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NASA NTRS1978

Gravitational and radiative effects on the escape of helium from the moon

On the moon, and probably on Mercury and other similar regolith-covered bodies with tenuous atmosphere, the dominant gas is He-4. It arises as the radiogenic product of the decay of uranium and thorium within any planet, but its major source appears to be the alpha particle flux of the solar wind. The moon intercepts solar wind helium at an average rate of 1.1 times 10 to the 24th atom/sec, and loses it at the same rate. Some helium may escape directly as the result of the process of solar wind soil bombardment which may release previously trapped helium at superthermal speeds. Atmospheric models have been calculated with the total helium influx as source. Subsequent comparison of model and measured helium concentrations indicates that the fraction of helium escaping via the atmosphere may range from 20% to 100% of the solar wind influx. Of the escaping atmosphere, most of the helium (about 93%) becomes trapped in earth orbit, while about 5% gets trapped in satellite orbits about the moon. Owing to a 6 month lifetime for helium in solar radiation, the satellite atoms form a lunar corona that exceeds the lunar atmosphere in total abundance by a factor of 4 to 5.

Hodges, R. R., Jr.↗

NASA NTRS1988

Active region coronal loops - Structural and variability

X-ray images of a pair of active region loops are studied which show significant, short time-scale variability in the line fluxes of O VIII, Ne IX, and Mg XI and in the 3.5-11.5 keV soft X-ray bands. Vector magnetograms and high-resolution UV images were used to model the three-dimensional characteristics of the loops. X-ray light curves were generated spanning four consecutive orbits for both loops individually, and light curves of the loop tops and brightest points were also generated. The largest variations involve flux changes of up to several hundred percent on time scales of 10 minutes. No significant H-alpha flare activity is reported, and loop temperatures remain in the four to six million K range. The decay phases of the light curves indicate radiative cooling, inhibition of conduction, and some type of 'continued heating' due to ongoing, underlying activity at the microflare level.

Haisch, Bernhard M.↗

NASA NTRS1992

He I absorption by Lyman-alpha clouds and low-redshift Lyman-alpha clouds

Sources and sinks of radiation are used to model the evolution of the metagalactic ionizing background radiation field. It is shown that, if the comoving number density of quasars approached constancy at high redshift, as suggested by some recent observations, the observed ionizing background might possibly have been produced by the observed quasars alone. Consideration is also given to the UV radiation from decaying neutrons proposed by Sciama (1990), as an extra possible source. If is found that, if the background spectrum were as soft as in the Sciama scenario, the observed Ly-alpha clouds would contain detectable amounts of neutral helium, producing an 'He I forest' almost as dense as the hydrogen forest, due to the 584-A transition 1s-squared-1s2p. It is argued that observations of the Ly-alpha forest contradict the Sciama hypothesis.

Miralda-Escude, Jordi↗

NASA NTRS2012

A Correlation Between Intrinsic Brightness and Average Decay Rate of Swift UVOT GRB Optical/UV Light Curves

We examine a sample of 48 Swift/UVOT long Gamma-ray Burst light curves and find a correlation between the logarithmic luminosity at 200s and average decay rate determined from 200s onwards, with a Spearman rank coefficient of -0.58 at a significance of 99.998% (4.2 sigma ). We discuss the causes of the log L200s - alpha (greater than) 200s correlation, finding it to be an intrinsic property of long GRBs, and not resulting from the selection criteria. We find two ways to produce the correlation. One possibility is that there is some property of the central engine, outflow or external medium that affects the rate of energy release so that the bright afterglows release their energy more quickly and decay faster than the fainter afterglows. Alternatively, the correlation may be produced by variation of the observers viewing angle, with observers at large viewing angles observing fainter and slower decaying light curves.

Oates, S. R.↗

NASA NTRS1975

Slow X-ray bursts and chromospheric flares with filament disruption

The data from OGO-5 and OSO-7 X-ray experiments have been analyzed to study six chromospheric flares with filament disruption associated with slow thermal X-ray bursts. Filament activation accompanied by a slight X-ray enhancement precedes the first evidence of H alpha flare by a few minutes. Rapid increase of the soft X-ray flux is accompanied by a sudden brightening of the filament when viewed on-band H alpha. Thereafter the bright chromospheric strands reach their maximum brightness with maximum X-ray flux. Any plateau or slow decay phase in the X-ray flux is accompanied by a quieting in filament activity and even by filament re-appearance. The height of the disrupted prominence is proportional to the soft X-ray flux for the August 3, 1970 limb occulted event.

Roy, J. R.↗

NASA NTRS1985

Magnetic shear. II - Hale region 17244

A B-gamma(delta) sunspot group with growing delta-spots of trailing polarity shows evidence in H-alpha filament structure of a transition from a state of weak magnetic shear to a state of strong shear. The shear develops in the chromosphere and transition region to the corona overlying the photospheric magnetic neutral line separating the delta-spots from the leading polarity at a time when the delta-spots are undergoing rapid growth. Several major flares occur along the sheared portion of the neutral line following the shear development. Other segments of the neutral line far removed from the delta-spots show similar evidence of shear in the H-alpha filament structure and in C IV velocity patterns as well. These 'quiescent' regions of shear are relatively steady or decaying with time and show very little related activity.

Athay, R. G.↗

DOE OSTI2024

Demonstrating the β-Ga 2 O 3 Schottky diodes for alpha radiation detection

Schottky barrier diodes were fabricated on (001) monoclinic β-Ga 2 O 3 wafers with low doped epitaxial layers of 7.0 × 10 15 cm −3 . Circular Ni Schottky contacts with area 2 mm 2 were deposited by electron beam evaporation. Devices were characterized electrically by performing forward and reverse current-voltage sweeps with a range of −100 V–2 V, as well as capacitance-voltage sweeps to −30 V. The breakdown voltage was also determined to be −180 V for the devices. Experiments measuring the electrical response from incident X-ray radiation was performed. A response time to X-ray radiation of less than 1 s was recorded and a decay time of approximately 2 s after removing X-ray source, which primarily attribute to X-ray switching on and off time. Energy spectra of alpha particles from a 0.9 μCi 241 Am button source was collected at various voltage biases using devices with the lowest measured leakage current while reverse biased. The total count rate was observed to increase linearly with increasing device bias. In conclusion, the peak channel number was observed to increase with increasing bias with the best resolution of 9.5% at −100 V reverse bias.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

NASA NTRS1971

Study of energetic solar particle events of 18 November 1968, 25 February 1969, and 30 March 1969

The solar particle events of 18 November 1968, 25 February 1969, and 30 March 1969 were studied using data from the detector system aboard the lunar orbiting satellite Explorer 35. Protons, alpha particles, and Z or = 3 nuclei were registered in the solid state detector of the system. Interplanetary propagation, particle anisotropy, and the intensity ratios of protons to alpha particles and of alpha particles to C, N, and O nuclei above a common specific energy of 0.5 MeV/nucleon were studied. Diffusion coefficients and decay constants for the three events are given, as well as magnitudes and directions of anisotropies.

Venkatarangan, P.↗

NASA NTRS1984

IUE observations of Centaurus X-4 during the 1979 May outburst

Ultraviolet spectrophotometry of the X-ray transient/burst source Centaurus X-4 at several intervals during the peak and decay of the May 1979 X-ray transient event was obtained. The spectrum was characterized by a blue continuum with alpha = 0.0 + or - 0.3 (F/nu/ varies as nu to the alpha power) and strong emission lines of N V lambda 1240, C IV lambda 1550, and Si IV lambda 1398. The relative intensities of the emission lines and the ratio of line to continuum strengths remained nearly constant during the decline. The emission lines may have arisen from a 'disk chromosphere', from X-ray heating of the K4 V companion star, or both. The ultraviolet data are combined with previously published optical and X-ray data to determine some of the physical characteristics of the system and to show that X-ray reprocessing plays an important role in producing the optical and ultraviolet continua.

Blair, W. P.↗

NASA NTRS1973

Time variations of magnetospheric intensities of outer zone protons, alpha particles and ions (Z greater than or equal to 2)

A comprehensive study of the temporal behavior of trapped protons, alpha particles and ions (Z 2) in outer zone of the earth's magnetosphere has been made. These observations were made by the Injun V satellite during the first 21 months of operation, August 1968 to May 1970. Rapid increases in the observed number of particles followed by slower exponential decay characterize the data. Comparisons are made with the temporal behavior of interplanetary particles of the same energy observed by Explorer 35. Increases in the trapped fluxes generally correspond to enhanced interplanetary activity. The energy spectra of protons and alpha particles at L = 3 have similar shapes when compared on an energy per charge basis while the respective polar cap spectra have similar shape on an energy per nucleon basis. Apparent inward trans-L motion of energetic protons is observed. These particles are diffused inward by a process involving fluctuating electric fields. The loss of trapped low altitude protons, alpha particles and ions (Z 2) is controlled by coulombic energy loss in the atmosphere.

Randall, B. A.↗

NASA NTRS1978

Proton-associated alpha-irradiation in the early solar system - A possible K-41 anomaly

It is shown that alpha-particle fluences associated with proton fluences sufficiently high to produce the Al-correlated excess of Mg-26 found in the Allende meteorite produce equally significant amounts of Ca-41. The Ca-41 is produced by Ar-38(alpha,n)Ca-41 reactions occurring in the gas and condenses into the Ca-Al-rich grains forming at that time. After the decay of Ca-41, these grains will have a Ca-correlated excess of K-41. The question is considered whether the proposed scheme is capable of producing an observable excess of K-41. A calculation is conducted of the magnitude of the K-41 excess expected to be found in Ca-Al-rich grains for various ratios of Ca/K by developing an irradiation-condensation model. It is shown that on the basis of the currently available data it is not possible to come to firm conclusions regarding the validity of the irradiation model.

Dwek, E.↗

NASA NTRS1989

Approximate formulation of redistribution in the Ly-alpha, Ly-beta, H-alpha system

Simple approximate formulas are given for the coupled redistribution of Ly-alpha, Ly-beta, and H-alpha, by using well-defined approximations to an essentially exact formulation. These formulas incorporate all the essential physics including Raman scattering, lower state radiative decay, and correlated terms representing emission during a collision which must be retained in order that the emission coefficients are properly behaved in the line wings. Approximate expressions for the appropriate line broadening parameters are collected. Finally, practical expressions for the source functions are given. These are formulated through newly introduced nonimpact redistribution functions, which are shown to be reasonably approximated by existing (ordinary and generalized) redistribution functions.

Cooper, J.↗

NASA NTRS1971

Tritium trick

Large controlled amounts of helium in uniform concentration in thick samples can be obtained through the radioactive decay of dissolved tritium gas to He3. The term, tritium trick, applies to the case when helium, added by this method, is used to simulate (n,alpha) production of helium in simulated hard flux radiation damage studies.

Green, W. V.↗

NASA NTRS1975

Slow X-ray bursts and flares with filament disruption

The data from OGO-5 and OSO-7 X-ray experiments have been compared with optical data from six chromospheric flares with filament disruption associated with slow thermal X-ray bursts. Filament activation accompanied by a slight X-ray enhancement precedes the first evidence of H-alpha flare by a few minutes. Rapid increase of the soft X-ray flux accompanies the phase of fastest expansion of the filament. Plateau or slow decay phases in the X-ray flux are associated with slowing and termination of filament expansion. The soft X-ray flux increases as F approaches (A + Bh)h, where h is the height of the disrupted prominence at any given time and A and B are constants. We suggest that the soft X-ray emission originates from a growing shell of roughly constant thickness of high-temperature plasma due to the compression of the coronal gas by the expanding prominence.

Roy, J.-R.↗

NASA NTRS1990

Preliminary plume characteristics of an arcjet thruster

An experimental investigation of a low power arcjet plume was conducted using emission spectroscopy. A laboratory model arcjet incorporating a segmented anode was run on simulated hydrazine at a flow rate of 5 x 10(exp -5) kg/s. The complete visible spectrum measured in the exit plane of the arcjet showed the presence of N2, N2(+), NH, and H. Radial intensity profiles for the H alpha, H sub beta, and the NH A(sup 3)Pi yields X(sup 3)Sigma(0,0) transitions at four different axial locations were measured. These line of sight intensity measurements, spaced 0.05 mm apart, were deconvoluted to give the radial intensity distribution using an inverse Abel transformation. The ratio between the intensities from the H sub alpha and H sub beta transitions indicated a non-Boltzmann energy distribution between excited states in the plume. Axial intensity profiles taken on center line indicated the decay rate of excited states in the plume. An electron number density of 2 x 10(exp 13)/cu cm at the exit plane was determined based on Stark broadening of the H sub beta line. Rotational temperatures of 750 K, 1750 K, and 2500 K were determined for N2, N2(+), and NH respectively. The results demonstrate that the location of the current attachment on the anode has a measurable effect on the electronically excited species in the plume and that dissociation is the dominant frozen flow loss mechanism in low power arcjets.

Manzella, David H.↗

NASA NTRS1992

P/Machholz 1986 8 and quadrantid meteoroid stream. Orbital evolution and relationship

The evolution of the P/Machholz's meteoroid stream was simulated. It shows that this stream may produce eight meteor showers. There are the known observed meteor showers such as the Quadrantids, Ursids, Northern and Southern delta-Aquarids, Daytime Arietids, and alpha-Cetids. A satisfactory agreement of the theoretical and observed geocentric radiants and orbits allows one to conclude that the above showers could have been resulted from the decay of the P/Machholz nucleus. The age of the stream is estimated to be 7.5 millennia.

Babadzhanov, Pulat B.↗

NASA NTRS2000

Numerical Simulations of Homogeneous Turbulence Using Lagrangian-Averaged Navier-Stokes Equations

The Lagrangian-averaged Navier-Stokes (LANS) equations are numerically evaluated as a turbulence closure. They are derived from a novel Lagrangian averaging procedure on the space of all volume-preserving maps and can be viewed as a numerical algorithm which removes the energy content from the small scales (smaller than some a priori fixed spatial scale alpha) using a dispersive rather than dissipative mechanism, thus maintaining the crucial features of the large scale flow. We examine the modeling capabilities of the LANS equations for decaying homogeneous turbulence, ascertain their ability to track the energy spectrum of fully resolved direct numerical simulations (DNS), compare the relative energy decay rates, and compare LANS with well-accepted large eddy simulation (LES) models.

Mohseni, Kamran↗

NASA NTRS1971

The evolution of hydrogen-helium stars.

Investigation of the premain sequence evolution and the main sequence evolution of stars of 5, 10, 20, 30, 100, and 200 solar masses. Normal stars in this entire mass range normally convert hydrogen into helium by the CN-cycle on the main sequence. The present hydrogen-helium stars of 5 and 10 solar masses must reach higher central temperatures in order to convert hydrogen to helium by the proton-proton chains. Consequently, the mean densities in the stars are greater, and the surface temperatures are higher than in normal stars. In the stars of 20 solar masses and larger, the proton-proton chains do not succeed in supplying the necessary luminosity of the stars by the time the contraction has produced a central temperature near 10 to the 8th K. At that point triple-alpha reactions generate small amounts of C12, which then acts as a catalyst in the CN-cycle, the rate of which is then limited by the beta-decays occurring within the cycle. During the evolution of these more massive stars, the central temperature remains in the vicinity of 10 to the 8th K, and the surface temperature on the main sequence approaches 100,000.

Ezer, D.↗