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NASA NTRS1973

Measurements of recombination of electrons with HCO(plus) ions

Recombination coefficients of electrons with HCO(+) ions were determined with a microwave afterglow/mass spectrometer apparatus. Afterglow measurements of electron density decays in neon-hydrogen-carbon monoxide mixtures are correlated with the decay of mass-identified ion currents to the wall of the microwave cavity. At the appropriate partial pressures of hydrogen and carbon monoxide in the mixture, the ion HCO(+) dominates the ion composition and its wall current approximately tracks the electron density decay curve. From recombination controlled electron density decay curves, the values alpha (HCO(+)) = (3.3 + or - 0.5) and (2.0 + or - 0.3) 0.0000001 cu cm/sec are obtained at 205 and 300 K, respectively. The implications of these results for models of polyatomic molecule formation in dense interstellar clouds are briefly discussed.

Leu, M. T.↗

NASA NTRS1973

Measurements of recombination of electrons with H3(plus) and H5(plus) ions

The electron-ion recombination coefficients for H3(+) and H5(+) ions were determined by means of a microwave afterglow/mass spectrometer apparatus. Measurements of electron density decays in helium-hydrogen mixtures are correlated with the decay of mass-identified ion currents to the wall of the microwave cavity. At low partial pressures of hydrogen in the mixture, the ion H3(+) dominates the ion composition and the ion wall current tracks the electron density decay curves. From recombination controlled electron density decay curves, the values alpha (H3(+)) = (2.9 + or - 0.3), (2.3 + or - 0.3), and (2.0 + or - 0.2) x 0.0000001 cu cm per sec, are obtained at 205, 300 and 450 K, respectively. At higher partial pressures of hydrogen and low temperatures, where (H5(+)) is the dominant ion, the value alpha (H5(+)) = (3.6 + or - 1.0) x 0.0000001 cu cm per sec is obtained at 205 K. The implications of these results concerning ionization levels in the atmospheres of the outer planets and in the interstellar medium are discussed.

Leu, M. T.↗

NASA NTRS1973

Primary electron spectrometer, 18:63 UE: Electrostatic analyzer description and energy spectrum determination

The primary electron spectrometer used to detect auroral electrons on sounding rocket 18:63 UE is described. The spectrometer used exponentially decaying positive and negative voltages applied to spherical deflection plates for energy analysis. A method for determining the analyzer response which does not require the assumptions that the ratio of plate separation to mean radius, the entrance or the exit apertures are small is described. By comparison with experiment it is shown that the effect of neither entrance nor exit collimation can be ignored. The experimental and calculated values of the limiting orbits agree well. A non-iterative technique of unfolding the electron differential energy spectrum is described. This method does not require the usual assumption of a flat or histogram-type energy spectrum. The unfolded spectra using both this technique and one which assumes a flat spectrum are compared to actual input spectra. This technique is especially useful in analyzing peaked auroral electron energy spectra.

Pongratz, M. B.↗

NASA NTRS1972

Evidence for electron excitation of type III radio burst emission.

Type III radio bursts observed at kilometric wavelengths (less than or about equal to 0.35 MHz) by the Ogo-5 spacecraft are compared with greater than 45 keV solar electron events observed near 1 AU by the IMP-5 and Explorer 35 spacecraft for the period from March 1968 to November 1969. Fifty-six distinct type III bursts extending to less than or about equal to 0.35 MHz were observed above the threshold of the Ogo-5 detector; all but two were associated with solar flares. Twenty-six of the bursts were followed less than or about equal to 40 min later by greater than 45 keV solar electron events observed at 1 AU. All of these 26 bursts were identified with flares located west of W09 solar longitude. Of the bursts not associated with electron events only three were identified with flares west of W09, 18 were located east of W09, and seven occurred during times when electron events would be obscured by high background particle fluxes.

Alvarez, H.↗

NASA NTRS1972

Calculation of electron energy flux distributions in noble gases.

The electron flux spectrum has been calculated over the entire range from delta-ray energies to ionization-potential energies. Estimates based on the Born approximation indicate that electron-gas atom elastic losses can be neglected. Gryzinski's (1965) classical cross sections show that electron-thermalized electron interactions can be ignored. Under those conditions the energy degradation is primarily due to the excitation and ionization of background gas.

Lo, R.↗

NASA NTRS1973

Solar and geomagnetic modulation of low-energy secondary cosmic ray electrons.

Balloon exposures of hodoscope instruments at Churchill, Manitoba; Minneapolis, Minnesota; and Sioux Falls, South Dakota, have established that the flux of return albedo electrons does not depend upon launch latitude and varies with solar modulation in proportion to the intensity of atmospheric secondary electrons. Only one flight out of 21 showed any indication of a magnetospheric electron flux significantly in excess of that attributable to albedo. Diurnal changes in geomagnetic cutoffs exhibit marked variability from day to day, as was illustrated by one flight in which a low cutoff was observed at Churchill throughout the daytime hours. The intensity increase of 15- to 65-MeV primary cosmic ray electrons due to solar modulation was no more than a factor of 2 from 1969-1970 to 1971.

Luhmann, J. G.↗

NASA NTRS1973

Thermal electron energy distribution measurements in the ionosphere.

A recoverable payload instrumented for twilight airglow studies was launched by an Aerobee 150 from the White Sands Test Range on Feb. 8, 1971 at 13.56 UT. The payload included a low energy electron spectrometer (HARP) and a cylindrical Langmuir probe. The HARP electron spectrometer is a new device designed to make high resolution differential electron flux measurements. Measurements of ionospheric electron energy distribution in the range from about 0.2 to 4.0 eV are presented.

Hays, P. B.↗

NASA NTRS1973

Electron observations in the solar wind and magnetosheath.

Electron temperature measurements taken by a triaxial electron analyzer on Ogo 5 in the solar wind and in the magnetosheath are interpreted. In the interplanetary medium, observations made on the bow shock connected lines of magnetic force have been separated from those made on non-bow-shock connected lines. The dependence of electron thermal properties on the local field geometry is discussed together with features of electron temperature and density discontinuities across the bow shock. The velocity distribution function is characterized together with temperature and density variations in a part of the dawn magnetosheath.

Scudder, J. D.↗

NASA NTRS1973

A study of cosmic-ray positron and electron spectra in interplanetary and interstellar space and the solar modulation of cosmic rays

The differential energy spectra of cosmic-ray positrons and negatrons with energies between approximately 11 and 1500 MeV was measured during the period 1968-1971 using a balloon-borne magnetic spectrometer. These measurements fill a gap in the previously existing data and permit the determination of the interstellar spectra of cosmic-ray positrons and electrons. Knowledge of these spectra provides a crucial tool for studies of the distribution and density of matter and magnetic fields in the interstellar medium and the origin and dynamics of energetic particles contained in the fields. The differential energy spectrum of interstellar electrons may be represented as a power-law, j alpha T to the -1.8 power for 100 MeV approximately T approximately 2 GeV, but must flatten considerably at lower energies. From the measured electron charge composition, it is concluded that the majority of cosmic-ray electrons with energies above approximately 10 MeV originate in primary sources.

Cummings, A. C.↗

NASA NTRS1973

Electron-optic limitations on image resolution

Various approaches are considered to the solution of the electron-optical problem of designing an image tube configuration. Emphasis is placed on the method of computer design, and an illustration is given in which the technique is used in the design of an 80-mm image tube with a zoom capability of 3:1. The solutions are discussed to such problems as image distortion, magnification, and electron bundles striking the zoom electrode. Three types of an electron-optical configuration are examined for the electron-optic limitations to resolution: (1) the proximity image tube, (2) the magnetic-type image tube having uniform electric and magnetic fields, and (3) the electrostatic-type image tube such as the 80-mm zoom tube.

Engstrom, R. W.↗

NASA NTRS1973

Energetic electrons in the midlatitude nighttime E region

Nike Apache 14.439 was launched from Wallops Island at 0003 EST on 1 November 1972, a very disturbed night (K sub P = 8). A Geiger counter in the payload detected electrons ( keV) with a maximum flux of 1086 + or -261/sq cm/sec/ster. The height-averaged ionization rate in the upper E region is calculated from the measured electron density profile and has a value of 35 1/cu/cm/sec. The ionization rate can be reconciled with the observed flux of electrons ( 70 2 keV) if the spectrum ( keV) is of the form J ( E) = J sub O exp(-E/E sub O) with E sub O equal to 8.3 keV. The ionization rate on this and other nights is found to be strongly dependent on geomagnetic activity. It is suggested that energetic electrons are the principal source of ionization at midlatitudes in the upper E region near midnight, even under rather quiet geomagnetic conditions.

Smith, L. G.↗

NASA NTRS1974

The energy spectrum of 0.16 to 2 MeV electrons during solar quiet times

New observations of the quiet-time energy spectrum of 0.16 to 2 MeV electrons were made with the Caltech Electron/Isotope Spectrometer which was launched on IMP-7 in September 1972. Earlier measurements of quiet-time electrons in this energy range by other groups have resulted in spectra differing by more than an order of magnitude in intensity. A minimum quiet-time flux somewhat lower than the lowest previously reported spectra and consistent with an extrapolation of the spectrum measured at higher energies was found. A galactic secondary source of knock-on electrons is consistent with the results and with independent studies of the interstellar spectra of cosmic ray nuclei provided that solar modulation does not suppress the 0.162 MeV electron flux by more than a factor of approximately 3. Although not required, other recently suggested sources may also contribute to the observed fluxes.

Hurford, G. J.↗

NASA NTRS1974

Electron collection theory for a D-region subsonic blunt electrostatic probe

Blunt probe theory for subsonic flow in a weakly ionized and collisional gas is reviewed, and an electron collection theory for the relatively unexplored case, Deybye length approximately 1, which occurs in the lower ionosphere (D-region), is developed. It is found that the dimensionless Debye length is no longer an electric field screening parameter, and the space charge field effect can be negelected. For ion collection, Hoult-Sonin theory is recognized as a correct description of the thin, ion density-perturbed layer adjacent the blunt probe surface. The large volume with electron density perturbed by a positively biased probe renders the usual thin boundary layer analysis inapplicable. Theories relating free stream conditions to the electron collection rate for both stationary and moving blunt probes are obtained. A model based on experimental nonlinear electron drift velocity data is proposed. For a subsonically moving probe, it is found that the perturbed region can be divided into four regions with distinct collection mechanisms.

Wai-Kwong Lai, T.↗

NASA NTRS1974

Fluorescence and phosphorescence of photomultiplier window materials under electron irradiation

The fluorescence and phosphorescence of photomultiplier window materials under electron irradiation were investigated using a Sr-90/Y-90 beta emitter as the electron source. Spectral emission curves of UV grade, optical grade, and electron-irradiated samples of MGF2 and LiF, CaF2, BaF2, sapphire, fused silica, and UV transmitting glasses were obtained over the spectral range of 200 nm to 650 nm. Fluorescence yields, expressed as the number of counts in a solid angle of 2 pi steradian per 1MeV of incident electron energy deposited, were determined on these materials utilizing photomultiplier tubes with cesium telluride, bialkali, and trialkali (S-20) photocathodes, respectively.

Viehmann, W.↗

NASA NTRS1974

Processings of the Workshop on Electron Contamination in X-Ray Astronomy Experiments

The proceedings of a conference to investigate the effects of extraterrestrial radiation and particle contamination of X-ray astronomical data are presented. The subjects discussed include the following: (1) electrons at low altitudes which affect soft X-ray astronomy, (2) the geographical distribution of 100 keV electrons above the earth's atmosphere, (3) midlatitude electron precipitation, (4) particle background observed by X-ray detectors on board Copernicus satellite, and (5) a survey of trapped low energy electrons near the inner boundary of the inner radiation zone as determined by OSO-7.

Holt, S. S.↗

NASA NTRS1974

Electrons at low altitudes: A difficult background problem for soft X-ray astronomy

Quasi-trapped and precipitating electrons have been observed with rocket-borne X-ray astronomy detectors in the altitude range 150 to 500 km. Because the flights occured at low magnetic latitudes the electrons were unexpected. Data from many flights are combined to derive altitude dependence, an average electron spectrum, and variation with solar activity. Development of electron-rejecting collimators is discussed, and laboratory and flight data on these collimators are presented.

Seward, F. D.↗

NASA NTRS1974

Midlatitude electron precipitation: A possible source of contamination of galactic X and gamma-ray measurements

The effect of trapped and precipitated particles in the magnetosphere on the measurement of galactic X-rays and gamma rays is discussed. To minimize contamination caused by electron precipitation, most galactic X-ray and gamma ray measurements are conducted at equatorial or relatively low to middle latitudes where the influence of auroral effects is expected to be small. Substorm-related VLF phase perturbations also affect the measurements. If such perturbation are indicative of electron precipitation at middle to low latitudes, then their relatively high frequency of occurrence, as many as 100 per year, is evidence that electron precipitation at these latitudes may pose a problem to some galactic X-ray and gamma ray measurements. Charts and maps are presented to show: (1) phase recordings from sixteen sub-ionospheric VLF propagation paths, (2) map of great circle propagation paths, (3) ionization rates in the nighttime ionosphere due to several sources, and (4) computer phase variation for the NLK-APL path versus electron flux for different e-folding energies.

Rosenberg, T. J.↗

NASA NTRS1974

Soft X-ray bremsstrahlung and fluorescent line production in the atmosphere by low energy electrons

The effect of low energy quasi-trapped or precipitating electrons which impact on the counter windows of soft X-ray detectors are discussed. The errors caused by X-rays produced in the residual atmosphere above a rocket-borne detector because of the resemblance to X-rays of cosmic origin are examined. The design and development of counter windows which make it possible to identify the atmospherically produced X-rays are described. Curves are presented to show the following: (1) preliminary low energy electron data from Atmospheric Explorer C, (2) X-ray flux in electron-excited nitrogen and oxygen, (3) typical proportional counter response to low energy cosmic rays, and (4) proportional counter response to X-radiation produced by electrons incident upon a gas of oxygen to nitrogen number of 0.4.

Kraushaar, W. L.↗