Delbrück scattering of 2.754 MeV photons by Bi and Th

Differential cross sections for the elastic scattering of 2.754 MeV photons by Bi and Th have been measured for angles ranging from 60° to 120°. The results deviate from the predictions of lowest-order Delbrück theory by factors between 1.1 and 1.4. The strong increase of these deviations with charge number, previously reported for Pb and U, has been confirmed. An interpretation in terms of the effect of the Coulomb correction is given.     

Small-angle neutron scattering from Pb and 238U between 0.6 and 2.2 MeV

Differential cross sections for neutrons scattered from natural Pb and 99.9 % isotopically pure ²³⁸U have been measured at 0.5°, 1.0°, and 1.5°. A neutron energy continuum was produced by bombarding a thick natural lithium target with a 4 MeV, nanosecond-pulsed proton beam. Neutron energies were determined by time-of-flight techniques. Flight paths from the neutron source to the scatterer and from the scatterer to the detector were each about 5 m. For the 0.5° measurements an annular detector geometry with an angular resolution of ± 0.1° was developed to maximize detection solid angle. Data were averaged over 100 keV intervals from 0.6 to 2.2 MeV and were corrected for backgrounds, multiple scattering and inelastic scattering. Measured cross sections were compared to optical-model calculations which included electromagnetic interactions of neutrons with the nuclear Coulomb field. Inclusion of an induced neutron electric dipole moment interaction was not warranted by the data. The angular dependence of the cross section was fitted with a function $\text{A + B}\text{cot}{}^2\text{case1}\text{2}$θ at each energy. Mean values of B for ²³⁸U are in agreement with theoretical predictions. Values of B for Pb are apparently 15 % too low.     

The energy dependence of Delbrück scattering investigated at Z = 73, 82 and 92

Using neutron capture γ-rays from a ¹⁴⁰CeO₂ source installed in the Grenoble high-flux reactor, differential cross sections for the elastic scattering of photons by Ta, Pb and U through θ = 120° have been measured for E = 4.291 and 4.767 MeV. These data have been supplemented by measuring elastic differential cross sections for U, θ = 120° and energies ranging from 0.279 to 1.332 MeV, using radioactive sources. The experimental differential cross sections below 1 MeV confirm the predicted Rayleigh amplitudes based on the second-order S-matrix within 3%. An excellent agreement between experiment and lowest-order Delbrück theory is observed between 1.0 and 1.4 MeV, showing that Coulomb corrections are small close to the threshold for pair production. At 4.291 and 4.767 MeV experiment and lowest-order Delbrück theory agree within ~12%     

The 208Pb(n,p)208Tl reaction at En = 97 MeV

Double-differential cross sections of the ²⁰⁸Pb(n,p) reaction have been measured at 97 MeV in the angular range 0°–30° for excitation energies up to 40 MeV. The experimental proton spectra have been compared with calculated spectra obtained with a statistical multistep direct reaction theory, in which charge exchange and inelastic response functions are described microscopically in the quasiparticle random phase approximation. The direct parts of the spectra have also been distributed on different multipole components by using a decomposition technique, based on sample angular distributions calculated within the distorted-wave Born approximation.     

7Li(α,n)10B differential cross-section measurements from threshold to Eα = 5.1 MeV

Differential cross sections for the ⁷Li(α, n)¹⁰B reaction have been measured at lab angles of 0°, 20°, 31°, 50°, 60°, 70°, 80°, 90°, 100° and 114° for α-particle energies between 4.385 and 5.1 MeV. A thick natural lithium target was bombarded with a 5.2 MeV, nanosecond-pulsed ⁴He⁺ beam and neutron velocity spectra at each angle were measured by time-of-flight techniques. These data have been converted to cross sections at 10 keV intervals in α-particle energy. Angular distributions have been fitted with a series of Legendre polynomials. Angle-integrated cross sections, the 0° excitation function, and angular distributions are compared to past measurements and R-matrix calculations.     

Elastic scattering of 2.754 MeV photons by Ta and interference between Rayleigh,Thomson and Delbrück scattering

Differential cross sections for the elastic scattering of 2.754 MeV photons by Ta have been measured for angles ranging from 30° to 150°. A comparison with lowest-order Delbrück theory reveals discrepancies of the same size as previously observed for Pb and Bi. Consideration is given to interference phenomena between Delbrück, Rayleigh and nuclear Thomson scattering.     

Discording power of Hamiltonian interactions

In this paper, we report the coherent scattering cross sections of some lanthanides at low momentum transfer in four angular ranges of (0°?4°), (0°?6°), (0°?8°) and for ²⁴¹Am (59.54 keV) and ¹³⁷Cs (661.6 keV) gamma rays. The coherent scattering cross sections were derived by subtracting the small contribution of the corresponding angle integrated incoherent scattering cross sections from the experimentally measured total (coherent + incoherent) scattering cross sections for the elements and energies of interest. The coherent scattering cross sections were found to agree with the corresponding theoretical cross sections within the range of experimental errors. The theoretical coherent scattering cross sections were computed by numerically integrating the S-matrix data of the elements in the angular ranges of interest. The incoherent scattering cross sections were based on the compilations which make use of the non-relativistic Hartree-Fock (NRHF) model for the atomic charge distribution.     

Differential cross sections of proton compton scattering at photon laboratory energies between 700 and 1000 MeV

Differential cross sections of proton Compton scattering have been measured at the Bonn 2.5 GeV synchrotron. 78 data points are presented as angular distributions at photon lab energies of 700, 750, 800, 850, 900, and 950MeV. The c.m. scattering angle ranges from 40°–130°, corresponding to a variation of the four momentum transfer squared betweent=?0.10 tot=?0.96 GeV² at 700 and 950 MeV, respectively. Two additional differential cross sections have been measured at 1000MeV, 35.6° and 47.4°. The angular distributions show forward peaks whose extrapolations to 0° are consistent with calculated forward cross sections taken from literature. The small angle data (|t| ?0.2 GeV²) together with the calculated cross sections at 0° are also consistent with the assumption of a slope parameterB of 5 GeV^?2. For the first time a rerise of the angular distributions towards backward angles has been observed. It becomes less steep with increasing energy. The most interesting feature of the angular distributions is a sharp structure which appears betweent=?0.55 GeV² at 700MeV andt=?0.72 GeV² at 950 MeV. Such a rapid varation of the differential cross section witht has never been ovserved in elastic hadron-hadron scattering or photoproduction processes. It indicates the existence of a dynamical mechanism which could be a peculiarity of Compton scattering.     

The Z-dependence of the elastic scattering of γ-rays

The differential cross sections for elastic scattering of 662 keV and 279 keV γ-rays from Pb, Ta, Nd, Sn, Mo, and Zn have been measured at angles ranging from 45° to 135°. The results are compared with theoretical predictions taking into account Rayleigh scattering and nuclear Thomson scattering. The theoretical Rayleigh amplitudes are based on second order perturbation theory according to Brown et al. and on form factors calculated from relativistic HFS wave functions. A semi-empirical method of correcting the form factors is developed, valid for energies between 150 keV and 750 keV and charge numbers up to Z = 82. The average difference between calculated and measured differential cross sections was found to be 6%.     

Scattering of negative pions on helium

Differential cross sections for negative pion scattering on ⁴He have been measured at five pion kinetic energies between 110 and 260 MeV in the angular range from 5° to 180°. Total cross sections have also been measured at eleven energies between 67 and 285 MeV. The differential cross sections have been fitted with a phenomenological expression for the nuclear scattering amplitude. Conventional phase shifts have been reconstructed starting from the parameters of the fits.     

Coherent π0-photoproduction on deuterium in the first resonance region

Differential cross sections for coherent π⁰-photoproduction from deuterium have been measured in the photon energy range from 240 to 400 MeV and for pion c.m. angles between 70 ° and 160 °. The recoil deuterons were analysed in angle and momentum by a magnetic spectrometer. The cross sections obtained were higher by a factor of about 2 compared with the results from Stanford [7], the only data available up to now in the first resonance region. Below the resonance the measured cross sections give a smooth extension to the low energy data from Glasgow [5] and Orsay [6].     

Cross sections of spallation residues produced in 1A GeV 208Pb on proton reactions

Spallation residues produced in 1 GeV per nucleon 208Pb on proton reactions have been studied using the Fragment Separator facility at GSI. Isotopic production cross sections of elements from 61Pm to 82Pb have been measured down to 0.1 mb with a high accuracy. The recoil kinetic energies of the produced fragments were also determined. The obtained cross sections agree with most of the few existing gamma-spectroscopic data. The data are compared with different intranuclear-cascade and evaporation-fission models. Drastic deviations were found for a standard code used in technical applications.     

Small-angle elastic scattering of 2.5 MeV neutrons

Differential cross sections and asymmetries of 2.50 MeV polarized neutrons elastically scattered by In, Ho, Hg, Bi and U have been determined for scattering angles from 2.1° to 9.1°. The measurements were carried out by the use of a neutron positional spectrometer. The results, when compared with the predictions of the electromagnetic interaction, indicate some deviation of 〈σ(θ)P(θ)〉 from the expected values. The observed cross sections are systematically greater than those evaluated within the framework of the optical model.     

Absolute triple differential cross sections for electron impact ionization of helium: Comparison between experimental and theoretical results at 256 eV collision energy

Triple differential cross sections have been measured for electron impact ionization of helium at 256 eV collision energy, 3 eV energy of the slow outgoing electrons and scattering angles of the fast outgoing electrons of 4°, 6°, 8°, and 10°. The data have been put on absolute scale by extrapolating the generalized oscillator strength to zero momentum transfer. In this optical limit the triple differential cross sections can be normalized by using the well-known cross sections for photoionization. The experimental data are compared with results of different theoretical approaches. For nearly all calculated curves rather good agreement with the measurements is obtained for the relative shape of the binary peak, while often its absolute cross section is overestimated. Concerning the recoil peak, larger discrepancies are found with respect to both, relative shapes and cross sections. A perceptible improvement can be stated for calculations which have been performed in a distorted wave approximation and in second Born approximation.     

Does break-up affect 9Be +209Bi fusion at the barrier?

The ⁹Be +²⁰⁹Bi fusion cross sections were measured in the 36.0 MeV ≤ E_lab≤ 50.0 MeV range, down to 0.6 mb, with high accuracy via in-beam detection of the ground state α-decay of the evaporation residues produced. The elastic scattering cross sections around 150° and 135° were also obtained with moderate angular resolution. The cross sections below the barrier are reproduced by coupled channel calculations which include only one break-up channel with a moderate strength and a phenomenological renormalization of the potential depth. These simple calculations overestimate the cross sections above the barrier most likely due to the fact that the ⁹Be break-up process becomes much stronger. The barrier distributions extracted do not have evident break-up signature since they show one-barrier structure. Received: 22 February 1999 / Revised version: 26 March 1999     

Rayleigh scattering of 59.54 keV photons from Zn,Mo, Sn,Ta, Au and Pb through angles from 60° to 150°

Differential cross sections for Rayleigh scattering of 59.54 keV photons by Zn, Mo, Sn, Ta, Au and Pb have been measured for angles ranging from 60° to 150°. The results are in an overall agreement with the predictions of second-order perturbation theory within the experimental error of about 4%. A comparison with the form factor approximation reveals pronounced dispersion effects at photon energies close to theK-shell binding energies. The agreement with the predictions of the dispersion theory is only of the order of 10% with discrepancies up to 25%.     

Charge exchange in collisions between heavy low-charged ions

The probabilities and the effective cross sections of collision-induced one-electron charge exchange between singly charged and four-charged heavy Xe, Cs, Ba, Pb, Bi, and U ions at energies E>0.1 keV/u are calculated by a method of multichannel normalization in the impact parameter representation. The cross sections are rather large with a maximum σ_m≈10⁻¹⁵ cm² at relative energies E _m ≈10–30 keV/u. For collision energies E<10 keV/u, the cross sections sharply decrease with growing resonance defect of the reaction. At high energies E>1 MeV/u, the charge exchange proceeds largely by the capture of inner shell electrons of the ionic targets. The charge exchange cross sections calculated for low-charged Xe, Cs, Ba, Pb, Bi, and U ions are compared with available theoretical and experimental data.     

COMPARISON OF RAYLEIGH AND COMPTON SCATTERING IN THE PHOTON-MOMENTUM TRANSFER REGION OF 2.219 × 3.814 Å−1

Rayleigh and Compton scattering differential cross sections for Mo, Ag and Sn have been measured from 55° and 105° at 59.5 keV using an Hp Ge detector. The ratios of measured cross sections are compared with ratios of theoretical scattering cross section values calculated using nonrelativistic form factors.     

Richtungskorrelation für Kernresonanzfluoreszenz und Lebensdauer des 412 keV-Niveaus von198Hg

Using the method of thermal Doppler-broadening of the emission line, the effective differential cross sections for nuclear resonance scattering for 412 keV photons by¹⁹⁸Hg has been measured for well defined scattering angles of 120° and 160°. The results indicate a partial mean lifetime for this energy level of τ_γ=(5·12±0·23)·10^?11 sec. This result differs appreciably from the values reported by other workers. Possible reasons for these discrepancies are discussed. The ratio of the differential cross sections for resonance scattering at angles of 120° and 160° is consistent with a 0-2-0 transition.     

Double-differential cross sections and kerma coefficients for light-charged particles produced by 96 MeV neutrons on carbon

Double-differential cross sections of inclusive light-ion (p, d, t, ³He and α) production in carbon induced by 96 MeV neutrons have been measured at eight laboratory angles from 20° to 160° in steps of 20°. Experimental techniques, as well as procedures for data taking and data reduction, are presented. Deduced energy-differential and production cross sections are herewith reported. Experimental cross sections are compared with theoretical reaction model calculations and experimental data in the literature. The measured production cross sections for protons, deuterons, tritons, ³He, and α particles support the trends suggested by data at lower energies. Deduced partial kerma coefficients for carbon are also shown.