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At least 1,207 records · Page 67

Borehole Calibration Facilities to Support Gamma Logging for Hanford Subsurface Investigation and Contaminant Monitoring - 13516

Repeated gamma logging in cased holes represents a cost-effective means to monitor gamma-emitting contamination in the deep vadose zone over time. Careful calibration and standardization of gamma log results are required to track changes and to compare results over time from different detectors and logging systems. This paper provides a summary description of Hanford facilities currently available for calibration of logging equipment. Ideally, all logging organizations conducting borehole gamma measurements at the Hanford Site will take advantage of these facilities to produce standardized and comparable results. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

Evaluate an impact of incident alpha particle and gamma ray on human blood components: A comparison study

An impact of alpha and gamma irradiation on human blood components have been evaluated and compared for healthy blood samples (male and females). Irradiation dose and time of irradiation calibrated and considered as a main comparison factors. Density of blood components measured for each in vitro irradiation before and after irradiation for males and females. Survey radiation dosimeter (Inspector Exp) and nuclear track detectors type CR-39 used to evaluate exposure dose rate and incident density of alpha particles, respectively. Experiment results verified that the irradiation of blood makes ionizing of blood components, either alpha or gamma irradiation dose, and the impacts of ionizing radiation were relativity for WBC, RBC, and PLT. Limited irradiation doses of 1-5 μSv/hr considered as a low radiation dose of alpha and gamma radiation sources ({sup 226}Ra, and {sup 137}Cs). Density of alpha particles accumulated on the blood surface was 34 (alpha particle/cm{sup 2}) for selected dose of incident alpha particle. Optimum value of irradiation dose and time of irradiation were 5 μSv/hr and 4 second for males and females. On the other hands, the values of irradiation dose and time of irradiation were 2.1 μSv/hr and 2 second for males and females for gamma irradiation. Thus, present results demonstrated that densities of RBC and WBC cells are capable of inducing reproduction in vitro for both type of irradiation. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Maximum Likelihood Expectation-Maximization Algorithms Applied to Localization and Identification of Radioactive Sources with Recent Coded Mask Gamma Cameras

In this work, we tested Maximum likelihood expectation-maximization (MLEM) algorithms optimized for gamma imaging applications on two recent coded mask gamma cameras. We respectively took advantage of the characteristics of the GAMPIX and Caliste HD-based gamma cameras: noise reduction thanks to mask/anti-mask procedure but limited energy resolution for GAMPIX, high energy resolution for Caliste HD. One of our short-term perspectives is the test of MAPEM algorithms integrating specific prior values for the data to reconstruct adapted to the gamma imaging topic. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Considerations and Lessons Learned from the Use of Gamma Spectroscopy Systems at FUSRAP Project Sites - 17459

This paper will discuss the application of gamma spectroscopy systems for analysis of environmental media samples for parents and daughter progeny of the Natural Uranium and Thorium Decay Series radionuclides. The concentrations and relative ratios of naturally occurring isotopes are used to confirm the presence of FUSRAP-related wastes and for understanding the associated potential dose and health risks. Focus will be given to lessons learned from the set-up and operation of onsite gamma spectroscopy laboratories used to provide stakeholders with defensible and timely results to support FUSRAP site investigations and remediation including adaptive survey design implementation, physical remediation and waste transport, and confirmatory final status survey activities. This paper focuses on the potential impacts to gamma spectroscopy measurement accuracy from the following: - Bias caused by sample matrix effects as well as use of different library reference values between performance evaluation study providers and testing laboratories; - Use of calibration sources with limited energy ranges, and; - Selection of available alternative isotopic decay reference data for the input of line energies and their intensities. These lessons learned include discussing how inter-laboratory measurement differences from blind performance evaluation samples are affected by the manufacturer's measurement method, including equilibrium assumptions; the isotope decay information source library used by the study provider and participating laboratories; and calibration source geometry/density variances from actual sample conditions. Any of these factors can significantly impact the accuracy of reported results data. Deepening the reader's understanding of the various factors that impact the accuracy, interpretation, and overall usability of gamma spectroscopy results data from laboratories will help ensure defensible decision-making and cost-effective mission implementation within FUSRAP and similar remediation programs. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

New approach to gamma scans for processed natural uranium at a FUSRAP site - 15470

The Superior Steel Site is part of the FUSRAP because the former facility processed natural uranium metal in support of the Atomic Energy Commission (AEC) fuel-element development program in the 1950's. Previous investigations of the site have identified uranium contamination both inside and outside of the building associated with the uranium work and some limited remediation was performed in the past. As part of the remedial investigation (RI) process for the site, gamma scan surveys were completed in order to define the nature and extent of elevated residual uranium associated with AEC activities. One of the challenges with investigating for processed natural uranium versus unprocessed natural uranium is that the processed uranium is practically devoid of its decay progeny, which produce gamma photon radiation emissions commonly relied upon to detect the presence of uranium. To address this challenge, a sodium iodide (NaI) detector was designed and fabricated to optimize the signal to noise ratio for U-238 low energy gammas (59-127 keV) and to reduce interferences from other radionuclides that may be present from non-FUSRAP sources. Gamma scan surveys were performed with the optimized NaI detector in conjunction with typical, commercially available 0.35 liter NaI detectors. The results of this survey and a comparison between the detectors is presented. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

Minimum detectable activity for tomographic gamma scanning system - 15648

For any radiation measurement system, it is useful to explore and establish the detection limits and a minimum detectable activity (MDA) for the radionuclides of interest, even if the system is to be used at far higher values. The MDA serves as an important figure of merit, and often a system is optimized and configured so that it can meet the MDA requirements of a measurement campaign. The non-destructive assay (NDA) systems based on gamma ray analysis are no exception and well established conventions, such the Currie method, exist for estimating the detection limits and the MDA. However, the Tomographic Gamma Scanning (TGS) technique poses some challenges for the estimation of detection limits and MDAs. The TGS combines high resolution gamma ray spectrometry (HRGS) with low spatial resolution image reconstruction techniques. In non-imaging gamma ray based NDA techniques measured counts in a full energy peak can be used to estimate the activity of a radionuclide, independently of other counting trials. However, in the case of the TGS each 'view' is a full spectral grab (each a counting trial), and each scan consists of 150 spectral grabs in the transmission and emission scans per vertical layer of the item. The set of views in a complete scan are then used to solve for the radionuclide activities on a voxel by voxel basis, over 16 layers of a 10x10 voxel grid. Thus, the raw count data are not independent trials any more, but rather constitute input to a matrix solution for the emission image values at the various locations inside the item volume used in the reconstruction. So, the validity of the methods used to estimate MDA for an imaging technique such as TGS warrant a close scrutiny, because the pair-counting concept of Currie is not directly applicable. One can also raise questions as to whether the TGS, along with other image reconstruction techniques which heavily intertwine data, is a suitable method if one expects to measure samples whose activities are at or just above MDA levels. The paper examines methods used to estimate MDAs for a TGS system, and explores possible solutions that can be rigorously defended. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Considerations on the use of an Anti-Compton Suppression Technique for the Measurement of Low Energy Gamma Rays in Dense Waste Materials - 18144

The Anti-Compton Spectrometry (ACS) technique is a gamma-ray measurement method which, in the presence of gamma rays sources emitting at higher energies, may improve the signal-to-continuum ratio of lower energy photo-peaks. It is used to improve assay precision and statistical detection limits. The typical approach surrounds the collimated High Purity Germanium (HPGe) detector by a NaI(Tl) guard which vetoes detected gamma-rays scattered out of the Ge-spectrometer and therefore by definition events do not contribute to a full energy peak in the HPGe detector. The present publication focuses on the applicability, advantages and drawbacks of ACS when considered for the purpose of enhancing measurement performances of non-destructive waste assay systems. In particular, the applicability and benefit of implementing ACS for the quantification of {sup 241}Am in high density waste will be presented. Such an application is directly relevant to measurement scenarios where the accuracy of the {sup 241}Am quantification is central to the radioactive waste meeting some acceptance criteria for near surface disposal, such as total alpha decay activity limits in 300 years. This work is also relevant to any measurement applications for which the Compton background generated by higher energy nuclides present in the waste and interacting with the detector significantly degrade the performance of standard high resolution gamma spectroscopy for low energy nuclides. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

Simulated Gamma Doses to Coating Materials for Use in High Level Waste Packages

An outer shield barrier for spent nuclear fuel is being developed in order to improve dry cask performance under mechanical, chemical, and radiological degradation and stresses. The materials proposed for the outer shield barrier are titanium nitride (TiN), a composite oxide layer consisting of ZrO{sub 2}, TiO{sub 2}, and Al{sub 2}O{sub 3}, and a final layer of molybdenum disulfide (MoS{sub 2}). The ultimate aim of this research is to develop a multi component shield material either as multiple layers or a multi material composite that will improve the performance of steel used in long-term storage casks. Two approaches are being examined through this research effort: multilayer and composite. The composition of the oxide layer is crucial to optimizing the shield's properties and performance. At equal oxide compositions the mixture of these specific oxides is commonly known as zirconolite. This material has been shown to provide a water barrier and to provide substantial corrosion resistance to the dry cask. In order to optimize the radiological performance of this layer the compositions of each oxide have been varied and analyzed for chemical, mechanical, and radiological effects on performance. Through the course of this research effort materials performance changes after gamma and neutron exposure as well as gamma and neutron attenuation of the potential shield materials have been measured and correlated to coating composition. As it is particularly difficult to design a novel, five component material with the goal of improving corrosion, wear behavior, heat tolerance, radiation tolerance, and general survivability, it is necessary to understand which coating components contribute to each property enhancement, and which are critical to design and eventual coating survivability. To compliment the experimental research effort, a study of gamma radiation doses using the relevant zirconolite constituent oxides and assorted combinations off all three, ZrO{sub 2}-TiO{sub 2}-Al{sub 2}O{sub 3}, has been conducted in order to gain insight into which, if any, ratios of the three constituent oxides may provide optimal gamma radiation shielding. Analyzing and comparing the oxides to each other it is apparent that the outer shield barrier with no zirconia has the highest absorbed dose rate at 4.88 E6 mrad/hr. The simulations run with no alumina and no titania are remarkably similar in absorbed dose rates. Alumina and titania compositions increase the absorbed dose rate increase. This is to be expected as during these simulations the zirconia composition is decreasing.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

Characterization of the degradation of gamma-irradiated elastomers using Raman spectroscopy

This report presents key findings from Raman spectroscopic analysis of gamma-irradiated rubber samples extracted from a laminated lead-damped rubber (LDR) seismic isolation device. The samples were exposed to gamma radiation from a 60Co source in a Foss Therapy Services gamma irradiator, reaching absorbed doses up to 1600 kGy. A distinct threshold near 400 kGy was identified, beyond which significant spectral changes were observed. Two Raman peaks - at approximately 425 cm-1 and 2440 cm-1 - were tracked as a function of dose using Gaussian fitting. The 425 cm-1 peak, attributed to sulfur–sulfur (S–S) bond stretching (resulting from vulcanization of the rubber), exhibited a dose-dependent upshift, indicating radiation-induced crosslinking within the sulfur-based polymer network. Conversely, the 2440 cm-1 peak, likely associated with vibrational modes of additives or impurities, showed a downward shift with increasing dose, suggesting chain scission and degradation of non-rubber constituents. These results provide first-of-a-kind insights into the microstructural evolution of elastomers under high-dose gamma irradiation and establish a preliminary dose threshold for significant degradation. Future work will incorporate multi-modal characterization—including Fourier Transform Infrared (FTIR) spectroscopy, scanning electrom microscopy (SEM) of the rubber surface morphology, thermogravimetric analysis (TGA) to determine changes in thermal stability, and mechanical testing—to correlate molecular-level changes with macroscopic performance of these elastomers as damping media in seismic isolation devices. These findings are expected to provide regulatory guidance and design criteria for qualifying low-damping rubber seismic isolators in advanced nuclear reactor applications.

36 - MATERIALS SCIENCE↗

ON THE LACK OF TIME DILATION SIGNATURES IN GAMMA-RAY BURST LIGHT CURVES

We examine the effects of time dilation on the temporal profiles of gamma-ray burst (GRB) pulses. By using prescriptions for the shape and evolution of prompt gamma-ray spectra, we can generate a simulated population of single-pulsed GRBs at a variety of redshifts and observe how their light curves would appear to a gamma-ray detector here on Earth. We find that the observer frame duration of individual pulses does not increase with redshift as 1 + z, which one would expect from cosmological expansion. This time dilation is masked by an opposite and often stronger effect: with increasing redshift and decreasing signal-to-noise ratio only the brightest portion of the light curve can be detected. The results of our simulation are consistent with the fact that the simple time dilation of GRB light curves has not materialized in either the Swift or Fermi detected GRBs with known redshift. We show that the measured durations and associated E{sub iso} estimates for GRBs detected near the instrument's detection threshold should be considered lower limits to the true values. Furthermore, we conclude that attempts at distinguishing between long and short GRBs, at even moderate redshifts, cannot be done based on a burst's temporal properties alone.

79 ASTRONOMY AND ASTROPHYSICS↗

Non-destructive assay of mechanical components using gamma-rays and thermal neutrons

This work presents the results obtained in the inspection of several mechanical components through neutron and gamma-ray transmission radiography. The 4.46 Multiplication-Sign 10{sup 5} n.cm{sup -2}.s{sup -1} thermal neutron flux available at the main port of the Argonauta research reactor in Instituto de Engenharia Nuclear has been used as source for the neutron radiographic imaging. The 412 keV {gamma}-ray emitted by {sup 198}Au, also produced in that reactor, has been used as interrogation agent for the gamma radiography. Imaging Plates - IP specifically designed to operate with thermal neutrons or with X-rays have been employed as detectors and storage devices for each of these radiations.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

Copper doping of ZnO crystals by transmutation of {sup 64}Zn to {sup 65}Cu: An electron paramagnetic resonance and gamma spectroscopy study

Transmutation of {sup 64}Zn to {sup 65}Cu has been observed in a ZnO crystal irradiated with neutrons. The crystal was characterized with electron paramagnetic resonance (EPR) before and after the irradiation and with gamma spectroscopy after the irradiation. Major features in the gamma spectrum of the neutron-irradiated crystal included the primary 1115.5 keV gamma ray from the {sup 65}Zn decay and the positron annihilation peak at 511 keV. Their presence confirmed the successful transmutation of {sup 64}Zn nuclei to {sup 65}Cu. Additional direct evidence for transmutation was obtained from the EPR of Cu{sup 2+} ions (where {sup 63}Cu and {sup 65}Cu hyperfine lines are easily resolved). A spectrum from isolated Cu{sup 2+} (3d{sup 9}) ions acquired after the neutron irradiation showed only hyperfine lines from {sup 65}Cu nuclei. The absence of {sup 63}Cu lines in this Cu{sup 2+} spectrum left no doubt that the observed {sup 65}Cu signals were due to transmuted {sup 65}Cu nuclei created as a result of the neutron irradiation. Small concentrations of copper, in the form of Cu{sup +}-H complexes, were inadvertently present in our as-grown ZnO crystal. These Cu{sup +}-H complexes are not affected by the neutron irradiation, but they dissociate when a crystal is heated to 900 °C. This behavior allowed EPR to distinguish between the copper initially in the crystal and the copper subsequently produced by the neutron irradiation. In addition to transmutation, a second major effect of the neutron irradiation was the formation of zinc and oxygen vacancies by displacement. These vacancies were observed with EPR.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

A broadband gamma-ray spectrometry using novel unfolding algorithms for characterization of laser wakefield-generated betatron radiation

We present a high-flux, broadband gamma-ray spectrometry capable of characterizing the betatron radiation spectrum over the photon energy range from 10 keV to 20 MeV with respect to the peak photon energy, spectral bandwidth, and unique discrimination from background radiations, using a differential filtering spectrometer and the unfolding procedure based on the Monte Carlo code GEANT4. These properties are experimentally verified by measuring betatron radiation from a cm-scale laser wakefield accelerator (LWFA) driven by a 1-PW laser, using a differential filtering spectrometer consisting of a 15-filter and image plate stack. The gamma-ray spectra were derived by unfolding the photostimulated luminescence (PSL) values recorded on the image plates, using the spectrometer response matrix modeled with the Monte Carlo code GEANT4. The accuracy of unfolded betatron radiation spectra was assessed by unfolding the test PSL data simulated with GEANT4, showing an ambiguity of less than 20% and clear discrimination from the background radiation with less than 10%. The spectral analysis of betatron radiation from laser wakefield-accelerated electron beams with energies up to 3 GeV revealed radiation spectra characterized by synchrotron radiation with the critical photon energy up to 7 MeV. The gamma-ray spectrometer and unfolding method presented here facilitate an in-depth understanding of betatron radiation from LWFA process and a novel radiation source of high-quality photon beams in the MeV regime.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Performance of the prototype LaBr{sub 3} spectrometer developed for the JET gamma-ray camera upgrade

In this work, we describe the solution developed by the gamma ray camera upgrade enhancement project to improve the spectroscopic properties of the existing JET γ-ray camera. Aim of the project is to enable gamma-ray spectroscopy in JET deuterium-tritium plasmas. A dedicated pilot spectrometer based on a LaBr{sub 3} crystal coupled to a silicon photo-multiplier has been developed. A proper pole zero cancellation network able to shorten the output signal to a length of 120 ns has been implemented allowing for spectroscopy at MHz count rates. The system has been characterized in the laboratory and shows an energy resolution of 5.5% at E{sub γ} = 0.662 MeV, which extrapolates favorably in the energy range of interest for gamma-ray emission from fast ions in fusion plasmas.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

REGULATION OF THE SPECTRAL PEAK IN GAMMA-RAY BURSTS

Observations indicate that the peak of a gamma-ray burst spectrum forms in the opaque region of an ultrarelativistic jet. Recent radiative transfer calculations support this picture and show that the spectral peak is inherited from initially thermal radiation, which is changed by heating into a broad photon distribution with a high-energy tail. We discuss the processes that regulate the observed position of the spectral peak E {sub pk}. The opaque jet has three radial zones: (1) the Planck zone r < R {sub P} where a blackbody spectrum is enforced; this zone ends where the Thomson optical depth decreases to {tau} Almost-Equal-To 10{sup 5}, (2) the Wien zone R {sub P} < r < R {sub W} with a Kompaneets parameter y >> 1 where radiation has a Bose-Einstein spectrum, and (3) the Comptonization zone r > R {sub W} where the radiation spectrum develops a high-energy tail. Besides the initial jet temperature, an important factor regulating E {sub pk} is internal dissipation (of bulk motions and magnetic energy) at large distances from the central engine. Dissipation in the Planck zone reduces E {sub pk}, and dissipation in the Wien zone can increase E {sub pk}. In jets with subdominant magnetic fields, the predicted E {sub pk} varies around 1 MeV up to a maximum value of about 10 MeV. If the jet carries an energetically important magnetic field, E {sub pk} can be additionally increased by dissipation of magnetic energy. This increase is suggested by observations, which show E {sub pk} up to about 20 MeV. We also consider magnetically dominated jets; then a simple model of magnetic dissipation gives E {sub pk} Almost-Equal-To 30 {Gamma}{sub W} keV where {Gamma}{sub W} is the jet Lorentz factor at the Wien radius R {sub W}.

79 ASTRONOMY AND ASTROPHYSICS↗

VARIABLE GAMMA-RAY EMISSION FROM THE CRAB NEBULA: SHORT FLARES AND LONG 'WAVES'

Gamma-ray emission from the Crab Nebula has been recently shown to be unsteady. In this paper, we study the flux and spectral variability of the Crab above 100 MeV on different timescales ranging from days to weeks. In addition to the four main intense and day-long flares detected by AGILE and Fermi-LAT between 2007 September and 2012 September, we find evidence for week-long and less intense episodes of enhanced gamma-ray emission that we call 'waves'. Statistically significant 'waves' show timescales of 1-2 weeks, and can occur by themselves or in association with shorter flares. We present a refined flux and spectral analysis of the 2007 September-October gamma-ray enhancement episode detected by AGILE that shows both 'wave' and flaring behavior. We extend our analysis to the publicly available Fermi-LAT data set and show that several additional 'wave' episodes can be identified. We discuss the spectral properties of the 2007 September 'wave'/flare event and show that the physical properties of the 'waves' are intermediate between steady and flaring states. Plasma instabilities inducing 'waves' appear to involve spatial distances l {approx} 10{sup 16} cm and enhanced magnetic fields B {approx} (0.5-1) mG. Day-long flares are characterized by smaller distances and larger local magnetic fields. Typically, the deduced total energy associated with the 'wave' phenomenon (E{sub w} {approx} 10{sup 42} erg, where E{sub w} is the kinetic energy of the emitting particles) is comparable with that associated to the flares, and can reach a few percent of the total available pulsar spin-down energy. Most likely, flares and waves are the product of the same class of plasma instabilities that we show acting on different timescales and radiation intensities.

79 ASTRONOMY AND ASTROPHYSICS↗

REVISITING THE GAMMA-RAY SOURCE 2FGL J1823.8+4312

One of the great challenges of gamma-ray astronomy is identifying the lower energy counterparts to these high-energy sources. Recently, in this journal, Massaro et al. attempted to find the counterpart of 2FGL J1823.8+4312, a gamma-ray active galactic nucleus (AGN) of uncertain type from the Second Fermi Large Area Telescope catalog. After considering mid-infrared data in the field from the Wide-field Infrared Survey Explorer (WISE), those authors conclude that the preferred identification of 2FGL J1823.8+4312 is WISE J182352.33+431452.5, despite the fact that the mid-infrared source is undetected at radio energies. They claim that WISE J182352.33+431452.5 constitutes the discovery of a new class of extragalactic X-ray source, either a radio-faint blazar or the prototype of a new class of active galaxy with an enigmatic spectral energy distribution. This conclusion is claimed to be independent of whether or not the WISE source is the actual counterpart to 2FGL J1823.8+4312. Based on a re-analysis of public data in this field and new spectroscopy from Palomar, we conclude that WISE J182352.33+431452.5 is a dust-reddened quasar at z = 0.560, a representative example of a very common extragalactic AGN class. Were WISE J182352.33+431452.5 to be associated with the gamma-ray emission, this would be an unusual and exciting discovery. However, we argue that 2FGL J1823.8+4312 is more likely associated with either WISE J182409.25+431404.7 or, more likely, WISE J182419.04+430949.6, two radio-loud sources in the field. The former is a radio-loud quasar and the latter is an optically variable source with a featureless blue spectrum.

79 ASTRONOMY AND ASTROPHYSICS↗

New Mexico Play Fairway Analysis: Gamma Ray Logs and Heat Generation Calculations for SW New Mexico

For the New Mexico Play fairway Analysis project, gamma ray geophysical well logs from oil wells penetrating the Proterozoic basement in southwestern New Mexico were digitized. Only the portion of the log in the basement was digitized. The gamma ray logs are converted to heat production using the equation (Bucker and Rybach, 1996) : A[microW/m3] = 0.0158 (Gamma Ray [API] - 0.8).

15 GEOTHERMAL ENERGY↗