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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Simulations of table-top watt-class 1 THz radiation sources with two-section periodic structure

Two types of terahertz sources with two-section periodical waveguide structure are studied by simulations. The operation frequency of the rear section (section-II) is the fourth harmonic of that of the front section (section-I), and section-II can operate both in the forward wave region and backward wave region. The critical factor that may affect the proper functioning of this kind of sources—overbunching—is discussed, and the corresponding solutions are proposed. These sources, with millimeter in length, can generate 1 THz wave radiation with power over 1 W, so, they are promising table-top and relatively high power terahertz sources.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2021

A hierarchical Bayesian model for background variation in radiation source localization

In this paper, we apply a new model to account for varying background radiation in radiological source localization. We present a hierarchical Bayesian model that simultaneously infers background and source location parameters without requiring separate estimation of the background radiation at each detector location. We employ a simplified photon transport model to reduce the computational expense of Bayesian model calibration. Furthermore, we demonstrate the model accuracy by localizing a cesium-137 source in a simulated city block, and we analyze experimental field measurements with varying background. In both cases, the model provides sufficient fidelity that we can locate the source while simultaneously estimating background radiation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Development of Partially-Coherent Wavefront Propagation Simulation Methods for 3rd and 4th Generation Synchrotron Radiation Sources.

Partially-coherent wavefront propagation calculations have proven to be feasible and very beneficial in the design of beamlines for 3rd and 4th generation Synchrotron Radiation (SR) sources. These types of calculations use the framework of classical electrodynamics for the description, on the same accuracy level, of the emission by relativistic electrons moving in magnetic fields of accelerators, and the propagation of the emitted radiation wavefronts through beamline optical elements. This enables accurate prediction of performance characteristics for beamlines exploiting high SR brightness and/or high spectral flux. Detailed analysis of radiation degree of coherence, offered by the partially-coherent wavefront propagation method, is of paramount importance for modern storage-ring based SR sources, which, thanks to extremely small sub-nanometer-level electron beam emittances, produce substantial portions of coherent flux in X-ray spectral range. We describe the general approach to partially-coherent SR wavefront propagation simulations and present examples of such simulations performed using 'Synchrotron Radiation Workshop' (SRW) code for the parameters of hard X-ray undulator based beamlines at the National Synchrotron Light Source II (NSLS-II), Brookhaven National Laboratory. These examples illustrate general characteristics of partially-coherent undulator radiation beams in low-emittance SR sources, and demonstrate advantages of applying high-accuracy physical-optics simulations to the optimization and performance prediction of X-ray optical beamlines in these new sources.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Experimental and theoretical study of organometallic radiation-protective materials adapted to radiation sources with a complex isotopic composition

The significance of optimizing the content of components of a radiation-protective material, which is determined by the isotopic composition of radioactive contamination, depending on the reactor type, operating time, and other factors is demonstrated. The results of computational and experimental investigation of the gamma-radiation attenuation capacity of homogenous radiation-protective materials with different fillers are reported.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2012

Point-like pulse-periodic UV radiation source with a short pulse duration

The radiation of discharge plasma was investigated in the nanosecond breakdown of short interelectrode gaps in a nonuniform electric field. Voltage pulses with an incident wave amplitude of {approx}10 kV, a FWHM duration of {approx}1 ns, and a rise time of {approx}200 ps were used. X-ray radiation from the discharge gap was recorded for an interelectrode gap of 0.5 mm, which confirms the generation of runaway electrons in the discharge formation. In the pulse-periodic air breakdown of a 0.5-mm wide gap at atmospheric pressure, the lines of electrode materials and the continuum were shown to make the main contribution to the plasma emission; the highest radiation intensity fell on the 200 - 300 nm region, which accounted for {approx}40% of the total emission energy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Bayesian Radiation Source Localization

We present an approach to localizing radiological sources that uses numerical adjoints and a Bayesian formulation and demonstrate the approach on two simple example scenarios. Results indicate accurate estimates of source locations. We briefly study the effect of neglecting the contribution of all scattered radiation in the adjoints, as analytical transport approximations do, for a case with moderately attenuating material between detectors and sources. The source location accuracy of the uncollided-only solutions appears to be significantly worse at the source strength considered here, suggesting that the higher physical fidelity that is provided by full numerical adjoint-based solutions may provide an advantage in operational settings

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2018

A New Method of Suppressing Peripheral Absorption in a Laser-Plasma Short-Wave Radiation Source with a Xe Gas-Jet Target

A more than tenfold increase in the intensity of EUV radiation from a laser-produced plasma source is observed experimentally under the illumination of a Xe gas-jet target with a wide laser beam covering its densest part compared with the radiation intensity at the traditional geometry, when the beam is sharply focused on the jet axis. As an explanation, it is assumed that in this case almost the whole dense part of the jet is heated and ionized under the action of laser irradiation and becomes transparent to the quanta of the studied radiation. The thickness of the absorbing peripheral shell of a laser spark decreases accordingly, that leads to the increase in the radiation intensity reaching the observer.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Dosimetric evaluation of new approaches in GRID therapy using nonconventional radiation sources

Purpose: Spatial fractionation of the dose has proven to be a promising approach to increase the tolerance of healthy tissue, which is the main limitation of radiotherapy. A good example of that is GRID therapy, which has been successfully used in the management of large tumors with low toxicity. The aim of this work is to explore new avenues using nonconventional sources: GRID therapy by using kilovoltage (synchrotron) x-rays, the use of very high-energy electrons, and proton GRID therapy. They share in common the use of the smallest possible grid sizes in order to exploit the dose–volume effects. Methods: Monte Carlo simulations (PENELOPE/PENEASY and GEANT4/GATE codes) were used as a method to study dose distributions resulting from irradiations in different configurations of the three proposed techniques. As figure of merit, percentage (peak and valley) depth dose curves, penumbras, and central peak-to-valley dose ratios (PVDR) were evaluated. As shown in previous biological experiments, high PVDR values are requested for healthy tissue sparing. A superior tumor control may benefit from a lower PVDR. Results: High PVDR values were obtained in the healthy tissue for the three cases studied. When low energy photons are used, the treatment of deep-seated tumors can still be performed with submillimetric grid sizes. Superior PVDR values were reached with the other two approaches in the first centimeters along the beam path. The use of protons has the advantage of delivering a uniform dose distribution in the tumor, while healthy tissue benefits from the spatial fractionation of the dose. In the three evaluated techniques, there is a net reduction in penumbra with respect to radiosurgery. Conclusions: The high PVDR values in the healthy tissue and the use of small grid sizes in the three presented approaches might constitute a promising alternative to treat tumors with such spatially fractionated radiotherapy techniques. The dosimetric results presented here support the interest of performing radiobiology experiments in order to evaluate these new avenues.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2012

Emittance Adapter for a Diffraction Limited Synchrotron Radiation Source

We investigate the possibility of reaching very small horizontal and vertical emittances inside an undulator in a storage ring, by means of a local exchange of the apparent horizontal and vertical emittances, performed with a combination of skew quadrupoles and one solenoid in a dedicated insertion line in the storage ring. The insertion leaves the ring parameters and its optical properties unaffected. This scheme could greatly relax the emittance requirements for a diffraction limited synchrotron light source. The lattice derivation and design is described.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Hypothesis tests for the detection of constant speed radiation moving sources

Radiation Portal Monitors are deployed in linear network to detect radiological material in motion. As a complement to single and multichannel detection algorithms, inefficient under too low signal to noise ratios, temporal correlation algorithms have been introduced. Test hypothesis methods based on empirically estimated mean and variance of the signals delivered by the different channels have shown significant gain in terms of a tradeoff between detection sensitivity and false alarm probability. This paper discloses the concept of a new hypothesis test for temporal correlation detection methods, taking advantage of the Poisson nature of the registered counting signals, and establishes a benchmark between this test and its empirical counterpart. The simulation study validates that in the four relevant configurations of a pedestrian source carrier under respectively high and low count rate radioactive background, and a vehicle source carrier under the same respectively high and low count rate radioactive background, the newly introduced hypothesis test ensures a significantly improved compromise between sensitivity and false alarm, while guaranteeing the stability of its optimization parameter regardless of signal to noise ratio variations between 2 to 0.8. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Performance analysis of Wald-statistic based network detection methods for radiation sources

There have been increasingly large deployments of radiation detection networks that require computationally fast algorithms to produce prompt results over ad-hoc sub-networks of mobile devices, such as smart-phones. These algorithms are in sharp contrast to complex network algorithms that necessitate all measurements to be sent to powerful central servers. In this work, at individual sensors, we employ Wald-statistic based detection algorithms which are computationally very fast, and are implemented as one of three Z-tests and four chi-square tests. At fusion center, we apply the K-out-of-N fusion to combine the sensors hard decisions. We characterize the performance of detection methods by deriving analytical expressions for the distributions of underlying test statistics, and by analyzing the fusion performances in terms of K, N, and the false-alarm rates of individual detectors. We experimentally validate our methods using measurements from indoor and outdoor characterization tests of the Intelligence Radiation Sensors Systems (IRSS) program. In particular, utilizing the outdoor measurements, we construct two important real-life scenarios, boundary surveillance and portal monitoring, and present the results of our algorithms.

Sen, Satyabrata↗
DOE OSTI2013

Upgraded X-ray topography and microtomography beamline at the Kurchatov synchrotron radiation source

An upgraded X-ray Topography and Microtomography (XRT-MT) station is described, the parameters of the optical schemes and detectors are given, and the experimental possibilities of the station are analyzed. Examples of tomographic reconstructions are reported which demonstrate spatial resolutions of 2.5 and 10 {mu}m at fields of view of 2.5 and 10 mm, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2010

3-Dimensional modeling of large diameter wire array high intensity K-shell radiation sources.

Large diameter nested wire array z-pinches imploded on the Z-generator at Sandia National Laboratories have been used extensively to generate high intensity K-shell radiation. Large initial radii are required to obtain the high implosion velocities needed to efficiently radiate in the K-shell. This necessitates low wire numbers and large inter-wire gaps which introduce large azimuthal non-uniformities. Furthermore, the development of magneto-Rayleigh-Taylor instabilities during the implosion are known to generate large axial non-uniformity These effects motivate the complete, full circumference 3-dimensional modeling of these systems. Such high velocity implosions also generate large voltages, which increase current losses in the power feed and limit the current delivery to these loads. Accurate representation of the generator coupling is therefore required to reliably represent the energy delivered to, and the power radiated from these sources. We present 3D-resistive MHD calculations of the implosion and stagnation of a variety of large diameter stainless steel wire arrays (hv {approx} 6.7 keV), imploded on the Z-generator both before and after its refurbishment. Use of a tabulated K-shell emission model allows us to compare total and K-shell radiated powers to available experimental measurements. Further comparison to electrical voltage and current measurements allows us to accurately assess the power delivered to these loads. These data allow us to begin to constrain and validate our 3D MHD calculations, providing insight into ways in which these sources may be further optimized.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Saturnian kilometric radiation: Source locations

The surce locations of both polariation components of the saturn kilometer wavelength radiation were deduced using Voyager 1 and Voyager 2 planetary radio astronomy data and assumptions about radiation beam geometry. Radio source footprints were compared with the surface locations of saturns ultraviolet aurorae, its polar cap boundary, and its polar cusp.

Kaiser, M. L.↗
DOE OSTI2017

THz and Sub-THz Capabilities of a Table-Top Radiation Source Driven by an RF Thermionic Electron Gun

Design features and experimental results are presented for a sub-mm wave source [1] based on APS RF thermionic electron gun. The setup includes compact alpha-magnet, quadrupoles, sub-mm-wave radiators, and THz optics. The sub-THz radiator is a planar, oversized structure with gratings. Source upgrade for generation frequencies above 1 THz is discussed. The THz radiator will use a short-period undulator having 1 T field amplitude, ~20 cm length, and integrated with a low-loss oversized waveguide. Both radiators are integrated with a miniature horn antenna and a small ~90°-degree in-vacuum bending magnet. The electron beamline is designed to operate different modes including conversion to a flat beam interacting efficiently with the radiator. The source can be used for cancer diagnostics, surface defectoscopy, and non-destructive testing. Sub-THz experiment demonstrated a good potential of a robust, table-top system for generation of a narrow bandwidth THz radiation. This setup can be considered as a prototype of a compact, laser-free, flexible source capable of generation of long trains of Sub-THz and THz pulses with repetition rates not available with laser-driven sources.

Smirnov, Alexei V.↗