Photoelectric Cross Sections Research Articles

Characterization of Nonmarine and Shallow Marine Sediments Using Electrofacies and Advanced Volumetric Methods, Eastern San Joaquin Valley: ABSTRACT

The Delmontian Chanac and Pliocene Etchegoin Formations of the Kern Front field, Kern County, California, were studied to relate log response to lithofacies in nonmarine and transitional marine depositional environments. Six wells in a roughly north-south cross section were analyzed by the Multiwell Faciolog data-reduction technique. A lithology-sensitive data base created by the bulk-density, neutron-porosity, gamma-ray (also a relative grain-size indicator), and effective photoelectric cross section index logs was calibrated using detailed core and side-wall data. VOLAN volumetric analyses, using wireline-log data including EPT measurements, then provided reservoir property measures of porosity, permeability, and saturation. Ten electrofacies were identified, including three types of claystone, a siltstone, and six types of sandstone. A spectrum of sandstone composition ranged from very argillaceous to somewhat clayey with carbonaceous stringers to silty to relatively clean. Two sands showing gas effect were also defined. The thin-bedded shaly Chanac strata are characterized by rapid vertical and horizontal changes in lithology, which make well-to-well correlations difficult. The beds were deposited chiefly as fluvial channels and alluvial fans with interbedded lutites representing overbank or ephemeral lacustrine deposits. Many channels are stacked. Etchegoin strata are composed of an upward-coarsening shoreface sequence, culminated by seaward-prograding tidal channels. Stratigraphy at leastmore » partly controls the trap and complicates steamflood efforts.« less

Individual atoms and molecules as dielectric media

A clear physical connection is made between the optical response of atoms and molecules and elementary textbook discussions of the electrostatics of dielectric media. Electrons within atoms and molecules are shown to respond to the Coulomb fields of neighboring electrons in just the same way as the dipole moment of an atom responds to the fields established by dipoles on neighboring atoms. In the presence of a uniform static electric field, a nonuniform internal effective field within the electronic system can be displayed explicitly. Both screening and antiscreening of the external field are found. At finite frequency, the dielectric properties of atoms and molecules are reflected in the photoelectric cross section. The effective field at finite frequency is presented in a pictorial fashion, which helps elucidate the physics of the photoelectric emission process. Calculations of the cross section using the dielectric approach yield extremely accurate values when compared to experiment.

Photoelectric effect aroundK-edges in the elements Ce, Sm, Dy and Yb

Photoelectric cross-sections are determined in the elements Ce, Sm, Dy and Yb in the photon energy range from 24 to 122 KeV employing Si(Li) and Ge(Li) detecting systems and using subtraction technique. The deduced photoelectric cross-sections and theK-shell photoelectric cross-sections atK-edges are found to be in satisfactory agreement with the theoretical values of Storm and Israel and Scofleld.

Photoelectric cross sections in heavy elements derived from total attenuation measurements

Total photon cross sections for four elements, Ta, W, Au and Pb, were measured at photon energies of 30.85, 36.9, 81.0 and 320.0 keV using a good geometrical setup and a single channel scintillation spectrometer. The measured total photon cross sections are compared with the theoretical compilations of Storm and Israel and the available data of earlier investigations. The scattering cross sections obtained by interpolation using the values of Hubbell et al. were subtracted from the measured total photon cross sections to obtain the total photoelectric cross sections. The total photoelectric cross sections thus derived are compared with the latest theoretical compilations of Scofield.

Photoelectric cross sections of 279 and 661 KeV gamma rays in Y, Ce, Dy and Yb

Total photoelectric cross sections were measured for 279 and 661 keV photons in Y, Ce, Dy and Yb by direct measurement of the photoelectron intensity using a well-type plastic scintillation spectrometer in conjunction with a multichannel analyser. The experimental values were found to be more or less in agreement with the interpolated theoretical values of Storm and Israel (1970) and of Scofield (1973) and with the values of Veigele (1973) which were mostly based on previous experimental results.

Transmitted photon spectra of low-energy gamma rays through water

From the transmitted spectra of point sources it is concluded that in a medium of low effective atomic number, a multiple-scatter peak is observed at an energy below 100 keV where Compton collisions are not very effective in energy-degradation and photoelectric cross-section is negligible. The energy of the peak does not depend on the thickness and physical state of the medium, or on the primary photon energy. The intensity of the peak decreases exponentially with the thickness of the medium. Measured build-up factors are compared with the calculated ones available in the literature.

Atomic photoelectric effect near threshold edges.

Total photon attenuation coefficients near absorption edges are determined in certain suitable elements and compounds. Photoelectric cross sections for elements are deduced from these by subtracting the coherent and incoherent scattering cross sections as well as other elemental cross sections in the cases of compounds. Certain deviations are observed on comparison with the available theoretical and experimental compilations. The I/sub L//sub ..cap alpha..//Il x-ray intensity ratio measured by photon excitation near threshold is found to agree better with the theory than the other available experimental data.

Measured energy dependence of K-shell photoelectric cross sections for Ti, Fe, Ni, and Zn in the energy region 9-18 keV.

Our earlier measurements of the energy dependence of K-shell photoelectric cross sections for Y, Mo, Ag, and Sn in the energy region 18--44 keV have been extended to elements Ti, Fe, Ni, and Zn in the energy range 9\ensuremath{\le}E\ensuremath{\le}18 keV. The experiment has been performed under improved experimental conditions using a modified double-reflection geometrical setup and Si(Li) detector in place of a NaI (Tl) detector used in the earlier measurements. The results compare well with the theoretical calculations, confirming the earlier trend down to 9 keV.

Measurement of Ll, L alpha, L beta, and L gamma x-ray-production cross sections in some high-Z elements by 60 keV photons.

Ll, L\ensuremath{\alpha}, L\ensuremath{\beta}, and L\ensuremath{\gamma} x-ray-production cross sections have been measured in elements Ta, W, Au, Hg, Tl, Pb, Bi, Th, and U for 60-keV photons. The measured values have been interpreted in terms of photoelectric cross sections, fluorescence yields, Coster-Kronig transition probabilities, and radiative decay rates. A fairly good agreement is found between the experimental and calculated values.

Total photon cross sections in Pt-Rh alloys.

Total photon cross sections at energies 6.4, 7.1, 8.04, 10.53, 14.414, 17.44, and 22.1 keV are reported in four Pt-Rh alloys of different proportions. Small deviations are observed from the data compilations, based primarily on experimental determination at certain energies. However, agreement is generally good between the theoretical photoelectric cross sections and the photoelectric cross sections which are deduced from the measured totals. Thus the deviations, though small, suggest the need for more accurate experimental compilations perhaps based on certain criteria for selecting the data from the available measurements for each element in the region of absorption edges.

High energy xps using a monochromated Ag Lα source: resolution, sensitivity and photoelectric cross sections

Resolution, sensitivity and calibration data are presented for a novel high energy XPS source, monochromated Ag Lα radiation ( hv = 2984.3 eV). Adequate resolution is attainable for good signal/noise spectra, whilst values for experimental sensitivity factors agree well with theoretical cross section values calculated by Nefedov. This allows an evaluation of ESCA 3 Mk. II transmission function up to 3000 eV, which appears to obey an approximate E −1 2 dependence. Monochromated Ag Lα (linewidth 1.3 eV) overcomes the problem of broad natural linewidths for high energy sources, such that chemical state information can be gained. Various new core level and Auger peaks are developed, a notable feature being the 1s core level and KLL Auger transition capability from Al through to Cl. Improved sensitivity is experienced for elements whose major peaks occur in the 1500–3000 eV BE range, whilst there is no serious reduction of sensitivity in the conventional XPS energy range.

Total mass attenuation cross sections of rare earth elements in the energy range 30 to 662 keV and derived photoelectric cross sections

Total mass attenuation cross sections in fourteen rare earth elements at ten photon energies are measured in a narrow beam geometry using two NaI (T1) scintillation detectors for low- and medium-energy photons. Measured total mass attenuation cross sections are compared with the theoretical compilations of Storm and Israel. Total photoelectric cross sections are derived from the measured total mass attenuation cross sections and are compared with theoretical values of Schofield. The experimental results were also compared with earlier reports. In general there is an overall agreement with previous investigations. The experimental total mass attenuation cross sections and total photoelectric cross sections are in good agreement with theoretical predictions.

Enhancement of Chromosomal Damage in Human Lymphocytes Irradiated with X Rays in the Presence of Iodine

The production of chromosomal aberrations resulting from X irradiation of peripheral human blood lymphocytes in the presence or absence of Angioconray-80%, an iodised contrast medium, was investigated. This experiment confirmed an enhanced radiation effect, which is essentially explained by the increase of absorbed dose due to the high photoelectric cross section of iodine for X rays. Nevertheless the cytotoxicity of contrast medium alone cannot be neglected, and at a 0.1 M concentration in unirradiated blood it produced chromosome damage equivalent to 0.5 Gy. The distributions of aberrations among the cells, with and without contrast medium, were analysed using two statistical tests of goodness-of-fit for the Poissonian distribution. The results are discussed mostly in terms of dose enhancement factors.

Total and photoelectric cross sections in some rare-earth elements

Total photon cross sections for four rare-earth elements, Y, Gd, Dy, and Er, were measured at photon energies of 30.85, 32.1, 36.9, 52, 72.1, 81.0, 84.3, and 145.5 keV using a good geometrical setup and a single-channel scintillation spectrometer. The results of some of the elements are new. The measured total photon cross sections are compared with the theoretical compilations of Storm and Israel and the available data of earlier investigations. The scattering cross sections obtained by interpolation using the values of Hubbell et al. were subtracted from the measured total photon cross sections to obtain the total photoelectric cross sections. The total photoelectric cross sections thus derived are compared with the latest theoretical compilations of Scofield.

Experimental K-shell fluorescence yield of monocrystalline germanium

The result of an experimental evaluation of the K-shell fluorescence yield, omega K, of monocrystalline Ge is reported. The procedure makes use of the information contained in the escape peaks which are present in the characteristic X-ray spectra given by an HP Ge detector. Details of the experimental methodology, peak area evaluations and uncertainty treatments are described. A value omega K=0.549+or-0.011 is obtained and compared with recent values obtained from experiment, theory, interpolation or normalisation. The authors consider the effects of the outer-shell configuration and the use of theoretical photoelectric cross section values.

Interpretation of wireline log and core data from a mid-Jurassic sand/shale sequence

AbstractInterpretation of downhole wireline logs is generally a major source of information used to build up a picture of the quality and distribution of reservoir rocks. Logging tools respond to a number of variables and comparison of a suite of different logs is usually required to isolate and identify the response due to a single factor, e.g. porosity or clay content. A new tool, the litho-density tool (LDT), has been used along with conventional logging tools in a mid-Jurassic sand/shale sequence. The LDT simultaneously measures Pe (effective photoelectric cross-section) and ρa (apparent bulk density). Pe is a function of atomic number which in turn reflects lithology or mineral composition. By using cross-plots derived from the LDT and other logs, patterns of mineral abundance are indicated.

Cubic spline techniques for fitting X-ray cross sections

Cubic spline least squares fitting algorithms are developed for continous functions and functions with jump discontinuities. The cubic spline coefficients for incoherent and coherent scattering cross sections for elements from sodium through cobalt are reported for energies from 1 to 150 keV, and when two interior knots (three regions) are used they yield accuracies better than those obtined by a single cubic polynomial. Specialized discontinuous cubic spline functions are used to fit X-ray photoelectric cross sections to allow accurate fitting across the absorption edge discontinuities for a wide range of energies with a very simple function. Cubic spline coefficients for photoelectric cross sections of all elements in the atomic number range from 11 to 27 and in the energy range from 1 to 150 keV are reported. The cubic spline representation provides a computationally faster method of using X-ray cross sections than polynomial interpolation from discrete data sets and requires much less computer storage.

Measurement ofL-shell photoelectric cross-sections in lower intermediateZ elements at 6 keV

L-shell photoelectric cross-sections have been measured at 6 keV for eight elements in the range 40⩽Z⩽53. The measurements agree with theoretical calculations.

Energy dependence of photon-induced L-shell X-ray intensity ratios in some high-Z elements

The L-shell X-ray intensity ratios I(Lalpha )/I(Ll), L(Lalpha )/I(Lbeta ) and I(Lalpha )/I(Lgamma ) in Au, Pb, Th and U at various photon energies 15<or=E<or=60 keV have been measured and their energy dependence is studied. A comparison of the experimental values is made with those calculated using the X-ray emission rates and subshell photoelectric cross sections from Schofield (1973), subshell fluorescence yields and Coster-Kronig transition probabilities from Chen and Crasemann (1981), Krause et al. (1978), McGuire (1971) and Rao et al. (1969, 1971). Fairly good agreement is observed between the present experimental results and the calculations, within the uncertainties of the determinations. To the best of the authors' knowledge, the results in the elements Pb, Th and U, at the present experimental energies, are reported for the first time.

Photoelectric cross sections around the K edge

Total attenuation cross sections for four elements, Ta, W, Au and Pb, were measured at the photon energies 32.1, 52, 72.1, 84.3, 145.4 and 279.2 keV. A good narrow beam geometry with two NaI(Tl) scintillation counters in conjunction with a single-channel analyser was used for the detection of low and medium energy photons. The measured total attenuation cross sections are compared with the theoretical compilations of Storm and Israel and the available earlier investigations. The scattering cross sections obtained by interpolation using the atomic data tables of Storm and Israel were subtracted from the measured total cross sections to obtain the photoelectric cross sections. The photoelectric cross sections thus derived are compared with the latest theoretical values of Scofield.