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At least 1,153 records · Page 64
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Super-CMB fluctuations and the Hubble tension

We study the covariance in the angular power spectrum estimates of CMB fluctuations when the primordial fluctuations are non-Gaussian. The non-Gaussian covariance comes from a nonzero connected four-point correlation function -- or the trispectrum in Fourier space -- and can be large when long-wavelength (super-CMB) modes are strongly coupled to short-wavelength modes. The effect of such non-Gaussian covariance can be modeled through additional freedom in the theoretical CMB angular power spectrum and can lead to different inferred values of the standard cosmological parameters relative to those in ΛCDM. Taking the collapsed limit of the primordial trispectrum in the quasi-single field inflation model as an example, we study how the six standard ΛCDM parameters shift when two additional parameters describing the trispectrum are allowed. The reduced statistical significance of the Hubble tension in the extended model allows us to combine the {\it Planck} temperature data and the type Ia supernovae data from Panstarrs with the distance-ladder measurement of the Hubble constant. Here, this combination of data shows strong evidence for a primordial trispectrum-induced non-Gaussian covariance, with a likelihood improvement of Δχ 2 ≈ –15 (with two additional parameters) relative to ΛCDM.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

OC5 Project Phase Ib: Validation of hydrodynamic loading on a fixed, flexible cylinder for offshore wind applications

This paper summarizes the findings from Phase Ib of the Offshore Code Comparison, Collaboration, Continued with Correlation (OC5) project. OC5 is a project run under the International Energy Agency (IEA) Wind Research Task 30, and is focused on validating the tools used for modelling offshore wind systems through the comparison of simulated responses of select offshore wind systems (and components) to physical test data. For Phase Ib of the project, simulated hydrodynamic loads on a flexible cylinder fixed to a sloped bed were validated against test measurements made in the shallow water basin at the Danish Hydraulic Institute (DHI) with support from the Technical University of Denmark (DTU). The first phase of OC5 examined two simple cylinder structures (Phase Ia and Ib) to focus on validation of hydrodynamic models used in the various tools before moving on to more complex offshore wind systems and the associated coupled physics. As a result, verification and validation activities such as these lead to improvement of offshore wind modelling tools, which will enable the development of more innovative and cost-effective offshore wind designs.

17 WIND ENERGY↗
DOE OSTI2013

Conceptualising the effectiveness of impact assessment processes

This paper aims at conceptualising the effectiveness of impact assessment processes through the development of a literature-based framework of criteria to measure impact assessment effectiveness. Four categories of effectiveness were established: procedural, substantive, transactive and normative, each containing a number of criteria; no studies have previously brought together all four of these categories into such a comprehensive, criteria-based framework and undertaken systematic evaluation of practice. The criteria can be mapped within a cycle/or cycles of evaluation, based on the ‘logic model’, at the stages of input, process, output and outcome to enable the identification of connections between the criteria across the categories of effectiveness. This framework is considered to have potential application in measuring the effectiveness of many impact assessment processes, including strategic environmental assessment (SEA), environmental impact assessment (EIA), social impact assessment (SIA) and health impact assessment (HIA). -- Highlights: • Conceptualising effectiveness of impact assessment processes. • Identification of factors influencing effectiveness of impact assessment processes. • Development of criteria within a framework for evaluating IA effectiveness. • Applying the logic model to examine connections between effectiveness criteria.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Impact assessment: Eroding benefits through streamlining?

This paper argues that Governments have sought to streamline impact assessment in recent years (defined as the last five years) to counter concerns over the costs and potential for delays to economic development. We hypothesise that this has had some adverse consequences on the benefits that subsequently accrue from the assessments. This hypothesis is tested using a framework developed from arguments for the benefits brought by Environmental Impact Assessment made in 1982 in the face of the UK Government opposition to its implementation in a time of economic recession. The particular benefits investigated are ‘consistency and fairness’, ‘early warning’, ‘environment and development’, and ‘public involvement’. Canada, South Africa, the United Kingdom and Western Australia are the jurisdictions tested using this framework. The conclusions indicate that significant streamlining has been undertaken which has had direct adverse effects on some of the benefits that impact assessment should deliver, particularly in Canada and the UK. The research has not examined whether streamlining has had implications for the effectiveness of impact assessment, but the causal link between streamlining and benefits does sound warning bells that merit further investigation. -- Highlights: • Investigation of the extent to which government has streamlined IA. • Evaluation framework was developed based on benefits of impact assessment. • Canada, South Africa, the United Kingdom, and Western Australia were examined. • Trajectory in last five years is attrition of benefits of impact assessment.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Conceptualizing strategic environmental assessment: Principles, approaches and research directions

Increasing emphasis has been placed in recent years on transitioning strategic environmental assessment (SEA) away from its environmental impact assessment (EIA) roots. Scholars have argued the need to conceptualize SEA as a process designed to facilitate strategic thinking, thus enabling transitions toward sustainability. The practice of SEA, however, remains deeply rooted in the EIA tradition and scholars and practitioners often appear divided on the nature and purpose of SEA. This paper revisits the strategic principles of SEA and conceptualizes SEA as a multi-faceted and multi-dimensional assessment process. It is suggested that SEA can be conceptualized as series of approaches operating along a spectrum from less to more strategic – from impact assessment-based to strategy-based – with each approach to SEA differentiated by the specific objectives of SEA application and the extent to which strategic principles are reflected in its design and implementation. Advancing the effectiveness of SEA requires a continued research agenda focused on improving the traditional SEA approach, as a tool to assess the impacts of policies, plans and programs (PPPs). Realizing the full potential of SEA, however, requires a new research agenda — one focused on the development and testing of a deliberative governance approach to SEA that can facilitate strategic innovations in PPP formulation and drive transitions in short-term policy and initiatives based on longer-term thinking. - Highlights: • SEA facilitates strategic thinking, enabling transitions toward sustainability. • SEA is conceptualized as a spectrum of approaches, from IA-based to strategy-based. • Each approach variably emphasizes strategic principles in its design and practice. • There is no one conceptualization of SEA that is best, SEA is fit for PPP purpose. • Research is needed to advance SEA to facilitate strategic PPP transformations.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Long duration X-ray drive hydrodynamics experiments relevant for laboratory astrophysics

The advent of high-power lasers facilities such as the National Ignition Facility (NIF), and the Laser Megajoule (LMJ) in the near future, opens a new era in the field of High Energy Density Laboratory Astrophysics. These versatile laser facilities will provide unique platforms to study the rich physics of nonlinear and turbulent mixing flows. The extended laser pulse duration could be harnessed to accelerate targets over much larger distances and longer time periods than previously achieved. Here, we report on the first results acquired on NIF with the ablative Rayleigh–Taylor Instability (RTI) platform. A 20-ns X-ray drive is tailored to accelerate planar modulated samples into the highly-nonlinear bubble merger regime. Based on the analogy between flames front and ablation front, highly nonlinear RTI measurements at ablation front can provide important insights into the initial deflagration stage of thermonuclear supernova of Type Ia. We also report on an innovative concept used to create even longer drive on multi-beam laser facilities. The multi-barrel hohlraum (Gattling Gun) approach consists, here, of three adjacent cavities, driven in succession in time. This novel concept has been validated on the Omega EP laser system. The three cavities were irradiated with three 6–10 ns pulse UV beams and a 30 ns, 90 eV X-ray radiation drive was measured with the time-resolved X-ray spectrometer μDMX. This concept is promising to investigate the pillar structures in the Eagle Nebula or for photoionization studies which require a steady light source of sufficient duration to recreate relevant physics.

Molecular clouds↗
DOE OSTI2011

Stereotactic Body Radiotherapy (SBRT) for Operable Stage I Non-Small-Cell Lung Cancer: Can SBRT Be Comparable to Surgery?

Purpose: To review treatment outcomes for stereotactic body radiotherapy (SBRT) in medically operable patients with Stage I non-small-cell lung cancer (NSCLC), using a Japanese multi-institutional database. Patients and Methods: Between 1995 and 2004, a total of 87 patients with Stage I NSCLC (median age, 74 years; T1N0M0, n = 65; T2N0M0, n = 22) who were medically operable but refused surgery were treated using SBRT alone in 14 institutions. Stereotactic three-dimensional treatment was performed using noncoplanar dynamic arcs or multiple static ports. Total dose was 45-72.5 Gy at the isocenter, administered in 3-10 fractions. Median calculated biological effective dose was 116 Gy (range, 100-141 Gy). Data were collected and analyzed retrospectively. Results: During follow-up (median, 55 months), cumulative local control rates for T1 and T2 tumors at 5 years after SBRT were 92% and 73%, respectively. Pulmonary complications above Grade 2 arose in 1 patient (1.1%). Five-year overall survival rates for Stage IA and IB subgroups were 72% and 62%, respectively. One patient who developed local recurrences safely underwent salvage surgery. Conclusion: Stereotactic body radiotherapy is safe and promising as a radical treatment for operable Stage I NSCLC. The survival rate for SBRT is potentially comparable to that for surgery.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2011

Impact of Adjuvant External-Beam Radiation Therapy in Early-Stage Uterine Papillary Serous and Clear Cell Carcinoma

Purpose: Adjuvant radiation therapy (RT) in early-stage high- to intermediate-risk endometrioid adenocarcinoma is well established and has been shown to improve locoregional control. Its role in the management of early-stage clear cell carcinoma and uterine papillary serous carcinoma (UPSC) remains controversial. Methods and Materials: Using the Surveillance Epidemiology and End Results database, we identified women with American Joint Committee on Cancer Stage Sixth Edition. Stage IA-IIB clear cell carcinoma or UPSC who underwent hysterectomy with or without adjuvant RT between 1988 and 2003. We used Kaplan-Meier and Cox regression analysis to compare overall survival (OS) for all patients. Results: We identified 1,333 women of whom 451 had clear cell carcinoma and 882 had UPSC. Of those patients, 775 underwent surgery alone and 558 received adjuvant RT as well. For Stages I-IIB disease, the median OS with surgery alone was 106 months, vs. 151 months with adjuvant RT (p = 0.006). On subgroup analysis, we saw the benefit from adjuvant RT only in Stage IB-C patients. For Stage IB disease, patients undergoing surgery alone had a median OS of 117 months, vs. median survival not reached with the addition of RT (p = 0.006). For Stage IC disease, surgery alone had a median OS of 35 months vs. 120 months with RT (p = 0.001). Although the apparent benefit of RT diminished when measured via multivariate analysis, the impact of RT on survival did show a trend toward significance (hazard ration 0.808, confidence interval 95% 0.651-1.002, p = 0.052) Conclusion: In FIGO Stage IB-C papillary serous and clear cell uterine carcinoma, adjuvant RT seems to play an important role in improving survival.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2012

Immortal Time Bias: A Frequently Unrecognized Threat to Validity in the Evaluation of Postoperative Radiotherapy

Purpose: To evaluate the influence of immortal time bias on observational cohort studies of postoperative radiotherapy (PORT) and the effectiveness of sequential landmark analysis to account for this bias. Methods and Materials: First, we reviewed previous studies of the Surveillance, Epidemiology, and End Results (SEER) database to determine how frequently this bias was considered. Second, we used SEER to select three tumor types (glioblastoma multiforme, Stage IA-IVM0 gastric adenocarcinoma, and Stage II-III rectal carcinoma) for which prospective trials demonstrated an improvement in survival associated with PORT. For each tumor type, we calculated conditional survivals and adjusted hazard ratios of PORT vs. postoperative observation cohorts while restricting the sample at sequential monthly landmarks. Results: Sixty-two percent of previous SEER publications evaluating PORT failed to use a landmark analysis. As expected, delivery of PORT for all three tumor types was associated with improved survival, with the largest associated benefit favoring PORT when all patients were included regardless of survival. Preselecting a cohort with a longer minimum survival sequentially diminished the apparent benefit of PORT. Conclusions: Although the majority of previous SEER articles do not correct for it, immortal time bias leads to altered estimates of PORT effectiveness, which are very sensitive to landmark selection. We suggest the routine use of sequential landmark analysis to account for this bias.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2012

Comparative Effectiveness of 5 Treatment Strategies for Early-Stage Non-Small Cell Lung Cancer in the Elderly

Purpose: The incidence of early-stage non-small cell lung cancer (NSCLC) among older adults is expected to increase because of demographic trends and computed tomography-based screening; yet, optimal treatment in the elderly remains controversial. Using the Surveillance, Epidemiology, and End Results (SEER)-Medicare cohort spanning 2001-2007, we compared survival outcomes associated with 5 strategies used in contemporary practice: lobectomy, sublobar resection, conventional radiation therapy, stereotactic ablative radiation therapy (SABR), and observation. Methods and Materials: Treatment strategy and covariates were determined in 10,923 patients aged {>=}66 years with stage IA-IB NSCLC. Cox regression, adjusted for patient and tumor factors, compared overall and disease-specific survival for the 5 strategies. In a second exploratory analysis, propensity-score matching was used for comparison of SABR with other options. Results: The median age was 75 years, and 29% had moderate to severe comorbidities. Treatment distribution was lobectomy (59%), sublobar resection (11.7%), conventional radiation (14.8%), observation (12.6%), and SABR (1.1%). In Cox regression analysis with a median follow-up time of 3.2 years, SABR was associated with the lowest risk of death within 6 months of diagnosis (hazard ratio [HR] 0.48; 95% confidence interval [CI] 0.38-0.63; referent is lobectomy). After 6 months, lobectomy was associated with the best overall and disease-specific survival. In the propensity-score matched analysis, survival after SABR was similar to that after lobectomy (HR 0.71; 95% CI 0.45-1.12; referent is SABR). Conventional radiation and observation were associated with poor outcomes in all analyses. Conclusions: In this population-based experience, lobectomy was associated with the best long-term outcomes in fit elderly patients with early-stage NSCLC. Exploratory analysis of SABR early adopters suggests efficacy comparable with that of surgery in select populations. Evaluation of these therapies in randomized trials is urgently needed.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Tumor Size on Abdominal MRI Versus Pathologic Specimen in Resected Pancreatic Adenocarcinoma: Implications for Radiation Treatment Planning

Purpose: We assessed the accuracy of abdominal magnetic resonance imaging (MRI) for determining tumor size by comparing the preoperative contrast-enhanced T1-weighted gradient echo (3-dimensional [3D] volumetric interpolated breath-hold [VIBE]) MRI tumor size with pathologic specimen size. Methods and Materials: The records of 92 patients who had both preoperative contrast-enhanced 3D VIBE MRI images and detailed pathologic specimen measurements were available for review. Primary tumor size from the MRI was independently measured by a single diagnostic radiologist (P.M.) who was blinded to the pathology reports. Pathologic tumor measurements from gross specimens were obtained from the pathology reports. The maximum dimensions of tumor measured in any plane on the MRI and the gross specimen were compared. The median difference between the pathology sample and the MRI measurements was calculated. A paired t test was conducted to test for differences between the MRI and pathology measurements. The Pearson correlation coefficient was used to measure the association of disparity between the MRI and pathology sizes with the pathology size. Disparities relative to pathology size were also examined and tested for significance using a 1-sample t test. Results: The median patient age was 64.5 years. The primary site was pancreatic head in 81 patients, body in 4, and tail in 7. Three patients were American Joint Commission on Cancer stage IA, 7 stage IB, 21 stage IIA, 58 stage IIB, and 3 stage III. The 3D VIBE MRI underestimated tumor size by a median difference of 4 mm (range, −34-22 mm). The median largest tumor dimensions on MRI and pathology specimen were 2.65 cm (range, 1.5-9.5 cm) and 3.2 cm (range, 1.3-10 cm), respectively. Conclusions: Contrast-enhanced 3D VIBE MRI underestimates tumor size by 4 mm when compared with pathologic specimen. Advanced abdominal MRI sequences warrant further investigation for radiation therapy planning in pancreatic adenocarcinoma before routine integration into the treatment planning process.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

Prospective Evaluation of Dual-Energy Imaging in Patients Undergoing Image Guided Radiation Therapy for Lung Cancer: Initial Clinical Results

Purpose: A prospective feasibility study was conducted to investigate the utility of dual-energy (DE) imaging compared to conventional x-ray imaging for patients undergoing kV-based image guided radiation therapy (IGRT) for lung cancer. Methods and Materials: An institutional review board-approved feasibility study enrolled patients with lung cancer undergoing IGRT and was initiated in September 2011. During daily setup, 2 sequential respiration-gated x-ray images were obtained using an on-board imager. Imaging was composed of 1 standard x-ray image at 120 kVp (1 mAs) and a second image obtained at 60 kVp (4 mAs). Weighted logarithmic subtraction of the 2 images was performed offline to create a soft tissue-selective DE image. Conventional and DE images were evaluated by measuring relative contrast and contrast-to-noise ratios (CNR) and also by comparing spatial localization, using both approaches. Imaging dose was assessed using a calibrated ion chamber. Results: To date, 10 patients with stage IA to IIIA lung cancer were enrolled and 57 DE images were analyzed. DE subtraction resulted in complete suppression of overlying bone in all 57 DE images, with an average improvement in relative contrast of 4.7 ± 3.3 over that of 120 kVp x-ray images (P<.0002). The improvement in relative contrast with DE imaging was seen for both smaller (gross tumor volume [GTV] ≤5 cc) and larger tumors (GTV >5 cc), with average relative contrast improvement ratios of 3.4 ± 4.1 and 5.4 ± 3.6, respectively. Moreover, the GTV was reliably localized in 95% of the DE images versus 74% of the single energy (SE images, (P=.004). Mean skin dose per DE image set was 0.44 ± 0.03 mGy versus 0.43 ± 0.03 mGy, using conventional kV imaging parameters. Conclusions: Initial results of this feasibility study suggest that DE thoracic imaging may enhance tumor localization in lung cancer patients receiving kV-based IGRT without increasing imaging dose.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Simple Factors Associated With Radiation-Induced Lung Toxicity After Stereotactic Body Radiation Therapy of the Thorax: A Pooled Analysis of 88 Studies

Purpose: To study the risk factors for radiation-induced lung toxicity (RILT) after stereotactic body radiation therapy (SBRT) of the thorax. Methods and Materials: Published studies on lung toxicity in patients with early-stage non–small cell lung cancer (NSCLC) or metastatic lung tumors treated with SBRT were pooled and analyzed. The primary endpoint was RILT, including pneumonitis and fibrosis. Data of RILT and risk factors were extracted from each study, and rates of grade 2 to 5 (G2+) and grade 3 to 5 (G3+) RILT were computed. Patient, tumor, and dosimetric factors were analyzed for their correlation with RILT. Results: Eighty-eight studies (7752 patients) that reported RILT incidence were eligible. The pooled rates of G2+ and G3+ RILT from all 88 studies were 9.1% (95% confidence interval [CI]: 7.15-11.4) and 1.8% (95% CI: 1.3-2.5), respectively. The median of median tumor sizes was 2.3 (range, 1.4-4.1) cm. Among the factors analyzed, older patient age (P=.044) and larger tumor size (the greatest diameter) were significantly correlated with higher rates of G2+ (P=.049) and G3+ RILT (P=.001). Patients with stage IA versus stage IB NSCLC had significantly lower risks of G2+ RILT (8.3% vs 17.1%, odds ratio = 0.43, 95% CI: 0.29-0.64, P<.0001). Among studies that provided detailed dosimetric data, the pooled analysis demonstrated a significantly higher mean lung dose (MLD) (P=.027) and V20 (P=.019) in patients with G2+ RILT than in those with grade 0 to 1 RILT. Conclusions: The overall rate of RILT is relatively low after thoracic SBRT. Older age and larger tumor size are significant adverse risk factors for RILT. Lung dosimetry, specifically lung V20 and MLD, also significantly affect RILT risk.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Constrained optimization framework for interface-aware sub-scale dynamics models for voids closure in Lagrangian hydrodynamics

In hydrocodes, voids are used to represent vacuum and model free boundaries between vacuum and real materials. We give a systematic description of a new treatment of void closure in the framework of the multimaterial arbitrary Lagrangian–Eulerian (ALE) methods. This includes a new formulation of the interface-aware sub-scale-dynamics (IA-SSD) closure model for multimaterial cells with voids, which is used in the Lagrangian stage of our indirect ALE scheme. The results of the comprehensive testing of the new model are presented for one- and two-dimensional multimaterial calculations in the presence of voids. Finally, we also present a sneak peek of a realistic shaped charge calculation in the presence of voids and solids.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

The Structures of Coiled-Coil Domains from Type III Secretion System Translocators Reveal Homology to Pore-Forming Toxins

Many pathogenic Gram-negative bacteria utilize type III secretion systems (T3SSs) to alter the normal functions of target cells. Shigella flexneri uses its T3SS to invade human intestinal cells to cause bacillary dysentery (shigellosis) that is responsible for over one million deaths per year. The Shigella type III secretion apparatus is composed of a basal body spanning both bacterial membranes and an exposed oligomeric needle. Host altering effectors are secreted through this energized unidirectional conduit to promote bacterial invasion. The active needle tip complex of S. flexneri is composed of a tip protein, IpaD, and two pore-forming translocators, IpaB and IpaC. While the atomic structure of IpaD has been elucidated and studied, structural data on the hydrophobic translocators from the T3SS family remain elusive. We present here the crystal structures of a protease-stable fragment identified within the N-terminal regions of IpaB from S. flexneri and SipB from Salmonella enterica serovar Typhimurium determined at 2.1 {angstrom} and 2.8 {angstrom} limiting resolution, respectively. These newly identified domains are composed of extended-length (114 {angstrom} in IpaB and 71 {angstrom} in SipB) coiled-coil motifs that display a high degree of structural homology to one another despite the fact that they share only 21% sequence identity. Further structural comparisons also reveal substantial similarity to the coiled-coil regions of pore-forming proteins from other Gram-negative pathogens, notably, colicin Ia. This suggests that these mechanistically separate and functionally distinct membrane-targeting proteins may have diverged from a common ancestor during the course of pathogen-specific evolutionary events.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2012

In-situ X-ray diffraction study of phase transformations in the Am-O system

In the frame of minor actinides recycling, americium can be transmuted by adding it in UO{sub 2} or (U, Pu)O{sub 2} fuels. Americium oxides exhibiting a higher oxygen potential than U or Pu oxides, its addition alters the fuel properties. To comprehend its influence, a thorough knowledge of the Am-O phase equilibria diagram and of thermal expansion behavior is of main interest. Due to americium scarcity and high radiotoxicity, few experimental reports on this topic are available. Here we present in-situ high-temperature XRD results on the reduction from AmO{sub 2} to Am{sub 2}O{sub 3}. We show that fluorite (Fm-3m) AmO{sub 2} is reduced to cubic (Ia-3) C Prime -type Am{sub 2}O{sub 3+{delta}}, and then into hexagonal (P6{sub 3}/mmc) A-type Am{sub 2}O{sub 3}, which remains stable up to 1840 K. We also demonstrate the transitional existence of the monoclinic (C2/m) B-type Am{sub 2}O{sub 3}. At last, we describe, for the first time, the thermal expansion behavior of the hexagonal Am{sub 2}O{sub 3} between room temperature and 1840 K. - Graphical abstract: Americium dioxide was in situ studied by high-temperature X-ray diffraction. First, fluorite AmO{sub 2} is reduced to cubic C Prime -type Am{sub 2}O{sub 3+{delta}} and then transforms into hexagonal A-type Am{sub 2}O{sub 3}, which remains stable up to 1840 K. Then, we demonstrate the transitional existence of monoclinic B-type Am{sub 2}O{sub 3}. At last, we describe, for the first time, the thermal expansion of A-type Am{sub 2}O{sub 3} between room temperature and 1840 K. This work may contribute to a better understanding of Am oxide behavior. Highlights: Black-Right-Pointing-Pointer We realize an in-situ high-temperature X-ray diffraction study on an AmO{sub 2} sample. Black-Right-Pointing-Pointer Fluorite AmO{sub 2} transforms to cubic Am{sub 2}O{sub 3+{delta}} and then to hexagonal Am{sub 2}O{sub 3}. Black-Right-Pointing-Pointer Little-known monoclinic Am{sub 2}O{sub 3} is observed during the cubic-to-hexagonal transition. Black-Right-Pointing-Pointer Lattice parameter thermal expansion of hexagonal Am{sub 2}O{sub 3} is given up to 1840 K. Black-Right-Pointing-Pointer We give additional data on AmO{sub 2} lattice parameter expansion under self-irradiation.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Self-irradiation and oxidation effects on americium sesquioxide and Raman spectroscopy studies of americium oxides

Americium oxides samples were characterized by X-ray diffraction (XRD) and Raman spectroscopy, with an emphasis on their structural behavior under oxidation and self-irradiation. Raman spectra of americium dioxide (AmO{sub 2}) and sesquioxide (Am{sub 2}O{sub 3}) were obtained for the first time. With the help of literature data on isostructural oxides, Raman signatures of Ia-3 C-type Am{sub 2}O{sub 3} and P-3m1 A-type Am{sub 2}O{sub 3} are identified. For AmO{sub 2,} a clear band is noted at 390 cm{sup −1}. Its nature is compared to that of the other actinide dioxides. Am{sub 2}O{sub 3} evolution under ambient conditions and against {sup 241}Am α self-irradiation was monitored by powder XRD. The sample, initially composed of A-type Am{sub 2}O{sub 3} as major phase as well as C2/m B-type and C-type structures as minor phases, progressively oxidizes to Fm-3m AmO{sub 2−δ} over a few months. On the basis of diffractogram refinements, evolutions of unit cell volumes caused by self-irradiation are also determined and discussed. - Graphical abstract: The evolution of americium oxide under ambient conditions was monitored using XRD (X-ray diffraction) and Raman spectroscopy. After a thermal treatment under reducing conditions, a polyphasic sample mainly composed of A- and C-type americium sesquioxides is evidenced by XRD and Raman spectroscopy. The sample then evolves through two processes: oxidation and self-irradiation. The first one provokes the progressive appearance of F-type americium dioxide while the initial phases disappear, whereas the main effect of the second is a structural swelling with time. - Highlights: • The first Raman spectroscopy measurements on americium oxides were performed. • Observed Am{sub 2}O{sub 3} Raman bands were identified thanks to data on analogue compounds. • AmO{sub 2} assumed T{sub 2g} band presents a shift compared to the actinide dioxide series. • Am{sub 2}O{sub 3} evolution under self-irradiation and oxidation was also monitored by XRD. • The three Am{sub 2}O{sub 3} phases observed have different behaviors under self-irradiation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗