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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Method and system for calibrating gamma radiation flux levels in a solid state gamma radiation detection system

One aspect of the present disclosure comprises a method for calibrating a drive level of a non-radioactive calibration source. Another aspect of the present disclosure comprises a method for using a non-radioactive calibration source to verify correct operation of a radiation detector. Another aspect of the present disclosure comprises a radiation detection system that comprises a radiation detector and a non-radioactive calibration source that is used to verify correct operation of the radiation detector.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Measuring the Charged Pion Polarizability in the $\gamma\gamma\rightarrow\pi^{+{}}\pi^{-{}}$ Reaction

A new measurement of the charged pion polarizability ????? is approved to run at Jefferson Lab using the GlueX detector in experimental Hall D. The charged pion polarizability ranks among the most important tests of low-energy QCD presently unresolved by experiment. Analogous to precision measurements of ?0??? that test the intrinsic odd-parity (anomalous) sector of QCD, the pion polarizability tests the intrinsic even-parity sector of QCD. The ????+?? cross section will be accessed via the Primakoff mechanism on a nuclear target. The linearly polarized photon source in Hall D will allow the separation of the Primakoff cross section from coherent ?0(770) production. An additional detector will also need to be constructed to help distinguish ?+?? and ?+?? events. An update on the status of the experiment will be given.

Lawrence, David↗
DOE OSTI2017

Validation of Methodology to Simulate Gamma Doses from Historical Weapons Tests

The United States tested nuclear weapons in the atmosphere (aboveground) from 1945 until 1963, when the nation became a signatory to the Partial Test Ban Treaty. During those tests, gamma doses were often measured within kilometers of the point of detonation. Additional gamma dose measurements were made in and around the location of any personnel conducting the test, possibly with personal dosimeters. These gamma dose measurements have been declassified to provide the personnel involved with an estimate of the total dose they received while involved with the aboveground testing program. Several years ago, interest in these gamma doses was renewed by organizations that would need to provide the public with dose estimates in the event of a radiological or nuclear weapon terrorist attack on the United States. This work provides an initial validation of the computational methods used to simulate dose from a radiological or nuclear weapon. This initial work will focus on dose from gamma rays. The sources of gamma rays from a nuclear weapon include prompt fission gammas, gammas generated via neutron interactions (capture, inelastic scattering, and activation), and gammas produced by the decay of fission products. All of these gamma ray sources for a nuclear weapon are also potential sources of gammas from a radiological weapon. However, the sources of gamma rays from a radiological weapon depend on the material present in the device, and prompt fission gammas will mostly come from spontaneous fission instead of induced fission. This paper focuses on validation using gamma ray dose measurements from nuclear detonations, which is adequate to validate the requisite transport methodologies, source term generation, and cross sections needed to model gamma doses delivered by most radiological weapons. The 1961 report on Operation Plumbbob provides an overview of how the total gamma dose delivered by a nuclear weapon is broken down by the different sources specified above. The prompt fission gamma rays contribute about 5% of the total gamma dose. The gamma rays produced by neutron interactions usually deliver the largest portion of the total gamma dose, which is typically between 55% and 85% of the total. The remainder of the total gamma ray dose is attributed to decay of fission products.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2018

Neutron Capture Energies for Flux Normalization and Approximate Model for Gamma-Smeared Power

The Consortium for Advanced Simulation of Light Water Reactors (CASL) Virtual Environment for Reactor Applications (VERA) neutronics simulator MPACT has used a single recoverable fission energy for each fissionable nuclide assuming that all recoverable energies come only from fission reaction, for which capture energy is merged with fission energy. This approach includes approximations and requires improvement by separating capture energy from the merged effective recoverable energy. This report documents the procedure to generate recoverable neutron capture energies and the development of a program called CapKappa to generate capture energies. Recoverable neutron capture energies have been generated by using CapKappa with the evaluated nuclear data file (ENDF)/B-7.0 and 7.1 cross section and decay libraries. The new capture kappas were compared to the current SCALE-6.2 and the CASMO-5 capture kappas. These new capture kappas have been incorporated into the Simplified AMPX 51- and 252-group libraries, and they can be used for the AMPX multigroup (MG) libraries and the SCALE code package. The CASL VERA neutronics simulator MPACT does not include a gamma transport capability, which limits it to explicitly estimating local energy deposition from fission, neutron, and gamma slowing down and capture. Since the mean free path of gamma rays is typically much longer than that for the neutron, and the total gamma energy is about 10% to the total energy, the gamma-smeared power distribution is different from the fission power distribution. Explicit local energy deposition through neutron and gamma transport calculation is significantly important in multi-physics whole core simulation with thermal-hydraulic feedback. Therefore, the gamma transport capability should be incorporated into the CASL neutronics simulator MPACT. However, this task will be timeconsuming in developing the neutron induced gamma production and gamma cross section libraries. This study is to investigate an approximate model to estimate gammasmeared power distribution without performing any gamma transport calculation. A simple approximate gamma smearing model has been investigated based on the facts that pinwise gamma energy depositions are almost flat over a fuel assembly, and assembly-wise gamma energy deposition is proportional to kappa-fission energy deposition. The approximate gamma smearing model works well for single assembly cases, and can partly improve the gamma smeared power distribution for the whole core model. Although the power distributions can be improved by the approximate gamma smearing model, still there is an issue to explicitly obtain local energy deposition. A new simple approach or gamma transport/diffusion capability may need to be incorporated into MPACT to estimate local energy deposition for more robust multi-physics simulation.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS1995

Pair cascades in extragalactic jets. 1: Gamma rays

A model of the approximately 0.1-10 GeV gamma-ray jets observed by the EGRET instrument on the Compton Gamma Ray Observatory (CGRO) is developed. It is shown that the soft X-ray background in an active galactic nuclei (AGN) contributes an opacity to pair production and that a gamma-ray photosphere or 'gamma-sphere' can be defined whose radius increases with gamma-ray energy E(sub gamma). It is proposed that the observed gamma-ray emission is due to inverse Compton scattering of the ambient soft X-rays by relativistic pairs accelerated in situ by shock fronts in a relativistic jet. For a wide range of assumed physical conditions, the emission at a given E(sub gamma) originates from near the associated gamma-spheres; emission from below the gamma-sphere initiates a cascade down to the energy where the gamma-rays can escape freely. In this model, the slope of the emergent gamma-ray spectrum is determined by the scattered, soft X-ray spectrum and the variation of the particle acceleration rate with jet radius. In general it is expected that the variation in the gamma-ray flux will be either slower or later at higher energy. It is also shown that the efficiency of conversion of energy from injected high-energy pairs to 0.1-10 GeV gamma-rays is typically high so that the models are radiatively efficient. It is argued that the observed gamma-ray jets are likely to be particle-dominated, though magnetically confined. The gamma-ray spectrum should continue down to an energy approximately 5 MeV emitted from an annihilation radius within which the pair content of the jet is limited by annihilation. This is probably the site of the beamed hard X-ray emission. It is speculated that the relativistic jets associated with radio-loud AGNs are powered electromagnetically by a spinning black hole and that they are collimated by an encircling MHD wind leaving the accretion disk at a slower speed. Powerful FR2 radio sources are formed when the hole spins rapidly and the relativistic core accelerates the MHD sheath; low-power FR1 sources ensue when the opposite occurs. Finally, it is suggested that the key factor which determines whether or not a given active nucleus can form a jet and a radio to gamma-ray nonthermal continuum is the central density of mass-losing stars which, when large, precludes the formation of a super-Alfvenic, collimating wind.

Blandford, R. D.↗
NASA NTRS1997

The Effects of Composition and gamma'/gamma Lattice Parameter Mismatch on the Critical Resolved Shear Stresses for Octahedral and Cube Slip in NiAlCrX Alloys

Prototypical single-crystal NiAlCrX superalloys were studied to examine the effects of the common major alloying elements, Co, Mo, Nb, Ta, Ti, and W, on yielding behavior. The alloys contained about 10 at. pct Cr, 60 vol pct of the gamma' phase, and about 3 at. pct of X in the gamma'. The critical resolved shear stresses (CRSSs) for octahedral and primary cube slip were measured at 760 C, which is about the peak strength temperature. The CRSS(sub oct) and CRSS(sub cube) are discussed in relation to those of Ni, (Al, X) gamma' alloys taken from the literature and the gamma'/gamma lattice mismatch. The CRSS(sub oct) of the gamma + gamma' alloys reflected a similar compositional dependence to that of both the CRSS(sub cube) of the gamma' phase and the gamma'/gamma lattice parameter mismatch. The CRSS(sub cube) of the gamma + gamma' alloys also reflected the compositional dependence of the gamma'/gamma mismatch, but bore no similarity to that of CRSS(sub cube) for gamma' alloys since it is controlled by the gamma matrix. The ratio of CRSS(sub cube)/CRSS(sub oct) was decreased by all alloying elements except Co, which increased the ratio. The decrease in CRSS(sub cube)/CRSS(sub oct) was related to the degree in which elements partition to the gamma' rather than the gamma phase.

Miner, R. V.↗
DOE OSTI2022

Validation of realistic Monte Carlo plasma gamma-ray source on JET discharges

A novel modelling methodology has been developed for the creation of a realistic plasma gamma-ray source for Monte Carlo transport simulations in the tokamak JET. The methodology couples the TRANSP code for plasma transport calculations with the MCNP Monte Carlo particle transport code, thus connecting plasma physics with gamma-ray transport. Here, we present the validation of the developed source methodology by comparing calculated gamma-ray spectra with measurements performed at JET. The validation focuses on gamma-ray spectra measured by the tangential gamma-ray spectrometer during two JET three ion RF scenario discharges, performed in the JET 2019 deuterium experimental campaign. For validation the calculated plasma gamma-ray spectrum was combined with the neutron induced prompt gamma-ray background, originating in the vacuum vessel, and scaled to absolute values calculating the total number of plasma gamma-ray and neutron emitting reactions. The comparison between calculated and measured gamma-ray spectra shows good agreement with the shape of the calculated gamma-ray spectra matching that of measurements for both studied discharges. Moreover, the calculated absolute values of the gamma-ray spectra were of the same order of magnitude at the position of the gamma-ray detector located at the end of a long line-of-sight in a biological shield. Finally, the comparison has validated the developed plasma gamma-ray source methodology for MCNP photon transport calculations at JET. The validation provides a basis for the developed plasma gamma-ray source to be used as a support for the development of future tokamaks such as DEMO.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Coupled Neutron and Gamma Heating Calculation Based on VARIANT Nodal Transport Method

Accurate determination of temperature distributions in fuel pins and duct walls is essential for fuel-pin performance and assembly bowing analyses. Currently, the multi-assembly, sub-channel analysis code SE2-ANL is used in thermalhydraulic analysis of sodium cooled fast reactors (SFR). SE2- ANL is interfaced with the DIF3D/GAMSOR/DIF3D procedure for coupled neutron and gamma heating calculations, developed at Argonne National Laboratory (ANL). In this procedure, the neutron flux distribution is first calculated using the finite-difference diffusion theory option of the DIF3D code. Using the neutron flux solution, the GAMSOR code computes the gamma source distribution for the subsequent gamma flux calculation with DIF3D. However, in the current heating calculation scheme, the neutron and gamma flux calculations are limited to six triangular meshes per hexagonal assembly. In addition, the pin power distributions are estimated by assuming that the power distribution within an assembly is separable in the radial and axial directions. In each assembly, the axial power profile is obtained by averaging the power densities of six triangular meshes at each axial mesh interval. The radial power profile is evaluated at a single axial mesh (e.g., at the core mid-plane) by approximating the neutron and gamma flux distributions by a linear or quadratic polynomial of two variables x and y, depending on the polynomial order specified by the user. The coefficients of the linear and quadratic polynomials are determined by the least squares fit of six and 24 triangular mesh fluxes, respectively. Furthermore, the total heat generation rate in an assembly duct wall is simply determined by a user-specified fraction of the total gamma heating within that assembly. With the advancement of computer technology, the nodal transport theory code VARIANT is routinely used in core design analyses of SFR instead of DIF3D. It is therefore necessary to develop a new heating calculation procedure based on VARIANT neutron and gamma transport calculations. In this study, a new, coupled neutron and gamma heating calculation scheme has been developed to determine the pin power distributions more accurately by eliminating the aforementioned limitations of the current procedure. For this, the GAMSOR code has been extended to generate the intra-nodal gamma source distribution to be consistent with the trial functions of VARIANT. In the new heating calculation procedure, the neutron flux distribution is determined first by solving an eigenvalue transport problem using VARIANT. The obtained neutron flux is then used in GAMSOR to calculate the gamma source distribution. Using this gamma source distribution, the gamma flux distribution is determined by solving a fixed-source transport problem using VARIANT again. Using the computed neutron and gamma flux distributions, the power distribution in each fuel pin and duct wall is determined using a new utility code CURVE, which has been developed to evaluate the VARIANT flux solution at each fuel pin position and along the duct mid-wall. For each pin segment contained in a VARIANT node, the axial power shape is represented as a quadratic profile. The performance of the new heating calculation scheme based on VARIANT transport solutions has been tested against the existing method of SE2-ANL, using the ABR-1000 metal core design. The gamma source distribution and the assembly, fuel pin and duct wall power distributions were calculated and compared. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

IMRT QA: Selecting gamma criteria based on error detection sensitivity

Purpose: The gamma comparison is widely used to evaluate the agreement between measurements and treatment planning system calculations in patient-specific intensity modulated radiation therapy (IMRT) quality assurance (QA). However, recent publications have raised concerns about the lack of sensitivity when employing commonly used gamma criteria. Understanding the actual sensitivity of a wide range of different gamma criteria may allow the definition of more meaningful gamma criteria and tolerance limits in IMRT QA. We present a method that allows the quantitative determination of gamma criteria sensitivity to induced errors which can be applied to any unique combination of device, delivery technique, and software utilized in a specific clinic. Methods: A total of 21 DMLC IMRT QA measurements (ArcCHECK®, Sun Nuclear) were compared to QA plan calculations with induced errors. Three scenarios were studied: MU errors, multi-leaf collimator (MLC) errors, and the sensitivity of the gamma comparison to changes in penumbra width. Gamma comparisons were performed between measurements and error-induced calculations using a wide range of gamma criteria, resulting in a total of over 20 000 gamma comparisons. Gamma passing rates for each error class and case were graphed against error magnitude to create error curves in order to represent the range of missed errors in routine IMRT QA using 36 different gamma criteria. Results: This study demonstrates that systematic errors and case-specific errors can be detected by the error curve analysis. Depending on the location of the error curve peak (e.g., not centered about zero), 3%/3 mm threshold = 10% at 90% pixels passing may miss errors as large as 15% MU errors and ±1 cm random MLC errors for some cases. As the dose threshold parameter was increased for a given %Diff/distance-to-agreement (DTA) setting, error sensitivity was increased by up to a factor of two for select cases. This increased sensitivity with increasing dose threshold was consistent across all studied combinations of %Diff/DTA. Criteria such as 2%/3 mm and 3%/2 mm with a 50% threshold at 90% pixels passing are shown to be more appropriately sensitive without being overly strict. However, a broadening of the penumbra by as much as 5 mm in the beam configuration was difficult to detect with commonly used criteria, as well as with the previously mentioned criteria utilizing a threshold of 50%. Conclusions: We have introduced the error curve method, an analysis technique which allows the quantitative determination of gamma criteria sensitivity to induced errors. The application of the error curve method using DMLC IMRT plans measured on the ArcCHECK® device demonstrated that large errors can potentially be missed in IMRT QA with commonly used gamma criteria (e.g., 3%/3 mm, threshold = 10%, 90% pixels passing). Additionally, increasing the dose threshold value can offer dramatic increases in error sensitivity. This approach may allow the selection of more meaningful gamma criteria for IMRT QA and is straightforward to apply to other combinations of devices and treatment techniques.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1997

Gamma-Ray Astrophysics: New Insight Into the Universe

During the 15 years that have passed since the first edition of this book was published, there has been a major increase in our knowledge of gamma-ray astronomy. Much of this advance arises from the extensive results that have been forthcoming from the Compton Gamma-Ray Observatory. There has been the discovery of a new class of gamma-ray objects, namely high-energy gamma- ray-emitting blazars, a special class of Active Galactic Nuclei, whose basic high-energy properties now seem to be understood. A much improved picture of our galaxy now exists in the frequency range of gamma rays. The question of whether cosmic rays are galactic or metagalactic now seems settled with certainty. Significant new information exists on the gamma-ray properties of neutron star pulsars, Seyfert galaxies, and gamma-ray bursts. Substantial new insight has been obtained on solar phenomena through gamma-ray observations. Hence, this seemed to be an appropriate time to write a new edition of this book to add the important scientific implications of these many new findings. The special importance of gamma-ray astrophysics had long been recognized by many physicists and astronomers, and theorists had pursued many aspects of the subject well before the experimental results began to become available. The slower development of the experimental side was not because of a lack of incentive, but due to the substantial experimental difficulties that had to be overcome. Thus, as the gamma-ray results became available in much greater number and detail, it was possible to build upon the theoretical work that already existed and to make substantial progress in the study of many of the phenomena involved. Consequently, a much better understanding of many of the astrophysical phenomena mentioned here and others is now possible. Our principal aims in writing this book are the same as they were for the first edition: to provide a text which describes the significance of gamma-ray astrophysics and to assemble in one place a treatment of gamma rays emitted from bodies in the solar i system, from objects in our galaxy, as well as from interactions between cosmic rays and the interstellar medium, and from beyond our galaxy. Thus, this book is intended for those in astrophysics who wish to have the opportunity to learn more about the evolving field of gamma-ray astronomy and its relationship to the high-energy, evolutionary processes occurring in the universe. The last three chapters of the book provide a general discussion of the experimental aspects of the field that seemed best treated together, separately from the astrophysical aspects of gamma-ray astronomy that are discussed in the first ten chapters.

Fichtel, Carl E.↗
DOE OSTI2017

Effects of Correlated and Uncorrelated Gamma Rays on Neutron Multiplicity Counting

Neutron multiplicity counting relies on time correlation between neutron events to assay the fissile mass, (α,n) to spontaneous fission neutron ratio, and neutron self-multiplication of samples. Gamma-ray sensitive neutron multiplicity counters may misidentify gamma rays as neutrons and therefore miscalculate sample characteristics. Time correlated and uncorrelated gamma-ray-like signals were added into gamma-ray free neutron multiplicity counter data to examine the effects of gamma ray signals being misidentified as neutron signals on assaying sample characteristics. Multiplicity counter measurements with and without gamma-ray-like signals were compared to determine the assay error associated with gamma-ray-like signals at various gamma-ray and neutron rates. Correlated and uncorrelated gamma-ray signals each produced consistent but different measurement errors. Correlated gamma-ray signals most strongly led to fissile mass overestimates, whereas uncorrelated gamma-ray signals most strongly lead to (α,n) neutron overestimates. Gamma-ray sensitive neutron multiplicity counters may be able to account for the effects of gamma-rays on measurements to mitigate measurement uncertainties.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗