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Borehole Geometry

The Experts below are selected from a list of 222 Experts worldwide ranked by ideXlab platform

R J De Meijer – 1st expert on this subject based on the ideXlab platform

  • mcnp modelling of scintillation detector γ ray spectra from natural radionuclides
    Applied Radiation and Isotopes, 2002
    Co-Authors: P H G M Hendriks, Marko Maucec, R J De Meijer

    Abstract:

    gamma-ray spectra of natural radionuclides are simulated for a BGO detector in a Borehole Geometry using the Monte Carlo code MCNP. All gamma-ray emissions of the decay of K-40 and the series of Th-232 and U-238 are used to describe the source. A procedure is proposed which excludes the time-consuming electron tracking in less relevant areas of the Geometry. The simulated gamma-ray spectra are benchmarked against laboratory data. (C) 2002 Elsevier Science Ltd. All rights reserved.

  • sediment density dependency of natural gamma ray spectra in a Borehole Geometry
    Applied Mathematics and Computation, 2001
    Co-Authors: P H G M Hendriks, Marko Maucec, R J De Meijer

    Abstract:

    The Nuclear Geophysics Division of the Kernfysisch Versneller Instituut (NL) is developing and applying tools based on nuclear principles for in-situ measurements such as towed waterbed, airborne and Borehole measurements. One of these tools, the MEDUSA system, is tailored for in-situ high-efficiency measurements of natural gamma ray spectra [1]. The concentrations of the natural radionuclides 40K, 232Th and 238U present in the sediment are extracted from the (nearly) full natural gamma-ray spectrum utilizing so-called “standard spectra”

J.r. Giles – 2nd expert on this subject based on the ideXlab platform

  • The efficiency calibration and development of correction factors for an in-situ high-resolution gamma spectroscopy well logging system
    Health Physics, 1996
    Co-Authors: J.r. Giles, R.r. Brey, T.f. Gesell

    Abstract:

    A Gamma Spectroscopy Logging System (GSLS) has been developed to study sub-surface radionuclide contamination. Absolute efficiency calibration of the GSLS was performed using simple cylindrical Borehole Geometry. The calibration device incorporated NORM that emitted photons ranging from 186 keV to 2,614 keV. More complex Borehole geometries were modeled using commercially available shielding software. A linear relationship was found between increasing source thickness and relative photon fluence rates at the detector. Examination of varying porosity and moisture content showed that as porosity increases, relative photon fluence rates also increase for all energies. Due to build-up, relative photon fluence rates increase with decreasing energy at higher porosities and moisture contents. Attenuation effects due to iron, water, PVC, and concrete cylindrical shields were found to agree with previous studies. Regression analyses produced energy dependent equations for efficiency corrections applicable to spectral gamma-ray well logs collected under nonstandard Borehole conditions.

  • The efficiency calibration and development of environmental correction factors for an in situ high-resolution gamma spectroscopy well logging system
    , 1996
    Co-Authors: J.r. Giles

    Abstract:

    A Gamma Spectroscopy Logging System (GSLS) has been developed to study sub-surface radionuclide contamination. Absolute efficiency calibration of the GSLS was performed using simple cylindrical Borehole Geometry. The calibration source incorporated naturally occurring radioactive material (NORM) that emitted photons ranging from 186-keV to 2,614-keV. More complex Borehole geometries were modeled using commercially available shielding software. A linear relationship was found between increasing source thickness and relative photon fluence rates at the detector. Examination of varying porosity and moisture content showed that as porosity increases, relative photon fluence rates increase linearly for all energies. Attenuation effects due to iron, water, PVC, and concrete cylindrical shields were found to agree with previous studies. Regression analyses produced energy-dependent equations for efficiency corrections applicable to spectral gamma-ray well logs collected under non-standard Borehole conditions.

Carey M. Rappaport – 3rd expert on this subject based on the ideXlab platform

  • Microwave Subsurface Imaging Using Direct Finite-Difference Frequency-Domain-Based Inversion
    IEEE Transactions on Geoscience and Remote Sensing, 2009
    Co-Authors: Qiuzhao Dong, Carey M. Rappaport

    Abstract:

    We have developed a new algorithm for electromagnetic inverse scattering problems in inhomogeneous media using finite-difference frequency-domain (FDFD) forward modeling, referred to as the FDFD-based inversion method. The key issue of this method is to build a linear expression for the inverse problem from an FDFD forward model by using Born approximation to neglect mutual coupling between scattered pixels and to then solve for the inverse coefficient matrix. An important advantage of this matrix-based method is that there is no need to specify a Green’s function. As such, this inverse scattering algorithm is easily implemented and is robust to the heterogeneity in the background. We test the algorithm with a microwave subsurface object detection application using cross-well radar. The new method is compared with conventional inversion using Green’s function-based Born approximation. Numerical experiments are presented for a 2-D Borehole Geometry for buried object detection in uniform soil and in multilayered soil backgrounds.

  • Microwave Subsurface Crosswell Imaging using Finite Difference Frequency Domain Modeling
    IGARSS 2008 – 2008 IEEE International Geoscience and Remote Sensing Symposium, 2008
    Co-Authors: Qiuzhao Dong, Carey M. Rappaport

    Abstract:

    We have developed a new algorithm for electromagnetic inverse scattering problem in inhomogeneous media using finite difference frequency domain (FDFD) forward modeling, referred as FDFD-based inversion method. The key issue of this method is to build a linear expression for the inverse problem from the FDFD forward modeling by using the Born approximation. An important advantage of this matrix-based method is that there is no need to specify a Green’s function. This inversion algorithm is applied to microwave subsurface object detection using cross well radar. The new method is compared with the conventional inversion using Green function-based Born Approximation (GFBA). This EM scattering inverse algorithm is easily implemented and is robust to the heterogeneity of background. Numerical experiments are presented for a two dimensional Borehole Geometry for buried object detection in soil.

  • IGARSS (4) – Microwave Subsurface Crosswell Imaging using Finite Difference Frequency Domain Modeling
    IGARSS 2008 – 2008 IEEE International Geoscience and Remote Sensing Symposium, 2008
    Co-Authors: Qiuzhao Dong, Carey M. Rappaport

    Abstract:

    We have developed a new algorithm for electromagnetic inverse scattering problem in inhomogeneous media using finite difference frequency domain (FDFD) forward modeling, referred as FDFD-based inversion method. The key issue of this method is to build a linear expression for the inverse problem from the FDFD forward modeling by using the Born approximation. An important advantage of this matrix-based method is that there is no need to specify a Green’s function. This inversion algorithm is applied to microwave subsurface object detection using cross well radar. The new method is compared with the conventional inversion using Green function-based Born Approximation (GFBA). This EM scattering inverse algorithm is easily implemented and is robust to the heterogeneity of background. Numerical experiments are presented for a two dimensional Borehole Geometry for buried object detection in soil.