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At least 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

A Mobile Automated Tomographic Gamma Scanning System - 13231

Canberra Industries have recently designed and built a new automated Tomographic Gamma Scanning (TGS) system for mobile deployment. The TGS technique combines high-resolution gamma spectroscopy with low spatial resolution 3-dimensional image reconstruction to provide increased accuracy over traditional approaches for the assay of non-uniform source distributions in low-to medium-density, non-heterogeneous matrices. Originally pioneered by R. Estep at Los Alamos National Laboratory (LANL), the TGS method has been further developed and commercialized by Canberra Industries in recent years. The present system advances the state of the art on several fronts: it is designed to be housed in a standard cargo transport container for ease of transport, allowing waste characterization at multiple facilities under the purview of a single operator. Conveyor feed, drum rotator, and detector and collimator positioning mechanisms operated by programmable logic control (PLC) allow automated batch mode operation. The variable geometry settings can accommodate a wide range of waste packaging, including but not limited to standard 220 liter drums, 380 liter overpack drums, and smaller 20 liter cans. A 20 mCi Eu-152 transmission source provides attenuation corrections for drum matrices up to 1 g/cm{sup 3} in TGS mode; the system can be operated in Segmented Gamma Scanning (SGS) mode to measure higher density drums. To support TGS assays at higher densities, the source shield is sufficient to house an alternate Co-60 transmission source of higher activity, up to 250 mCi. An automated shutter and attenuator assembly is provided for operating the system with a dual intensity transmission source. The system's 1500 kg capacity rotator turntable can handle heavy containers such as concrete lined 380 liter overpack drums. Finally, data acquisition utilizes Canberra's Broad Energy Germanium (BEGE) detector and Lynx MCA, with 32 k channels, providing better than 0.1 keV/channel resolution to support both isotopic analysis with the MGA/MGAU software and a wide 3 MeV dynamic range. The calibration and verification of the system is discussed, and quantitative results are presented for a variety of drum types and matrices. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2017

High Resolution Scanning Configurations for the Canberra Tomographic Gamma Scanner - 17323

The Canberra Tomographic Gamma Scanner (TGS) is a Non-Destructive Assay (NDA) system that combines high resolution gamma ray spectroscopy (HRGS) with low-spatial-resolution imaging for the measurement of heterogeneous drummed waste with matrix densities in the range of 0 to 1 g/cc. The TGS methodology uses a two-pass scanning protocol; a 10-15 μCi {sup 152}Eu transmission source is used to interrogate density and composition of the matrix in the first pass, and passive gamma ray spectroscopy is used to collect emission spectra in the second, while the drum is rotated and translated to vary the view path. In standard implementations, the transmission and emission data are used to reconstruct three dimensional images of the matrix and activity distribution inside the drum on a 10x10x16 grid of discrete volume elements or 'voxels'. These images allow attenuation corrections to be calculated and applied on a view by view, and voxel by voxel basis, reducing the over- and under-correction biases obtained by assay techniques which assume homogeneous distributions of material. The most recent TGS system deployed by Canberra featured, among other new developments, the ability to perform higher resolution image re-construction, which may prove beneficial for the assay of more highly mixed matrices or oddly shaped assay items within a container. These additional scanning protocols reconstruct the image data into 14x14 and 20x20 voxel grids, using a smaller collimator aperture size. The hardware and software implementations of these higher resolution scans are discussed, and the calibration and initial evaluations of performance are presented. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Photo-Transmutation of {sup 100}Mo to {sup 99m}Tc with Laser-Compton Scattering Gamma-Ray

Technetium-99m ({sup 99m}Tc) is an important medical radioisotope which is largely used in hospitals for diagnosis of cancer. It is produced in the form of {sup 99}Mo which decays to {sup 99m}Tc with a half-life of 66 hours. More than 90% of the world's demand of {sup 99}Mo are sourced from five nuclear reactors. Two of these reactors have already been closed and the rest are more than 45 years old. Relatively short half-life of the parent {sup 99}Mo requires continuous re-supply to meet the medical industry's requirement. Therefore there is an urgent need to produce the {sup 99}Mo and {sup 99m}Tc isotopes by alternative ways. This paper presents one such alternative via the use of laser-Compton scattering (LCS) gamma beam. In this paper, production rate (reaction rate) of {sup 99}Mo using the photonuclear (γ, n) reaction is evaluated. It is expected that the LCS technique can be used to generate the gamma ray required for the aforementioned photonuclear reaction. Rigorous optimization of the LCS spectrum is also performed to maximize production of the {sup 99}Mo. The optimal maximum energy of the LCS photon is about 17 MeV for the production of {sup 99}Mo. The analysis shows that production of {sup 99}Mo using LCS gamma beam offers a promising alternative for the production of {sup 99m}Tc. (authors)

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2019

A Gamma Assay System for Characterizing Excavated Soil with High {sup 137}Cs and {sup 90}Sr Contamination - 19460

We report on the recent development of a remote gamma-assay system for the measurement and characterization of high-activity soil excavated as part of an ongoing remediation project. The soil below a hot cell in our customer's facility has been contaminated with high concentrations of radionuclides {sup 137}Cs and {sup 90}Sr over the past several decades. The contaminated soil is to be remotely excavated from beneath the hot cell floor, to a depth of several feet, and placed in steel-walled waste bins for assay and disposition. The project requires measuring the {sup 137}Cs activity to a minimum detectable concentration (MDC) of 1 micro curie per gram. The high dose-rate of the material and the expectation of high Bremsstrahlung background, due to an unknown ratio of {sup 90}Sr admixture with the {sup 137}Cs, present unique measurement challenges. A novel assay system was designed to make measurements through a small access port in a 4-foot thick concrete wall isolating operators from the high-dose excavation area. Waste bins filled with soil are placed by a remotely operated crane onto an automated turntable, and initial dose measurements are taken for all bins. When excavation has proceeded to the point that dose rates below 20 Rad/hr on contact are reached, gamma spectroscopy will be used to characterize the {sup 137}Cs content. Gamma assay is performed with a 1 cm{sup 3} CZT detector in a collimated tungsten shield, which is extended through the access port toward the side of the bin by means of a seven foot long aluminum pipe. Each of the four sides of the bin is assayed in a discrete measurement, and the individual segments and summed result are reported. Canberra's NDA2000 software is used to collect and analyze the spectroscopic data and to control the turntable movement during the assay. The system is expected to meet the required MDC limits within a forty minute assay time under the most adverse conditions anticipated, with total measurement uncertainty of less than 25%. We describe in this paper the design and construction of the assay system, its calibration using the ISOCS software, and the evaluation of performance estimates. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Prompt Gamma Neutron Activation Analysis of Niobium for Characterization of Light Interstitials

High purity niobium metal is used in the construction of superconducting radio frequency (SRF) cavities in superconducting particle accelerators. The Spallation Neutron Source at Oak Ridge National Laboratory is an example of an SRF linear accelerator (LINAC) that requires this high purity niobium material. For the SRF cavities to function well, it is necessary that the cavity wall have a high thermal conductivity so that the radio frequency (RF) power can be dissipated into the liquid helium coolant. For a high thermal conductivity of the niobium metal to be achieved, it is required to have extremely low levels of impurities. The current industry standard for determining the quality of the high purity niobium material is the residual resistivity ratio (RRR) technique. In this technique, the temperature dependency of a niobium metal sample is determined at temperatures near that of liquid helium in order to establish where the superconducting jump occurs. With this method, it is possible to find the general level of impurity of the metal sample, but not the specific elements that are contributing to the impurity. The impurities that are of particular interest to manufacturers of niobium for SRF use are tantalum and light interstitials, such as hydrogen, carbon, nitrogen, and oxygen. In this research, we focus on determining the analytical sensitivity of the detector system and characterizing the light interstitial content in high purity niobium metal through the use of Prompt Gamma Neutron Activation Analysis (PGNAA). PGNAA is an analytical technique that can be utilized to determine the concentration of elemental components in a wide variety of materials with high precision and reproducibility. In this process, neutrons bombard a sample material, causing the emission of gamma rays from the sample. Each element emits a unique spectrum of gamma radiation, which allows for identification of the elements present in the sample. (authors)

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Feasibility study on real-time {gamma}-ray spectrum / dose measurement system

In recent years, radiations have been used very often especially in the medical field. Radiation protection is carried out properly there. However, the medical staffs sometimes focus not so seriously on their exposure dose, because treatment of patients is the first priority in hospitals. In the past study, there were radiation monitors developed which can indicate the pulse height spectrum and/or dose. However, there were no monitors which can show the gamma-ray energy spectrum and dose at the same time. A monitor, which we design, can estimate the energy spectrum of gamma-rays in the medical atmosphere, with which the dose can be evaluated simultaneously and accurately. The purpose of this study is to develop a spectrometer (monitor) which can show gamma-ray spectrum / dose simultaneously in real time to make the medical staffs understand the risk of radiation precisely and to finally decrease their exposure dose. For this purpose we newly developed a conversion procedure from the measured pulse height spectrum to energy spectrum in real time. The details are also described in this paper.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

OBSERVATION OF THE TeV GAMMA-RAY SOURCE MGRO J1908+06 WITH ARGO-YBJ

The extended gamma-ray source MGRO J1908+06, discovered by the Milagro air shower detector in 2007, has been observed for {approx}4 years by the ARGO-YBJ experiment at TeV energies, with a statistical significance of 6.2 standard deviations. The peak of the signal is found at a position consistent with the pulsar PSR J1907+0602. Parameterizing the source shape with a two-dimensional Gauss function, we estimate an extension of {sigma}{sub ext} = 0.{sup 0}49 {+-} 0.{sup 0}22, which is consistent with a previous measurement by the Cherenkov Array H.E.S.S. The observed energy spectrum is dN/dE = 6.1 {+-} 1.4 Multiplication-Sign 10{sup -13} (E/4 TeV){sup -2.54{+-}0.36} photons cm{sup -2} s{sup -1} TeV{sup -1}, in the energy range of {approx}1-20 TeV. The measured gamma-ray flux is consistent with the results of the Milagro detector, but is {approx}2-3 times larger than the flux previously derived by H.E.S.S. at energies of a few TeV. The continuity of the Milagro and ARGO-YBJ observations and the stable excess rate observed by ARGO-YBJ and recorded in four years of data support the identification of MGRO J1908+06 as the steady powerful TeV pulsar wind nebula of PSR J1907+0602, with an integrated luminosity over 1 TeV {approx} 1.8 times the luminosity of the Crab Nebula.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

LIMITS TO THE FRACTION OF HIGH-ENERGY PHOTON EMITTING GAMMA-RAY BURSTS

After almost four years of operation, the two instruments on board the Fermi Gamma-ray Space Telescope have shown that the number of gamma-ray bursts (GRBs) with high-energy photon emission above 100 MeV cannot exceed roughly 9% of the total number of all such events, at least at the present detection limits. In a recent paper, we found that GRBs with photons detected in the Large Area Telescope have a surprisingly broad distribution with respect to the observed event photon number. Extrapolation of our empirical fit to numbers of photons below our previous detection limit suggests that the overall rate of such low flux events could be estimated by standard image co-adding techniques. In this case, we have taken advantage of the excellent angular resolution of the Swift mission to provide accurate reference points for 79 GRB events which have eluded any previous correlations with high-energy photons. We find a small but significant signal in the co-added field. Guided by the extrapolated power-law fit previously obtained for the number distribution of GRBs with higher fluxes, the data suggest that only a small fraction of GRBs are sources of high-energy photons.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

The particle-gamma coincidence method: A brief introduction

Excitation energy information from particle detectors can significantly improve the analysis process of {gamma}-ray spectra and result in more detailed nuclear structure information. Therefore, a new setup at the HORUS {gamma}-ray spectrometer at the University of Cologne has been installed, housing silicon particle detectors at up to eight positions.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Perspectives for neutron and gamma spectroscopy in high power laser driven experiments at ELI-NP

The measurement of energy spectra of neutrons and gamma rays emitted by nuclei, together with charge particles spectroscopy, are the main tools for understanding nuclear phenomena occurring also in high power laser driven experiments. However, the large number of particles emitted in a very short time, in particular the strong X-rays flash produced in laser-target interaction, impose adaptation of technique currently used in nuclear physics experiment at accelerator based facilities. These aspects are discussed (Section 1) in the context of proposed studies at high power laser system of ELI-NP. Preliminary results from two experiments performed at Titan (LLNL) and ELFIE (LULI) facilities using plastic scintillators for neutron detection (Section 2) and LaBr{sub 3}(Ce) scintillators for gamma detection (Section 3) are presented demonstrating the capabilities and the limitations of the employed methods. Possible improvements of these spectroscopic methods and their proposed implementation at ELI-NP will be discussed as well in the last section.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Gamma-ray spectroscopy at MHz counting rates with a compact LaBr{sub 3} detector and silicon photomultipliers for fusion plasma applications

Gamma-ray spectroscopy measurements at MHz counting rates have been carried out, for the first time, with a compact spectrometer based on a LaBr{sub 3} scintillator and silicon photomultipliers. The instrument, which is also insensitive to magnetic fields, has been developed in view of the upgrade of the gamma-ray camera diagnostic for α particle measurements in deuterium-tritium plasmas of the Joint European Torus. Spectra were measured up to 2.9 MHz with a projected energy resolution of 3%-4% in the 3-5 MeV range, of interest for fast ion physics studies in fusion plasmas. The results reported here pave the way to first time measurements of the confined α particle profile in high power plasmas of the next deuterium-tritium campaign at the Joint European Torus.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

ON THE X-RAY OUTBURSTS OF TRANSIENT ANOMALOUS X-RAY PULSARS AND SOFT GAMMA-RAY REPEATERS

We show that the X-ray outburst light curves of four transient anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs), namely, XTE J1810-197, SGR 0501+4516, SGR 1627-41, and CXOU J164710.2-455216, can be produced by the fallback disk model that was also applied to the outburst light curves of persistent AXPs and SGRs in our earlier work. The model solves the diffusion equation for the relaxation of a disk that has been pushed back by a soft gamma-ray burst. The sets of main disk parameters used for these transient sources are very similar to each other and to those employed in our earlier models of persistent AXPs and SGRs. There is a characteristic difference between the X-ray outburst light curves of transient and persistent sources. This can be explained by the differences in the disk surface density profiles of the transient and persistent sources in quiescence indicated by their quiescent X-ray luminosities. Our results imply that a viscous disk instability operating at a critical temperature in the range of {approx}1300-2800 K is a common property of all fallback disks around AXPs and SGRs. The effect of the instability is more pronounced and starts earlier for the sources with lower quiescent luminosities, which leads to the observable differences in the X-ray enhancement light curves of transient and persistent sources. A single active disk model with the same basic disk parameters can account for the enhancement phases of both transient and persistent AXPs and SGRs. We also present a detailed parameter study to show the effects of disk parameters on the evolution of the X-ray luminosity of AXPs and SGRs in the X-ray enhancement phases.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

NEW CLASS OF VERY HIGH ENERGY {gamma}-RAY EMITTERS: RADIO-DARK MINI SHELLS SURROUNDING ACTIVE GALACTIC NUCLEUS JETS

We explore non-thermal emission from a shocked interstellar medium, which is identified as an expanding shell, driven by a relativistic jet in active galactic nuclei (AGNs). In this work, we particularly focus on parsec-scale size mini shells surrounding mini radio lobes. From the radio to X-ray band, the mini radio lobe emission dominates the faint emission from the mini shell. On the other hand, we find that inverse-Compton (IC) emission from the shell can overwhelm the associated lobe emission at the very high energy (VHE; E > 100 GeV) {gamma}-ray range, because energy densities of synchrotron photons from the lobe and/or soft photons from the AGN nucleus are large and IC scattering works effectively. The predicted IC emission from nearby mini shells can be detected with the Cherenkov Telescope Array and they are potentially a new class of VHE {gamma}-ray emitters.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

ON THERMALIZATION IN GAMMA-RAY BURST JETS AND THE PEAK ENERGIES OF PHOTOSPHERIC SPECTRA

The low-energy spectral slopes of the prompt emission of most gamma-ray bursts (GRBs) are difficult to reconcile with radiatively efficient optically thin emission models irrespective of the radiation mechanism. An alternative is to ascribe the radiation around the spectral peak to a thermalization process occurring well inside the Thomson photosphere. This quasi-thermal spectrum can evolve into the observed non-thermal shape by additional energy release at moderate to small Thomson optical depths, which can readily give rise to the hard spectral tail. The position of the spectral peak is determined by the temperature and Lorentz factor of the flow in the thermalization zone, where the total number of photons carried by the jet is established. To reach thermalization, dissipation alone is not sufficient and photon generation requires an efficient emission/absorption process in addition to scattering. We perform a systematic study of all relevant photon production mechanisms searching for possible conditions in which thermalization can take place. We find that a significant fraction of the available energy should be dissipated at intermediate radii, {approx}10{sup 10} to a few Multiplication-Sign 10{sup 11} cm, and the flow there should be relatively slow: the bulk Lorentz factor could not exceed a few tens for all but the most luminous bursts with the highest E {sub pk} values. The least restrictive constraint for successful thermalization, {Gamma} {approx}< 20, is obtained if synchrotron emission acts as the photon source. This requires, however, a non-thermal acceleration deep below the Thomson photosphere transferring a significant fraction of the flow energy to relativistic electrons with Lorentz factors between 10 and 100. Other processes require bulk flow Lorentz factors of order of a few for typical bursts. We examine the implications of these results to different GRB photospheric emission models.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

A LINGERING NON-THERMAL COMPONENT IN THE GAMMA-RAY BURST PROMPT EMISSION: PREDICTING GeV EMISSION FROM THE MeV SPECTRUM

The high-energy GeV emission of gamma-ray bursts (GRBs) detected by Fermi/LAT has a significantly different morphology compared to the lower energy MeV emission detected by Fermi/GBM. Though the late-time GeV emission is believed to be synchrotron radiation produced via an external shock, this emission as early as the prompt phase is puzzling. A meaningful connection between these two emissions can be drawn only by an accurate description of the prompt MeV spectrum. We perform a time-resolved spectroscopy of the Gamma-ray Burst Monitor (GBM) data of long GRBs with significant GeV emission, using a model consisting of two blackbodies and a power law. We examine in detail the evolution of the spectral components and find that GRBs with high GeV emission (GRB 090902B and GRB 090926A) have a delayed onset of the power-law component in the GBM spectrum, which lingers at the later part of the prompt emission. This behavior mimics the flux evolution in the Large Area Telescope (LAT). In contrast, bright GBM GRBs with an order of magnitude lower GeV emission (GRB 100724B and GRB 091003) show a coupled variability of the total and the power-law flux. Further, by analyzing the data for a set of 17 GRBs, we find a strong correlation between the power-law fluence in the MeV and the LAT fluence (Pearson correlation: r = 0.88 and Spearman correlation: ρ = 0.81). We demonstrate that this correlation is not influenced by the correlation between the total and the power-law fluences at a confidence level of 2.3σ. We speculate the possible radiation mechanisms responsible for the correlation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE BATSE 5B GAMMA-RAY BURST SPECTRAL CATALOG

We present systematic spectral analyses of gamma-ray bursts (GRBs) detected with the Burst and Transient Source Experiment (BATSE) on board the Compton Gamma-Ray Observatory during its entire nine years of operation. This catalog contains two types of spectra extracted from 2145 GRBs, and fitted with five different spectral models resulting in a compendium of over 19,000 spectra. The models were selected based on their empirical importance to the spectral shape of many GRBs, and the analysis performed was devised to be as thorough and objective as possible. We describe in detail our procedures and criteria for the analyses, and present the bulk results in the form of parameter distributions. This catalog should be considered an official product from the BATSE Science Team, and the data files containing the complete results are available from the High-Energy Astrophysics Science Archive Research Center (HEASARC)

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

FERMI LIMIT ON THE NEUTRINO FLUX FROM GAMMA-RAY BURSTS

If gamma-ray bursts (GRBs) produce high-energy cosmic rays, neutrinos are expected to be generated in GRBs via photo-pion productions. However, we stress that the same process also generates electromagnetic (EM) emission induced by the secondary electrons and photons, and that the EM emission is expected to be correlated with neutrino flux. Using Fermi/Large Area Telescope results on gamma-ray flux from GRBs, the GRB neutrino emission is limited to be <20 GeV m{sup -2} per GRB event on average, which is independent of the unknown GRB proton luminosity. This neutrino limit suggests that IceCube, operating at full scale, requires stacking of more than 130 GRBs in order to detect one GRB muon neutrino.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

AN OBSERVED CORRELATION BETWEEN THERMAL AND NON-THERMAL EMISSION IN GAMMA-RAY BURSTS

Recent observations by the Fermi Gamma-ray Space Telescope have confirmed the existence of thermal and non-thermal components in the prompt photon spectra of some gamma-ray bursts (GRBs). Through an analysis of six bright Fermi GRBs, we have discovered a correlation between the observed photospheric and non-thermal γ-ray emission components of several GRBs using a physical model that has previously been shown to be a good fit to the Fermi data. From the spectral parameters of these fits we find that the characteristic energies, E {sub p} and kT, of these two components are correlated via the relation E {sub p}∝T {sup α} which varies from GRB to GRB. We present an interpretation in which the value of the index α indicates whether the jet is dominated by kinetic or magnetic energy. To date, this jet composition parameter has been assumed in the modeling of GRB outflows rather than derived from the data.

79 ASTRONOMY AND ASTROPHYSICS↗