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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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670 records · Page 38
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

TH-CD-BRA-09: Towards Absolute Dose Measurement in MRI-Linac and Gamma-Knife: Design and Construction of An MR-Compatible Water Calorimeter

Purpose: The purpose of this work is to design and optimize a portable Water Calorimeter (WC) for use in a commercial MRI-linac and Gamma-knife in addition to conventional radiotherapy linacs. Water calorimeters determine absorbed dose to water at a point by measuring radiation-induced temperature rise of the volume (the two are related by the medium specific heat capacity). In this formalism, one important correction factor is heat transfer correction k-ht. It compensates for heat gain/loss due to conductive and convective effects, and is numerically calculated as ratio of temperature rise in the absence of heat loss to that in the presence of heat loss. Operating at 4°C ensures convection is minimal. Methods: A commercial finite element software was used to evaluate several WC designs with different insulation materials and thicknesses; channels allowing coolant to travel around WC (to sustain WC at 4°C) were modeled, and worst-case scenario variation in the temperature of the coolant was simulated for optimization purposes (2.6 mK/s). Additionally, several calorimeter vessel design parameters (front/back glass thickness/separation, diameter) were also simulated and optimized. Optimization is based on minimizing long term calorimeter drift (24h) as well as variation and magnitude of k-ht. Results: The final selected WC design reached a modest drift of 11µK/s after 15h for the worst-case coolant temperature variation. This design consists of coolant channels being encompassed on both sides by cryogel insulation. For the MRI-linac beam, glass thickness plays the largest effect on k-ht with variation of upto 0.6% in the first run for thicknesses ranging between 0.5–1.7mm. Subsequent runs vary only within 0.1% with glass thickness. Other factors such as vessel radius and top/bottom glass separation have sub 0.1% effects on k-ht. Conclusion: An MR-safe 4°C stagnant WC appropriate for dosimetry in MRI-linac and Gamma-Knife was designed, optimized, and construction is nearly completed. NSERC Discovery Grant RGPIN-435608.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2019

Towards Vendor and Operating System Independence of USB-based portable multi-channel analyzers

The nuclear measurements group is called on to develop portable, user friendly systems that performs at, or near, laboratory standards. These systems typically consist of a detector and a USB-based multi-channel analyzer. An ORTEC digi-Base is an example of a USB-based portable multi-channel analyzer with 14-pin photomultiplier tube base for gamma-ray spectroscopy applications with NaI(Tl) and other scintillation detectors. Operating system independence - we want to be able to develop applications that are 'future-proof' and can run on the best hardware for the job: desktop, laptop, tablet, phone, or embedded device. To do that we need our software to be operating system independent. Hardware vendor independence - to use the most appropriate equipment for the job, while still maintaining our rapid method development, we would like our software that uses this equipment to be independent of the specific vendor or model of the hardware. To do that we need a common interface to each vendor's equipment (high voltage, gain, start, stop, clear, etc.) In prior work, we were able to use an existing library to communicate with an ORTEC digi-base via Linux and Android. However the application developed did not have a user friendly front-end. Part of this work was to develop a simple user interface to control the settings of the hardware from Android. While OS independence is the final goal, another goal is standardized software for user-application development. For current purposes those standard systems are Windows 7, Windows 10, and Python 3. Our next step was to develop a common software interface between a front-end user interface and back-end hardware communication software. This was done using Python's Ctypes library. Ctypes is a foreign function library for Python. It provides C compatible data types, and allows calling functions in DLLs or shared libraries. It can be used to wrap these libraries in pure Python. Ctypes exports the cdll, and Windows windll and oledll objects, for loading dynamic link libraries. You load libraries by accessing them as attributes of these objects. cdll loads libraries which export functions using the standard cdecl calling convention. The first steps of developing the common software interface have been done. Once the software interface has been developed the next goal will be to develop hardware specific back-end software that way rapid user facing software can be developed using equipment that is 'on-hand' and once finished prototyping, the 'best' hardware can be chosen for the specific implementation.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

A Portable Quantitative High-Resolution Gamma System for In-Situ Waste, D and D, and Emergency Measurements - 18573

The Canberra ISOCS system has been a highly successful and technologically innovative product since its introduction about 22 years ago. The combination of field-portable HPGe detectors, flexible shield/collimator set, and accurate mathematical efficiency calibration software made in-situ gamma spectroscopy measurements very practical. Good quality in-situ measurements are economically beneficial for items that are either large or complex, in comparison to the cost, time and impracticality of extracting a sample for laboratory measurements or producing representative calibration standards. And where the item is not homogeneous [most of the time for in-situ measurement situations] an assay of a large part of the item has been shown to be more accurate than a few widely dispersed extracted samples [the normal case]. However the size, weight, cost and complexity of the full-size ISOCS system limit its usefulness in some situations. A companion device was recently introduced, and is the subject of this document. The gamma sensor is a 1 cm{sup 3} CZT detector. It is surrounded by an optional tungsten shield/collimator set with a tripod for support. The detector is powered solely by a USB connection from a laptop PC. The full power of the ISOCS efficiency calibration software can be used with this detector. This entire package is less than 15 kg, needs no cooling, and is quite rugged, in comparison to the 120 kg for ISOCS with sensitive HPGe detectors which need Liquid Nitrogen or electro-mechanical cooling. Furthermore this CZT package is about 1/3 the cost. This is a very complementary device for the many current ISOCS users, especially for quick initial evaluations or simple situations where the full energy resolution and sensitivity of the HPGe ISOCS are not needed. Operating nuclear power plants or those in the initial phases of decommissioning are prime examples. Their complex layout often precludes the deployment of the full-sized ISOCS system, whereas the CZT system can be hand-carried there and very quickly setup for a measurement. The small detector size, and therefore low efficiency, is not a disadvantage, and in many cases is an advantage due to the elevated radioactivity of the items. This can be used to assay items in tanks, spills on floors, activity on filters, waste or items in small containers, and waste in drums. In the event of an emergency, it can be quickly deployed to measure gas or liquid effluent streams, air particulate and iodine filters in the field, or even in-vivo thyroid activity. Examples of measurements at nuclear facilities are shown and discussed in further detail, along with estimated detection limits. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Informative Path Planning for Mapping Radiation

This project involves making measurements of contaminated areas using portable radiation detectors and small robots. Tasks involve operating detectors and small robots, combining data acquisition for the two systems, and automating the systems. The end result is a radiation map of contamination areas. Localization of radioactive sources and mapping of contamination distribution is essential when responding to emergencies, or when dealing with cleanup efforts. Radiation maps are used for situational awareness and for establishing a safe perimeter. However, it may be hazardous or impossible for humans to safely enter the site and survey the area. Informative Path Planning (IPP) is used to design a path for a robotic sensor platform to gather the most information about the radiation distribution while operating under the set of constraints given by the dynamics of the robot and other requirements such as minimizing the overall mission time. The key challenge for IPP is the tight coupling in multiple layers of decisions: Selection of locations to visit; Allocation of sensors to those locations; Processing of information gathered. Given a robot equipped with a basic gamma detector and Lidar sensor, how can we efficiently explore an unknown environment in such a way that we can satisfy the robot's constraints while simultaneously maximizing the accuracy of the map and minimizing the total runtime? This work presents a systematic procedure for IPP and environmental mapping that: Selects the best locations at which to sample; Finds the best path for robots; Estimates the measurement value at unknown locations using a Gaussian Process regression framework. Given a set of points where radiation measurements were taken, we are utilizing a Gaussian Process Regression with a Matern kernel to reconstruct the shape of the underlying ground truth. Mapping is done via the Robot Operating System's OpenSlam Gmapping package, which creates a 2D occupancy grid map. Simulated trials were run with a radiation source placed at random locations, and allowing the robot to select and move towards 20 samples at separate locations, as well as sampling along the path while moving. The simulated sensor model assumed an efficiency of 0.3, collection time of 1 second. Various weighting schemes were tested and compared. Quantitative evaluations often favored exploitation-heavy weighting schemes where μ was emphasized, with the Root Mean Squared Error (RMSE) quickly tending towards 2, whereas qualitative comparisons would favor exploration-biased schemes with greater weight on σ. The difference comes from operators often favoring knowing the general location of a source, rather than the exact properties of a source. Weighting of the path-length π often reduced the quality of the regression as less exploration occurred, however this may be deemed a worthwhile trade-off under certain circumstances, such as with sensitive robots. Successfully developed a methodology for informative path-planning for a robot to efficiently gather information and create a map of radiation. In the future, we would like to focus on: Hardware trials with integration of the robot platform and the IPP software; More refined sensor and environmental modeling; Multiple robot platforms.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗