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Buffington, A.

Publications and source records attributed to Buffington, A..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Measurement of the size of the isoplanatic patch using a phase-correcting telescope

In the presence of several-arc-second seeing at Mt. Wilson observatory, a flexible mirror image-sharpening telescope produced diffraction-limited (0.5 arcsec) images of the primary stars in the double star systems of Castor (alpha Gem), Algieba (gamma Leo) and Almach (gamma And). The images of both the primary and the companion star were simultaneously sharpened for Castor (separation 2 arcsec) and Algieba (4 arcsec) but not for Almach (10 arcsec). Thus the size of the isoplanatic patch came to lie between 4 and 10 arcsec. Using a simple model, we conclude that the bulk of the turbulent air responsible for the seeing was situated between 1.1 and 1.7 km above ground.

Pollaine, S.↗
NASA NTRS1978

Abundances and spectra for cosmic-ray nuclei from lithium to iron for 2 to 150 GeV per nucleon

Measurements of primary cosmic-ray composition and energy spectra made with a balloon-borne superconducting magnetic spectrometer are described. Results for both 6.7 g/sq cm equivalent vertical atmospheric depth and the top of the atmosphere are presented for the absolute and relative integral abundances, the differential energy spectra, and the spectral indices for cosmic-ray nuclei from Li to Fe and energies of 2 to 50 GeV/n. It is found that propagation effects can explain essentially all the elemental abundances, that the abundances of Li, Be, and B for rigidities below 10 GV/c are consistent with an energy-independent mean interstellar path length of 4.5 + or - 0.5 g/sq cm for the 'leaky box' propagation model, that the abundances of all elements above 10 GV/c are consistent with a path length that decreases as the inverse n-th power of rigidity, and that n equals 0.6 (+0.4, -0.3) for the simplest assumptions made in fitting the source spectra.

Orth, C. D.↗
NASA NTRS1978

A measurement of cosmic-ray beryllium isotopes from 200 to 1500 MeV per nucleon

A balloon-borne superconducting magnetic spectrometer was used in the measurement of cosmic-ray isotopic abundances from lithium through oxygen in the energy range 200-1500 MeV per nucleon. Except for Be-7 all isotopic composition is essentially energy-independent. Be-10 is nearly absent, indicating a mean cosmic-ray age of 6(-3, +10) x 10 to the 6th years. Above about 500 MeV per nucleon, Be-7 drops dramatically in abundance relative to Be-9 and C. By 1500 MeV per nucleon, the relative abundance of Be-7 has become one-half of its lower-energy value. Since Be-7 is the only isotope measured which decays by electron capture, this result is interpreted as indicating that higher-energy Be-7 had an appreciable probability of not being stripped of all its electrons before entering interstellar space where electron pickup is negligible.

Buffington, A.↗
NASA NTRS1978

Relativistic Be-7 - A probe of cosmic-ray acceleration

The cosmic-ray Be-7/Be ratio was observed to be 0.6 below 500 MeV/nucleon, as expected from spallation reactions, but then to drop sharply to 0.4 by 1500 MeV/nucleon. This measurement suggests that primary cosmic rays traverse some material at their sources, producing Be-7 which picks up electrons and decays by K capture during or after the acceleration to relativistic energies. All cosmic rays then enter interstellar space, where further pickup is negligible.

Buffington, A.↗
NASA NTRS1978

Experiment definition and integration study for the accommodation of magnetic spectrometer payload on Spacelab/shuttle missions

A super-cooled magnetic spectrometer for a cosmic-ray experiment is considered for application in the high energy astronomical observatory which may be used on a space shuttle spacelab mission. New cryostat parameters are reported which are appropriate to shuttle mission weight and mission duration constraints. Since a super-conducting magnetic spectrometer has a magnetic fringe field, methods for shielding sensitive electronic and mechanical components on nearby experiments are described.

Buffington, A.↗
NASA NTRS1978

Sharpening stellar images

A prototype telescope system with six movable elements has been used with sharpness detection procedures to observe objects as dim as fifth magnitude. The real-time image sharpening technique does not rely on the use of a reference star. By correcting for atmospherically induced phase perturbations, the sharpening system has permitted restoration of stellar images to the diffraction limit (in one dimension) for a 30-cm telescope. Application of the system to the separation of double stars is reported.

Buffington, A.↗
NASA NTRS1978

A review and interpretation of recent cosmic ray beryllium isotope measurements

Beryllium-10 is of interest for cosmic ray propagation, because its radioactive decay half-life is well matched to the expected cosmic ray age. Recent beryllium isotope measurements from satellites and balloon covered an energy range from about 30 to 300 MeV/nucleon. At the lowest energies, most of the Be-10 is absent, indicating a cosmic ray lifetime of order 2 x 10 to the 7th power years and the rather low average density of 0.2 atoms/cc traversed by the cosmic rays. At higher energies, a greater propagation of Be-10 is observed, indicating a somewhat shorter lifetime. These experiments will be reviewed and then compared with a new experiment covering from 100 to 1000 MeV/nucleon. Although improved experiments will be necessary to realize the full potential of cosmic ray beryllium isotope measurements, these first results are already disclosing interesting and unexpected facts about cosmic ray acceleration and propagation.

Buffington, A.↗
NASA NTRS1977

Correction of atmospheric distortion with an image-sharpening telescope

A 30 x 5 cm aperture telescope employing six movable mirrors to compensate for atmospherically induced phase distortion is built and tested. A feedback system adjusts the mirrors in real time to maximize the intensity of light passing through a narrow slit in the image plane. Essentially diffraction-limited performance is achieved when imaging both laser and white-light objects through 250 m of turbulent atmosphere. The behavior of the telescope is accurately predicted by computer simulations. The system has yet to achieve its full potential, but has already operated successfully for objects as dim as 5th magnitude.

Buffington, A.↗
NASA NTRS1977

First observatory results with an image-sharpening telescope

Measurements of characteristic speckle change times are presented for stars observed with an image-sharpening telescope installed and operated on equatorial mounts at Leuschner Observatory in Lafayette, California, and Lick Observatory at Mount Hamilton, California. Despite the short speckle change times encountered, it was possible to record dramatically improved stellar images on nights when the speckles changes relatively slowly. Sharpened images of Sirius and Arcturus are discussed.

Buffington, A.↗
NASA NTRS1976

Secondary cosmic-ray electrons and positrons from 1 to 100 GeV in the upper atmosphere and interstellar space, and interpretation of a recent positron flux measurement

Secondary electron and positron fluxes generated in interstellar space and in the atmosphere from the decays of pions and kaons in inelastic nuclear interactions are calculated by Monte Carlo techniques for lepton energies in the range from 1 to 100 GeV and an assumed thickness of 10 g/sq cm or less for the interstellar or atmospheric material. A simple and accurate analytical model which summarizes the Monte Carlo results and identifies the essential parameters involved is developed and used to interpret a previous positron measurement. It is found that the thickness of interstellar and source material is about 4.3 g/sq cm for cosmic-ray positrons with energies exceeding 4 GeV, a result that is difficult to reconcile with recently proposed two-containment-volume propagation models which predict a thickness of 1.8 g/sq cm for the same energies on the basis of the energy dependence of the measured (Li+Be+B)/(C+O) ratio. It is shown that single-containment-volume (galactic) models invoking an energy-dependent leakage lifetime are compatible with the positron data, but lack a mechanism to explain the energy dependence.

Orth, C. D.↗
NASA NTRS1976

Active image restoration with a flexible mirror

The 30 by 5 cm aperture telescope described uses six moveable mirrors to compensate for phase distortions induced by the atmosphere. A feedback system is used to adjust the mirrors in real time to maximize the intensity of light passing through a narrow slit in the image plane. Using the telescope, diffraction-limited images of objects were obtained, using both laser and white light, through 250 meters of turbulent atmosphere.

Buffington, A.↗
NASA NTRS1975

Image, optical

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Muller, R. A.↗
NASA NTRS1975

Measurement of primary cosmic-ray electrons and positrons from 4 to 50 GeV

We have used a bremsstrahlung-identification technique to measure electron and positron spectra in the primary cosmic rays from 4 to 50 GeV. Above our average geomagnetic cutoff of 4.0 GV/c, we find fluxes of 4.4 (plus or minus 0.3) electrons and 0.37 (plus or minus 0.09 positrons) per sq m/sr/sec. The electron events follow a differential power law whose spectral index is 2.8 (plus or minus 0.1). Our ratio electrons/(electrons + positrons) = 0.08 (plus or minus 0.02) implies traversal of an equivalent slab thickness of 4.3 (plus or minus 1.5) g/sq cm of interstellar and source material.

Buffington, A.↗
NASA NTRS1975

Search for cosmic-ray antimatter

It appears probable that some fraction of the cosmic rays has extragalactic origin. A search for antimatter nuclei was conducted with the aid of a balloon-borne superconducting magnetic spectrometer. The investigation made use of the fact that matter and antimatter nuclei, because of their opposite signs of charge, would be deflected in opposite directions when passing through a magnetic field. The antimatter flux limits set by the experiments are discussed.

Smoot, G. F.↗
NASA NTRS1974

Real-time correction of atmospherically degraded telescope images through image sharpening

We present a new technique for the correction of atmospheric distortion in telescope images. Most of this distortion arises from a random phase variation of the incoming light across the telescope aperture. This variation limits the resolving power of even large telescopes to about one arc second. If the sharpness of the images is defined in a suitable way, this sharpness is maximized only when the phase distortion of the incoming light is zero. We present computer simulations of a simple feedback system in which active optical elements, set to maximize the sharpness, correct most of the atmospheric distortion. Photon statistics set the limiting magnitude of the object for which a practical feedback system can work. Details in a sixth magnitude object smaller than 0.1 sec of arc should be resolvable. The system can be conveniently employed within existing telescopes.

Muller, R. A.↗