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All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Anisotropic Optical-Response of Eu-doped Yttrium Orthosilicate

Eu-doped yttrium orthosilicate (Eu(3+) : Y2SiO5) had been a subject being investigated for coherent time-domain optical memory and information processing applications since its ultraslow optical dephasing was discovered several years ago. In this crystal the weakly allowed (7)F0 - (5)D0 transition of europium ions exhibits a sufficient long dephasing time and no spectral difli.usion on a time scale of several hours at low temperature, thus an information pattern or data can be stored as a population grating in the ground state hyperfine levels. On the other hand, the study on photon-echo relaxation shows that the dephasing time T2 of Eu (3+) and other rare-earth ions doped YAG, YAlO3 strongly depends on the intensity of the excitation pulses. In Eu (3+) :YAlO3, an exponential decay of photon-echo with T2 = 53 microseconds if the excitation pulses are weak (5 vJ/pulse) was observed. However, when the excitation pulses are strong (80 pJ/pulse) they observed a much shortened T2 with a highly nonexponential decay pattern. The conclusion they derived is that the intensity-dependent dephasing rate effects are quite general, and it depends on how much the excitation intensity varies. In this paper we use transient grating formation technique showing that a temporal lattice distortion may only occur along crystal c axis, caused by EU (3+) excitation. At high excitation level the produced exciton in conduction band may also couple to the dynamical lattice relaxation process, giving rise to an apparently much shortened dephasing time.

Liu, Huimin↗
NASA NTRS1992

Characteristics of hard X-ray spectra of impulsive solar flares

The typical characteristics of the hard X-ray emission of impulsive solar flares are examined. At times of hard X-ray peaks, spectra that break downward are the rule rather than the exception. The break energy is typically at about 100 keV and rarely exceed 150 keV. There is little or no dependence of spectral slopes or of the break energy on the hard X-ray fluxes. During the burst decay phases, there is a strong tendency for the spectra to evolve to either a single power law or to cross over to one that breaks upward. The break energy is usually lower after the crossover, but in about 30 percent of the cases it is higher. During the rise phase of many fast bursts, the rise in flux at high energies occurs later than that at lower energies. In most cases the high-energy flux catches up by the time of the burst peak and the lag is rarely or never observed in bursts whose rise time is more than about 10 s.

Dulk, G. A.↗
NASA NTRS1997

Optical Characterization and 2,525 micron Lasing of Cr(2+):Cd(0.85)Mn(0.15)Te

Transition metal doped solids are of significant current interest for the development of tunable solid-state lasers for the near and mid-infrared (1-4 pm) spectral region. Applications of these lasers include basic research in atomic, molecular, and solid-state physics, optical communication, medicine, and environmental studies of the atmosphere. In transition metal based laser materials, absorption and emission of light arises from electronic transitions between crystal field split energy levels of 3d transition metal ions. The optical spectra generally exhibit broad bands due to the strong interaction between dopant and host (electron-phonon coupling). Broad emission bands offer the prospect of tunable laser activity over a wide wavelength range, e.g. the tuning range of Ti:Sapphire extends from 700-1100 run. The only current transition metal laser operating in the mid-infrared wavelength region (1.8-2.4 micro-m) is CO(2+):MgF2, but its performance is severely limited due to strong nonradiative decay at room temperature. Based on lifetime data, the quantum efficiency is estimated to be less than 3 deg/0 11,21. In general, the probability for non-radiative decay via multi-phonon relaxation increases with decreasing energy gap between ground and excited state. Therefore, efficient transition metal lasers beyond -1.6 micro-m are rare. Recently, tunable laser activity around 2.3 micro-m was observed from Cr doped ZnS and ZnSe. The new lasing center in these materials was identified as Cr(2+) occupying the tetrahedral Zn site. Tetrahedrally coordinated optical centers are rather unusual among transition metal lasers. Their potential usefulness, however, has been demonstrated by the recent development of near infrared laser materials such as Cr:forsterite and Cr:YAG, which are based on tetrahedrally coordinated Cr(4+) ions. According to the Laporte selection rule, electric-dipole transition within the optically active 3d-electron shells are parity forbidden. However, a static acentric electric crystal field or the coupling of asymmetric phonons can force electric-dipole transitions by the admixture of wave functions with opposite parity. Tetrahedral sites lack inversion symmetry which provides the odd-parity field necessary to relax the parity selection rule. Therefore, high absorption and emission cross sections are observed. An enhanced radiative emission rate is also expected to reduce the detrimental effect of non-radiative decay. Motivated by the initial results on Cr doped ZnS and ZnSe, we have started a comprehensive effort to study Cr(2+) doped II-VI semiconductors for solid-state laser applications. In this paper we present the optical properties and the demonstration of mid-infrared lasing from Cr doped Cd(0.85)Mn(0.15)Te.

Davis, V. R.↗
NASA NTRS1974

Nuclear composition of solar cosmic rays

Experimental observations of the elemental and isotopic composition of solar flare particles are discussed. Sources and characteristics of particle-emitting solar flare events are reviewed, and techniques for separating particle species are briefly described. Data are presented for the elemental composition of the solar atmosphere, and the possibility of determining the solar helium abundance from solar cosmic-ray observations is explored. The main experimental determinations of heavy element abundances at energies greater and less than 10 MeV/nucleon are summarized, and techniques for measuring the ionic charge composition of solar cosmic rays are outlined. Models explaining heavy element enhancements are described along with processes leading to gamma-ray emission during solar flare events. Observations of the rare isotopes of hydrogen and helium during solar flare events are noted, and a lower atmospheric limit is derived for nuclear reactions leading to positron decay. The possibility of investigating low-energy solar cosmic rays by measuring the relative abundances of different elements is evaluated.

Hovestadt, D.↗
NASA NTRS1994

He, Xe and Ne isotopes in a steady-state mass transport model and implications about terrestrial volatiles

We present a model of the steady-state transport assuming three reservoirs: a lower mantle (P) with a relatively undepleted inventory of U, Th, Pu, I, He, Ne, Xe, Ar; an upper mantle that has been extensively outgassed (D); and the atmosphere. There is mass transport at a rate M(sub PD) by plumes from the lower mantle, a fraction of which is outgassed directly into the atmosphere, while the remainder feeds matter and associated nuclei into D. D is well outgassed at spreading centers and has material containing atmospheric gases added to it by subduction. In the case of He, there is no subduction component. The approach follows the treatment of Kellogg and Wasserburg. A summary of the pertinent equations and constraints was reported earlier. The U, Th and Pu in P are estimated for Earth models from refractory element abundances in meteorites. In this model the inventory of rare gases in D is governed by the simple mixing of components from P (both radiogenic and original) with distinctive atmospheric components. In addition, alpha decay and spontaneous fission of U, and (alpha, n) reaction on oxygen from energetic alpha particles produce radiogenic/nuclear daughter products in D. These include (4)He, (136)Xe and (21)Ne. (40)K in D generates excess radiogenic (40)Ar.

Wasserburg, G. J.↗
NASA NTRSDate not supplied

Temperature Sensing to Above 1500 °C Using Y 2 SiO 5 :Er Phosphor Thermometry

A transition from metallic to ceramic turbine components that can operate at higher turbine engine temperatures will push component surface temperatures from below 1200 °C into a 1300 to 1500 °C temperature range that is much more challenging for phosphor thermometry measurements. To address this challenge, Y 2 SiO 5 :Er was selected for its high temperature sensing performance by both luminescence lifetime and luminescence intensity ratio (LIR) methods as well as its thermochemical compatibility with the current generation of rare earth silicate environmental barrier coatings (EBCs) that are required to protect SiC/SiC ceramic composite components. Lifetime measurements that monitor the Er3+ 4S3/2→4I15/2 emission decay at 542 nm exhibited a slow decrease in decay time with temperature up to 1300° C, above which the decay decreased steeply to provide good temperature sensitivity in the 1300 to 1500 °C range (Fig. 1). LIR images were obtained where each pixel represented the ratio I488/I561 (I488 and I561 are the detected 488 nm 4F7/2→4I15/2 and the 561 nm 4S3/2→4I15/2 emission band intensities, respectively). Good temperature sensitivity (Fig. 2) and signal-to-background ratios were observed to above 1500 °C. Contrary to conventional guidance on selecting phosphors for high temperature sensing, the detected emission band intensities and decay times exhibited remarkably slow decreases with temperature up into the 1300 to 1500 °C range despite high phonon energies (>900 cm-1) that allow the energy gap between the 4S3/2 emitting reservoir level and the 4F9/2 level below it to be bridged by as few as three phonons. The benefits of utilizing a thermographic phosphor at very high temperatures that exhibits strong nonradiative multiphonon relaxation even at room temperature is explained by a competition between spontaneous and stimulated multiphonon emission, and the more temperature-sensitive decay time above 1300 °C is explained by a transition from high to low effective phonon energies.

temperature measurement↗
NASA NTRS1988

Shatter cones: Diagnostic impact signatures

Uniquely fractured target rocks known as shatter cones are associated with more than one half the world's 120 or so presently known impact structures. Shatter cones are a form of tensile rock failure in which a positive conical plug separates from a negative outer cup or mold and delicate ornaments radiating from an apex are preserved on surfaces of both portions. Although distinct, shatter cones are sometimes confused with other striated geologic features such as ventifacts, stylolites, cone-in-cone, slickensides, and artificial blast plumes. Complete cones or solitary cones are rare, occurrences are usually as swarms in thoroughly fractured rock. Shatter cones may form in a zone where an expanding shock wave propagating through a target decays to form an elastic wave. Near this transition zone, the expanding primary wave may strike a pebble or other inhomogeneity whose contrasting transmission properties produce a scattered secondary wave. Interference between primary and secondary scattered waves produce conical stress fields with axes perpendicular to the plane of an advancing shock front. This model supports mechanism capable of producing such shatter cone properties as orientation, apical clasts, lithic dependence, and shock pressure zonation. Although formational mechanics are still poorly understood, shatter cones have become the simplest geologic field criterion for recognizing astroblemes (ancient terrestrial impact structures).

Mchone, J. F.↗
NASA NTRS2003

Ar-39-Ar-40 Age Dating Of Two Angrites and Two Brachinites

Angrites are a rare group (approximately 7 known) of igneous meteorites with basalt-like composition, which probably derive from a relatively small parent body that differs from those of other igneous meteorites. Angrites show evidence for extinct Mn-53, Sm-146, and Pu-244, and precise U-Pb, and Pb-Pb ages of 4.558 Gyr for two angrites define the time of early parent body differentiation. The Sm-147-Nd-143 ages of two angrites range between 4.53 +/- 0.04 and 4.56 +/- 0.04 Gyr, but no Ar-39-Ar-40 or Rb-Sr ages have been reported. Most angrites show no evidence for either shock brecciation or metamorphism. Brachinites are another very rare group' of differentiated meteorites consisting primarily of olivine, with minor augite, chromite, Fe-sulfides, and sometimes plagioclase and opx. Presence of excess Xe-129 and excess Cr53 from decay of Mn-53 in some brachinites indicate that they also formed very early. Brachinite petrogenesis is poorly defined. They may be igneous cumulates or metamorphic products of chondritic-like starting material. If after their formation, angrites and brachinites cooled quickly with minimal subsequent heating, then one might expect them to show uniquely old K-Ar ages, at least in comparison to other differentiated meteorites such as eucrites and mesosiderites. Most angrites and brachinites contain very little, if any K-feldspar, which has deterred measurements of their Ar-Ar ages. We made Ar-39-Ar-40 analyses on two angrites, LEW86010 (metamorphosed) and D'Orbigny, and on two brachinites, EET99402 and Brachina. All are finds. Any feldspar in angrites is highly calcic, with expected K concentrations of <100 ppm. We selected LEW86010 and D'Orbigny because they have been the objects of several other studies and because chemical analyses suggested [K] was approximately 70 ppm in both meteorites. Brachina contains approximately 9.9% plagioclase of higher K-content than angrites, and EET99402 is estimated to contain approximately 5% K-poor plagioclase. Other brachinites contain little to no feldspar. We have successfully measured Ar-Ar ages on a few meteorites and lunar anorthosites with [K] <100 ppm.

Garrison, Daniel↗
NASA NTRS2013

Surface Temperature Measurements from a Stator Vane Doublet in a Turbine Engine Afterburner Flame using Ultra-Bright Cr-Doped GdAlO3 Thermographic Phosphor

Luminescence-based surface temperature measurements from an ultra-bright Cr-doped GdAlO3 perovskite (GAP:Cr) coating were successfully conducted on an air-film-cooled stator vane doublet exposed to the afterburner flame of a J85 test engine at University of Tennessee Space Institute (UTSI). The objective of the testing at UTSI was to demonstrate that reliable thermal barrier coating (TBC) surface temperatures based on luminescence decay of a thermographic phosphor could be obtained from the surface of an actual engine component in an aggressive afterburner flame environment and to address the challenges of a highly radiant background and high velocity gases. A high-pressure turbine vane doublet from a Honeywell TECH7000 turbine engine was coated with a standard electron-beam physical vapor deposited (EB-PVD) 200-m-thick TBC composed of yttria-stabilized zirconia (YSZ) onto which a 25-m-thick GAP:Cr thermographic phosphor layer was deposited by EB-PVD. The ultra-bright broadband luminescence from the GAP:Cr thermographic phosphor is shown to offer the advantage of over an order-of-magnitude greater emission intensity compared to rare-earth-doped phosphors in the engine test environment. This higher emission intensity was shown to be very desirable for overcoming the necessarily restricted probe light collection solid angle and for achieving high signal-to-background levels. Luminescence-decay-based surface temperature measurements varied from 500 to over 1000C depending on engine operating conditions and level of air film cooling.

Eldridge, Jeffrey I.↗
NASA NTRS1993

On possible Mn-53 heterogeneity in the early solar system

The effects of influence of shock wave propagation on the energy spectrum of accelerated particles that lead to different production rates of radionuclides, in particular, Mn-53, on small scales in the early solar system are shown. Search for evidence for extinct Mn-53 has stimulated investigations of Cr isotope anomalies in meteorites. The linear correlation between the magnitude of the Cr-53* excesses and the Mn/Cr ratio that unambiguously proves the in situ decay of Mn-53 was detected, really, in different mineral phases of some carbonaceous and enstatite chondrites, primitive achondrites, pallasites and iron meteorites. However, the data on the Cr-53* excess rarely defines a single linear array on a Mn-53-Cr-52 evolution diagram even for meteorites of the same chemical group. A clear isochron with Mn-53/Mn-55 = 4.4 plus or minus 1.0 x 10(exp -5) (in range of approximately 2.4 to approximately 9 x 10(exp -5)) is observed for CAI of the Allende C3-chondrite while the data for the Murchison C2- and Orgueil C1-chondrites fall much lower corresponding rather to Mn-53/Mn-55 less than 2 x 10(exp -5). In the case of iron meteorites it ranges from less than 5 x 10(exp -8) to less than 5 x 10(exp -5).

Lavrukhina, A. K.↗
NASA NTRS1977

Clues in the rare gas isotopes to early solar system history

The results of the radioactive dating and the discovery of gas-rich meteorites on the Moon surface are reviewed. Special attention is paid to the extinct radioactivity iodine-129. This radioactivity is produced by r-process of nucleosynthesis and it decays with a half-life of 17 m.y. It provides a clock sensitive to small changes in the early years of the solar system.

Reynolds, J. H.↗
NASA NTRS2008

Multi-wavelength Observations and Modelling of a Solar Flare

Aims: The aim of this work is to investigate the dynamic behavior of a C-class solar flare through the evolution of temperature, emission measure, energy loss and velocity. In particular, the variation of these properties with time are studied using multi-wavelength observations in combination with a recently developed 0-D hydrodynamic model. Methods: The temperature and emission measure evolution were studied using several instruments covering a wide range of temperatures - the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI, >5 MK), GOES-12 (5- 30 MK), the Transition Region and Coronal Explorer (TRACE 171 A, 1 MK) and the Coronal Diagnostic Spectrometer (CDS, 0.03-8 MK). The temperature and emission measure were analysed through the systematic cooling of flare plasma through the response functions of these instruments. These parameters were then investigated using the Enthalpy Based Thermal Evolution of Loops model (EBTEL). The Doppler shifts at both flare footpoints were analysed using five emission lines seen by CDS. Results: The flare began with clear evidence for pre-flare heating. Upflows of approx.90 km/s and low level emission, both observed in Fe XIX before the main impulsive phase were explained by pre-flare gentle chromospheric evaporation. During the main impulsive phase, the flare plasma was heated to a temperature of >13 MK in approximately 10 minutes. Explosive chromospheric evaporation was observed, driving upflows of approx.80 km/s in Fe XIX and simultaneous downflows of approx.20 km/s in He I and O v. At the peak of the Rare, conduction modelled by EBTEL was found to be the dominant loss mechanism, working efficiently to both lower the temperatures and drive gentle chromospheric evaporation. As the temperature fell below approx.8 MK, radiation became the dominant loss mechanism. During the final stages of the decay phase, downflowing plasma was observed at the footpoints in He I, O v and Mg x at velocities of up to approx.40 km/s, suggesting loop draining occurred. Conclusions. This is the first extensive study of the evolution of flare plasma using both spectroscopic and broad-band instruments in conjunction with a comprehensive hydrodynamic model. The flare began with pre-flare heating and then evolved following the predictions of the standard flare model. Detailed analysis of the plasma heating mechanisms was carried out and the heating function most consistent with observations was found to be Gaussian in shape. The simulations suggested that both direct heating and heating by a non-thermal beam played significant roles in this event.

Raftery, Claire L.↗
NASA NTRS1989

Ozone profile measurements of McMurdo Station, Antarctica, during the spring of 1987

Ozone and temperature profiles were measured in 50 balloon flights at McMurdo Station (78 deg S) during the spring of 1987. Compared to similar data obtained in 1986, stratospheric temperatures were lower and the spring time Antarctic ozone reduction was greater in magnitude, extended to higher altitude, and proceeded at a higher rate in 1987. Ozone partial pressures reached values as low as 3 nbar (as compared to about 10 nbar in 1986) in the 16- to 18-km region in early and late October, down from about 150 nbar in late August. These low values suggest essentially complete removal of ozone in this region. The upper boundary of the depletion region was observed to be 2-3 km higher than in 1986, extending to altitudes as high as 24 km in mid-September. When averaged over September, the ozone mixing ratio at 18 km decayed with a half-life of only 12.4 days, as compared to about 28 days in 1986. Adiabatic vertical motions over 1- to 2-km intervals between 12 and 20 km with consequent ozone reductions were observed in association with the formation of nacreous clouds, indicating these to be rare events on a local scale probably associated with mountain lee waves.

Hofmann, D. J.↗
NASA NTRS2003

High-Temperature Sprayable Phosphor Coating Developed for Measuring Surface Temperatures

The use of phosphor thermography for noncontact temperature measurements in harsh environments has been proven over the last decade, but it has suffered from difficult application procedures such as vapor deposition or sputtering techniques. We have developed a high-temperature-sensitive paint that is easily applied with commercially available paint-spraying equipment and have successfully demonstrated it to temperatures up to 1500 C. Selected phosphors have also shown measurable signals to 1700 C, thus allowing a combination of phosphors to be used in high-temperature binders to make surface temperature measurements from ambient to over 1500 C. Phosphor thermography is an optical technique that measures the time response of fluorescence light, which is a function of the phosphor temperature. The phosphors are excited with short wavelength light (ultraviolet or blue), and they emit light at a longer wavelength. This technique has a benefit over other temperature measurements, such as thermocouples and infrared thermography, in difficult environments such as high blackbody backgrounds, vibration, flames, high electromagnetic noise, or where special windows may be needed. In addition, the sprayable phosphor paints easily cover large or complicated structures, providing full-surface information with a single measurement. Oak Ridge National Laboratories developed and tested the high-temperature binders and phosphors under the direction of the NASA Glenn Research Center. Refractory materials doped with rare earth metals were selected for their performance at high temperature. Survivability, adhesion, and material compatibility tests were conducted at high temperatures in a small furnace while the fluorescent response from the phosphors was being measured. A painted sample in a furnace with a clearly visible fluorescing dot excited by a pulsed laser is shown. Measuring the decay time of this fluorescence yields the surface temperature. One new paint was recently tested in a rocket test stand at Glenn. The floor of a square duct nozzle was painted, and full-field lifetime decay measurements were acquired for multiple firings of the rocket. Good agreement with predicted results was obtained, matching temperature gradients along the length of the nozzle and clearly showing shock structures. These good results were very satisfactory given that the measurements were made looking through the combustion plume. Infrared pyrometry was incapable of making the surface measurements because of the interference from the rocket exhaust, which contaminated the infrared signature.

Bencic, Timothy J.↗
NASA NTRS1987

Microstructures in type III events in the solar wind

A model is presented for the generation and evolution of bump-in-tail driven Langmuir waves in the solar wind during type III emission which removes a number of apparent inconsistencies between theory and observations. Growth rates and energy densities of Langmuir waves are considerably enhanced, permitting growth to overcome linear scattering losses, and also allowing nonlinear decay into ion-acoustic waves, in line with observations. Estimates are made of the probability distribution p(E), of wave field strengths E, based on linear and nonlinear wave-packet evolution, yielding p(E) approximately equal to E exp -alpha, alpha greater than or equal to 3. This helps explain why very high values of E are rarely found in the measured spiky wave turbulence.

Melrose, D. B.↗
NASA NTRS1993

Dynamic of Langmuir and Ion-Sound Waves in Type 3 Solar Radio Sources

The evolution of Langmuir and ion-sound waves in type 3 sources is investigated, incorporating linear growth, linear damping, and nonlinear electrostatic decay. Improved estimates are obtained for the wavenumber range of growing waves and the nonlinear coupling coefficient for the decay process. The resulting prediction for the electrostatic decay threshold is consistent with the observed high-field cutoff in the Langmuir field distribution. It is shown that the conditions in the solar wind do not allow a steady state to be attained; rather, bursty linear and nonlinear interactions take place, consistent with the highly inhomogeneous and impulsive waves actually observed. Nonlinear growth is found to be fast enough to saturate the growth of the parent Langmuir waves in the available interaction time. The resulting levels of product Langmuir and ion-sound waves are estimated theoretically and shown to be consistent with in situ ISEE 3 observations of type 3 events at 1 AU. Nonlinear interactions slave the growth and decay of product sound waves to that of the product Langmuir waves. The resulting probability distribution of ion-sound field strengths is predicted to have a flat tail extending to a high-field cutoff. This prediction is consistent with statistics derived here from ISEE 3 observations. Agreement is also found between the frequencies of the observed waves and predictions for the product S waves. The competing processes of nonlinear wave collapse and quasilinear relaxation are discussed, and it is concluded that neither is responsible for the saturation of Langmuir growth. When wave and beam inhomogeneities are accounted for, arguments from quasi-linear relaxation yield an upper bound on the Langmuir fields that is too high to be relevant. Nor are the criteria for direct wave collapse of the beam-driven waves met, consistent with earlier simulation results that imply that this process is not responsible for saturation of the beam instability. Indeed, even if the highest observed Langmuir fields are assumed to he part of a long-wavelength 'condensate' produced via electrostatic decay, they still fall short of the relevant requirements for wave collapse. The most stringent requirement for collapse is that collapsing wave packets not be disrupted by ambient density fluctuations in the solar wind. Fields of several mV m(exp -1) extending over several hundred km would be needed to satisfy this requirement; at 1 AU such fields are rare at best.

Robinson, P. A.↗
NASA NTRS1996

Trace Element Zoning and Incipient Metamictization in a Lunar Zircon: Application of Three Microprobe Techniques

We have determined major (Si, Zr, Hf), minor (Al, Y, Fe, P), and trace element (Ca, Sc, Ti, Ba, REE, Th, U) concentrations and Raman spectra of a zoned, 200 microns zircon grain in lunar sample 14161,7069, a quartz monzodiorite breccia collected at the Apollo 14 site. Analyses were obtained on a thin section in situ with an ion microprobe, an electron microprobe, and a laser Raman microprobe. The zircon grain is optically zoned in birefringence, a reflection of variable (incomplete) metamictization resulting from zo- nation in U and Th concentrations. Variations in the concentrations of U and Th correlate strongly with those of other high-field-strength trace elements and with changes in Raman spectral parameters. Concentrations of U and Th range from 21 to 55 ppm and 6 to 31 ppm, respectively, and correlate with lower Raman peak intensities, wider Raman peaks, and shifted Si-O peak positions. Concentrations of heavy rare earth elements range over a factor of three to four and correlate with intensities of fluorescence peaks. Correlated variations in trace element concentrations reflect the original magmatic differentiation of the parental melt approx. 4 b.y. ago. Degradation of the zircon structure, as reflected by the observed Raman spectral parameters, has occurred in this sample over a range of alpha-decay event dose from approx. 5.2 x 10(exp 14) to 1.4 x 10(exp 15) decay events per milligram of zircon, as calculated from the U and Th concentrations. This dose is well below the approx. 10(exp 16) events per milligram cumulative dose that causes complete metamictization and indicates that laser Raman microprobe spectroscopy is an analytical technique that is very sensitive to the radiation-induced damage in zircon.

Wopenka, Brigitte↗
NASA NTRS1971

Inorganic photochromic and cathodochromic recording materials.

Discussion of studies at RCA Laboratories of the properties of rare-earth-doped CaF2, transition-metal-doped SrTiO3 and iron- or sulfur-doped sodalite as photochromic materials which change color during light or electron beam exposures. Particular attention is given to their photochromic characteristics in single-crystal and powder forms and to their cathodochromic properties in powder form. Details are given on the photochromic mechanisms, spectra, optical density, thermal decay rates, and coloring and bleaching efficiency of their single crystals and on the diffuse reflectance spectra, saturated photochromic contrast ratio, switching and erase sensitivities, and cathodochromic excitation of their photochromic powders. The many attractive characteristics of these materials when used in display storage systems are indicated.

Duncan, R. C., Jr.↗