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.     

Dispersion corrections to the forward Rayleigh scattering amplitudes around the L‐shell of tantalum and lead

Dispersion corrections to the forward Rayleigh scattering amplitudes of tantalum and lead in the photon energy range 6.4–24.14 keV were determined by a numerical evaluation of the dispersion integral that relates them through the optical theorem to the photoelectric cross‐sections. The photoelectric cross‐sections were extracted by subtracting the coherent and incoherent scattering contribution from the measured total attenuation cross‐section, using a high‐resolution, high‐purity germanium detector in a narrow‐beam good geometry setup. The real part of the dispersion correction to which the relativistic corrections calculated by Kissel and Pratt (S‐matrix approach) or Creagh and McAuley (multipole corrections) have been included are in better agreement with the available theoretical values than those values to which the relativistic corrections calculated by Cromer and Liberman (dipole corrections) are added. Copyright © 2006 John Wiley & Sons, Ltd.     

MASS ATTENUATION COEFFICIENTS FOR ELEMENTS MEASURED WITH CHARACTERISTIC X-RAYS FROM TARGETS EXCITED BY ENERGETIC PROTON

The characteristic X-rays from elemental or compound targets excited by energetic proton are quasi-monochromatic X-ray sources. The advantages of high line/ background ratio, controllable intensity as well as many available energies, make them suitable for applications in many important fields. The total mass attenuation cross sections of yttrium have been systematically measured by using this kind of X-ray source. The accuracy of experimental data has been improved to ±1%, which is much better than that of earlier results. The contributions of the coherent and incoherent scattering crees sections have been calcu-lated in accordance with the present experimental condition. And the total photoelectric cross sections have been obtained by subtracting the scattering cross section from the measured total cross sections. The com-parisons of our experimental results with the available data of earlier investigations as well as with the theo-retical calculations have been presented and discussed.     

Bistatic scattering by arbitrarily shaped objects with rough surface at optical and infrared frequencies

The scattering cross sections for arbitrarily shaped dielectric objects with rough surface are determined for optical and infrared frequencies using the Kirchhoff approximation. The formula of the coherent scattering cross section is derived, and numerical method of incoherent scattering cross section is given. As a specific example, the infrared laser scattering cross sections of rough spheres are calculated at 1.06 m.     

On the propagation of coherent radiation in gases

The propagation of coherent light of high amplitude is governed by the refractive index found herein. Light scattering occurs because of conversion of the coherent into incoherent radiation. Appropriate cross sections are found.Translated from Izvestiya Uchebnykh Zavedenii, Fizika, No. 4, pp. 40–45, April, 1973.     

The scattering of slow neutrons by phosphorus and nitrogen

The coherent scattering lengthsb and the free cross sections for the scattering of slow neutrons by P and N were measured on powdered samples. From the results we derived data for the incoherent cross sections and for the spin state scattering lengths. We found for phosphorus:b=5.13±0.01 fm, σ_free=3.134±0.010b and σ_inc=0.006±0.016b, and for nitrogen:b=9.36±0.02 fm, σ_free=10.03 ±0.08 b and σ_inc=0.4±0.1 b. Derived values for resonance parameters of N are given.     

Total toK-shell photoelectric cross section ratios in Zr,Ag, Ta,and Th

Total photon atomic cross sections in elements Zr, Ag, Ta and Th were determined around theirK-edges in the energy region 6 to 400 keV with a good geometry set-up using proportional counter or Ge(Li) detector system. From these values the photoelectric cross sections were obtained by subtracting the theoretical values of coherent and incoherent scattering cross sections. The resulting photoelectric cross sections were fitted to curves above and below theK-edge for each element and extrapolated on either side and the total toK-shell photoelectric cross section ratios were determined with an error not exceeding 2%. The ratios were compared with the theoretical values obtained by Grodstein and others, as also from the empirical relation of Hubbell. The present values show good agreement with those of Scofield. A definite trend of decrease of the ratio as the energy increases is observed in the case of Th unlike in the previous experimental studies.     

Gaussian beam scattering from arbitrarily shaped objects with rough surfaces

The scattered field of Gaussian beam scattering from arbitrarily shaped dielectric objects with rough surfaces is investigated for optical and infrared frequencies by using the plane wave spectrum method and the Kirchhoff approximation, and the formulae for the coherent and incoherent scattering cross sections are obtained theoretically based on geometrical optics and tangent plane approximations. The infrared laser scattering cross sections of a rough sphere are calculated at 1.06 μm, and the influence of the beam size is analysed numerically. It is shown that when the beam size is much larger than the size of the object, the results in this paper will be close to those of an incident plane wave.     

Gaussian beam scattering from arbitrarily shaped objects with rough surfaces

Abstract

The scattered field of Gaussian beam scattering from arbitrarily shaped dielectric objects with rough surfaces is investigated for optical and infrared frequencies by using the plane wave spectrum method and the Kirchhoff approximation, and the formulae for the coherent and incoherent scattering cross sections are obtained theoretically based on geometrical optics and tangent plane approximations. The infrared laser scattering cross sections of a rough sphere are calculated at 1.06 μm, and the influence of the beam size is analysed numerically. It is shown that when the beam size is much larger than the size of the object, the results in this paper will be close to those of an incident plane wave.     

Interactions of slow neutrons with nuclides of antimony,tellurium and iodine

Coherent neutron scattering lengths and total cross sections have been measured on samples of ordinary Sb, Te, I and on isotopically enriched compounds. From the experimental data for neutron energies of 0.57 meV, 1.26 eV and 5.2 eV the following data were obtained: the coherent scattering lengths (in fm) of the bound atoms Sb (5.57±0.03);¹²¹Sb(5.71±0.06),¹²³Sb(5.38±0.07); Te(5.80±0.03) and for its isotopes of the mass number 122(3.8±0.2); 123(?0.05±0.25?i·0.100); 124(7.95±0.10); 125(5.01±0.08); 126(5.55±0.07); 128 (5.88±0.07); 130(6.01±0.07). the thermal absorption cross sections (in barn) for Sb(4.91±0.05);¹²¹Sb(5.77±0.12);¹²³Sb(3.8±0.2); Te(4.05±0.05) and I(6.15±0.06). The combination of the measured values of scattering lengths and -cross sections resulted in data for coherent and incoherent cross sections. Taking account of resonance data a complete set of spin state- and reconance scattering lengths has been obtained and discussed.     

eta-->gammagamma decay width via the Primakoff cross section

Incoherent eta photoproduction in nuclei is evaluated at forward angles within 4 to 9 GeV using a multiple scattering Monte Carlo cascade calculation with full eta-nucleus final-state interactions. The Primakoff, nuclear coherent and nuclear incoherent components of the cross sections fit remarkably well previous measurements for Be and Cu from Cornell, suggesting a destructive interference between the Coulomb and nuclear coherent amplitudes for Cu. The inelastic background of the data is consistently attributed to the nuclear incoherent part, which is clearly not isotropic as previously considered in Cornell's analysis. The respective Primakoff cross sections from Be and Cu give Gamma(eta-->gammagamma)=0.476(62) keV, where the quoted error is only statistical. This result is consistent with the Particle Data Group average of 0.510(26) keV and in sharp contrast (approximately 50%) with the value of 0.324(46) keV obtained at Cornell.     

Angular and energy distribution of electrons produced by 200–500 keV protons in gases

The cross beam method was used to measure double differential ionization cross sections for electron production by 200–500 keV protons incident on a molecular beam. The ejected secondary electrons were detected by an electron multiplier and an electrostatic 90 °-spectrometer which was movable in the scattering chamber from 18 °–155 ° with respect to the incident proton direction. After the elimination of disturbing electric and magnetic fields, electrons were measured at energies down to 1 eV. The absorption of the very slow electrons along their path through the spectrometer could be minimized by using a relatively low gas pressure in the scattering chamber of a few 10^?5 Torr. The efficiency of the electron detector was determined with an electron source whose emission rate per solid angle was known. Absolute cross sections and their angular dependence were obtained by measuring the slow electrons—ejected with a relatively high rate—without the molecular beam; these data being used to normalize the electron spectra acquired with the molecular beam. Ionization cross sections with 300 keV protons incident on helium are discussed and except for the very slow electrons, a good agreement is found with results of Ruddet al.     

Calculations of Infrared Laser Beam Scattering from Rough Dielectric Objects

The coherent and incoherent scattering cross sections of Infrared Laser Gaussian beam scattering from arbitrarily shaped convex dielectric objects with rough surfaces are investigated by using plane wave spectrum method and physical optics approximation. In the paper, the infrared laser scattering cross sections of rough sphere are calculated at 10.6 m , and the influence of the beam size, permittivity, and polarization as well as roughness parameters is analyzed numerically. When the beam size is much larger than the size of object, the results in the paper can reduce to those of an incident plane wave. On the other hand, for the case of roughness statistical parameter close to zero, only the forward scattering has a parent difference compared with the result of gaussian beam scattering from smooth sphere.     

Rayleigh Scattering of 59.5 keV γ-Rays by Mo and Sn

The differential cross sections for coherent scattering of 59.5 keV γ-rays by Mo and Sn were measured using a high-purity germanium detector. The results were compared with predictions of form factor theories and S-matrix calculations.     

Streuung von Helium-Atomstrahlen in Edelgasen

The scattering of Helium atomic beams in rare gases is investigated by measurements of total elastic scattering cross sections. With the device described the dependence of total scattering cross sections of the relative velocity of the scattering atoms was measured. For variation of the beam velocity in the range of 1:8 a He beam source was used which could be cooled down with liquid helium from room temperature to 4.8 °K. The detector is of the universal-detector-type. A Wien filter is used as mass filter. The lowest detectable particle density is 6.3 · 10³ He-atoms/cm³. The measured scattering cross sections are in qualitative agreement with the theory ofBernstein.     

Measurement of cross sections for inelastic cold-neutron scattering in metals and polymers by the method of (<Emphasis Type="Italic">n, γ</Emphasis>) analysis

The results obtained by measuring the cross sections for the inelastic scattering of very cold neutrons for a number of metals and polymers by the method of a neutron-irradiation analysis are presented. The method is based on simultaneously measuring events of inelastic scattering and neutron capture in the sample under investigation via recording gamma radiation with a semiconductor germanium detector. Neutron capture by a nucleus of the sample is accompanied by the prompt radiation of gamma rays having a known spectrum. Upon inelastic scattering, a neutron acquires thermal energy. Upon leaving the sample, this neutron is absorbed in a special converter that contains the isotope ¹⁰B. The capture of the neutron by a ¹⁰B nucleus is followed by the emission of a 477-keV gamma ray. The probabilities of capture and inelastic scattering are proportional to the respective neutron-interaction cross sections, and the ratio of the recorded detector counts corresponding to events of the two types does not depend on the spectrum of the incident flux of very cold neutrons or on the trajectory of neutron motion in the sample. The sought inelastic-scattering cross section at a fixed sample temperature is calculated by using this ratio and the known cross section for neutron capture by the sample isotope having a known gamma-radiation spectrum.     

Incoherent bremsstrahlung in nuclei

We have studied the processes A(e, e′γ)X in nuclei, or incoherent bremsstrahlung, and determined expressions for the cross section in terms of the same nuclear response functions R_L, R_T, which appear in inclusive electron scattering (e, e′) in nuclei. Calculations of the cross sections are carried out using a Fermi gas model, complemented by the local-density approximation, to evaluate the response functions. We have carried out a study which shows that the reaction can be used to determine reliably the response functions from experimental data. On the other hand we have compared the incoherent bremsstrahlung with the coherent one in order to see the limits to the tagging technique, which produces monochromatic photons based on the assumption of the dominance of the coherent process. We observe that at energies E_γ < 1 GeV the dominance of the coherent process extends to relatively large scattering angles, making the present technique completely safe. However, as the energy of the electron increases, the region of dominance of the coherent process is reduced to smaller scattering angles. These results should be of use when extending the tagging technique to planned or future electron facilities.     

Coherent photon production in heavy-ion collisions at intermediate energies

We have studied photon production in heavy-ion collisions at intermediate energies in the Molecular Dynamics approach, where the radiation amplitudes have been derived from the many-body dynamics in the classical bremsstrahlung formalism. This concept allows for a comparison of cross sections obtained by coherent and incoherent summation of amplitudes. The numerical results show a significant enhancement of the coherent cross section for photon energies below 40 MeV due to the dynamical influence of the nuclear mean field.     

Photon interaction cross-sections and anomalous scattering factors of Cu and Ag

Total attenuation cross sections of copper and silver have been measured in the energy range 5 to 85 keV in a narrow beam good geometry set up using X- andγ-rays emitted from radio isotopes, by employing a high resolution hyper pure germanium detector. From the measured values, the photoeffect cross-sections have been derived by subtracting a small contribution of the sum of the theoretical coherent and incoherent scattering cross sections. The photoeffect cross-sections so obtained are found to be in better agreement with the unrenormalized values of Scofield [10]. These photoeffect cross-sections have been used to evaluate the dispersion corrections (also called anomalous scattering factors)f ⁺ andf″ for the forward Rayleigh scattering amplitude by a numerical evaluation of the dispersion integral that relates them at the energies at which the cross-sections have been measured. To thef ⁺ values so obtained, the relativistic corrections proposed by different investigators are included separately and the valuesf′ so obtained are compared with the available data and discussed. Possible conclusions are drawn from the present study.