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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Characterization of the Exradin W1 scintillator for use in radiotherapy

Purpose: To evaluate the main characteristics of the Exradin W1 scintillator as a dosimeter and to estimate measurement uncertainties when used in radiotherapy. Methods: We studied the calibration procedure, energy and modality dependence, short-term repeatability, dose-response linearity, angular dependence, temperature dependence, time to reach thermal equilibrium, dose-rate dependence, water-equivalent depth of the effective measurement point, and long-term stability. An uncertainty budget was derived for relative and absolute dose measurements in photon and electron beams. Results: Exradin W1 showed a temperature dependence of −0.225% °C{sup −1}. The loss of sensitivity with accumulated dose decreased with use. The sensitivity of Exradin W1 was energy independent for high-energy photon and electron beams. All remaining dependencies of Exradin W1 were around or below 0.5%, leading to an uncertainty budget of about 1%. When a dual channel electrometer with automatic trigger was not used, timing effects became significant, increasing uncertainties by one order of magnitude. Conclusions: The Exradin W1 response is energy independent for high energy x-rays and electron beams, and only one calibration coefficient is needed. A temperature correction factor should be applied to keep uncertainties around 2% for absolute dose measurements and around 1% for relative measurements in high-energy photon and electron beams. The Exradin W1 scintillator is an excellent alternative to detectors such as diodes for relative dose measurements.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-108: An Investigation of Cerenkov Light Production in the Exradin W1 Scintillator Under Various Measurement Conditions

Purpose: To investigate the effects of depth, fiber-optic cable bends, and incident radiation angle on Cerenkov production in the Standard Imaging Exradin W1. Methods: Measurements were completed using a Varian Clinac 21EX linear accelerator with an Exradin W1 scintillator as well as a cable-only scintillator (no scintillation material) to isolate the Cerenkov signal. The effects of cable bend radius and location were investigated by bending the fiber-optic cable into a circle with radii ranging from 1.0 to 10.8 cm and positioning the center of the coil at distances ranging from 10.0 to 175.0 cm from the photodiode. The effects of depth and incident radiation angle were investigated by performing measurements in water at depths ranging from 1.0 cm to 25.0 cm and angles ranging from 0° to 80°. Eclipse treatment-planning software was utilized to ensure a consistent dose was delivered to the W1 regardless of depth or angle. Results: Measured signal in both channels of the cable-only scintillator decreased as the bend radius decreased and as the distance between the bend and photodiode increased. A fiber bend of 1.0 cm radius produced a 17.1% decrease in the green channel response in the cable-only scintillator. The effect of depth was less severe; a maximum increase of 6.6% in the green channel response was observed at a depth of 25.0 cm in the W1. In the angular dependence investigation, the signal in both channels of the W1 peaked at an angle of 40°; which is in agreement with the nominal Cerenkov emission angle of 45°. Conclusion: The green channel response in the W1 (mainly Cerenkov signal) varied with depth, fiber-optic cable bends, and incident radiation angle. Fully characterizing Cerenkov production is essential to ensure it is properly accounted for in scintillator measurements. Research funding and materials received by Standard Imaging, Inc. (Middleton WI)

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2016

SU-F-J-50: Study On the Magnetic Field Effect On the Exradin W1 Plastic Scintillation Detector

Purpose: To study the response of the Exradin W1 plastic scintillator detector to a 6 MV photon field in the presence of a strong magnetic field (B). Methods: An Exradin W1 scintillator detector coupled to a SuperMax two-channel electrometer, both manufactured by Standard Imaging, Inc., was first calibrated in a Co-60 beam. The Cerenkov Light Ratio (CLR) was obtained following the procedure recommended by the manufacturer. Subtracting signal in channel 2 multiplied by CLR from the signal in channel 1 should lead to a Cerenkov-free signal. The W1 scintillator was placed in a plastic phantom inside a dipole electromagnet (GMW Associates) that could produce a strong B field, and irradiated using a 6 MV beam from an Elekta Versa HD LINAC. Signals from both channels of the W1 scintillator were acquired as a function of B (0 - 1.5 T). Results: The signals from both channels increased as a function of the B field strength. At 1.5 T, channel 1 increased by 11% compared to the baseline (B=0 T), while channel 2 increased by 22%. Applying the recommended Cerenkov correction led to a 2% difference between dose measurement with and without a magnetic field. The values between B=0.3 T and B=1.5 T remained constant. Conclusion: Signals from the Exradin W1 plastic scintillation detector increased as the B field increased. This increase mainly comes from a change in the amount of Cerenkov light coupled within the optical fiber. Removing the Cerenkov component following the procedure recommended by the manufacturer showed to be an effective way to measure dose accurately in strong magnetic fields. The cause for the residual 2% difference is currently under investigation. We acknowledge research support from Elekta AB.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

On R − W1 as a diagnostic to discover obscured active galactic nuclei in wide-area X-ray surveys

Capitalizing on the all-sky coverage of WISE and the 35% and 50% sky coverage from Sloan Digital Sky Survey and Pan-STARRS, respectively, we explore the efficacy of m{sub R} (optical) – m{sub 3.4μm} (mid-infrared), hereafter R−W1, as a color diagnostic to identify obscured supermassive black hole accretion in wide-area X-ray surveys. We use the ∼16.5 deg{sup 2} Stripe 82 X-ray survey data as a test bed to compare R−W1 with R − K, an oft-used obscured active galactic nucleus (AGN) selection criterion, and examine where different classes of objects lie in this parameter space. Most stars follow a well-defined path in R − K versus R−W1 space. We demonstrate that optically normal galaxies hosting X-ray AGNs at redshifts 0.5 4 color cut, while they typically are not selected as AGNs based on their W1−W2 colors. Additionally, different observed X-ray luminosity bins favor different regions in R−W1 parameter space: moderate-luminosity AGNs (10{sup 43} erg s{sup −1} 10{sup 45} erg s{sup −1}) have bluer colors; higher spectroscopic completeness of the Stripe 82X sample is needed to determine whether this is a selection effect or an intrinsic property. Finally, we parameterize X-ray obscuration of Stripe 82X AGNs by calculating their hardness ratios (HRs) and find no clear trends between HR and optical reddening. Our results will help inform best-effort practices in following up obscured AGN candidates in current and future wide-area, shallow X-ray surveys, including the all-sky eROSITA mission.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The calibration of the WISE W1 and W2 Tully-Fisher relation

In order to explore local large-scale structures and velocity fields, accurate galaxy distance measures are needed. We now extend the well-tested recipe for calibrating the correlation between galaxy rotation rates and luminosities—capable of providing such distance measures—to the all-sky, space-based imaging data from the Wide-field Infrared Survey Explorer (WISE) W1 (3.4 μm) and W2 (4.6 μm) filters. We find a correlation of line width to absolute magnitude (known as the Tully-Fisher relation, TFR) of M{sub W1}{sup b,i,k,a}=−20.35−9.56(log W{sub mx}{sup i}−2.5) (0.54 mag rms) and M{sub W2}{sup b,i,k,a}=−19.76−9.74(log W{sub mx}{sup i}−2.5) (0.56 mag rms) from 310 galaxies in 13 clusters. We update the I-band TFR using a sample 9% larger than in Tully and Courtois. We derive M{sub I}{sup b,i,k}=−21.34−8.95(log W{sub mx}{sup i}−2.5) (0.46 mag rms). The WISE TFRs show evidence of curvature. Quadratic fits give M{sub W1}{sup b,i,k,a}=−20.48−8.36(log W{sub mx}{sup i}−2.5)+3.60(log W{sub mx}{sup i}−2.5){sup 2} (0.52 mag rms) and M{sub W2}{sup b,i,k,a}=−19.91−8.40(log W{sub mx}{sup i}−2.5)+4.32(log W{sub mx}{sup i}−2.5){sup 2} (0.55 mag rms). We apply an I-band –WISE color correction to lower the scatter and derive M{sub C{sub W{sub 1}}}=−20.22−9.12(log W{sub mx}{sup i}−2.5) and M{sub C{sub W{sub 2}}}=−19.63−9.11(log W{sub mx}{sup i}−2.5) (both 0.46 mag rms). Using our three independent TFRs (W1 curved, W2 curved, and I band), we calibrate the UNION2 Type Ia supernova sample distance scale and derive H {sub 0} = 74.4 ± 1.4(stat) ± 2.4(sys) km s{sup –1} Mpc{sup –1} with 4% total error.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

SU-E-T-486: In Vivo Skin Dosimetry Using the Exradin W1 Plastic Scintillation Detector for Passively Scattered Proton Beam Therapy

Purpose: To evaluate the accuracy and usefulness of plastic scintillation detectors used for skin dosimetry of patients undergoing passive scatter proton therapy. Methods: Following an IRB approved protocol, six patients undergoing passively scattered proton beam therapy for prostate cancer were selected for in vivo skin dosimetry using the Exradin W1 plastic scintillator. The detector was calibrated on a Cobalt-60 unit, and phantom measurements in the proton beam with the W1 and a calibrated parallel plate ion chamber were used to account for the under-response due to high LET at energies used for treatment. Measurements made in a heated water tank were used to account for temperature dependence. For in vivo measurements, the W1 is fixed to the patient’s skin with medical tape in the center of each of two laterally opposed treatment fields. Measurements will be performed once per week for each patient for the duration of treatment, for a total of thirty six measurements. The measured dose will be compared to the expected dose, extracted from the Eclipse treatment planning system. The average difference over all measurements and per-patient will be computed, as well as standard deviations. Results: The calibrated detector exhibited a 7% under-response in 225 and 250 MeV beams, and a 4% under-response when used at 37 °C (relative to the response at the calibration temperature of 20 °C). Patient measurements are ongoing. Conclusion: The Exradin W1 plastic scintillator detector is a strong candidate for in vivo skin dosimetry in passively scattered proton beams as PSDs are water equivalent and very small (2mm in diameter), permitting accurate measurements that do not perturb the delivered dose. This project was supported in part by award number CA182450 from the National Cancer Institute.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Cecropin P1 antimicrobial peptide modulates differential expression of immune relevant genes in rainbow trout ( Oncorhynchus mykiss ) gill cell line, RTgill-W1

Accumulated evidence indicates that antimicrobial peptides modulate immune activities in fish. In this study, we profiled the differential expression patterns of representative immune relevant genes in an epithelial-like cell line of rainbow trout gill, RTgill-W1, in response to exposure of cecropin P1 antimicrobial peptide. RTgill-W1 cells were treated with synthetic cecropin P1 over time (0, 2, 4 and 24 h) with or without the present of lipopolysaccharide (LPS) or polyinosinic polycytidylic acid (PolyI:C). The relative abundances of each mRNA were measured by real-time quantitative PCR. The dose-response study revealed significant perturbations of mRNA levels of genes related to pro-inflammation, acute phase, surface proteins and transcription factors at 30 μM of cecropin P1. In addition, cecropin P1 altered the differential expression patterns that were induced by LPS or PolyI:C, at different time points in RTgill-W1. Overall, our results indicate that cecropin P1 exhibits pro-inflammation activity, modulate cell-cell interaction and cytokine signal transduction in rainbow trout gill cell, and may suggest a potential application of this peptide as an immune adjuvant for disease control in aquaculture.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Identification and properties of isolated field elliptical galaxies from CFHTLS-W1

We present a catalogue of isolated field elliptical (IfE) galaxies drawn from the W1 field of the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). 228 IfEs were identified from a flux-limited (r < 21.8) galaxy catalogue which corresponds to a density of 3 IfE/sq.deg. For comparison we consider a sample of elliptical galaxies living in dense environments, based on identification of the brightest cluster galaxies (BGCs) in the same survey. Using the same dataset for the comparison sample ensures a uniform selection, including in the redshift range as IfEs (i.e. 0.1 < z <0.9). A comparison of elliptical galaxies in different environments reveals that IfEs and BCGs have similar behaviours in their colours, star formation activities, and scaling relations of mass–size and size–luminosity. IfEs and BCGs have similar slopes in the scaling relations with respect to cluster ellipticals within the $ -24 \leq M_{r} \leq -22 $ magnitude and $10.2 < \textrm{log}(M_{*}/ \textrm M_\odot)\leq12.0 $ mass ranges. Three IfEs identified in this study can be associated with fossil groups found in the same survey area which gives clues for future studies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

SEARCHING FOR PLANET NINE WITH COADDED WISE AND NEOWISE-REACTIVATION IMAGES

A distant, as yet unseen ninth planet has been invoked to explain various observations of the outer solar system. While such a “Planet Nine,” if it exists, is most likely to be discovered via reflected light in the optical, it may emit much more strongly at 3−5 μm than simple blackbody predictions would suggest, depending on its atmospheric properties. As a result, Planet Nine may be detectable at 3.4 μm with the Wide-field Infrared Survey Explorer, but single exposures are too shallow except at relatively small distances (d{sub 9}≲430 au). We develop a method to search for Planet Nine far beyond the W1 single-exposure sensitivity, to distances as large as 800 au, using inertial coadds of W1 exposures binned into ∼1 day intervals. We apply our methodology to a ∼2000 square degree testbed sky region which overlaps a southern segment of Planet Nine’s anticipated orbital path. We do not detect a plausible Planet Nine candidate, but are able to derive a detailed completeness curve, ruling out its presence within the parameter space searched at W1 < 16.66 (90% completeness). Our method uses all publicly available W1 imaging, spanning 2010 January to 2015 December, and will become more sensitive with future NEOWISE-Reactivation releases of additional W1 exposures. We anticipate that our method will be applicable to the entire high Galactic latitude sky, and we will extend our search to that full footprint in the near future.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

SU-F-T-68: Characterizes of Microdetectors in Electron Beam Dosimetry

Purpose: Electron beam dosimetry requires high resolution data due to finite range that can be accomplished with small volume detectors. The small-field used in advance technologies in photon beam has created a market for microdetectors, however characteristics are significantly variable in photon beams and relatively unknown in electron beam that is investigated in this study. Methods: Among nearly 2 dozen microdetectors that have been investigated in small fields of photon beam, two popular detectors (microDiamond 60019 (PTW)) and W1 plastic scintillator detector (Standard Imaging)) that are tissue equivalent and have very small sensitive volume are selected. Electron beams from Varian linear accelerators were used to investigate dose linearity dose rate dependence, energy dependence, depth dose and profiles in a reference condition in a water phantom. For W1 that has its own Supermax electrometer point by point measurements were performed. For microDiamond, a PTW-scanning tank was used for both scanning and point dose measurements. Results: W1 detector showed excellent dose linearity (r{sup 2} =1.0) from 5–500 MU either with variation of dose rate or beam energy. Similar findings were also observed for microdiamond with r{sup 2}=1.0. Percent variations in dose/MU for W1 and microDiamond were 0.2–1.1% and 0.4–1.2%, respectively among dose rate and beam energy. This variation was random for microDiamond, whereas it decreased with beam energy and dose rate for W1. The depth dose and profiles were within ±1 mm for both detectors. Both detectors did not show any energy dependence in electron beams. Conclusion: Both microDiamond and W1 detectors provided superior characteristics of beam parameters in electron beam including dose, dose rate linearity and energy independence. Both can be used in electron beam except W1 require point by point measurements and microdiamond requires 1500 MU for initial quenching.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2014

Testing for Controlled Rapid Pressurization

Borehole W1 is a NQ core hole drilled at our test site in Socorro. The rock is rhyolite. Borehole W1 which was used to test gas-gas explosive mixtures is 55 feet deep with casing (pinkish in the drawing) set to 35 feet. The model is a representation of the borehole and the holes we cored around the central borehole after the test. The brown colored core holes showed dye when we filled W1 with water and slightly pressurized it. This indicates there was some path between W1 and the colored core hole. The core holes are shown to their TD in the drawing. The green plane is a fracture plane which we believe is the result of the explosions of the gas mixture in W1. Data resource is a 2D .pdf Solid Works Drawing of borehole W1.

15 GEOTHERMAL ENERGY↗
DOE OSTI2019

Scission of the Five-Membered Ring in 1- H -Inden-1-one C 9 H 6 O and Indenyl C 9 H 7 in the Reactions with H and O Atoms

Quantum chemical G3(MP2,CC)//B3LYP/6-311G(d,p) calculations of the C 9 H 7 O potential energy surface were utilized to investigate the mechanism of the 1-H-inden-1-one (C 9 H 6 O) + H and indenyl (C 9 H 7 ) + O reactions and were combined with Rice–Ramsperger–Kassel–Marcus Master Equation (RRKM-ME) calculations to predict temperature- and pressure-dependent reaction rate constants and product branching ratios. The most favorable reaction pathways for C 9 H 6 O + H lead to the bimolecular C 8 H 7 + CO products, which are slightly endothermic with respect to the reactants. The reaction begins with H addition to the ortho or meta C atoms in the five-membered ring, C 9 H 6 O + H → w2/w3, and then proceeds by isomerization to w1, (w3 →) w2 → w1. From thereon, the w1 → w9 → w8 → p1 and w2 → w8 → p1 pathways lead to ortho-vinyl phenyl + CO, whereas w1 → w10 → w11 → p2 and C 9 H 6 O + H → w10 → w11 → p2 produce styrenyl + CO. The results of the RRKM-ME calculations showed that only the well-skipping C 9 H 6 O + H → C 8 H 7 (p1/p2) + CO mechanism is relevant under combustion conditions. A comparison with a smaller prototype 2,4-cyclopentadienone + H → C 4 H 5 + CO reaction demonstrated that the H atom is a less efficient destroyer of a cyclopentadienone-like moiety when this moiety is linked to an aromatic or a PAH structure. The C 9 H 7 + O reaction begins with highly exothermic barrierless addition of the oxygen atom to the radical site in the five-membered ring of indenyl producing w1 and then, the reaction mostly proceeds by β-scission in the five-membered ring, which may be preceded by H migration to w2 or w10, and completes by the CO loss forming the highly exothermic C 8 H 7 radical products. Modified Arrhenius expressions for the rate constants of all reactions pertinent to the formation of C 8 H 7 + CO from C 9 H 6 O + H, C 9 H 7 + H, and unimolecular decomposition of benzopyranyl have been generated and suggested for combustion kinetic modeling. Furthermore, it is concluded that the oxidation reactions of a five-membered ring with atomic oxygen remain fast in the presence of attached or surrounding six-membered rings.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

SU-F-T-73: Experimental Determination of the Effective Point of Measurement in Electron Beams Using a Commercial Scintillation Detector

Purpose: The aim of this work was to determine experimentally the effective point of measurement (EPOM) in clinical electron beams for three cylindrical ionization chambers using a commercial scintillation detector as a reference detector. Methods: Percent depth dose (PDD) curves were measured using an Exradin W1 scintillation detector and were used as a representative PDD to water. Depth dose curves were measured with the Exradin A18, A1SL, and A28 ionization chambers. The raw ionization chamber curve data were corrected by the chamber fluence perturbation correction factor and restricted mass collisional stopping power ratio at each depth to obtain a percent depth dose curve to the gas volume (PDDGV) of the detector. Ratios of the W1 PDD to the ion chamber PDDGV were calculated for each measurement depth. The W1 PDD curve was shifted by small depth increments, Δz, until the ratio of the W1 PDD to the ion chamber PDDGV was depth-independent (optimal Δz). A MATLAB routine was developed to determine the optimal Δz value. Results: The optimal Δz shift was used as an estimate of the EPOM for each chamber. The average calculated EPOM shifts (expressed as a fraction of the chamber cavity radius) for the A18, A1SL, and A28 ionization chambers were 0.21 ± 0.04, 0.10 ± 0.05, and 0.22 ± 0.03, respectively. Conclusion: The experimentally determined EPOM values for the A18 and A1SL in this work agreed with the simulated values of Muir and Rogers (MedPhys 2014). The results also indicate that the Exradin W1 scintillator is water equivalent for electron energies of 6 MeV, 9 MeV, 12 MeV, and 16 MeV. In addition, we confirmed that the AAPM TG51 recommended EPOM shift of 0.5 times the cavity radius is not accurate for the A18 and A1SL chambers.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

The CatWISE Preliminary Catalog: Motions from WISE and NEOWISE Data

CatWISE is a program to catalog sources selected from combined WISE and NEOWISE all-sky survey data at 3.4 and 4.6 μm (W1 and W2). The CatWISE Preliminary Catalog consists of 900,849,014 sources measured in data collected from 2010 to 2016. This data set represents four times as many exposures and spans over 10 times as large a time baseline as that used for the AllWISE Catalog. CatWISE adapts AllWISE software to measure the sources in coadded images created from six-month subsets of these data, each representing one coverage of the inertial sky, or epoch. The catalog includes the measured motion of sources in eight epochs over the 6.5 yr span of the data. From comparison to Spitzer, signal-to-noise ratio = 5 limits in magnitudes in the Vega system are W1 = 17.67 and W2 = 16.47, compared to W1 = 16.96 and W2 = 16.02 for AllWISE. From comparison to Gaia, CatWISE positions have typical accuracies of 50 mas for stars at W1 = 10 mag and 275 mas for stars at W1 = 15.5 mag. Proper motions have typical accuracies of 10 mas yr -1 and 30 mas yr -1 for stars with these brightnesses, an order of magnitude better than from AllWISE. The catalog is available in the WISE/NEOWISE Enhanced and Contributed Products area of the NASA/IPAC Infrared Science Archive.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Being WISE. I. Validating stellar population models and M {sub *}/L ratios at 3.4 and 4.6 μm

Using data from the Wide-field Infrared Survey Explorer mission, we have measured near infra-red (NIR) photometry of a diverse sample of dust-free stellar systems (globular clusters, dwarf and giant early-type galaxies) which have metallicities that span the range -2.2 < [Fe/H] (dex) < 0.3. This dramatically increases the sample size and broadens the metallicity regime over which the 3.4 (W1) and 4.6 μm (W2) photometry of stellar populations have been examined. We find that the W1 – W2 colors of intermediate and old (>2 Gyr) stellar populations are insensitive to the age of the stellar population, but that the W1 – W2 colors become bluer with increasing metallicity, a trend not well reproduced by most stellar population synthesis (SPS) models. In common with previous studies, we attribute this behavior to the increasing strength of the CO absorption feature located in the 4.6 μm bandpass with metallicity. Having used our sample to validate the efficacy of some of the SPS models, we use these models to derive stellar mass-to-light ratios in the W1 and W2 bands. Utilizing observational data from the SAURON and ATLAS3D surveys, we demonstrate that these bands provide extremely simple, yet robust stellar mass tracers for dust free older stellar populations that are freed from many of the uncertainties common among optical estimators.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Giant wormholes in ghost-free bigravity theory

We study Lorentzian wormholes in the ghost-free bigravity theory described by two metrics, g and f. Wormholes can exist if only the null energy condition is violated, which happens naturally in the bigravity theory since the graviton energy-momentum tensors do not apriori fulfill any energy conditions. As a result, the field equations admit solutions describing wormholes whose throat size is typically of the order of the inverse graviton mass. Hence, they are as large as the universe, so that in principle we might all live in a giant wormhole. The wormholes can be of two different types that we call W1 and W2. The W1 wormholes interpolate between the AdS spaces and have Killing horizons shielding the throat. The Fierz-Pauli graviton mass for these solutions becomes imaginary in the AdS zone, hence the gravitons behave as tachyons, but since the Breitenlohner-Freedman bound is fulfilled, there should be no tachyon instability. For the W2 wormholes the g-geometry is globally regular and in the far field zone it becomes the AdS up to subleading terms, its throat can be traversed by timelike geodesics, while the f-geometry has a completely different structure and is not geodesically complete. There is no evidence of tachyons for these solutions, although a detailed stability analysis remains an open issue. It is possible that the solutions may admit a holographic interpretation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

SU-C-304-03: Experimental Investigation On the Accuracy of Plastic Scintillation Dosimeters in Small Fields

Purpose: To investigate the accuracy of the Exradin W1 (SI) and of an “in-house” plastic scintillation dosimeter (CHUQ PSD) in small radiation fields. Methods: Output factor (OF) measurements with the W1 and CHUQ PSD were performed for field sizes of 0.5 x 0.5, 1 x 1 and 2 x 2 cm{sup 2}. Both detectors were placed parallel to the central axis (CAX) in water. The spectrum discrimination calibration method was performed in each set-up to account for the Cerenkov (CRV) signal created in the fiber. The OFs were compared to the expected field factors in water derived using i) Monte Carlo (MC) simulations of an accurate accelerator model and ii) microLion (PTW) and D1V diode (SI) OFs. MC-derived correction factors were applied to both the microLion and D1V OFs. For the CHUQ PSD the calibration was repeated in water (// CAX), solid water (perpendicular to CAX) and under a shielded configuration. The signal was collected using a spectrometer (wavelength range = 185–1100 nm). Spectral analysis was performed to evaluate potential changes of the spectral distributions under the various calibration set-up configurations. Results: The W1 OFs presented an over-response for the 0.5 x 0.5 cm{sup 2} in the range of 3 – 4.1% relative to the expected field factor. The CHUQ PSD presented an under-response in the range of 1.5 – 2.7%, without accounting for volume averaging. The CRV spectra under the various calibration procedures appeared similar to each other and only minor changes were observed to the respective OFs. Conclusion: The W1 and CHUQ PSD can be used in small fields down to a 1 x 1 cm{sup 2} field size. Discrepancies were encountered between the two detectors for the smallest field size of 0.5 x 0.5 cm{sup 2} with the CHUQ PSD exhibiting a closer agreement to the expected field factor. Funding sources: 1) Alexander S. Onassis Public Benefit Foundation in Greece and 2) CREATE Medical Physics Research Training Network grant of the Natural Sciences and Engineering Research Council, Grant number: 432290, RGPIN-2014-06475.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

SU-E-T-506: Intercomparison Study On Small Field Output Factor Measurements

Purpose In radiotherapy, uncertainties due to small field measurements (SFM) introduce systematic errors to the treatment process and the development of new dosimeters for quality assurance programs is a challenge. In this work we analyze the behavior of seven detectors measuring output factors of 6MV photon beam. Methods The dosimeters employed are: a single cristal diamond detector (SCCD) developed at the University of Rome Tor Vergata, a silicon diode developed within the project MAESTRO, a IBA Razor silicon diode, A1SL and A26 Exradin ion chambers, an EBT3 Gafchromic film and the Exradin W1 Scintillator.Diamond sensitive volume is a cylinder 2.2mm in diameter and 1μm thick. MAESTRO diode is 2×2mm2 active area. Razor sensitive volume is a cylinder 0.6 mm in diameter and 0.02 mm thick. A16 and A1Sl have a collecting volume of 0,015cc and 0,053cc. The W1 is an optical fiber with an active volume of 0.002cc. All measurements were performed in a water phantom, with detector positioned at the isocenter (SSD=90cm, d=10cm), MAESTRO diode being sandwiched in solid water to obtain an equivalent experimental setup. Results These measurements are challenging due to the absence of charged particle equilibrium conditions, detector size and positioning problems. They are in good agreement among each other, especially GAF, Razor, W1 and SCDD. Maximum deviations reported are related to the field 0.8×0.8cm2 for MAESTRO and chambers data with respect to EBT3: around 15% (A1SLvsEBT3), 16% (MAESTROvsEBT3). Razor and W1 show a deviation around 3% with respect to SCDD. Conclusion In this work measurements made with a variety of detectors are compared. These study show the possibility to choose different detectors for SFM and that smaller ion chambers are still not competitive with solid state detectors. Silicon, diamond and optical fiber dosimeters show a similar behavior with minor discrepancies for the smallest field.

60 APPLIED LIFE SCIENCES↗