The Experts below are selected from a list of 105 Experts worldwide ranked by ideXlab platform

William E Dickerson - One of the best experts on this subject based on the ideXlab platform.

  • guidance on the use of handheld survey meters for radiological triage time dependent Detector Count rates corresponding to 50 250 and 500 msv effective dose for adult males and adult females
    Health Physics, 2012
    Co-Authors: Wesley E Bolch, Jorge L Hurtado, R Manger, Eric Burgett, Nolan E Hertel, William E Dickerson
    Abstract:

    In June 2006, the Radiation Studies Branch of the Centers for Disease Control and Prevention held a workshop to explore rapid methods of facilitating radiological triage of large numbers of potentially contaminated individuals following detonation of a radiological dispersal device. Two options were discussed. The first was the use of traditional gamma cameras in nuclear medicine departments operated as makeshift wholebody Counters. Guidance on this approach is currently available from the CDC. This approach would be feasible if a manageable number of individuals were involved, transportation to the relevant hospitals was quickly provided, and the medical staff at each facility had been previously trained in this non-traditional use of their radiopharmaceutical imaging devices. If, however, substantially larger numbers of individuals (100 s to 1,000 s) needed radiological screening, other options must be given to first responders, first receivers, and health physicists providing medical management. In this study, the second option of the workshop was investigated by the use of commercially available portable survey meters (either NaI or GM based) for assessing potential ranges of effective dose (G50, 50Y250, 250Y500, and 9500 mSv). Two hybrid computational phantoms were used to model an adult male and an adult female subject internally contaminatedmore » with 241Am, 60Cs, 137Cs, 131I, or 192Ir following an acute inhalation or ingestion intake. As a function of time following the exposure, the net Count rates corresponding to committed effective doses of 50, 250, and 500 mSv were estimated via Monte Carlo radiation transport simulation for each of four different Detector types, positions, and screening distances. Measured net Count rates can be compared to these values, and an assignment of one of four possible effective dose ranges could be made. The method implicitly assumes that all external contamination has been removed prior to screening and that the measurements be conducted in a low background, and possibly mobile, facility positioned at the triage location. Net Count rate data are provided in both tabular and graphical format within a series of eight handbooks available at the CDC website (http://www.bt.cdc.gov/radiation/clinicians/evaluation).« less

N. Vana - One of the best experts on this subject based on the ideXlab platform.

  • PASSIVE IN-FLIGHT NEUTRON SPECTROMETRY BY MEANS
    2020
    Co-Authors: Michael Hajek, Thomas Berger, N. Vana
    Abstract:

    The spectral distribution of the neutron fluence rate was determined on-board a series of eight trans-atlantic flights between Cologne (Germany) and Washington, DC (USA), using a passive Bonner Sphere spectrometer based on thermoluminescence Detectors. Contrary to the commonly applied active systems, the passive instrument facilitates a complete discrimination of gamma ray and charged particle-induced events in the Detector Count rate. The system was calibrated in the CERN-EU High-Energy Reference Field (CERF). The measured spectra are compared with FLUKA Monte Carlo simulations and show excellent agreement.

  • Passive in-flight neutron spectrometry by means of bonner spheres
    Radiation Protection Dosimetry, 2004
    Co-Authors: Michael Hajek, Thomas Berger, N. Vana
    Abstract:

    : The spectral distribution of the neutron fluence rate was determined on-board a series of eight trans-atlantic flights between Cologne (Germany) and Washington, DC (USA), using a passive Bonner Sphere spectrometer based on thermoluminescence Detectors. Contrary to the commonly applied active systems, the passive instrument facilitates a complete discrimination of gamma ray and charged particle-induced events in the Detector Count rate. The system was calibrated in the CERN-EU High-Energy Reference Field (CERF). The measured spectra are compared with FLUKA Monte Carlo simulations and show excellent agreement.

Gerald Share - One of the best experts on this subject based on the ideXlab platform.

  • Compton Scattering of Deexcitation-Line and Continuum Gamma Rays in Solar Flares
    Solar Physics, 2018
    Co-Authors: Ronald Murphy, Gerald Share
    Abstract:

    Measurements of solar-flare electron-bremsstrahlung X-rays are affected by Compton scattering in the solar atmosphere of the downward-directed radiation. Here we study how Compton-scattered and energy-degraded radiation from nuclear-deexcitation gamma-ray lines and continua affect the measurements of the gamma-ray radiation. Deexcitation-line photons with trajectories directed away from the Sun escape without significant interactions even for flares at the limb. We calculate the Compton-scattered component spectrum from downward-directed deexcitation lines for typical solar-flare accelerated-ion kinetic-energy spectra. The scattered component only a makes a significant contribution to the emerging spectrum at energies below ≈ 600 keV and is most prominent for flares occurring near the center of the solar disk. We study Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spectra obtained from the 28 October 2003 disk-centered flare when the electron-bremsstrahlung contribution was relatively weak. We find that inclusion of the scattered component does not significantly affect any of the derived flare parameters. This is true, in part, because the scattered component is not detectable over the significant RHESSI Detector Count continuum due to partial energy depositions of higher-energy solar photons. The scattered component may affect flare spectral measurements obtained with gamma-ray Detectors having a more “diagonal” response.

Eric J Tkaczyk - One of the best experts on this subject based on the ideXlab platform.

  • pulse pileup statistics for energy discriminating photon Counting x ray Detectors
    Medical Physics, 2011
    Co-Authors: Adam Wang, Daniel David Harrison, Vladimir A Lobastov, Eric J Tkaczyk
    Abstract:

    Purpose: Energy discriminating photon Countingx-ray Detectors can be subject to a wide range of flux rates if applied in clinical settings. Even when the incident rate is a small fraction of the Detector’s maximum periodic rateN 0, pulse pileup leads to Count rate losses and spectral distortion. Although the deterministic effects can be corrected, the detrimental effect of pileup on imagenoise is not well understood and may limit the performance of photon Counting systems. Therefore, the authors devise a method to determine the Detector Count statistics and imaging performance. Methods: The Detector Count statistics are derived analytically for an idealized pileup model with delta pulses of a nonparalyzable Detector. These statistics are then used to compute the performance (e.g., contrast-to-noise ratio) for both single material and material decomposition contrastdetection tasks via the Cramer-Rao lower bound (CRLB) as a function of the Detector input Count rate. With more realistic unipolar and bipolar pulse pileup models of a nonparalyzable Detector, the imaging task performance is determined by Monte Carlo simulations and also approximated by a multinomial method based solely on the mean detected output spectrum. Photon Counting performance at different Count rates is compared with ideal energy integration, which is unaffected by Count rate. Results: The authors found that an ideal photon CountingDetector with perfect energy resolution outperforms energy integration for our contrastdetection tasks, but when the input Count rate exceeds 20%N 0, many of these benefits disappear. The benefit with iodine contrast falls rapidly with increased Count rate while water contrast is not as sensitive to Count rates. The performance with a delta pulse model is overoptimistic when compared to the more realistic bipolar pulse model. The multinomial approximation predicts imaging performance very close to the prediction from Monte Carlo simulations. The monoenergetic image with maximum contrast-to-noise ratio from dual energy imaging with ideal photon Counting is only slightly better than with dual kVp energy integration, and with a bipolar pulse model, energy integration outperforms photon Counting for this particular metric because of the Count rate losses. However, the material resolving capability of photon Counting can be superior to energy integration with dual kVp even in the presence of pileup because of the energy information available to photon Counting. Conclusions: A computationally efficient multinomial approximation of the Count statistics that is based on the mean output spectrum can accurately predict imaging performance. This enables photon Counting system designers to directly relate the effect of pileup to its impact on imaging statistics and how to best take advantage of the benefits of energy discriminating photon CountingDetectors, such as material separation with spectral imaging.

John E. Davis - One of the best experts on this subject based on the ideXlab platform.

  • The Formal Underpinnings of The Response Functions Used in X‐Ray Spectral Analysis
    The Astrophysical Journal, 2002
    Co-Authors: John E. Davis
    Abstract:

    This work provides an in-depth mathematical description of the response functions that are used for spatial and spectral analysis of X-ray data. The use of such functions is well known to anyone familiar with the analysis of X-ray data where they may be identiÐed with the quantities contained in the ancil-lary response Ðle (ARF), the redistribution matrix Ðle (RMF), and the exposure map. Starting from Ðrst principles, explicit mathematical expressions for these functions, for both imaging and dispersive modes, are arrived at in terms of the underlying instrumental characteristics of the telescope including the e ects of pointing motion. The response functions are presented in the context of integral equations relating the expected Detector Count rate to the source spectrum incident upon the telescope. Their application to the analysis of several source distributions is considered. These include multiple, possibly overlapping, spec-trally distinct point sources, as well as extended sources. Assumptions and limitations behind the usage of these functions, as well as their practical computation, are addressed. Subject headings : methods : analytical È methods : data analysis È X-rays : general 1. INTRODUCTION It is a basic tenet of X-ray spectral analysis that the source Ñux incident at the telescope is related to the observed Count rate through an integral equation involving the e ective area of the telescope. The most commonly accepted technique for dealing with this equation involves the use of spectral analysis programs such as xspec (Arnaud 1996). The e ective area is input into these programs via a Ðle called the ancillary response Ðle (ARF). In addition, the energy resolution of the Detector is speciÐed by the redistri-bution matrix Ðle (RMF). This work presents formal descriptions of the quantities embodied by the ARF and RMF in terms of the underlying instrumental responses, making a clear connection between the incident source Ñux and the observed Count rate. Roughly speaking, the e ective area of an X-ray telescope composed of a mirror and a Detector is more or less the product of the e ective area of the mirror with the quantum efficiency (QE) of the Detector. However, the ARF, which relates observed Counts to a source Ñux, also depends upon observation-dependent quantities such as the detailed aspect history of the telescope, its point-spread function (PSF), and details of the analysis itself, e.g., the Ðltering and binning of the observed data. With the advent of the Chandra X-Ray Observatory (CXC 2000), all of the subtleties introduced by the shape of the PSF and the telescope aspect motion were deemed important for the computation of an ARF. Chandra is well calibrated (Weisskopf et al. 2000), and with its unprece-dented combined spectral and spatial response, a precise deÐnition of the ARF that incorporates the e ects of space-craft motion and the PSF is necessary in order to perform spectral analysis at the highest resolution of the instrument. The main goal of this work is to present an explicit Ðrst principles derivation of the ARF by including the proper treatment of telescope motion (e.g., dither) and the PSF, as well as any Ðltering of the data. The bottom-up approach taken here necessarily implies that a meaningful and consis-tent derivation can be achieved by considering the role of the ARF in spectral analysis. As a result, the ARF is pre-sented in the context of integral equations that connect the incident X-ray Ñux to an expected Count rate. Traditionally, the ARF and RMF have been used pri-marily for the analysis of spectral image data. An important aspect of this work is to extend this approach to the analysis of dispersive spectral data, such as data obtained by Chandra or Newton. To this end, deÐnitions of an ARF and an RMF are presented that are suitable for dispersive data analysis and that may be utilized by existing spectral analysis software. One of the original motivations for this work was the need to create a related object, an exposure map, for use in the analysis of data obtained by the Chandra X-Ray Obser-vatory. This paper also gives a rigorous deÐnition of the exposure map and discusses some of its uses and its limi-tations in spectral image analysis. The resulting deÐnition is consistent with current use, intuition, and physics. The next section contains a discussion of the general response of an X-ray telescope and also serves to introduce the notation and conventions used throughout this paper. Although originally inspired by the need to create ARFs and exposure maps for Chandra, the presentation has been kept as general as possible without focusing on any particu-lar telescope or instrument. A derivation of the imaging ARF follows in ° 3, where its application to several prob-lems is considered. These include the problem of multiple overlapping point sources. Section 4 contains a deÐnition of the exposure map and explores its use as well as its limi-tations in dealing with extended sources. The deÐnition of a dispersive ARF and RMF that are suitable for use in the analysis of dispersive spectral data is given in ° 5. Following the summary of the paper is an appendix that considers the practical computation of these objects.