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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Differential scattering cross sections for collisions of 0.5-, 1.5-, and 5.0-keV helium atoms with He, H2, N2, and O2

This paper reports the first results of an experimental program established to provide cross section data for use in modeling various atmospheric processes. Absolute cross sections, differential in the scattering angle, have been measured for collisions of 0.5-, 1.5-, and 5.0-keV helium atoms with He, H2, N2, and O2 at laboratory scattering angles between 0.1 deg and 5 deg. The results are the sums of cross sections for elastic and inelastic scattering of helium atoms; charged collision products are not detected. Integration of the differential cross section data yields integral cross sections consistent with measurements by other workers. The apparatus employs a position-sensitive detector for both primary and scattered particles and uses a short target cell with a large exit aperture to ensure a simple and well-defined apparatus geometry.

Newman, J. H.↗
NASA NTRS1989

Differential elastic electron scattering cross sections for SO2

Differential cross sections for elastic electron scattering by SO2 were measured by utilizing a modulated, crossed-beam method and calibration against He. The energy and angular ranges were from 5 to 50 eV and from 12 to 156 deg, respectively. The present results are compared with earlier data of Orient et al. (1982), and it is suggested that their cross section values should be increased by about a factor of two.

Trajmar, Sandor↗
NASA NTRS1976

Differential cross-section for positronium formation in electron-atomic hydrogen collisions

The L=0 and 1 partial wave amplitudes obtained by a two-state coupled static approximation with correlation with the L greater than or equal to 2 Born amplitudes were combined to obtain the differential cross section for positronium formation in electron-atomic hydrogen collisions. For positron energies of 0.64 and 0.75 ryd, minima at the scattering angles of 57 deg and 51 deg are found. Total cross sections for positronium formation for low and intermediate impact energies are given. Measurement of the differential cross section for the process positron + helium yields positronium + helium ion for the detection of possible minima is suggested.

Drachman, R. J.↗
NASA NTRS1982

Elastic scattering of electrons from SO2

A crossed electron beam-molecular beam scattering geometry and the relative-flow technique are used to measure the ratios of the elastic differential cross sections of SO2 to those of He at electron impact energies of 12, 20, 50, 100, 150, and 200 eV. At each energy, an angular range of 15-150 deg is covered. The ratios are multiplied by previously known He elastic differential cross sections to obtain elastic differential cross sections for SO2. Integral and momentum transfer cross sections are then determined from a knowledge of differential cross sections. With the aid of the two-potential theory of e-molecule scattering, calculations are also performed and compared with the measurements.

Orient, O. J.↗
NASA NTRS1978

Absolute elastic differential electron scattering cross sections in the intermediate energy region. IV - CO

Using a crossed electron beam-molecular beam scattering geometry and a relative-flow technique, ratios of elastic differential cross sections of CO to those of He have been measured at electron impact energies of 3, 5, 7.5, 9.9, 15, 20, 30, 50, 75, and 100 eV. At each energy, an angular range of 15 to 130 deg has been covered. These ratios have been multiplied by previously known He elastic differential cross sections to obtain elastic differential cross sections for CO. Since pure rotational excitations were not resolved, the elastic differential cross sections are a sum of elastic and pure rotational excitations at room temperature. From a knowledge of differential cross sections (DCS), integral and momentum transfer cross sections have been calculated. Both the DCS and integral cross sections are compared at 50, 75, and 100 eV to a recent two-potential theory of e-molecule scattering. Present results show that the isoelectronic molecules CO and N2 have very similar magnitudes and shapes of their differential cross sections.

Tanaka, H.↗
NASA NTRS1982

Electron impact cross sections for the 2,2P state excitation of lithium

Electron impact excitation of the 2p 2P state of Li was studied at 10, 20, 60, 100, 150 and 200 eV. Relative differential cross sections in the angular range 3-120 deg were measured and then normalized to the absolute scale by using the optical f value. Integral and momentum transfer cross sections were obtained by extrapolating the differential cross sections to 0 deg and to 180 deg. The question of normalizing electron-metal-atom collision cross sections in general was examined and the method of normalization to optical f values in particular was investigated in detail. It has been concluded that the extrapolation of the apparent generalized oscillator strength (obtained from the measured differential cross sections) to the zero momentum transfer limit with an expression using even powers of the momentum transfer and normalization of the limit to the optical f value yields reliable absolute cross sections.

Vuskovic, L.↗
NASA NTRS1991

Differential collision cross-sections for atomic oxygen

Differential collision cross-sections of O on N2 and other gases were measured to understand vehicle-environmental contamination effects in orbit. The following subject areas are also covered: groundbased scientific observations of rocket releases during NICARE-1; data compression study for the UVI; science priorities for UV imaging in the mid-1990's; and assessment of optimizations possible in UV imaging systems.

Torr, Douglas G.↗
NASA NTRS1987

Correlation effects in elastic e-N2 scattering

The Schwinger multichannel formulation has been applied to study the role of electron correlation in low-energy e-N2 scattering. For the five nonresonant partial-wave channels studied here, angular correlation is found to be much more important than radial correlation. The calculated total and differential cross sections agree well with experiment except for the differential cross sections at 1.5 eV.

Huo, Winifred M.↗
NASA NTRS1992

Magnetic-sublevel cross sections for excitation of the n 1P levels of helium by electron impact

First-order many-body theory has been used to calculate collision-frame magnetic-sublevel differential cross sections for electron-impact excitation of the n 1P (n = 2,3,4,5,6) levels of helium for electrons with incident energy in the 25-500-eV range. By combining results from electron-impact differential-cross-section measurements and electron-photon coincidence measurements, experimental magnetic-sublevel cross sections have also been derived for the excitation of the 2 1P and 3 1P levels. The theory predicts a pronounced minimum for the M = 0 magnetic-sublevel differential cross section for incident electron energies around 30 eV. The theoretical results are compared to the experimental data and some other theoretical results.

Csanak, George↗
NASA NTRS1989

Studies of elastic e-NH3 collisions

Differential and momentum-transfer cross sections for the elastic scattering of electrons by NH3 have been obtained for collision energies of between 2.5 and 20 eV using the fixed-nuclei static-exchange approximation of the Schwinger variational principle. At intermediate and large scattering angles, good agreement is found between calculated and relative experimental cross sections. The differential cross sections reveal evidence of a weak d-wave enhancement around 8 eV.

Pritchard, H. P.↗
NASA NTRS1985

Studies of electron-polyatomic-molecule collisions Applications to e-CH4

The first application of the Schwinger multichannel formulation to low-energy electron collisions with a nonlinear polyatomic target is reported. Integral and differential cross sections are obtained for e-CH4 collisions from 3 to 20 eV at the static-plus-exchange interaction level. In these studies, the exchange potential is directly evaluated and not approximated by local models. An interesting feature of the small-angle differential cross section is ascribed to polarization effects and not reproduced at the static-plus-exchange level. These differential cross sections are found to be in reasonable agreement with existing measurements at 7.5 eV and higher energies.

Lima, M. A. P.↗
NASA NTRS2023

DDFRG2: Double-Differential FRaGmentation Model with Pion Production

A set of Double-Differential FRaGmentation (DDFRG) models for production of fragments from nucleon-nucleus and nucleus-nucleus collisions, relevant to space radiation, is currently being developed. DDFRG1 was a previous model developed for production of protons and light ions. A new model for pion production is developed in the present work and is called DDFRG2, which is based upon thermal production of pions from a central fireball source. The Lorentzinvariant double-differential cross section is calculated in the central fireball frame, and is Lorentz transformed to the laboratory frame, which results in a closed-form analytic formula involving no numerical integration, and which can be run very efficiently in radiation transport codes. The Lorentz-invariant double-differential cross section is then integrated over angle to give the singledifferential energy spectral distribution. Two versions of the DDFRG2 pion production are developed, namely DDFRG2-SIMPLE and DDFRG2-FULL. Both versions produce pion production Lorentz-invariant double-differential cross sections and also pion production single-differential spectral (energy) distributions. The SIMPLE version contains only one adjustable parameter. The FULL version contains three additional adjustable parameters. Both DDFRG2 versions are compared to over 1,000 data points. The SIMPLE version describes the p + 12 C → π − much better than the current HZETRN pion model. For other reactions, the SIMPLE version is of comparable quality to the current HZETRN pion model compared to data. For both the p + 12 C → π − reaction and all other reactions, DDFRG2-FULL describes the data much more accurately than the current HZETRN pion model.

John W. Norbury↗
NASA NTRS1990

Differential elastic scattering cross sections for 54.9eV positrons incident on helium

Absolute differential elastic scattering cross sections measured with the 3-m, high resolution, time-of-flight spectrometer are presented for 54.9eV positrons incident on He. Five point moving average differential cross sections are plotted against average scattering angles which range from 14 to 36 deg. Also the averages of five differential cross sections which have adjacent values of scattering angle are plotted versus the corresponding averages of the scattering angles. The curve fitted to these data is shaped like the theoretical curve but has its minimum and its maximum at scattering angles that are about 4 deg higher and 15 deg lower respectively than predicted by theory.

Chaplin, R. L.↗
NASA NTRS1986

Differential excitation cross section of atomic oxygen by electron impact - (3P-1D transition)

Results of an electron impact experiment in which a crossed-beam method was used to determine the differential excitation cross sections of atomic oxygen (3P-1D transition) are reported. The measurements cover energies of 7, 10, 15, 20, and 30 eV, with the angular range varying from 30 to 150 deg in 15-deg increments. The results are consistent, both in shape and in magnitude, with theoretical predictions, providing a direct confirmation of the theoretical total excitation cross sections of O(1D) state. Details of the experimental equipment and procedure are given.

Shyn, T. W.↗
NASA NTRS2016

Electromagnetic Dissociation and Spacecraft Electronics Damage

When protons or heavy ions from galactic cosmic rays (GCR) or solar particle events (SPE) interact with target nuclei in spacecraft, there can be two different types of interactions. The more familiar strong nuclear interaction often dominates and is responsible for nuclear fragmentation in either the GCR or SPE projectile nucleus or the spacecraft target nucleus. (Of course, the proton does not break up, except possibly to produce pions or other hadrons.) The less familiar, second type of interaction is due to the very strong electromagnetic fields that exist when two charged nuclei pass very close to each other. This process is called electromagnetic dissociation (EMD) and primarily results in the emission of neutrons, protons and light ions (isotopes of hydrogen and helium). The cross section for particle production is approximately defined as the number of particles produced in nucleus-nucleus collisions or other types of reactions. (There are various kinematic and other factors which multiply the particle number to arrive at the cross section.) Strong, nuclear interactions usually dominate the nuclear reactions of most interest that occur between GCR and target nuclei. However, for heavy nuclei (near Fe and beyond) at high energy the EMD cross section can be much larger than the strong nuclear interaction cross section. This paper poses a question: Are there projectile or target nuclei combinations in the interaction of GCR or SPE where the EMD reaction cross section plays a dominant role? If the answer is affirmative, then EMD mechanisms should be an integral part of codes that are used to predict damage to spacecraft electronics. The question can become more fine-tuned and one can ask about total reaction cross sections as compared to double differential cross sections. These issues will be addressed in the present paper.

Norbury, John W.↗
NASA NTRS1971

Backward elastic pd scattering at 316, 364, 470 and 590 MeV.

The elastic scattering of protons by deuterons in the backward hemisphere was studied at the NASA Space Radiation Effect Laboratory. Preliminary data resulting from this study, which include the proton laboratory scattering angle, the laboratory differential cross section, the proton center-of-mass scattering angle, and the center-of-mass differential cross section, are tabulated, given graphically, and analyzed.

Alder, J. C.↗
NASA NTRS1960

Slow-Neutron Scattering by Rotators. II

The methods developed in a previous paper for extending the neutron scattering formalism of Zemach and Glauber to any type of molecular rotator have been employed to derive generalized forms generalized forms of the differential cross sections for rotator scattering. A mass-ratio expansion for the treatment of the high-energy limit is illustrated on the classical cross section and then employed in the treatment of the more general quantum-mechanical expression for the differential cross section. The results apply to an arbitrarily asymmetric rotator. The very low energy approximation is carried out for the symmetric rotator, and the procedure is compared with the explicit summing of the partial cross sections for individual rotational transitions. The inelastic correction to the static approximation for interference scattering is calculated to an accuracy of first order in the mass ratios for the case of the symmetric rotator.

Volkin, Howard C.↗