Search NASA⌕ Search

SEARCH · Search NASA

Results for “Gamma Irradiations”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1971

Composite seals for liquid hydrogen and nuclear radiation environments.

Description of plastic composite seals for service in a liquid-hydrogen and nuclear-radiation environment. The radiation-resistant aromatic heterocyclic class of polymers, including polyimide, polybenzimidazole, and polyquinoxaline, were evaluated for this application. The seal developed is based on a design involving a resin-starved laminate consisting of alternating layers of woven glass fabric and polymer film. This design imparts a mechanical spring characteristic to the seal, resulting in essentially complete elastic recovery when unloaded, and eliminates cold flow. Encapsulating techniques employing the polyquinoxaline polymer were developed which rendered the seal impervious to liquid hydrogen. The seals were tested before and after gamma irradiation up to 10 to the 10th ergs/g. Load/deflection and leakage tests were performed over a temperature range from -423 through +500 F.

Van Auken, R. L.↗
NASA NTRS1971

Impurity color centers in quartz and trapped electron dating - Electron spin resonance, thermoluminescence studies.

Investigation of impurity-related electron-hole traps that are known to be sensitive to ionizing radiations. Electron spin resonance (ESR) equivalent natural doses were determined for the Al hole trap in virgin specimens; the doses agreed with estimates based on published data for the Ge electron trap. The 0.17 deg/sec 180 and 300 C thermoluminescence (TL) peaks in natural specimens were found to have activation energies approximately correct for the Ge trap. The 300 C peak was also found to be correlated with annealing of the Ge electron resonance in gamma-irradiated, step-annealed specimens. Although the 300 C peak occurs in virgin specimens, the corresponding natural Ge electron resonance was not observed.

Mcmorris, D. W.↗
NASA NTRS1974

A study of immunological reactions in dogs exposed to prolonged chronic radiation

Immunomorphological studies on dog tissues exposed to long term gamma irradiation show that the number of cells containing antibodies increased and that the blast transformation reaction was activated. Prolonged radiation did not cause a reliable change in the synthesis of nucleic acids in spleen cells.

Konstantinova, I. V.↗
NASA NTRS1976

Functional polymeric microspheres based on 2-hydroxyethyl methacrylate for immunochemical studies

Co gamma irradiation of 2-hydroxyethyl methacrylate in the presence or in the absence of other acrylic monomers was found to constitute an effective technique for the synthesis of hydrophilic functional microspheres in the size range of approximately 0.3 to 3 microns in diameter. The effect of monomer concentration, steric stabilization, and electrostatic interaction on the particle size was investigated. Experimental conditions were determined to obtain desired particle sizes of relatively narrow distribution. It was shown that particles may be formed without intermediate micelles, i.e., by homogeneous nucleation, and the rate of particle formation is affected primarily by the rate of particle coalescence in the initial stages of the reaction. When covalently bound to antibodies these microspheres were successfully used to label murine and human lymphocytes.

Rembaum, A.↗
NASA NTRS1979

Determination of physical and chemical states of lubricants in concentrated contacts, part 1

A Fourier emission infrared microspectrometer, set up on a vibration-proof optical table and interfaced to a dedicated minicomputer, was used to record infrared emission spectra from elastohydrodynamic bearing contacts. Its range was extended to cover the entire mid-infrared from 2 to 15 micron. A series of experiments with 5P4E polyphenyl ether showed the existence of a temperature gradient through the lubricant in an ehd contact, which is perpendicular to the flow direction. The experiments also show marked polarization of some of the spectral bands, indicating a molecular alignment. Alignment is less evident at high pressure than at low pressure. To account for this behavior, a model is suggested along the lines developed for the conformational changes observed in long-chain polymers when subjected to increased pressure--to accommodate closer packing, molecules become kinked and curl up. Experiments with a traction fluid showed periodic changes of flow pattern associated with certain spectral changes. These observations will be studied further. A study by infrared attenuated total reflection spectrophotometry was undertaken to determine whether gamma irradiation would change polyethylene wear specimens. The results were negative.

Lauer, J. L.↗
NASA NTRS1980

Change in radiosensitivity of rats during hypokinetic stress

The laws governing stress modification of radiation sickness in relation to hypokinetic stress were investigated. It was found that gamma irradiation (800 rad) of rats on the third day of exposure to hypokinesia increased the radiosensitivity of the animals which was determined by the survival rate and the dynamics of body weight and the weight of some internal organs. The same radiation dose was given on the 20th day of hypokinesia and on the third day of recovery from the 20 day hypokinesia decreased the radiosensitivity of rats. It is concluded that the variations in the radiosensitivity observed may be due to a stress effect of hypokinesia.

Chernov, I. P.↗
NASA NTRS1984

Room-temperature luminescence from kaolin induced by organic amines

Several new, room-temperature luminescent phenomena, resulting from the interaction of kaolin and various amino compounds, have been observed. The emission of light from kaolin pastes (treated with quinoline, pyridine, hydrazine, monoethanolamine, n-butylamine, and piperidine) was shown to decay monotonically over a period of hours to days. More light was released by a given amino compound after it was dried and purified. Hydrazine, in addition to the monotonically decaying photon release, produces delayed pulses of light with peak emission wavelength of 365 nm which last between several hours and several days. These photon bursts are acutely sensitive to the initial dryness of the hydrazine, both in the number of bursts and the integrated photon output. The amount of light and the capacity of the kaolin to produce the delayed burst appeared to be strongly dependent on preliminary heating and on gamma-irradiation, analogous to the dehydration-induced light pulse previously reported from the Ames Research Center. A small, delayed burst of photons occurred when piperidine and n-butylamine were removed by evaporation into an H2SO4 reservoir.

Coyne, L. M.↗
NASA NTRS1983

Luminescence induced by dehydration of kaolin - Association with electron-spin-active centers and with surface activity for dehydration-polymerization of glycine

Experimental data concerning emission of light upon dehydration as a function of preheating and pre-gamma-irradiation are correlated with reported studies of electron-spin resonance (ESR) activity after similar pretreatments. The effect of these pretreatments on the kaolin-promoted incorporation of glycine into peptide oligomers in a wet/cold, hot/dry fluctuating environment is compared to their effect on the ESR and luminescent signals. The existence of spectroscopically active centers appears to be loosely anticorrelated with reaction yield; these yields are increased by increasing the overall energy content of the material. It is concluded that some part of the chemical yield is produced by a mechanism involving intrinsic, excited electronic states of the clay crystal lattice. These states may be derived from thermally, interfacially, and/or mechanically induced charge reorganization within interspersed energy levels in the band structure of the material.

Coyne, L.↗
NASA NTRS1987

Neutron radiation tolerance of Au-activated silicon

Double injection devices prepared by the introduction of deep traps, using the Au activation method have been found to tolerate gamma irradiation into the Gigarad (Si) region without significant degradation of operating characteristics. Silicon double injection devices, using deep levels creacted by Au diffusion, can tolerate fast neutron irradiation up to 10 to the 15th n/sq cm. Significant parameter degradation occurs at 10 to the 16th n/sq cm. However, since the actual doping of the basic material begins to change as a result of the transmutation of silicon into phosphorus for neutron fluences greater than 10 to the 17th/sq cm, the radiation tolerance of these devices is approaching the limit possible for any device based on initially doped silicon.

Joyner, W. T.↗
NASA NTRS1991

Environmental test program for superconducting materials and devices

This report is divided into two parts. The first dealing with work involved with Clemson University and the second with the results from Westinghouse/Savannah River. Both areas of work involved low noise, low thermal conductivity superconducting grounding links used in the NASA-sponsored Spectroscopy of the Atmosphere using Far Infrared Emission (SAFIRE) Project. Clemson prepared the links from YBa2Cu3O(7-x) superconductor tape that was mounted on a printed circuit board and encapsulated with epoxy resin. The Clemson program includes temperature vs. resistance, liquid nitrogen immersion, water immersion, thermal cycling, humidity, and radiation testing. The evaluation of the links under a long term environmental test program is described. The Savannah River program includes gamma irradiation, vibration, and long-term evaluation. The progress made in these evaluations is discussed.

Haertling, Gene↗
NASA NTRS1991

Kaolinite-catalyzed air oxidation of hydrazine: Consideration of several compositional, structural and energetic factors in surface activation

Clay minerals have been shown to have numerous, curious, energetic properties by virtue of ultra-violet light release which can be triggered by gentle environmental changes such as wetting and dewetting by a variety of liquids, unique among them water and hydrazine. Since both water and hydrazine play multiple key roles in the air-oxidation of hydrazine on kaolinite surfaces, this reaction would seem to have prime potential for studying interrelationships of energy storage, release and chemical reactivity of clay surfaces, capacities basic to either the Bernal or Cairns-Smith roles of minerals in the origin of life. Establishment of the capacity for stored electronic energy to significantly alter surface chemistry is important, regardless of the reaction chosen to demonstrate it. Hydrazine air oxidation is overawingly complex, given the possibilities for step-wise control and monitoring of parameters. In the light of recently extended characterization of the kaolinite and model sheet catalysts we used to study hydrazine oxidation and gamma-irradiated silica, previous studies of hydrazine air-oxidation on aluminosilicate surfaces have been reevaluated. Our former conclusion remains intact that, whereas trace structural and surface contaminants do play some role in the catalysis of oxidation, they are not the only, nor even the dominant, catalytic centers. Initial intermediates in the oxidation can now be proposed which are consistent with production via O(-)-centers as well as ferric iron centers. The greater than square dependence of the initial reaction rate on the weight of the clay is discussed in the light of these various mechanistic possibilities.

Coyne, L. M.↗
NASA NTRS1992

Environmental testing of high Tc superconductive thermal isolators for space-borne cryogenic detector systems

Thick films of superconductive material on low thermal conductivity substrates (e.g., yttria-stabilized zirconia and fused silica) are considered as a replacement for the existing electrical connections between the detector array and data acquisition and storage electronics in the cryogenic detector systems being developed by NASA. The paper describes some of the design constraints on the superconducting device and presents results of a preliminary analysis of the effects of vibration, gamma irradiation, and long-term exposure to high vacuum and liquid nitrogen encountered in operating such a device in space.

Wise, Stephanie A.↗
NASA NTRS1993

Lifetime prediction of materials exposed to the natural space environment

The goal of this study is to model the lifetime of different types of seal materials based on results obtained from accelerated experiments. A semi-mechanistic approach was taken. Thermal aging data were taken from the literature whereas experiments were conducted at Auburn under this contract for selected environments. The seal materials of interest are Silicone 383, Silicone 650, Viton 835, and Viton 747. The relevant conditions include thermal, oxygen, inert gas, vacuum, and gamma radiation. Compression set data available from NASA were used to examine the thermal effect. Experiments were conducted at Auburn University and at NASA to isolate the role of thermal, oxygen, inert gas, vacuum, gamma irradiation, and proton irradiation. A simple discrete stress relaxation method was developed to determine the relaxation response of the elastomers. Dynamic mechanical thermal analysis was also used to characterize the mechanical response of the specimens. These provide a more meaningful correlation between mechanisms and degradation.

Zee, Ralph↗
NASA NTRS1998

Radiation Effects on Resonant Tunneling Diodes: Preliminary Results

We have observed enhanced bistability (hysteresis) in the current-voltage characteristics of gamma irradiated resonant tunneling diodes. This bistability occurs in the negative differential conductance region for voltages larger than 1.1 V. We discuss possible mechanisms for the observed phenomena and also discuss the measurements sensitivity to the external circuit.

Wilkins, R.↗
NASA NTRS2002

Cancer Risk-Assessment of Radiation Damage in Ataxia Telangiectasia Heterozygous Human Breast Epithelial Cell Cultures

This paper describes the study of the markers of cellular changes that are found during the onset of carcinogenesis. Several of the biological factors are markers of stress response, oncoprotein expression, and differentiation factors. Oxidative stress response agents such as heat shock proteins (HSPs) protect cells from oxidative stresses such as ionizing radiation. The onocoprotein HER-2/neu, a specific breast cancer marker, indicates early onset of cancer. Additional structural and morphogenetic markers of differentiation were considered in order to determine initial cellular changes at the initial onset of cancer. As an additional consideration, all-trans retinoic acid (RA), a differentiation agent, was considered because of its known role in regulating normal differentiation and inhibiting tumor proliferation via specific nuclear receptors. This paper discusses study and results of the preliminary analyses of gamma irradiation of AT heterozygous human breast epithelial cells (WH). Comparisons are also made of the effects various RA concentrations post-irradiation.

Lisa C. Applewhite↗
NASA NTRS1998

Estimate of true incomplete exchanges using fluorescence in situ hybridization with telomere probes

PURPOSE: To study the frequency of true incomplete exchanges in radiation-induced chromosome aberrations. MATERIALS AND METHODS: Human lymphocytes were exposed to 2 Gy and 5 Gy of gamma-rays. Chromosome aberrations were studied using the fluorescence in situ hybridization (FISH) technique with whole chromosome-specific probes, together with human telomere probes. Chromosomes 2 and 4 were chosen in the present study. RESULTS: The percentage of incomplete exchanges was 27% when telomere signals were not considered. After excluding false incomplete exchanges identified by the telomere signals, the percentage of incomplete exchanges decreased to 11%. Since telomere signals appear on about 82% of the telomeres, the percentage of true incomplete exchanges should be even lower and was estimated to be 3%. This percentage was similar for chromosomes 2 and 4 and for doses of both 2 Gy and 5 Gy. CONCLUSIONS: The percentage of true incomplete exchanges is significantly lower in gamma-irradiated human lymphocytes than the frequencies reported in the literature.

NASA Discipline Radiation Health↗
NASA NTRS1998

Radiation-induced total-deletion mutations in the human hprt gene: a biophysical model based on random walk interphase chromatin geometry

PURPOSE: To develop a biophysical model that explains the sizes of radiation-induced hprt deletions. METHODS: Key assumptions: (1) Deletions are produced by two DSB that are closer than an interaction distance at the time of DSB induction; (2) Interphase chromatin is modelled by a biphasic random walk distribution; and (3) Misrejoining of DSB from two separate tracks dominates at low-LET and misrejoining of DSB from a single track dominates at high-LET. RESULTS: The size spectra for radiation-induced total deletions of the hprt gene are calculated. Comparing with the results of Yamada and coworkers for gamma-irradiated human fibroblasts the study finds that an interaction distance of 0.75 microm will fit both the absolute frequency and the size spectrum of the total deletions. It is also shown that high-LET radiations produce, relatively, more total deletions of sizes below 0.5 Mb. The model predicts an essential gene to be located between 2 and 3 Mb from the hprt locus towards the centromere. Using the same assumptions and parameters as for evaluating mutation frequencies, a frequency of intra-arm chromosome deletions is calculated that is in agreement with experimental data. CONCLUSIONS: Radiation-induced total-deletion mutations of the human hprt gene and intrachange chromosome aberrations share a common mechanism for their induction.

NASA Center JSC↗