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NASA NTRS1973

On multidisciplinary research on the application of remote sensing to water resources problems

Research objectives during 1972-73 were to: (1) Ascertain the extent to which special aerial photography can be operationally used in monitoring water pollution parameters. (2) Ascertain the effectiveness of remote sensing in the investigation of nearshore mixing and coastal entrapment in large water bodies. (3) Develop an explicit relationship of the extent of the mixing zone in terms of the outfall, effluent and water body characteristics. (4) Develop and demonstrate the use of the remote sensing method as an effective legal implement through which administrative agencies and courts can not only investigate possible pollution sources but also legally prove the source of water pollution. (5) Evaluate the field potential of remote sensing techniques in monitoring algal blooms and aquatic macrophytes, and the use of these as indicators of lake eutrophication level. (6) Develop a remote sensing technique for the determination of the location and extent of hydrologically active source areas in a watershed.

Clapp, J. L.↗

DOE OSTI2015

A Prototype {sup 212}Pb Medical Dose Calibrator for Alpha Radioimmunotherapy

AREVA Med, an AREVA group subsidiary, is developing innovative cancer-fighting therapies involving the use of {sup 212}Pb for alpha radioimmunotherapy. Canberra Industries, the nuclear measurement subsidiary of AREVA, has been working with AREVA Med to develop a prototype measurement system to assay syringes containing a {sup 212}Pb solution following production by an elution system. The relative fraction of emitted radiation from the source associated directly with the {sup 212}Pb remains dynamic for approximately 6 hours after the parent is chemically purified. A significant challenge for this measurement application is that the short half-life of the parent nuclide requires assay prior to reaching equilibrium with progeny nuclides. A gross counting detector was developed to minimize system costs and meet the large dynamic range of source activities. Prior to equilibrium, a gross counting system must include the period since the {sup 212}Pb was pure to calculate the count rate attributable to the parent rather than the progeny. The dynamic state is determined by solving the set of differential equations, or Bateman equations, describing the source decay behavior while also applying the component measurement efficiencies for each nuclide. The efficiencies were initially estimated using mathematical modeling (MCNP) but were then benchmarked with source measurements. The goal accuracy of the system was required to be within 5%. Independent measurements of the source using a high resolution spectroscopic detector have shown good agreement with the prototype system results. The prototype design was driven by cost, compactness and simplicity. The detector development costs were minimized by using existing electronics and firmware with a Geiger-Mueller tube derived from Canberra's EcoGamma environmental monitoring product. The acquisition electronics, communications and interface were controlled using Python with the EcoGamma software development kit on a Raspberry Pi Linux computer mounted inside a standard project box. The results of initial calibration measurements are presented. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2019

Deciding Between an X-Ray and 137Cs Irradiator – It’s Not Just About Energy Spectra

Irradiators utilizing radioactive cesium-137 or cobalt-60 have been used for medical applications for many decades. This includes the irradiation of much of the nation’s blood supply, and radiation biology research. In 2005, the U.S. Nuclear Regulatory Commission was assigned to evaluate and prevent the misuse of radioactive materials with malicious intentions, with gamma-ray sources being high on the list. Licensees who possessed higher quantities of radioactive material of concern were required to set up increased security controls such as constant surveillance, controlled access, personnel background checks, and other security controls. As a result of introducing such regulations, and problems with disposing of high activity sources, many users of gamma-ray sources started to look into alternative technologies to replace their gamma-ray irradiators – the main alternative being an X-ray irradiator. To make an educated decision on whether a particular type of X-ray irradiator is equivalent to a particular type of cesium-137 irradiator for specific applications, one has to rely on relevant published comparison studies from other researchers, or perform the comparison studies on their own. This publication focuses on the authors’ technical performance comparison of two cesium-137 irradiator models and two X-ray irradiator models, for the purpose of determining whether the X-ray irradiator models could validly replace the cesium-137 irradiator models for certain applications. Utilizing 47 gram and 120 gram tissue-equivalent rodent dosimetry phantoms, our results indicate that, depending upon the user’s dose uncertainty budget and maximum size of specimens to be irradiated, the Model RS2000 160 kVp X-ray irradiator, Model XRAD-160 X-ray irradiator, or Model XRAD-320 X-ray irradiator, could successfully replace a cesium-137 irradiator. It is expected such equivalency could be extrapolated to other irradiated specimens of known sizes and density. Results also reveal that differences in inherent source geometry, field geometry and irradiation geometry can counter some of the influence due to differences in energy spectrum. It is hoped that this publication can be used as a guide for other similar studies, providing investigators guidance on important details that can make the difference between strong and weak comparison conclusions.

Cs-137 irradiator, X-ray Irradiator, self-containe↗

NASA NTRS1987

Anisotropic emission from comets: Fans versus jets. 2: Periodic Comet Tempel 2

The position of the rotation axis of P/Tempel 2 is constrained by projected orientations of the comet's sunward fan-like coma extension during 9 apparitions. The approach employed is based on the emission-cone concept formulated for a continuous (or quasi-continuous) collimated flow of dust ejected from discrete active regions on a rotating nucleus. The results show that the observations can be satisfied by assuming an invariable position of the pole, although this is not necessarily the only solution. The derived obliquity of 54 deg and the latitude of +60 deg for the southernmost boundary of the active source imply that the region experiences a polar day for 5 months about perihelion and a polar night for over 3 yr approximately centered on the aphelion point. Combining these results with scattered photometric and spectrophotometric information on the comet at large heliocentric distance, the outbursts observed near 3 AU are attributed to intermittent activity from the region shortly prior and following the polar night.

Sekanina, Z.↗

DOE OSTI2016

An analysis of key characteristics of the Frank-Read source process in FCC metals

A well-known intragranular dislocation source, the Frank-Read (FR) source plays an important role in size-dependent dislocation multiplication in crystalline materials. Despite a number of studies in this topic, a systematic investigation of multiple aspects of the FR source in different materials is lacking. Here, in this paper, we employ large scale quasistatic concurrent atomistic-continuum (CAC) simulations to model an edge dislocation bowing out from an FR source in Cu, Ni, and Al. First, a number of quantities that are important for the FR source process are quantified in the coarse-grained domain. Then, two key characteristics of the FR source, including the critical shear stress and critical dislocation configuration, are investigated. In all crystalline materials, the critical stresses and the aspect ratio of the dislocation half-loop height to the FR source length scale well with respect to the FR source length. In Al, the critical stress calculated by CAC simulations for a given FR source length agrees reasonably well with a continuum model that explicitly includes the dislocation core energy. Nevertheless, the predictions of the isotropic elastic theory do not accurately capture the FR source responses in Cu and Ni, which have a relatively large stacking fault width and elastic anisotropy. Our results highlight the significance of directly simulating the FR source activities using fully 3D models and shed light on developing more accurate continuum models.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Insulation Activation and Contamination in Low-Power Experiments

Among the diverse advanced nuclear reactor concepts being developed are designs that expect to operate at much higher temperatures than conventional light-water reactors, and therefore require alternative materials for components capable of withstanding these extreme temperatures. Insulation is one such component where alternative high-temperature industrial composites are being considered. Low-power experiments can provide an opportunity for advancing our understanding of material behavior under irradiation; however, these experiments are not without occupational hazards. The focus of this paper is the potential for activation of insulating composites when exposed to neutron fluence during reactor experiments, and to discuss the subsequent contamination of the testing area. This paper will also discuss practical measures for preventing the creation and inhalation of activated particulate matter (i.e., dust), such as engineering and administrative controls and personal protective equipment. This paper evaluates the suitability of several insulation materials for use in reactor experiments based on their activation from neutron irradiation. The materials considered are Pyrogel XTE by Aspen Aerogel, Cerablanket and Kaowool by Morgan Advanced Materials, Thermo-12 Gold by Johns Manville, and Maxsil CF6-2000 by McAllister Mills. Although these materials are not yet widely used in the nuclear industry, they are common in other industries due to their thermal insulating properties. These materials produce dust while handling that can pose health and safety hazards, which could be further exacerbated by activation. The analysis presented in this paper utilizes a deterministic method developed to predict the activation source term of the provided insulation materials. The method calculates the atomic density of each element within the composites and simulates their exposure to a specified neutron flux density representative of low power experimental conditions. During the irradiation phase and throughout the extensive cooling period, neutron absorptions and nuclear decays are tracked for relevant isotopes. The residual activity within each composite is then assessed to identify the material with the lowest potential radiological hazard to workers. Dust will be created during installation and removal of insulating materials and may also be generated during the experiment. Contamination of surrounding surfaces due to dispersion is highly likely unless preventative measures are taken. The results of this analysis are used to estimate an internal dose from inhalation of activated dust, which is significantly lower than the allowable whole-body dose. However, the risk of internal exposure may increase if the dust becomes a transport vector for nuclear material. The goals of this paper are to enhance the understanding of the potential activation and contamination hazards from the use of these insulating materials in low-power nuclear experiments and to foster safer work environments through informed decision-making and strategic planning. This work ultimately contributes to a broader understanding of how new non-nuclear materials for advanced reactors impact the radiological safety of co-located workers, helping to ensure the responsible management of radioactive materials during installation and decommissioning activities.

12 - MGMT OF RADIOACTIVE AND NON-RADIOACTIVE WASTE↗

DOE OSTI2015

SU-E-T-413: Examining Acquisition Rate for Using MatriXX Ion Chamber Array to Measure HDR Brachytherapy Treatments

Purpose: There are unique obstacles to implementing the MatriXX ionchamber array as a QA tool in Brachytherapy given that the device is designed for use in the MV energy range. One of the challenges we investigate is the affect of acquisition rates on dose measurement accuracy for HDR treatment plans. Methods: A treatment plan was optimized in Oncentra Brachy TPS to deliver a planar dose to a 5×5cm region at 10mm depth. The applicator was affixed to the surface of the MatriXX array. The plan was delivered multiple times using a Nucleatron HDR afterloader with a 2.9Ci Ir192 source. For each measurement the sampling rate of the MatriXX movie mode was varied (30ms and 500ms). This experiment was repeated with identical parameters, following a source exchange, with an 11.2Ci Ir192 source. Finally, a single snap measurement was acquired. Analysis was preformed to evaluate the fidelity of the dose delivery for each iteration of the experiment. Evaluation was based on the comparison between the measured and TPS predicted dose. Results: Higher sample rates induce a greater discrepancy between the predicted and measured dose. Delivering the plan using a lower activity source also produced greater discrepancy in the measurement due to the increased delivery time. Analyzing the single snap measurement showed little difference from the 500ms integral dose measurement. Conclusion: The advantage of using movie mode for HDR treatment delivery QA is the ability for real time source tracking in addition to dose measurement. Our analysis indicates that 500ms is an optimal frame rate.

61 RADIATION PROTECTION AND DOSIMETRY↗

DOE OSTI2017

Enhanced Monte Carlo Simulation of the Voxel Phantom Lattice Submersed in a Contaminated Air Environment

External dose coefficient calculations reported for submersions in semi-infinite clouds, as in the Environmental Protection Agency: Federal Guidance Report 12, assume a person standing on the ground submerged in a radioactive cloud. In the scope of the work presented here, Oak Ridge National Laboratory's Center for Radiation Protection Knowledge has computed dose coefficients for monoenergetic photons, electrons, and positrons for worker exposures in three rooms of finite sizes representing an office, laboratory, and warehouse. In the process of simulating these exposures, International Commission on Radiological Protection (ICRP) Publication 110 reference adult male and female voxel phantom lattices were placed in the rooms filled with contaminated air. It was apparent that additional simulations were need to treat the non-tissue voxels surrounding the phantoms as containing the contaminated air. Dose coefficients for three room sizes representing an office, laboratory, and warehouse were computed. The coefficients for electrons exhibit little dependence on room size for most energies. However, for organs within the range of electron transport, the dose from source activity within the non-tissue voxels of the lattice surrounding the phantom becomes increasingly important. The photon dose coefficients vary based on room size because of longer mean free paths. It is important to include the air surrounding the voxel phantom within the voxel lattice in the calculations, when simulating a voxel phantom submersed in air for source particle energies below 200-300 keV, otherwise, the organ dose coefficient would be underestimated. Organ and effective dose coefficients for each gender, energy, and room size will be tabulated on the Oak Ridge National Laboratory - Center for Radiation Protection Knowledge website: http://ornl.gov/crpk.

61 RADIATION PROTECTION AND DOSIMETRY↗

DOE OSTI2023

Examining Infrasound Propagation at High Spatial Resolution Using a Nodal Seismic Array

Infrasound—acoustic waves in the atmosphere below 20 Hz—is a useful monitoring tool. Topography and atmospheric structure strongly control infrasound propagation, and at common source–receiver distances neither of these effects can be ignored when quantitative source constraints are sought. Detailed spatial measurements of the infrasound wavefield would inform propagation models and improve source estimates. However, the “large-N” deployment strategy now well-known in seismology has not yet been realized for infrasound studies. Here, we use the 900-node seismic array from the 2014 Imaging Magma Under St. Helens (iMUSH) experiment as a proxy for a large-N infrasound network, by leveraging acoustic–seismic coupled arrivals. The active-source component of iMUSH consisted of 23 shallowly buried explosions around Mount Saint Helens volcano; these explosions produced epicentral infrasound recorded on the nodes. We find that the bulk presence of ground-coupled infrasound on the nodes is controlled by wind noise and source–receiver distance, with observed arrivals for eight explosions. Explosions with the most extensive coupling produce complex spatial waveform patterns across the array. These patterns are related to both topographic and atmospheric propagation effects, as well as spatially variable site (coupling) effects. We compare our observations to simple topographic diffraction and high-resolution wind advection models, and full-wave numerical simulations. We find strong spatial correlations between (a) coupled arrival strength and modeled topographic obstruction and (b) coupled arrival time and along-path winds. Our seismoacoustic analyses and results are applicable to other existing and future nodal seismic data sets and can expand the utility of such deployments.

58 GEOSCIENCES↗

DOE OSTI2017

Source characteristics and geological implications of the January 2016 induced earthquake swarm near Crooked Lake, Alberta

On 2016 January 12, an intraplate earthquake with an initial reported local magnitude (M L ) of 4.8 shook the town of Fox Creek, Alberta. While there were no reported damages, this earthquake was widely felt by the local residents and suspected to be induced by the nearby hydraulic-fracturing (HF) operations. We determine the earthquake source parameters using moment tensor inversions, and then detect and locate the associated swarm using a waveform cross-correlation based method. The broad-band seismic recordings from regional arrays suggest a moment magnitude (M) 4.1 for this event, which is the largest in Alberta in the past decade. Similar to other recent M ~ 3 earthquakes near Fox Creek, the 2016 January 12 earthquake exhibits a dominant strike-slip (strike = 184°) mechanism with limited non-double-couple components (~22 per cent). This resolved focal mechanism, which is also supported by forward modelling and P-wave first motion analysis, indicates an NE–SW oriented compressional axis consistent with the maximum compressive horizontal stress orientations delineated from borehole breakouts. Further detection analysis on industry-contributed recordings unveils 1108 smaller events within 3 km radius of the epicentre of the main event, showing a close spatial-temporal relation to a nearby HF well. The majority of the detected events are located above the basement, comparable to the injection depth (3.5 km) on the Duvernay shale Formation. The spatial distribution of this earthquake cluster further suggests that (1) the source of the sequence is an N–S-striking fault system and (2) these earthquakes were induced by an HF well close to but different from the well that triggered a previous (January 2015) earthquake swarm. Reactivation of pre-existing, N-S oriented faults analogous to the Pine Creek fault zone, which was reported by earlier studies of active source seismic and aeromagnetic data, are likely responsible for the occurrence of the January 2016 earthquake swarm and other recent events in the Crooked Lake area.

58 GEOSCIENCES↗

DOE OSTI2017

Beyond Californium—A Neutron Generator Alternative for Dosimetry and Instrument Calibration in the U.S.

Many evaluations of neutron survey instruments, area monitors and personal dosimeters rely on neutron reference radiations from 252Cf, a source of spontaneous fission neutrons that produces high dose rates from an almost point source geometry. Its characteristics are generally more favorable when compared to (a,n), photoneutron and reactor-based sources of neutrons. The source is typically used in two standardized configurations: unmoderated, to yield a fission energy spectrum, or placed within a heavy-water moderating sphere to produce a softened spectrum that is more appropriate for evaluating devices used in nuclear power plant work environments. The U.S. Department of Energy (DOE) 252Cf Loan/Lease Program was terminated in 2009, and the replacement of high-activity sources is increasingly cost prohibitive for laboratories that formerly benefited from that program, including the Pacific Northwest National Laboratory (PNNL) and National Institute of Standards and Technology (NIST). Neutron generators, based on the D-T and D-D fusion reactions, are becoming economically competitive with 252Cf and are recognized internationally as important calibration and test standards. Researchers from NIST and PNNLare jointly considering the practicality and technical challenges of implementing neutron generators as calibration standards in the U.S. This article reviews characteristics of isotope-based sources, leading to rationale behind increasing favor of electronically-generated neutron options. The evaluation of a D-T system at PNNL has revealed primary challenges in adapting generators to the task of calibration and testing in which neutron characteristics must be accurately determined. Concepts for modifying the generated neutron spectra to achieve particular targeted spectra, simulating 252Cf or workplace environments, are discussed.

Calibration, californium-252, Dosimeter Irradiatio↗

NASA NTRS1982

Io - A volcanic flow model for the hot spot emission spectrum and a thermostatic mechanism

The hot spots of Io are modeled as a steady state of active areas at 600 K, continuing creation of new lava flows and calderas, cooling off of recent flows and calderas, and the cessation of radiation of old flows and calderas from the accumulation of insulation added by resurfacing. There are three adjustable parameters in this model: the area of active sources at 600 K, the rate of production of new area that is cooling, and the temperature of cessation of emission as the result of resurfacing. The resurfacing rate sets constrains on this last parameter. The emission spectrum computed with reasonable values for these parameters is an excellent match to the spectrum from recent observations. A thermostatic mechanism is described whereby the volcanic activity is turned on for a long period of time and is then turned off for a nearly equal period. As a result the presently observed internal heat flow of approximately 1.5 W/sq m may be as much as twice the rate of production of internal heat. Thus the restrictions placed on theories of tidal dissipation by the observed heat flow may be partially relieved.

Sinton, V. M.↗

DOE OSTI2018

Pressure transient analysis during CO 2 push-pull tests into faults for EGS characterization

Here, with the goal of detecting and characterizing faults and fractures in enhanced geothermal systems (EGS), a new technology involving CO 2 push-pull testing, active-source geophysical imaging, and well logging has recently been proposed. This technique takes advantage of (1) the contrasting properties of supercritical CO 2 and water which cause CO 2 to appear distinct from surrounding brine in seismic and other geophysical logging approaches, (2) the non-wetting nature of CO 2 which keeps it localized to the faults and fractures to create contrast potentially sufficient for active seismic and well-logging approaches to image faults and fracture zones at EGS sites. In this study, we evaluate the feasibility of using pressure transient monitoring during CO 2 push-pull tests to complement active seismic and wireline well logging for EGS characterization. For this purpose, we developed a 2D model of a prototypical geothermal site (Desert Peak, NV) that includes a single fault. The fault zone consists of a slip plane, fault gouge, and damage zone, and is bounded by the surrounding matrix of the country rock. Through numerical simulation using iTOUGH2, we found that the pressure transient at the monitoring wells in the fault gouge shows unique traits due to the multiphase flow conditions developed by CO 2 injection, and varies sensitively on the arrival of the CO 2 plume and the degree of CO 2 saturation. A sensitivity analysis shows the pressure transient is most sensitive to the fault gouge permeability, but also depends on multiphase flow parameters and the boundary conditions of the fault. Lastly, an inversion study reveals that the fault gouge permeability can be best estimated with the pressure transient data, whereas additional CO 2 saturation data do not improve the accuracy of the inversion significantly.

58 GEOSCIENCES↗

DOE OSTI2012

Revision of the Branch Technical Position on Concentration Averaging and Encapsulation - 12510

The U.S. Nuclear Regulatory Commission (NRC) regulation governing low-level waste (LLW) disposal, 'Licensing Requirements for Land Disposal of Radioactive Waste', 10 CFR Part 61, establishes a waste classification system based on the concentration of specific radionuclides contained in the waste. The regulation also states, at 10 CFR 61.55(a)(8), that, 'the concentration of a radionuclide (in waste) may be averaged over the volume of the waste, or weight of the waste if the units are expressed as nanocuries per gram'. The NRC's Branch Technical Position on Concentration Averaging and Encapsulation provides guidance on averaging radionuclide concentrations in waste under 10 CFR 61.55(a)(8) when classifying waste for disposal. In 2007, the NRC staff proposed to revise the Branch Technical Position on Concentration Averaging and Encapsulation. The Branch Technical Position on Concentration Averaging and Encapsulation is an NRC guidance document for averaging and classifying wastes under 10 CFR 61. The Branch Technical Position on Concentration Averaging and Encapsulation is used by nuclear power plants (NPPs) licensees and sealed source users, among others. In addition, three of the four U.S. LLW disposal facility operators are required to honor the Branch Technical Position on Concentration Averaging and Encapsulation as a licensing condition. In 2010, the Commission directed the staff to develop guidance regarding large scale blending of similar homogenous waste types, as described in SECY-10-0043 as part of its Branch Technical Position on Concentration Averaging and Encapsulation revision. The Commission is improving the regulatory approach used in the Branch Technical Position on Concentration Averaging and Encapsulation by moving towards a making it more risk-informed and performance-based approach, which is more consistent with the agency's regulatory policies. Among the improvements to the Branch Technical Position on Concentration Averaging and Encapsulation are more risk-informed limits for the sizes of sealed sources for safe disposal. Using more realistic intruder exposure scenarios, the suggested limits for Class B and C waste disposal of sealed sources, particularly Cs-137 and Co-60, have been increased. These suggested changes, and others in the Branch Technical Position on Concentration Averaging and Encapsulation, if adopted by Agreement States, have the potential to eliminate numerous orphan sources (i.e., sources that currently have no disposal pathway) that are now being stored. Permanent disposal of these sources, rather than temporary storage, will help reduce safety and security risks. The revised Branch Technical Position on Concentration Averaging and Encapsulation has an alternative approach section which provides flexibility to generators and processors, while also ensuring that intruder protection will be maintained. Alternative approaches provide flexibility by allowing for consideration of likelihood of intrusion, the possibility of averaging over larger volumes and allowing for disposal of large activity sources. The revision has improved the organization of the Branch Technical Position on Concentration Averaging and Encapsulation, improved its clarity, better documented the bases for positions, and made the positions more risk informed while also maintaining protection for intruder as required by 10 CFR Part 61. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2013

A NOVEL APPROACH IN THE WEAKLY INTERACTING MASSIVE PARTICLE QUEST: CROSS-CORRELATION OF GAMMA-RAY ANISOTROPIES AND COSMIC SHEAR

Both cosmic shear and cosmological gamma-ray emission stem from the presence of dark matter (DM) in the universe: DM structures are responsible for the bending of light in the weak-lensing regime and those same objects can emit gamma rays, either because they host astrophysical sources (active galactic nuclei or star-forming galaxies) or directly by DM annihilations (or decays, depending on the properties of the DM particle). Such gamma rays should therefore exhibit strong correlation with the cosmic shear signal. In this Letter, we compute the cross-correlation angular power spectrum of cosmic shear and gamma rays produced by the annihilation/decay of weakly interacting massive particle DM, as well as by astrophysical sources. We show that this observable provides novel information on the composition of the extragalactic gamma-ray background (EGB), since the amplitude and shape of the cross-correlation signal strongly depend on which class of sources is responsible for the gamma-ray emission. If the DM contribution to the EGB is significant (at least in a definite energy range), although compatible with current observational bounds, its strong correlation with the cosmic shear makes such signal potentially detectable by combining Fermi Large Area Telescope data with forthcoming galaxy surveys, like the Dark Energy Survey and Euclid. At the same time, the same signal would demonstrate that the weak-lensing observables are indeed due to particle DM matter and not to possible modifications of general relativity.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1984

Power law X- and gamma-ray emission from relativistic thermal plasmas

Pair equilibrium in thermal plasmas emitting power law photon spectra by repeated Compton scatterings of a soft photon source active galactic nuclei was studied. Dependence of the spectral index on optical thickness and on temperature of the plasma is discussed. The equation for pair equilibrium is solved for the maximum steady luminosity. Analytical solutions for the subrelativistic region, and for the ultrarelativistic region are found. In the transrelativistic region the solutions are expressed by single integrals over the pair production cross sections, performed numerically. The constraints on soft photon source imposed by the condition that the soft photon flux cannot exceed the black-body flux are considered. For the Comptonized synchrotron radiation model a relation between magnetic field strength and output luminosity is found.

Zdziarski, A. A.↗

DOE OSTI2016

Increased Photochemical Efficiency in Cyanobacteria via an Engineered Sucrose Sink

In plants, a limited capacity to In plants, a limited capacity to utilize or export the end-products of the Calvin–Benson cycle (CB) from photosynthetically active source cells to non-photosynthetic sink cells can result in reduced carbon capture and photosynthetic electron transport (PET), and lowered photochemical efficiency. The down-regulation of photosynthesis caused by reduced capacity to utilize photosynthate has been termed ‘sink limitation’. Recently, several cyanobacterial and algal strains engineered to overproduce target metabolites have exhibited increased photochemistry, suggesting that possible source–sink regulatory mechanisms may be involved. Here, we directly examined photochemical properties following induction of a heterologous sucrose ‘sink’ in the unicellular cyanobacterium Synechococcus elongatus PCC 7942. We show that total photochemistry increases proportionally to the experimentally controlled rate of sucrose export. Importantly, the quantum yield of PSII (ΦII) increases in response to sucrose export while the PET chain becomes more oxidized from less PSI acceptor-side limitation, suggesting increased CB activity and a decrease in sink limitation. Enhanced photosynthetic activity and linear electron flow are detectable within hours of induction of the heterologous sink and are independent of pigmentation alterations or the ionic/osmotic effects of the induction system. These observations provide direct evidence that secretion of heterologous carbon bioproducts can be used as an alternative approach to improve photosynthetic efficiency, presumably by by-passing sink limitation. Our results also suggest that engineered microalgal production strains are valuable alternative models for examining photosynthetic sink limitation because they enable greater control and monitoring of metabolite fluxes relative to plants.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2019

Seismic Characterization of the Nevada National Security Site Using Joint Body Wave, Surface Wave, and Gravity Inversion

As a part of the series of Source Physics Experiments (SPE) conducted on the Nevada National Security Site in southern Nevada, we have developed a local–to–regional scale seismic velocity model of the site and surrounding area. Accurate earth models are critical for modeling sources like the SPE to investigate the role of earth structure on the propagation and scattering of seismic waves. We combine seismic body waves, surface waves, and gravity data in a joint inversion procedure to solve for the optimal 3D seismic compressional and shear–wave velocity structures and earthquake locations subject to model smoothness constraints. Earthquakes, which are relocated as part of the inversion, provide P – and S –body–wave absolute and differential travel times. Active source experiments in the region augment this dataset with P –body–wave absolute times and surface–wave dispersion data. Dense ground–based gravity observations and surface–wave dispersion derived from ambient noise in the region fill in many areas where body–wave data are sparse. In general, the top 1–2 km of the surface is relatively poorly sampled by the body waves alone. However, the addition of gravity and surface waves to the body–wave dataset greatly enhances structural resolvability in the near surface. Here, we discuss the methodology we developed for simultaneous inversion of these disparate data types and briefly describe results of the inversion in the context of previous work in the region.

58 GEOSCIENCES↗