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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Examination of the low-energy enhancement of the γ -ray strength function of Fe 56

A model-independent technique was used to determine the gamma-ray strength function (gamma SF) of Fe-56 down to gamma-ray energies less than 1 MeV for the first time with GRETINA using the (p, p') reaction at 16MeV. No difference was observed in the energy dependence of the gamma SF built on 2(+) and 4(+) final states, supporting the Brink hypothesis. In addition, angular distribution and polarization measurements were performed. The angular distributions are consistent with dipole radiation. The polarization results show a small bias towards magnetic character in the region of the enhancement.

Jones, M. D.↗
DOE OSTI2018

Intruder configurations of excited states in the neutron-rich isotopes P 33 and P 34

Here, excited states in the neutron-rich isotopes P 33 and P 34 were populated by the O 18 + O 18 fusion-evaporation reaction at E lab = 24 MeV. The Gammasphere array was used along with the Microball particle detector array to detect γ transitions in coincidence with the charged particles emitted from the compound nucleus S 36 . The use of Microball enabled the selection of the proton emission channel. It also helped in determining the exact position and energy of the emitted proton; this was later employed in kinematic Doppler corrections. 16 new transitions and 13 new states were observed in P 33 and 21 γ rays and 20 energy levels were observed in P 34 for the first time. The nearly 4 π geometry of Gammasphere allowed the measurement of γ -ray angular distributions leading to spin assignments for many states. The experimental observations for both isotopes were interpreted with the help of shell-model calculations using the (0+1) ℏ ω PSDPF interaction. The calculations accounted for both the 0p-0h and 1p-1h states reasonably well and indicated that 2p-2h excitations might dominate the higher-spin configurations in both P 33 and P 34 .

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

First Spectroscopy of the Near Drip-line Nucleus Mg 40

One of the most exotic light neutron-rich nuclei currently accessible for experimental study is 40 Mg , which lies at the intersection of the nucleon magic number N=28 and the neutron drip line. Low-lying excited states of 40 Mg have been studied for the first time following a one-proton removal reaction from 41 Al, performed at the Radioactive Isotope Beam Factory of RIKEN Nishina Center with the DALI2 γ-ray array and the ZeroDegree spectrometer. Two γ-ray transitions were observed, suggesting an excitation spectrum that shows unexpected properties as compared to both the systematics along the Z=12, N ≥ 20 Mg isotopes and available state-of-the-art theoretical model predictions. A possible explanation for the observed structure involves weak-binding effects in the low-lying excitation spectrum.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Effect of Alkyl Chain Branching Point on 3D Crystallinity in High N‐Type Mobility Indolonaphthyridine Polymers

Abstract Herein, this study investigates the impact of branching‐point‐extended alkyl chains on the charge transport properties of three ultrahigh n‐type mobility conjugated polymers. Using grazing incidence wide‐angle X‐ray scattering, analysis of the crystallinity of the series shows that while π–π interactions are increased for all three polymers as expected, the impact of the side‐chain engineering on polymer backbone crystallinity is unique to each polymer and correlates to the observed changes in charge transport. With the three polymers exhibiting n‐type mobilities between 0.63 and 1.04 cm 2 V −1 s −1 , these results ratify that the indolonaphthyridine building block has an unprecedented intrinsic ability to furnish high‐performance n‐type organic semiconductors.

Fallon, Kealan J.↗
DOE OSTI2017

Thiophene Rings Improve the Device Performance of Conjugated Polymers in Polymer Solar Cells with Thick Active Layers

Abstract Developing novel materials that tolerate thickness variations of the active layer is critical to further enhance the efficiency of polymer solar cells and enable large‐scale manufacturing. Presently, only a few polymers afford high efficiencies at active layer thickness exceeding 200 nm and molecular design guidelines for developing successful materials are lacking. It is thus highly desirable to identify structural factors that determine the performance of semiconducting conjugated polymers in thick‐film polymer solar cells. Here, it is demonstrated that thiophene rings, introduced in the backbone of alternating donor–acceptor type conjugated polymers, enhance the fill factor and overall efficiency for thick (>200 nm) solar cells. For a series of fluorinated semiconducting polymers derived from electron‐rich benzo[1,2‐ b :4,5‐ b′ ]dithiophene units and electron‐deficient 5,6‐difluorobenzo[2,1,3]thiazole units a steady increase of the fill factor and power conversion efficiency is found when introducing thiophene rings between the donor and acceptor units. The increased performance is a synergistic result of an enhanced hole mobility and a suppressed bimolecular charge recombination, which is attributed to more favorable polymer chain packing and finer phase separation.

Duan, Chunhui↗
DOE OSTI2018

The Impact of Device Polarity on the Performance of Polymer–Fullerene Solar Cells

Abstract Diketopyrrolopyrrole (DPP)‐conjugated polymers are a versatile class of semiconductors for application in organic solar cells because of their tunable optoelectronic properties. A record power conversion efficiency (PCE) of 9.4% was recently achieved for DPP polymers, but further improvements are required to reach true efficiency limits. Using five DPP polymers with different chemical structures and molecular weights, the device performance of polymer:fullerene solar cells is systematically optimized by considering device polarity, morphology, and light absorption. The polymer solubility is found to have a significant effect on the optimal device polarity. Soluble polymers show a 10–25% increase in PCE in inverted device configurations, while the device performance is independent of device polarity for less soluble DPP derivatives. The difference seems related to the polymer to fullerene weight ratio at the ZnO interface in inverted devices, which is higher for more soluble DPP polymers. Optimization of the nature of the cosolvent to narrow the fibril width of polymers in the blends toward the exciton diffusion length enhances charge generation. Additionally, the use of a retroreflective foil increases absorption of light. Combined, the effects afford a PCE of 9.6%, among the highest for DPP‐based polymer solar cells.

Li, Mengmeng↗
DOE OSTI2020

Precise Control of Phase Separation Enables 12% Efficiency in All Small Molecule Solar Cells

Abstract Compared to conjugated polymers, small‐molecule organic semiconductors present negligible batch‐to‐batch variations, but presently provide comparatively low power conversion efficiencies (PCEs) in small‐molecular organic solar cells (SM‐OSCs), mainly due to suboptimal nanomorphology. Achieving precise control of the nanomorphology remains challenging. Here, two new small‐molecular donors H13 and H14 , created by fluorine and chlorine substitution of the original donor molecule H11 , are presented that exhibit a similar or higher degree of crystallinity/aggregation and improved open‐circuit voltage with IDIC‐4F as acceptor. Due to kinetic and thermodynamic reasons, H13 ‐based blend films possess relatively unfavorable molecular packing and morphology. In contrast, annealed H14 ‐based blends exhibit favorable characteristics, i.e., the highest degree of aggregation with the smallest paracrystalline π–π distortions and a nanomorphology with relatively pure domains, all of which enable generating and collecting charges more efficiently. As a result, blends with H13 give a similar PCE (10.3%) as those made with H11 (10.4%), while annealed H14 ‐based SM‐OSCs have a significantly higher PCE (12.1%). Presently this represents the highest efficiency for SM‐OSCs using IDIC‐4F as acceptor. The results demonstrate that precise control of phase separation can be achieved by fine‐tuning the molecular structure and film formation conditions, improving PCE and providing guidance for morphology design.

Bin, Haijun↗
DOE OSTI2018

Improving Automation Transparency: Addressing Some of Machine Learning’s Unique Challenges

Abstract. A variety of factors can affect one’s reliance on an automated aid. Some of these factors include one’s per-ception of the system’s trustworthiness, such as perceived reliability of the system or one’s ability to understand the system’s underlying reasoning. A mismatch between the operator’s perception and the true capabilities and charac-teristics of the system can lead to inappropriate reliance on the tool. This improper use of the system can manifest as either underutilization of the technology or complacency resulting from over-trusting the system. Increasing an au-tomated tool’s transparency is one approach that enables the operator to more appropriately rely on the technology. Transparent automated systems provide additional infor-mation that allows the user to see the system’s intent and understand its underlying processes and capabilities. Sev-eral researchers have developed frameworks to support the design of more transparent automation. However, these frameworks may not fully consider the particular challeng-es to transparency design introduced by automation that leverages machine learning. Like all automation, these systems can benefit from transparency. However, artificial intelligence poses new challenges that must be considered when designing for transparency. Unique considerations must be made in terms of the type, and amount or level of transparency information conveyed to the user.

Transparency, Machine Learning, Automation↗
DOE OSTI2014

Clinical Evaluation of Normalized Metal Artifact Reduction in kVCT Using MVCT Prior Images (MVCT-NMAR) for Radiation Therapy Treatment Planning

Purpose: To evaluate the metal artifacts in diagnostic kilovoltage computed tomography (kVCT) images of patients that are corrected by use of a normalized metal artifact reduction (NMAR) method with megavoltage CT (MVCT) prior images: MVCT-NMAR. Methods and Materials: MVCT-NMAR was applied to images from 5 patients: 3 with dual hip prostheses, 1 with a single hip prosthesis, and 1 with dental fillings. The corrected images were evaluated for visualization of tissue structures and their interfaces and for radiation therapy dose calculations. They were compared against the corresponding images corrected by the commercial orthopedic metal artifact reduction algorithm in a Phillips CT scanner. Results: The use of MVCT images for correcting kVCT images in the MVCT-NMAR technique greatly reduces metal artifacts, avoids secondary artifacts, and makes patient images more useful for correct dose calculation in radiation therapy. These improvements are significant, provided the MVCT and kVCT images are correctly registered. The remaining and the secondary artifacts (soft tissue blurring, eroded bones, false bones or air pockets, CT number cupping within the metal) present in orthopedic metal artifact reduction corrected images are removed in the MVCT-NMAR corrected images. A large dose reduction was possible outside the planning target volume (eg, 59.2 Gy to 52.5 Gy in pubic bone) when these MVCT-NMAR corrected images were used in TomoTherapy treatment plans without directional blocks for a prostate cancer patient. Conclusions: The use of MVCT-NMAR corrected images in radiation therapy treatment planning could improve the treatment plan quality for patients with metallic implants.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

High-Dose-Rate Monotherapy for Localized Prostate Cancer: 10-Year Results

Purpose: High-dose-rate (HDR) brachytherapy was originally used with external beam radiation therapy (EBRT) to increase the dose to the prostate without injuring the bladder or rectum. Numerous studies have reported HDR brachytherapy is safe and effective. We adapted it for use without EBRT for cases not requiring lymph node treatment. Patients and Methods: We entered the patient demographics, disease characteristics, and treatment parameters into a prospective registry and serially added follow-up data for 448 men with low-risk (n=288) and intermediate-risk (n=160) prostate cancer treated from 1996 to 2009. Their median age was 64 years (range 42-90). The median prostate-specific antigen (PSA) level was 6.0 ng/mL (range 0.2-18.2). The Gleason score was ≤6 in 76% and 7 in 24%. The median dose was 43.5 Gy in 6 fractions. The clinical and biochemical disease control and survival rates were calculated. Adverse events were graded according to the Common Toxicity Criteria of Adverse Events. Results: The median follow-up period was 6.5 years (range 0.3-15.3). The actuarial 6- and 10-year PSA progression-free survival was 98.6% (95% confidence interval [CI] 96.9%-99.4%) and 97.8% (95% CI 95.5%-98.9%). Overall survival at 10 years was 76.7% (95% CI 69.9%-82.2%). The local control, distant metastasis-free survival, and cause-specific survival were 99.7% (95% CI 97.9%-99.9%), 98.9% (95% CI 96.3%-99.7%), and 99.1% (95% CI 95.8%-99.8%). T stage, initial PSA level, Gleason score, National Comprehensive Cancer Network risk group, patient age, and androgen deprivation therapy did not significantly correlate with disease control or survival. No late grade 3 to 4 rectal toxicities developed. Late grade 3 to 4 genitourinary toxicity occurred in 4.9% (grade 3 in 4.7%). Conclusions: HDR monotherapy is a safe and highly effective treatment of low- and intermediate-risk prostate cancer.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Second spatial derivative analysis of cortical surface potentials recorded in cat primary auditory cortex using thin film surface arrays: Comparisons with multi-unit data

Current source density analysis of recordings from penetrating electrode arrays has traditionally been used to examine the layer- specific cortical activation and plastic changes associated with changed afferent input. Here, we report on a related analysis, the second spatial derivative (SSD) of surface local field potentials (LFPs) recorded using custom designed thin-film polyimide substrate arrays.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

In-situ synchrotron X-ray study of microstructural evolution during creep deformation in Grade 91 steel

Here, creep deformation mechanism of Grade 91 steel at 650 °C was investigated in-situ via wide-angle X-ray scattering (WAXS). WAXS peak broadening and a modified Williamson-Hall analysis provided information on evolution of dislocation densities in the primary α–Fe phase, while WAXS peak shifts provided lattice strains in the α–Fe matrix, M 23 C 6 and MX precipitates. Load transfer was not evident during in-situ creep deformation, suggesting that precipitates did not significantly strengthen the matrix during creep deformation. Peak broadening results illustrated an increase in average dislocation density during primary stage creep. After onset of secondary creep, there was a decrease in dislocation density, attributed to annihilation and re-ordering of dislocations in the subgrain structure, followed by a relatively constant average dislocation density with increasing strain.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Photon Strength Function at Low Energies in 95 Mo

A new and model-independent experimental method has been developed to determine the energy dependence of the photon strength function. It is designed to study statistical feeding from the quasi continuum to individual low-lying discrete levels. This new technique is presented and results for 95 Mo are compared to data from the University of Oslo. In particular, questions regarding the existence of the low-energy enhancement in the photon strength function are addressed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

The performance of the γ-ray tracking array GRETINA for γ-ray spectroscopy with fast beams of rare isotopes

The gamma-ray tracking array GRETINA was coupled to the S800 magnetic spectrometer for spectroscopy with fast beams of rare isotopes at the National Superconducting Cyclotron Laboratory on the campus of Michigan State University. We describe the technical details of this powerful setup and report on GRETINA's performance achieved with source and in-beam measurements. The gamma-ray multiplicity encountered in experiments with fast beams is usually low, allowing for a simplified and efficient treatment of the data in the gamma-ray analysis in terms of Doppler reconstruction and spectral quality. Finally, the results reported in this work were obtained from GRETINA consisting of 8 detector modules hosting four high-purity germanium crystals each. Currently, GRETINA consists of 10 detector modules.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Energy reconstruction of an n-type segmented inverted coaxial point-contact HPGe detector

We have characterized, for the first time, an n-type segmented Inverted Coaxial Point-Contact detector. This novel detector technology relys on a large variation in drift time of the majority charge carriers, as well as image and net charges observed on the segments, to achieve a potential γ-ray interaction position resolution of better than 1 mm. However, the intrinsic energy resolution in such a detector is poor (more than 20 keV at 1332 keV) because of charge (electron) trapping effects. We propose an algorithm that enables restoration of the resolution to a value of 3.44 0.03 keV at 1332 keV for events with a single interaction. The algorithm is based on a measurement of the azimuthal angle and the electron drift time of a given event; the energy of the event is corrected as a function of these two values.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

LUX trigger efficiency

The Large Underground Xenon experiment (LUX) searches for dark matter using a dual-phase xenon detector. LUX uses a custom-developed trigger system for event selection. Here, the trigger efficiency, which is defined as the probability that an event of interest is selected for offline analysis, is studied using raw data obtained from both electron recoil (ER) and nuclear recoil (NR) calibrations. The measured efficiency exceeds 98% at a pulse area of 90 detected photons, which is well below the WIMP analysis threshold on the S2 pulse area. The efficiency also exceeds 98% at recoil energies of 1.3 keV and above, for both ER and NR. In conclusion, the measured trigger efficiency varies between 99% and 100% over the fiducial volume of the detector.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗