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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 OSTI2014

Application of a radiophotoluminescent glass dosimeter to nonreference condition dosimetry in the postal dose audit system

Purpose: The purpose of this study was to obtain a set of correction factors of the radiophotoluminescent glass dosimeter (RGD) output for field size changes and wedge insertions. Methods: Several linear accelerators were used for irradiation of the RGDs. The field sizes were changed from 5 × 5 cm to 25 × 25 cm for 4, 6, 10, and 15 MV x-ray beams. The wedge angles were 15°, 30°, 45°, and 60°. In addition to physical wedge irradiation, nonphysical (dynamic/virtual) wedge irradiations were performed. Results: The obtained data were fitted with a single line for each energy, and correction factors were determined. Compared with ionization chamber outputs, the RGD outputs gradually increased with increasing field size, because of the higher RGD response to scattered low-energy photons. The output increase was about 1% per 10 cm increase in field size, with a slight difference dependent on the beam energy. For both physical and nonphysical wedged beam irradiation, there were no systematic trends in the RGD outputs, such as monotonic increase or decrease depending on the wedge angle change if the authors consider the uncertainty, which is approximately 0.6% for each set of measured points. Therefore, no correction factor was needed for all inserted wedges. Based on this work, postal dose audits using RGDs for the nonreference condition were initiated in 2010. The postal dose audit results between 2010 and 2012 were analyzed. The mean difference between the measured and stated doses was within 0.5% for all fields with field sizes between 5 × 5 cm and 25 × 25 cm and with wedge angles from 15° to 60°. The standard deviations (SDs) of the difference distribution were within the estimated uncertainty (1SD) except for the 25 × 25 cm field size data, which were not reliable because of poor statistics (n = 16). Conclusions: A set of RGD output correction factors was determined for field size changes and wedge insertions. The results obtained from recent postal dose audits were analyzed, and the mean differences between the measured and stated doses were within 0.5% for every field size and wedge angle. The SDs of the distribution were within the estimated uncertainty, except for one condition that was not reliable because of poor statistics.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2016

Interfacial control of Dzyaloshinskii-Moriya interaction in heavy metal/ferromagnetic metal thin film heterostructures

The interfacial Dzyaloshinskii-Moriya interaction (DMI) in ultrathin magnetic thin film heterostructures provides a new approach for controlling spin textures on mesoscopic length scales. Here we investigate the dependence of the interfacial DMI constant D on a Pt wedge insertion layer in Ta/CoFeB/Pt(wedge)/MgO thin films by observing the asymmetric spin-wave dispersion using Brillouin light scattering. Continuous tuning of D by more than a factor of 3 is realized by inserting less than one monolayer of Pt. The observations in this work provide new insights for designing magnetic thin film heterostructures with tailored D for controlling skyrmions and magnetic domain-wall chirality and dynamics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Development of Cone Wedge Ring Expansion Test to Evaluate Mechanical Properties of Clad Tubing Structure

To determine the hoop tensile properties of irradiated fuel cladding in a hot cell, a cone wedge ring expansion test method was developed. A four-piece wedge insert was designed with tapered angles matched to the cone shape of a loading piston. The ring specimen was expanded in the radial direction by the lateral expansion of the wedges under the downward movement of the piston. The advantages of the proposed method are that implementation of the test setup in a hot cell is simple and easy, and that it enables a direct strain measurement of the test specimen from the piston’s vertical displacement soon after the wedge-clad contact resistance is initiated.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2016

Structural basis for promiscuous PAM recognition in type I–E Cascade from E. coli

Clustered regularly interspaced short palindromic repeats (CRISPRs) and the cas (CRISPR-associated) operon form an RNA-based adaptive immune system against foreign genetic elements in prokaryotes. Type I accounts for 95% of CRISPR systems, and has been used to control gene expression and cell fate. During CRISPR RNA (crRNA)-guided interference, Cascade (CRISPR-associated complex for antiviral defence) facilitates the crRNA-guided invasion of double-stranded DNA for complementary base-pairing with the target DNA strand while displacing the non-target strand, forming an R-loop. Cas3, which has nuclease and helicase activities, is subsequently recruited to degrade two DNA strands. A protospacer adjacent motif (PAM) sequence flanking target DNA is crucial for self versus foreign discrimination. Here we present the 2.45 Å crystal structure of Escherichia coli Cascade bound to a foreign double-stranded DNA target. The 5'-ATG PAM is recognized in duplex form, from the minor groove side, by three structural features in the Cascade Cse1 subunit. The promiscuity inherent to minor groove DNA recognition rationalizes the observation that a single Cascade complex can respond to several distinct PAM sequences. Optimal PAM recognition coincides with wedge insertion, initiating directional target DNA strand unwinding to allow segmented base-pairing with crRNA. The non-target strand is guided along a parallel path 25 Å apart, and the R-loop structure is further stabilized by locking this strand behind the Cse2 dimer. Furthermore, these observations provide the structural basis for understanding the PAM-dependent directional R-loop formation process.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2016

Experimental evaluation of neural probe’s insertion induced injury based on digital image correlation method

Purpose: The application of neural probes in clinic has been challenged by probes’ short lifetime when implanted into brain tissue. The primary goal is to develop an evaluation system for testing brain tissue injury induced by neural probe’s insertion using microscope based digital image correlation method. Methods: A brain tissue phantom made of silicone rubber with speckle pattern on its surface was fabricated. To obtain the optimal speckle pattern, mean intensity gradient parameter was used for quality assessment. The designed testing system consists of three modules: (a) load module for simulating neural electrode implantation process; (b) data acquisition module to capture micrographs of speckle pattern and to obtain reactive forces during the insertion of the probe; (c) postprocessing module for extracting tissue deformation information from the captured speckle patterns. On the basis of the evaluation system, the effects of probe wedge angle, insertion speed, and probe streamline on insertion induced tissue injury were investigated. Results: The optimal quality speckle pattern can be attained by the following fabrication parameters: spin coating rate—1000 r/min, silicone rubber component A: silicone rubber component B: softener: graphite = 5 ml: 5 ml: 2 ml: 0.6 g. The probe wedge angle has a significant effect on tissue injury. Compared to wedge angle 40° and 20°, maximum principal strain of 60° wedge angle was increased by 40.3% and 87.5%, respectively; compared with a relatively higher speed (500 μm/s), the maximum principle strain within the tissue induced by slow insertion speed (100 μm/s) was increased by 14.3%; insertion force required by probe with convex streamline was smaller than the force of traditional probe. Based on the experimental results, a novel neural probe that has a rounded tip covered by a biodegradable silk protein coating with convex streamline was proposed, which has both lower insertion and micromotion induced tissue injury. Conclusions: The established evaluation system has provided a simulation environment for testing brain tissue injury produced by various insertion conditions. At the same time, it eliminates the adverse effect of biological factors on tissue deformation during the experiment, improving the repeatability of measurement results. As a result, the evaluation system will provide support on novel neural probe design that can reduce the acute tissue injury during the implantation of the probe.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2013

Methodology for Mechanical Property Testing on Fuel Cladding Using an Expanded Plug Wedge Test

To determine the tensile properties of irradiated fuel cladding in a hot cell, a simple test was developed at ORNL and is described fully in US Patent Application 20060070455, Expanded plug method for developing circumferential mechanical properties of tubular materials. This method is designed for testing fuel rod cladding ductility in a hot cell utilizing an expandable plug to stretch a small ring of irradiated cladding material. The specimen strain is determined using the measured diametrical expansion of the ring. This method removes many complexities associated with specimen preparation and testing. The advantages are the simplicity of measuring the test component assembly in the hot cell and the direct measurement of specimen strain. It was also found that cladding strength could be determined from the test results. The basic approach of this test method is to apply an axial compressive load to a cylindrical plug of polyurethane (or other materials) fitted inside a short ring of the test material to achieve radial expansion of the specimen. The diameter increase of the specimen is used to calculate the circumferential strain accrued during the test. The other two basic measurements are total applied load and amount of plug compression (extension). A simple procedure is used to convert the load circumferential strain data from the ring tests into material pseudo-stress-strain curves. However, several deficiencies exist in this expanded-plug loading ring test, which will impact accuracy of test results and introduce potential shear failure of the specimen due to inherited large axial compressive stress from the expansion plug test. First of all, the highly non-uniform stress and strain distribution resulted in the gage section of the clad. To ensure reliable testing and test repeatability, the potential for highly non-uniform stress distribution or displacement/strain deformation has to be eliminated at the gage section of the specimen. Second, significant compressive stresses were induced by clad bending deformation due to a clad bulging effect (or the barreling effect). The barreling effect caused very large localized shear stress in the clad and left testing material at a high risk of shear failure. The above combined effects will result in highly non-conservative predictions both in strength and ductility of the tested clad, and the associated mechanical properties as well. To overcome/mitigate the mentioned deficiencies associated with the current expansion plug test, systematic studies have been conducted. Through detailed parameter investigation on specific geometry designs, careful filtering of material for the expansion plug, as well as adding newly designed parts to the testing system, a method to reconcile the potential non-conservatism embedded in the expansion plug test system has been discovered. A modified expansion plug testing protocol has been developed based on the method. In order to closely resemble thin-wall theory, a general procedure was also developed to determine the hoop stress $\sigma_\theta$ in the tested ring specimen. A scaling factor called $\chi$-factor is defined to correlate the ring load F ring into hoop stress $\sigma_\theta$, and written as $\sigma_\theta = \chi \frac{F_{ring}} {tl}$. The generated stress-strain curve agrees very well with tensile test data in both the elastic and plastic regions.

expansion plug test↗
DOE OSTI2014

SU-E-T-195: Gantry Angle Dependency of MLC Leaf Position Error

Purpose: The aim of this study was to investigate the gantry angle dependency of the multileaf collimator (MLC) leaf position error. Methods: An automatic MLC quality assurance system (AutoMLCQA) was developed to evaluate the gantry angle dependency of the MLC leaf position error using an electronic portal imaging device (EPID). To eliminate the EPID position error due to gantry rotation, we designed a reference maker (RM) that could be inserted into the wedge mount. After setting up the EPID, a reference image was taken of the RM using an open field. Next, an EPID-based picket-fence test (PFT) was performed without the RM. These procedures were repeated at every 45° intervals of the gantry angle. A total of eight reference images and PFT image sets were analyzed using in-house software. The average MLC leaf position error was calculated at five pickets (-10, -5, 0, 5, and 10 cm) in accordance with general PFT guidelines using in-house software. This test was carried out for four linear accelerators. Results: The average MLC leaf position errors were within the set criterion of <1 mm (actual errors ranged from -0.7 to 0.8 mm) for all gantry angles, but significant gantry angle dependency was observed in all machines. The error was smaller at a gantry angle of 0° but increased toward the positive direction with gantry angle increments in the clockwise direction. The error reached a maximum value at a gantry angle of 90° and then gradually decreased until 180°. In the counter-clockwise rotation of the gantry, the same pattern of error was observed but the error increased in the negative direction. Conclusion: The AutoMLCQA system was useful to evaluate the MLC leaf position error for various gantry angles without the EPID position error. The Gantry angle dependency should be considered during MLC leaf position error analysis.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2022

Scattering strings off quantum extremal surfaces

We consider a Hayden & Preskill like setup for both maximally chaotic and sub-maximally chaotic quantum field theories. We act on the vacuum with an operator in a Rindler like wedge R and transfer a small subregion I of R to the other wedge. The chaotic scrambling dynamics of the QFT Rindler time evolution reveals the information in the other wedge. The holographic dual of this process involves a particle excitation falling into the bulk and crossing into the entanglement wedge of the complement to r = R\I. With the goal of studying the locality of the emergent holographic theory we compute various quantum information measures on the boundary that tell us when the particle has entered this entanglement wedge. In a maximally chaotic theory, these measures indicate a sharp transition where the particle enters the wedge exactly when the insertion is null separated from the quantum extremal surface for r. For sub-maximally chaotic theories, we find a smoothed crossover at a delayed time given in terms of the smaller Lyapunov exponent and dependent on the time-smearing scale of the probe excitation. The information quantities that we consider include the full vacuum modular energy R\I as well as the fidelity between the state with the particle and the state without. Along the way, we find a new explicit formula for the modular Hamiltonian of two intervals in an arbitrary 1+1 dimensional CFT to leading order in the small cross ratio limit. We also give an explicit calculation of the Regge limit of the modular flowed chaos correlator and find examples which do not saturate the modular chaos bound. Finally, we discuss the extent to which our results reveal properties of the target of the probe excitation as a “stringy quantum extremal surface” or simply quantify the probe itself thus giving a new approach to studying the notion of longitudinal string spreading.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Enhanced positive and negative exchange bias in FeF 2 /Ni with dusted interfaces

An enhanced exchange bias was found in FeF 2 /Ni interfaces by inserting dusting of Pd and Cu atoms. We have used an ultrathin wedge to investigate systematically the effect of a discontinuous nonmagnetic spacer between the antiferromagnetic and ferromagnetic layers. Negative and positive exchange biases are symmetric and maximized for less than two angstroms of the nonmagnetic layer. Moreover, the dusting reduces the field cooling threshold to switch between the negative and the positive exchange bias. This finding demonstrates that nonmagnetic dusted layers can improve the interfacial exchange energy density in antiferromagnetic/ferromagnetic heterostructures and modify the bulk antiferromagnetic domain structure. Other dusting materials such as Ag, Ti, V, and SiO 2 showed no enhancement in FeF 2 /Ni bilayers, which indicates the atomic sensitivity of this effect.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Modular flow in JT gravity and entanglement wedge reconstruction

It has been shown in recent works that JT gravity with matter with two boundaries has a type II ∞ algebra on each side. As the bulk spacetime between the two boundaries fluctuates in quantum nature, we can only define the entanglement wedge for each side in a pure algebraic sense. As we take the semiclassical limit, we will have a fixed long wormhole spacetime for a generic partially entangled thermal state (PETS), which is prepared by inserting heavy operators on the Euclidean path integral. Under this limit, with appropriate assumptions of the matter theory, geometric notions of the causal wedge and entanglement wedge emerge in this background. In particular, the causal wedge is manifestly nested in the entanglement wedge. Different PETS are orthogonal to each other, and thus the Hilbert space has a direct sum structure over sub-Hilbert spaces labeled by different Euclidean geometries. The full algebra for both sides is decomposed accordingly. From the algebra viewpoint, the causal wedge is dual to an emergent type III 1 subalgebra, which is generated by boundary light operators. To reconstruct the entanglement wedge, we consider the modular flow in a generic PETS for each boundary. We show that the modular flow acts locally and is the boost transformation around the global RT surface in the semiclassical limit. It follows that we can extend the causal wedge algebra to a larger type III 1 algebra corresponding to the entanglement wedge. Within each sub-Hilbert space, the original type II ∞ reduces to type III 1 .

2D Gravity↗
DOE OSTI2020

Permanent magnets for the return loop of the Cornell-Brookhaven energy recovery linac test accelerator

214 neodymium permanent magnets have been manufactured for the return loop of the CBETA multi-turn ERL at Cornell University. There are 5 types of quadrupole and combined-function gradient magnets using a variant of the circular Halbach design. These are made out of NdFeB material and glued into an aluminium housing with water channels for temperature stabilisation. The NdFeB wedges and magnet construction were done by outside companies, while the final “tuning” using inserts containing 64 iron rods per magnet was done at BNL over a period of about 6 months. Average relative field errors of 2.2×10 -4 were achieved on the beam region. The magnet strengths vary by type but are of order 10 T/m for quadrupole component and up to 0.3 T for the dipole. This paper reports on the field quality and timeline achieved in this production process

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

SU-F-P-37: Implementation of An End-To-End QA Test of the Radiation Therapy Imaging, Planning and Delivery Process to Identify and Correct Possible Sources of Deviation

Purpose: To implement an end-to-end QA test of the radiation therapy imaging, planning and delivery process, aimed to assess the dosimetric agreement accuracy between planned and delivered treatment, in order to identify and correct possible sources of deviation. To establish an internal standard for machine commissioning acceptance. Methods: A test involving all steps of the radiation therapy: imaging, planning and delivery process was designed. The test includes analysis of point dose and planar dose distributions agreement between TPS calculated and measured dose. An ad hoc 16 cm diameter PMMA phantom was constructed with one central and four peripheral bores that can accommodate calibrated electron density inserts. Using Varian Eclipse 10.0 and Elekta XiO 4.50 planning systems, IMRT, RapidArc and 3DCRT with hard and dynamic wedges plans were planned on the phantom and tested. An Exradin A1SL chamber is used with a Keithley 35617EBS electrometer for point dose measurements in the phantom. 2D dose distributions were acquired using MapCheck and Varian aS1000 EPID.Gamma analysis was performed for evaluation of 2D dose distribution agreement using MapCheck software and Varian Portal Dosimetry Application.Varian high energy Clinacs Trilogy, 2100C/CD, 2000CR and low energy 6X/EX where tested.TPS-CT# vs. electron density table were checked for CT-scanners used. Results: Calculated point doses were accurate to 0.127% SD: 0.93%, 0.507% SD: 0.82%, 0.246% SD: 1.39% and 0.012% SD: 0.01% for LoX-3DCRT, HiX-3DCRT, IMRT and RapidArc plans respectively. Planar doses pass gamma 3% 3mm in all cases and 2% 2mm for VMAT plans. Conclusion: Implementation of a simple and reliable quality assurance tool was accomplished. The end-to-end proved efficient, showing excellent agreement between planned and delivered dose evidencing strong consistency of the whole process from imaging through planning to delivery. This test can be used as a first step in beam model acceptance for clinical use.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-C-BRB-01: Development of Dynamic Gimbaled X-Ray Head Swing Irradiation Technique

Purpose: The Vero4DRT has a unique gimbaled x-ray head with rotating around orthogonal two axes. The purpose of this study was to develop a new irradiation technique using the dynamic gimbaled x-ray head swing function. Methods: The Vero4DRT has maximum field size of 150Χ150 mm2. The expanded irradiation field (expanded-field) for the longitudinal direction which is vertical to the MLC sliding direction, was created by the MLC motion and the gimbaled x-ray head rotation. The gimbaled x-ray head was rotated ± 35 mm, and the expanded-field size was set as 150Χ220 mm2. To irradiate uniform dose distribution, the diamond-shaped radiation field was created and continuously moved for the longitudinal direction. It was achieved by combination of opening and closing of the MLC and gimbal swing rotation. To evaluate dosimetric characteristic of the expanded-field, films inserted in water-equivalent phantoms at 100 mm depth were irradiated and the field size, penumbra, flatness and symmetry were analyzed.In addition, the expanded-field irradiation technique was applied to virtual wedge irradiation. Wedged beam was acquired with the delta–shaped radiation field. 150Χ 220 mm2 fields with 15, 30, 45, and 60 degree wedge were examined. The wedge angles were measured with irradiated film and compared with assumed wedge angles. Results: The field size, penumbra, flatness and symmetry of the expanded-field were 150.0 mm, 8.1–8.4 mm, 2.8% and −0.8% for the lateral direction and 220.1 mm, 6.3–6.4 mm, 3.2% and −0.4% for the longitudinal direction at 100 mm depth. The measured wedge angles were 15.1, 30.2, 45.2 and 60.2 degrees. The differences between assumed and measured angles were within 0.2 degrees. Conclusion: A new technique of the gimbal swing irradiation was developed. To extend applied targets, especially for whole breast irradiation, the expanded-field and virtual wedge irradiations would be effective.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Observation of 0–π transition in SIsFS Josephson junctions

The 0–π transition in Superconductor-Insulator-superconductor-Ferromagnet-Superconductor (SIsFS) Josephson junctions (JJs) was investigated experimentally. As predicted by theory, an s-layer inserted into a ferromagnetic SIFS junction can enhance the critical current density up to the value of an SIS tunnel junction. We fabricated Nb′ | AlO{sub x} | Nb | Ni{sub 60}Cu{sub 40} | Nb JJs with wedge-like s (Nb) and F (Ni{sub 60}Cu{sub 40}) layers and studied the Josephson effect as a function of the s- and F-layer thickness, d{sub s} and d{sub F}, respectively. For d{sub s} = 11 nm, π-JJs with SIFS-type j{sub c}(d{sub F}) and critical current densities up to j{sub c}{sup π}=60 A/cm{sup 2} were obtained at 4.2 K. Thicker d{sub s} led to a drastic increase of the critical current decay length, accompanied by the unexpected disappearance of the 0–π transition dip in the j{sub c}(d{sub F}) dependence. Our results are relevant for superconducting memories, rapid single flux quantum logic circuits, and solid state qubits.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Generation of virtual monochromatic CBCT from dual kV/MV beam projections

Purpose: To develop a novel on-board imaging technique which allows generation of virtual monochromatic (VM) cone-beam CT (CBCT) with a selected energy from combined kilovoltage (kV)/megavoltage (MV) beam projections. Methods: With the current orthogonal kV/MV imaging hardware equipped in modern linear accelerators, both MV projections (from gantry angle of 0°–100°) and kV projections (90°–200°) were acquired as gantry rotated a total of 110°. A selected range of overlap projections between 90° to 100° were then decomposed into two material projections using experimentally determined parameters from orthogonally stacked aluminum and acrylic step-wedges. Given attenuation coefficients of aluminum and acrylic at a predetermined energy, one set of VM projections could be synthesized from two corresponding sets of decomposed projections. Two linear functions were generated using projection information at overlap angles to convert kV and MV projections at nonoverlap angles to approximate VM projections for CBCT reconstruction. The contrast-to-noise ratios (CNRs) were calculated for different inserts in VM CBCTs of a CatPhan phantom with various selected energies and compared with those in kV and MV CBCTs. The effect of overlap projection number on CNR was evaluated. Additionally, the effect of beam orientation was studied by scanning the CatPhan sandwiched with two 5 cm solid-water phantoms on both lateral sides and an electronic density phantom with two metal bolt inserts. Results: Proper selection of VM energy [30 and 40 keV for low-density polyethylene (LDPE), polymethylpentene, 2 MeV for Delrin] provided comparable or even better CNR results as compared with kV or MV CBCT. An increased number of overlap kV and MV projection demonstrated only marginal improvements of CNR for different inserts (with the exception of LDPE) and therefore one projection overlap was found to be sufficient for the CatPhan study. It was also evident that the optimal CBCT image quality was achieved when MV beams penetrated through the heavy attenuation direction of the object. Conclusions: A novel technique was developed to generate VM CBCTs from kV/MV projections. This technique has the potential to improve CNR at selected VM energies and to suppress artifacts at appropriate beam orientations.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Cygnus Dual Beam Radiographic Facility Refurbishment completed at U1A tunnel in Nevada NNSS meeting Level 2 milestone (P-23 Highlights 6/10/12)

A moratorium was placed on U.S. underground nuclear testing in 1992. In response, the Stockpile Stewardship Program was created to maintain readiness of the existing nuclear inventory through several efforts such as computer modeling, material analysis, and subcritical nuclear experiments (SCEs). As in the underground test era, the Nevada National Security Site (NNSS), formerly the Nevada Test Site, provides a safe and secure environment for SCEs by the nature of its isolated and secure facilities. A major tool for SCE diagnosis installed in the 05 drift laboratory is a high energy x-ray source used for time resolved imaging. This tool consists of two identical sources (Cygnus 1 and Cygnus 2) and is called the Cygnus Dual Beam Radiographic Facility (Figs. 2-6). Each Cygnus machine has 5 major elements: Marx Generator, Pulse Forming Line (PFL), Coaxial Transmission Line (CTL), 3-cell Inductive Voltage Adder (IVA), and Rod Pinch Diode. Each machine is independently triggered and may be fired in separate tests (staggered mode), or in a single test where there is submicrosecond separation between the pulses (dual mode). Cygnus must operate as a single shot machine since on each pulse the diode electrodes are destroyed. The diode is vented to atmosphere, cleaned, and new electrodes are inserted for each shot. There is normally two shots per day on each machine. Since its installation in 2003, Cygnus has participated in: 4 Subcritical Experiments (Armando, Bacchus, Barolo A, and Barolo B), a 12 shot plutonium physics series (Thermos), and 2 plutonium step wedge calibration series (2005, 2011), resulting in well over 1000 shots. Currently the Facility is in preparation for 2 SCEs scheduled for this calendar year - Castor and Pollux. Cygnus has performed well during 8 years of operations at NNSS. Many improvements in operations and performance have been implemented during this time. Throughout its service at U1a, major maintenance and replacement of many hardware items were delayed due to programmatic requirements. It is anticipated that Cygnus will be in service at U1a for another 5 years. With this assumption, it was realized that significant resources and effort should be allotted to bring the hardware back to its original condition, or even to improve elements when appropriate. The Cygnus Refurbishment and Enhancement Project started in April, 2011 with the intent to encompass a major overhaul of Cygnus.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Absorber for terahertz radiation management

A method and apparatus for minimizing the degradation of power in a free electron laser (FEL) generating terahertz (THz) radiation. The method includes inserting an absorber ring in the FEL beam path for absorbing any irregular THz radiation and thus minimizes the degradation of downstream optics and the resulting degradation of the FEL output power. The absorber ring includes an upstream side, a downstream side, and a plurality of wedges spaced radially around the absorber ring. The wedges form a scallop-like feature on the innermost edges of the absorber ring that acts as an apodizer, stopping diffractive focusing of the THz radiation that is not intercepted by the absorber. Spacing between the scallop-like features and the shape of the features approximates the Bartlett apodization function. The absorber ring provides a smooth intensity distribution, rather than one that is peaked on-center, thereby eliminating minor distortion downstream of the absorber.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

SU-F-T-176: Therapeutic Proton Beam Range Measurement Method with EBT3 Film

Purpose: Ocular proton therapy has the following advantages: i) sparing optic nerve, ii) the minimal dose is delivered to surrounding normal tissues. Since the proton therapy center was opened in 2007, 30 patients with ocular tumor have been treated at National Cancer Center using single scattering technique. To develop a solid eye phantom which can verify the output and the beam range with EBT3 film for independent patient QA in ocular proton therapy. Methods: The proton therapy is very effective to treat ocular tumor, because of the Bragg peak feature. In general, the beam shape of eye treatment is about 3 cm in diameter and the beam range is under 5 cm. However, proton therapy has uncertainty of beam range problem due to various stopping power of normal tissue, bone, air and so on, so that we should verify the beam range before treatment. For this purpose, a new PMMA phantom with wedge has been developed to use the film dosimetry and the ionization chamber. It is able to place a film on the slope of the phantom, which the spread out Bragg Peak by the water equivalent thickness value of PMMA can be made on the film. We considered to relation with quenching effect of proton energy and range for simple second check. In addition, the ionization chamber (Pin-point chamber, PTW 31014) can be inserted into a hole in the phantom to measure the absolute dose. Results: The output difference and beam range difference were less than 2% and 1.0 mm, respectively, between the measurement and the plan. Conclusion: An eye phantom was developed and its performance was evaluated successfully and it was useful to verify the output. Also with EBT3 film with the quenching effect for measurement depth-dose profile, range to patient QA.

60 APPLIED LIFE SCIENCES↗