroproduction transition matrix elements, to the familiar electromagnetic transition multipole moments involving excitation of a nuclear state J^π. The relation to previous work by de Forest and by Drechsel and Überall is discussed.Analytic expressions for the coincidence cross sections are given for spin-zero systems and some very simple, basic models of nuclear “giant resonance” excitations. It is hoped that they will be useful in obtaining insight into the coincidence cross section and in planning future experiments.Finally, a reanalysis of the recent Stanford data of Calarco et al. on ${}^{12}\text{C}\text{(e, e′ p}{}_0\text{)}{}^{11}\text{B}\text{(}\text{3}\text{2}{}^{\mathrm{?}}\text{)}$ in the vicinity of the giant dipole resonance in ¹²C is carried out using a very simple nuclear model but retaining all the terms in the coincidence cross section, some of which were previously neglected.     

State-selective radiative recombination cross sections of argon ions

The n-, (n,l)- and fine-structure level state-selective radiative recombinations (RR) cross sections of argon ions Ar¹⁸⁺,Ar¹³⁺,Ar⁷⁺ and Ar⁺ are obtained with the semi-classical Kramer formula, the relativistic self-consistent field (RSCF) method and the relativistic configuration interaction (RCI) method. It is found that for the highly charged ions with few electrons, the cross sections calculated with these three methods are in good agreement with each other. But as the number of electrons increases, the Kramer formula deviates from the RSCF and RCI results. For instance, when the energy of the incident electron is larger than 100 eV, the n-state selective cross sections of Ar⁷⁺ calculated from the Kramer formula are underestimated for more than 50%. The RSCF results are in general agreement with the RCI results. However, for the low charged ions, a clear distinction appears due to the strong configuration interaction, especially near the Cooper minimum. The n-resolved (n≤10) and total Maxwellian averaged rate coefficients are calculated, and the analytic fitting parameters are also provided.     

Temperature dependence of radiative strength functions and isomeric cross sections

The effect of a parametrization of the temperature dependence of radiative strength functions for electric dipole transitions on the cross sections for isomer excitation in (n, γ), (n, 2n), (n, p), (n, α), (γ, \g′), (γ, n), (γ, p), and (γ, 2n) reactions is investigated. It is shown that the agreement of the results of calculations with the observed isomeric cross sections can be considerably improved by using the proposed method.     

Compound-nucleus effects in spin-spin cross sections

By comparison with recent data, it is shown that spin-spin cross sections for low-energy neutrons may be dominated by a simple compound-elastic level-density effect, independent of spin-spin terms in the nucleon-nucleus optical-model potential.     

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.     

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.     

Target-spin effects on elastic scattering cross sections

It is shown, using a simple model and empirical results, that the odd-even differences in the scattering of He ions from ⁵⁹Co and ⁶⁰Ni can be explained as due to the scattering from the quadrupole moment which is allowed for the odd target nucleus but not the even.     

Nuclear structure effects in sub-barrier fusion cross sections

The total fusion cross sections around and down to ≈ 12 MeV below the Coulomb barrier in the c.m. system have been measured with the Munich heavy-ion recoil spectrometer for 30 projectile-target combinations: ^{32, 36}S + ^{92, 94, 96, 98, 100}Mo, ^{100, 101, 102, 104}Ru, ¹⁰³Rh, ^{104, 105, 106, 108, 110}Pd, The excitation functions can be reproduced with a one-dimensional barrier penetration model by increasing the nuclear radii by $\text{ΔR ? 0.255 ± 0.035}\text{fm}$ and introducing a gaussian distribution of the nuclear radius R with a standard deviation σ_fit(R). The σ_fit(R) can be explained as being due to quadrupole vibrational fluctuations of the surface-to-surface distance at the barrier and to two-neutron-transfer reactions with positive Q-values.     

On the calculation of scattering cross sections from absorption cross sections

A dispersion-type relation between photon scattering and absorption cross sections is derived. It is shown that the relation gives the correct scattering cross section in the low and high frequency limits, and is consistent with the Kramers-Heisenberg formula in the vicinity of a resonance. The practical application of the relation is illustrated by calculations of the scattering cross section and refractive index of He and Ne at STP and dry air at 1200°K from known absorption cross section data. The method is useful for obtaining scattering cross sections, polarizabilities, and refractive indices at elevated temperatures.     

Electron-impact excitation cross sections for neon

An analytic atomic independent particle model adjusted to experimental single-particle energy levels is used to generate wavefunctions for the excited states of neon. Using these wavefunctions in conjunction with the Born approximation and the Russell-Saunders LS-coupling scheme, we calculate generalized oscillator strengths and cross sections for electron-impact excitation of neon from the 2p⁶(¹ S ₀) ground state.     

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.     

Theoretical cross sections for keV antiprotons

Partial and total close-coupled semiclassical (impact parameter) cross sections and total classical Monte-Carlo cross sections for interactions in and , p+H collisions are computed in the intermediate keV range for antiprotons, , up to 100 keV lab. Total cross sections for antihydrogen, , formation are found to be large, 10−20×10⁻¹⁶ cm² in a wider energy range than was anticipated earlier, up to some 20 keV lab. New estimates of cross sections for ionisation of atomic hydrogen by antiproton impact are reported for the low-energy range 1–30 keV lab where they are 10−20×10⁻¹⁷ cm², being much larger than the corresponding cross sections for ionisation of hydrogen by proton impact. Data for excitation of H by impact is also presented.     

Exciton model comparison of the activation and the integrated 14 MeV neutron radiative capture cross sections

The exciton model for the γ-emission was tested in its abilities to describe the radiative capture of 14 MeV neutrons over a wide scale of atomic numbers (Al-27, Sc-45, V-51, Mn-55, I-127, Pr-141, Pb-208, and Bi-209). Special attention was paid to the difference between the activation cross section and the cross section integrated over the prompt capture γ-ray spectra. Relatively good agreement of theoretical and experimental data was obtained in this case, while the spectra agree in their gross structure only for medium weight and (possibly) heavy nuclei.     

Infrared absorption cross sections for methanol

Infrared absorption cross sections for methanol, CH₃OH, have been determined near 3.4 and 10 μm from spectra recorded using a high-resolution FTIR spectrometer (Bruker IFS 125HR) and a multipass cell with a maximum optical path length of 19.3 m. Methanol/dry synthetic air mixtures were prepared and spectra were recorded at 0.015 cm^?1 resolution (calculated as 0.9/MOPD) at a number of temperatures and pressures (50–760 Torr and 204–296 K) appropriate for atmospheric conditions. Intensities were calibrated using composite methanol spectra taken from the Pacific Northwest National Laboratory (PNNL) IR database. The new measurements in the 10 μm region indicate problems with the existing methanol spectroscopic line parameters in the HITRAN database, which will impact the accuracy of satellite retrievals.     

X-ray photoionization cross sections for quantitative analysis

The relative photoemission intensities from subshells of 51 elements and simple compounds have been measured using X-ray photoelectron spectroscopy. The chemical composition of each specimen surface was monitored by Auger electron spectroscopy and contamination was minimized by Ar⁺ ion bombardment. Experimental photoelectron cross sections derived for MgKα (1254 eV) radiation were compared with theoretical Hartree-Slater subshell photoionization cross sections calculated by Scofield. Good correlation (r = 0.96) between theory and experiment was observed over two orders of magnitude for most of the elements studied. Relative cross sections for subshells of a given element are also consistent with theoretical values, with several notable exceptions. The results indicate that quantitative analysis of ESCA spectra is possible using the Scofield cross sections.     

Transport cross sections for excited muonic hydrogen

Transport cross sections for scattering of excited muonic hydrogen on hydrogen are calculated in the quasi-classic approximation in the energy range 0.01–50 eV.