Coulomb Final State Interaction Research Articles

Neutron-proton interferometry in [formula omitted] collisions

Neutron-proton correlation functions in 30A MeV 40 Ar+ 197 Au, 12 C, CH 2 reactions have been measured. In contrast to the nn and pp correlations, which exhibit the shape expected from quantum symmetrization effects and nuclear+Coulomb (pp) final-state interaction, the np function shows much less correlation strength. This may be due to Coulomb repulsion on the proton and/or to a larger effective spin than expected. Selecting high energy nucleons strengthens both the np and pp correlations.

πK correlations in relativistic heavy-ion collisions

We show that strong and Coulomb final-state interactions induce correlations between π and K mesons emitted with small relative momenta (⩽ 100 MeV/ c) from relativistic heavy-ion collisions. Measurements of these correlations, estimated to have a (5–10)% effect, might further constrain source parameters and/or πK scattering lengths. Strong-interaction correlations ⩽ 5% are also estimated for π +π − pairs.

Configuration-space methods for Coulomb scattering in a laser field.

The Volkov wave function describing the motion of a charged particle in a laser field serves as a modified plane wave in the formulation of external-field collision theory and is widely used in applications. Exact solutions are unavailable for those cases in which the target, as well as the projectile, carries a net charge. It is shown that this difficulty may be overcome through the adoption of a variational formulation of the theory in configuration space. The essential feature of this procedure is the specification of boundary conditions to be satisfied by the trial functions whereby the combined effect of the Coulomb potential and the external field is accounted for with sufficient accuracy. Wave packets constructed from such trial functions satisfy the physical requirement that they follow classical trajectories at asymptotic times. The formalism is applied to the problem of potential scattering in a low-frequency external field and leads to an approximate transition amplitude that serves as a generalization of the Kroll-Watson approximation, reducing to it for potentials having no long-range Coulomb tail. In addition, a relatively simple Coulomb generalization of the cross-section sum rule is obtained. As a second application a low-frequency approximation is derived for the amplitude for laser-assisted electron-impact ionization. It is based on a choice of trial functions that accounts for the effect on the asymptotic motion of these particles of the long-range final-state Coulomb interactions among pairs of charged particles, in the presence of the laser field. The applicability of this approach to multiphoton-ionization processes is discussed briefly.

Reexamination of an anomaly in near-threshold pair production.

We investigated a reported anomaly in near-threshold pair production, using radioactive sources to measure the {gamma}+Ge{r arrow}{ital e}{sup +}+{ital e}{sup {minus}}+Ge cross-section at {ital E}{sub {gamma}}=1063, 1086, 1112, 1173, 1213, 1299, 1332, and 1408 keV. Although the data agree with the theory (numerical calculations based on an exact partial-wave formulation for a screened central potential) at the higher energies, the data lie above the theory at 1063, 1082, and 1112 keV. The discrepancy is reduced by including the final-state Coulomb interaction between the {ital e}{sup +} and {ital e}{sup {minus}}.

K s pictures of strangeness distillation

K s-K s interferometry is shown to contain a novel interference term that is sensitive to possible strangeness distillation phenomena in high energy nuclear reactions. The absence of Coulomb final state interaction, the reduced resonance distortions, and the above novel effect make it an especially attractive complement to conventional charged boson (π −π − or K +K +) interferometry.

Final-state Coulomb interactions for intermediate-mass fragment emission.

Information about the space-time characteristics of intermediate-mass fragment emission processes is contained in the shape of two-fragment correlation functions at small relative momenta. A classical approximation to the Koonin-Pratt formula is derived which allows the calculation of correlations resulting from the Coulomb interaction between the two detected fragments. Distortions in the Coulomb field of heavy reaction residues are evaluated by means of three-body Coulomb trajectory calculations.

Excitons and deexcitons in a neutral two-dimensional magnetoplasma with a strong population inversion.

Magnetoabsorption and emission by charge carriers in quantum wells under the conditions of a strong population inversion is investigated. The magnetoplasma is assumed to be neutral, the filling factor to be integer for both electrons and holes, and the temperature T=0. It is shown that under these conditions there exist two types of elementary excitations: excitons and deexcitons. The latter consist of a Fermi hole in the conduction band and an electron on an empty level in the valence band. The quasimomentum may be ascribed to deexcitons just as for excitons but the energy of the deexcitons is negative. It is shown that both excitons and deexcitons are stable near the direct Burstein edge (stability path), and a relation between their energies is found. Existence of deexcitons ensures the presence of narrow bands in the emission spectra due to final-state Coulomb interactions.

Pion correlations in ultra-relativistic heavy-ion collisions

We calculate two-pion correlation functions from the SPACER model of FRITIOF and from a Bjorken parameterization. The effects of hadronic decays and final-state Coulomb and strong interactions are included. Correlation functions are shown to depend strongly on both the total transverse momentum and the direction of the pair's relative momentum.

Detailed predictions for two-pion correlations in ultrarelativistic heavy-ion collisions.

We calculate two-pion correlation functions from a dynamical string model situation and from a Bjorken-scaling solution. The effects of hadronic decays and final-state Coulomb and strong interactions are included. Correlation functions are shown to depend strongly on both the total transverse momenta and the direction of the relative momentum of the pairs.

Fission in intermediate energy heavy ion reactions

A systematic study of reaction mechanisms at intermediate energies (50–100 MeV/A) has been performed at the Lawrence Berkeley Laboratory's BeValac using medium weight projectiles on medium and heavy element targets. A gas and plastic phoswich detector system was employed which gave large geometric coverage and a wide dynamic response. The particles identified with the gas detectors could be characterized into three components — intermediate mass fragments (IMF), fission fragments (FF) and heavy residues (HR). Major observed features are: the reaction yields are similar in the 50 to 100 MeV/A range, central collisions have high multiplicity of IMF's with broad angular correlations consitent with a large participant region, effects of final state Coulomb interactions are observed and give information on the size and temporal behavior of the source, true fission yields are dependent on target fissility and correlated with relatively peripheral collisions. Analysis of fission and evaporation yields implies limiting conditions for which fission decay remains a viable deexcitation channel.

KVV Auger spectra of tetracyanoouinodimethane semiconducting films

Auger measurements have been carried out on films of the semiconducting compound tetracyanoquinodimethane in order to interpret the observed line shape on the basis of the knowledge of the valence band of this organic molecule. A comparison has been made between the experimental spectra and the theory that takes into account the final state Coulomb interaction U between the two Auger holes. Such interaction affects the experimental line shapes which, in the unperturbed case, may be approximated by a self-convolution of the density of states. It has been found that U is small (about 2 eV) if compared with the valence band extension (43 eV). Thus, the Auger line shape may be described, with a good degree of approximation, by the self-convolution of the valence band density of states. The agreement between theory and experiment is quite satisfactory.

Coherence and Coulomb effects on pion interferometry.

The effects of coherence and final-state Coulomb interactions on the Bose-Einstein correlations of identical particles are studied. It is shown that these corrections can be important, reducing the apparent source size by 20%. Coherence effects are shown to significantly reduce the coherence parameters for small sources. Other causes of correlation are also discussed.

Double-Differential Neutron Emission Cross Sections of6Li and7Li at Incident Neutron Energies of 4.2, 5.4, 6.0 and 14.2 MeV

Energy-angle double-differential neutron emission cross sections of lithium isotopes were measured at incident neutron energies of 4.2, 5.4 and 14.2 MeV for 6Li and of 5.4, 6.0 and 14.2 MeV for 7Li using a time-of-flight spectrometer. Care was taken in background subtraction and in data correction for sample-size effects. Detailed comparison of the present results was made with the evaluated data in JENDL-3PR1. A spectrum fitting method was used to extract the 6,7Li(n, n'x)α and (n, 2n) reaction cross sections. Neutrons emitted from the (n, 2n) reactions were well described by the conventional evaporation model. A simple calculation with a final-state Coulomb interaction was effectively applied for the 6,7Li(n, n'x)α reactions. Angle-integrated cross sections of the 7Li(n, n't)α reaction were in good agreement with the JENDL-3PR1 data except the data measured at 6.0MeV. The angular distributions of elastically and inelastically scattered neutrons were successfully analyzed with the coupled-channel method at the incident neutron energy of 14.2 MeV.

Double-differential neutron emission cross sections of 6Li and 7Li at incident neutron energies of 4.2, 5.4, 6.0 and 14.2 MeV.

Energy-angle double-differential neutron emission cross sections of lithium isotopes were measured at incident neutron energies of 4.2, 5.4 and 14.2 MeV for 6Li and of 5.4, 6.0 and 14.2 MeV for 7Li using a time-of-flight spectrometer. Care was taken in background subtraction and in data correction for sample-size effects. Detailed comparison of the present results was made with the evaluated data in JENDL-3PR1. A spectrum fitting method was used to extract the 6,7Li(n, n'x)α and (n, 2n) reaction cross sections. Neutrons emitted from the (n, 2n) reactions were well described by the conventional evaporation model. A simple calculation with a final-state Coulomb interaction was effectively applied for the 6,7Li(n, n'x)α reactions. Angle-integrated cross sections of the 7Li(n, n't)α reaction were in good agreement with the JENDL-3PR1 data except the data measured at 6.0MeV. The angular distributions of elastically and inelastically scattered neutrons were successfully analyzed with the coupled-channel method ...

Reactions with three charged particles in final state

Three-particle Coulomb asymptotic states are derived. The knock-out reaction amplitude with distorted waves in the initial and final states is extracted using the Faddeev equations. The conditions are discussed under which this amplitude can be approximated by the distorted wave impulse amplitude. The influence of the Coulomb final state interaction on the differential quasielastic knock-out cross section is investigated. To this end the main singular part of the DWIA amplitude is singled out and compared with conventional approximations.

Inverted Cusps in Electron Spectra near Zero Velocity in an Attractive Coulomb Field

An inverted cusp in the near-zero-velocity electron-loss spectrum for a 2p (m = 0) initial state is predicted for an attractive final-state Coulomb interaction. The dip occurs in the singly differential cross section dsigma/dv/sub e/, calculated in Born approximation, at v/sub e/ = v/sub P/, where the electron velocity v/sub e/ matches the projectile velocity v/sub P/ and where the familiar cusp normally appears. The dip becomes more pronounced with increasing projectile velocities v/sub P/..-->..infinity. Its existence is traced to the odd Pi/sub z/ parity of the initial state.

Coulomb final state interaction and the charge effect in heavy ion projectile fragmentation at intermediate energies

In intermediate energy heavy-ion projectile fragmentation the width of the transverse momentum distribution for a given fragment mass depends on the charge number of the fragment. The greater the charge number, the smaller is the width of the transverse momentum distribution. Such a charge effect may be explained in terms of a Coulomb final state interaction between the fragment and the protons dissociated from the projectile. With simple assumptions concerning the fragmentation process, analytic expressions for the momentum dispersions are obtained and are found to give good agreement with experimental results.NUCLEAR REACTIONS Heavy ions. Projectile fragmentation. Intermediate energy. Coulomb final state interaction. Calculate ${{\ensuremath{\sigma}}_{\ensuremath{\perp}}}^{2}$, ${{\ensuremath{\sigma}}_{\ensuremath{\parallel}}}^{2}$.

Coulomb effects in relativistic nuclear collisions

We derive simple analytical formulas for Coulomb final-state interactions and apply them to the analysis of recent data on nuclear collisions. The π −/ π + ratio, the π + inclusive cross section, and the n/p ratio are studied. A relativistic field theoretic model is used to derive the formulas to first order in Zα. Using well-known non-perturbative results, we recast those formulas into an approximate non-perturbative form valid when finite-size effects are negligible. This allows us to calculate the important k → 0 limit. The final formulas are covariant and take into account multiple independently moving charged fragments of finite size and finite thermal expansion velocities. Our studies demonstrate analytically the complexity and importance of Coulomb distortions in nuclear collisions.

Acceptor-to-Band Transitions in Semiconductors: Photoluminescence, Exponential Absorption Edges, and Final-State Interactions

The effects of disorder and of final-state electron-hole interactions on acceptor-to-band absorption and photoluminescence spectra of semiconductors are treated theoretically within the effective-mass approximation. The results of the calculations are used to analyze photoluminescence spectra from lightly doped GaAs: Cd measured by Williams and Bebb. It is shown that although a proper one-electron calculation of optical absorption ${\ensuremath{\epsilon}}_{2}(\ensuremath{\omega})$ should include the effects of electron-hole spatial correlations, the excitonic Coulomb final-state interaction exactly cancels the spatial correlations in the case of infinite hole mass. Therefore the usual one-electron approximation, which neglects both spatial and Coulombic correlations, is valid for small electron-hole mass ratios (${m}_{e}\ensuremath{\ll}{m}_{h}$); for GaAs: Cd, the finite-mass-ratio corrections are nearly independent of energy and can be neglected. The major portion of the discrepancies between the Williams-Bebb data and Eagles's one-electron theory cannot be attributed to final-state interactions, but can be attributed to small internal microfields of strength ${10}^{3}$ to ${10}^{4}$ V/cm generated by disorder. The sources of these microfields are most likely to be piezoelectric phonons, but ionized impurities or excitons could possibly generate such fields. It is shown that photoluminescence lines are particularly sensitive to disorder and that the band-to-acceptor luminescence edge $L(\ensuremath{\omega})$ should not be a precisely exponential function of photon energy $\ensuremath{\hbar}\ensuremath{\omega}$. Instead the microfield model predicts that the edge shape should be approximately given by ln $L(\ensuremath{\omega})\ensuremath{\propto}{(\ensuremath{\hbar}{\ensuremath{\omega}}_{0}\ensuremath{-}\ensuremath{\hbar}\ensuremath{\omega})}^{\ensuremath{\alpha}}$, with $1<\ensuremath{\alpha}<\frac{3}{2}$. The existing data are compatible with $\ensuremath{\alpha}=\frac{3}{2}$, but the possibility of $\ensuremath{\alpha}=1$ cannot be ruled out without additional photoluminescence measurements further down the edge. If such measurements indicate that $\ensuremath{\alpha}$ is precisely equal to unity, the electric-microfield theory of exponential absorption edges may require revision.

A simple theory of the proton-proton final-state interaction in the reaction d + p → p + p + n

The amplitude for deuteron break-up in deuteron-proton collisions including Coulomb final-state interactions (in all partial waves) is derived analytically. The calculation is based on the assumption of a two-step reaction with a break-up mechanism of zero range. The nuclear final-state interaction is taken into account under the same approximations in the s-waves. A comparison with experiment indicates a clear improvement compared to the Watson-Migdal theory.