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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Evaluation of Exposure From a Low Energy X-Ray Device Using Thermoluminescent Dosimeters

The exposure from an electron beam welding device was evaluated using thermoluminescent dosimeters (TLDs). The device generated low energy X-rays which the current dose equivalent conversion algorithm was not designed to evaluate making it necessary to obtain additional information relating to TLD operation at the photon energies encountered with the device. This was accomplished by performing irradiations at the National Institute of Standards and Technology (NIST) using low energy X-ray techniques. The resulting data was used to determine TLD badge response for low energy X-rays and to establish the relationship between TLD element response and the dose equivalent at specific depths in tissue for these photon energies. The new energy/dose equivalent calibration data was used to calculate the shallow and eye dose equivalent of badges exposed to the device.

Edwards, David L.↗
NASA NTRS1994

p-MOSFET total dose dosimeter

A p-MOSFET total dose dosimeter where the gate voltage is proportional to the incident radiation dose. It is configured in an n-WELL of a p-BODY substrate. It is operated in the saturation region which is ensured by connecting the gate to the drain. The n-well is connected to zero bias. Current flow from source to drain, rather than from peripheral leakage, is ensured by configuring the device as an edgeless MOSFET where the source completely surrounds the drain. The drain junction is the only junction not connected to zero bias. The MOSFET is connected as part of the feedback loop of an operational amplifier. The operational amplifier holds the drain current fixed at a level which minimizes temperature dependence and also fixes the drain voltage. The sensitivity to radiation is made maximum by operating the MOSFET in the OFF state during radiation soak.

Buehler, Martin G.↗
NASA NTRS2007

A Radiation Dosimeter Concept for the Lunar Surface Environment

A novel silicon detector configuration for radiation dose measurements in an environment where solar energetic particles are of most concern is described. The dosimeter would also measure the dose from galactic cosmic rays. In the lunar environment a large range in particle flux and ionization density must be measured and converted to dose equivalent. This could be accomplished with a thick (e.g. 2mm) silicon detector segmented into cubic volume elements "voxels" followed by a second, thin monolithic silicon detector. The electronics needed to implement this detector concept include analog signal processors (ASIC) and a field programmable gate array (FPGA) for data accumulation and conversion to linear energy transfer (LET) spectra and to dose-equivalent (Sievert). Currently available commercial ASIC's and FPGA's are suitable for implementing the analog and digital systems.

Adams, James H.↗
NASA NTRS2008

An Analytical Model for the Prediction of a Micro-Dosimeter Response Function

A rapid analytical procedure for the prediction of a micro-dosimeter response function in low Earth orbit (LEO), correlated with the Space Transportation System (STS, shuttle) Tissue Equivalent Proportional Counter (TEPC) measurements is presented. The analytical model takes into consideration the energy loss straggling and chord length distribution of the detector, and is capable of predicting energy deposition fluctuations in a cylindrical micro-volume of arbitrary aspect ratio (height/diameter) by incoming ions through both direct and indirect (ray) events. At any designated (ray traced) target point within the vehicle, the model accepts the differential flux spectrum of Galactic Cosmic Rays (GCR) and/or trapped protons at LEO as input. On a desktop PC, the response function of TEPC for each ion in the GCR/trapped field is computed at the average rate of 30 seconds/ion. The ionizing radiation environment at LEO is represented by O'Neill fs GCR model (2004), covering charged particles in the 1 less than or equal to Z less than or equal to 28. O'Neill's free space GCR model is coupled with the Langley Research Center (LaRC) angular dependent geomagnetic cutoff model to compute the transmission coefficient in LEO. The trapped proton environment is represented by a LaRC developed time dependent procedure which couples the AP8MIN/AP8MAX, Deep River Neutron Monitor (DRNM) and F10.7 solar radio frequency measurements. The albedo neutron environment is represented by the extrapolation of the Atmospheric Ionizing Radiation (AIR) measurements. The charged particle transport calculations correlated with STS 51 and 114 flights are accomplished by using the most recent version (2005) of the LaRC deterministic High charge (Z) and Energy TRaNsport (HZETRN) code. We present the correlations between the TEPC model predictions (response function) and TEPC measured differential/integral spectra in the lineal energy (y) domain for both GCR and trapped protons, with the conclusion that the model correctly accounts for the increase in flux at low y values where energetic ions are the primary contributor. We further discuss that, even with the incorporation of angular dependency in the cutoffs, comparison of the GCR differential/integral flux between STS 51 and 114 TEPC measured data and current calculations indicates that there still exists an underestimation by the simulations at low to mid range y values. This underestimation is partly related the exclusion of the secondary pion particle production from the current version of HZETRN.

Badavi, Francis F.↗
NASA NTRSDate not supplied

Galactic Cosmic Radiation (GCR) Measurements Made by M-42 Active Dosimeters on NASA Balloon Flights (New Mexico & Antarctica) Resemble Levels Expected at Mars

Mimicking galactic cosmic radiation (GCR) is difficult with ground-based simulations and experimental results are limited by facility constraints. In the past year, we flew two consecutive missions on large NASA scientific balloons (to ~ 38 km altitude) launched from New Mexico (6.5-hr flight) and Antarctica (32-d flight) and will report GCR doses comparable to levels expected at the equatorial Mars surface. Measurements were made in collaboration with the DLR and utilizing the M-42 active radiation dosimeter developed for use on Artemis 1. The M-42 instrument stores data in flash memory, records charged particles over a substantial part of the trapped proton and the GCR LET spectrum, and can be easily integrated into payloads due to its compact size (182 x 44 x 22 mm; 237 g) and internal battery (up to 6 weeks of operation). Our presentation will provide an overview of the two recent balloon missions (payload description; flight profiles), and summarize the radiation data collected in the middle stratosphere, highlighting how robust, real GCR exposures can be achieved without needing to fly orbital or deep space experiments.

radiation↗
NASA NTRS1995

Multi-Shielded p-FET Dosimeter

A compact device was developed for dose measurements where each of four p-FETs has a different shield. Radiation data from the STRV-1b shows that p-FETs can be used to map the radiation inside a spacecraft.

p-FET dosimeters↗
NASA NTRS1969

Tungsten thermal neutron dosimeter

Tungsten-185 activity, which is produced by neutron activation of tungsten-184, determines thermal neutron flux. Radiochemical separation methods and counting techniques for irradiated tungsten provide accurate determination of the radiation exposure.

Ball, L. L.↗
NASA NTRS1976

Development of a dosimeter for distributed body organs

Calculational methods for estimation of dose from external proton exposure of aribtrary convex bodies is briefly reviewed and all of the necessary information for the estimation of dose in soft tissue is presented. Special emphasis is on retaining the effects of nuclear reaction especially in relation to the dose equivalent.

Khandelwal, G. S.↗
NASA NTRS1981

Delayed darkening of radiation-exposed radiochromic dye dosimeters

Experiments have verified the existence of considerable delayed darkening in FWT-60 dosimetry films that may, depending on relative humidity, last for several hours. The amount of delayed darkening depends very strongly on the relative humidity at which the films are equilibrated before irradiation. It is pointed out that the delayed darkening effect must be taken into account before any meaningful dosimetric measurements may be made using these nylon-based thin dosimetry films. The particular radiation-sensitive compound used in the FWT-60 films is the hexahydrosyethyl pararosanaline cyanide with the Dupont nylon resin, Elvamide 8061, which forms the host matrix of a solid-state solution.

Danchenko, V.↗
NASA NTRS1994

Advanced p-MOSFET Ionizing-Radiation Dosimeter

Circuit measures total dose of ionizing radiation in terms of shift in threshold gate voltage of doped-channel metal oxide/semiconductor field-effect transistor (p-MOSFET). Drain current set at temperature-independent point to increase accuracy in determination of radiation dose.

Buehler, Martin G.↗
NASA NTRS1996

Solid State Radiation Dosimeters for Space and Medical Applications

This report describes the development of two radiation monitors (RADMON's) for use in detecting total radiation dose and high-energy particles. These radiation detectors are chip-size devices fabricated in 1.2 micrometer CMOS and have flown in space on both experimental and commercial spacecraft. They have been used to characterize protons and electrons in the Earth's radiation belts, particles from the Sun, and protons used for medical therapy. Having proven useful in a variety of applications, the detector is now being readied for commercialization.

Buehler, Martin G.↗
NASA NTRS1998

Analysis of the pre-flight and post-flight calibration procedures performed on the Liulin space radiation dosimeter

Liulin, a dosimetry-radiometry system, was developed to satisfy the requirements for active flux and dose rate measurements for the flight of the second Bulgarian cosmonaut in 1988. The system consists of a compact battery-operated silicon solid state detector unit and a read/write microcomputer and telemetry unit. We describe the pre-flight calibrations with charged particles, using radioactive sources and accelerated 170 MeV/nucleon proton and alpha particles at the Dubna, Russia cyclotron. We discuss comparisons with data obtained on Mir with the French-built tissue equivalent LET spectrometer NAUSICAA. Lastly, we describe post-flight calibrations performed with 1 GeV/nucleon 56Fe ions at the Brookhaven National Laboratory AGS accelerator, where the instrument was mounted in tandem with several thin position-sensitive silicon detectors behind a stopping target. The silicon detectors provided an energy spectrum for the surviving charged nuclear fragments for which the flux and absorbed dose were recorded by Liulin.

long duration↗