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At least 847 records · Page 47
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NASA NTRS1977

Energy spectra of cosmic ray nuclei - Z of 4 to 26 and E of 0.3 to 2 GeV/amu

The differential kinetic-energy spectra of cosmic-ray nuclei in the charge range from 4 to 28 are determined using data obtained from a high-altitude balloonborne detector. The data are derived from the response of an acrylic plastic Cerenkov counter and cover the kinetic-energy range from 400 to 2100 MeV/amu. A Cerenkov pulse-height histogram is obtained for each charge, and the kinetic-energy spectra are derived by means of a formal mathematical deconvolution of these histograms. Results of the deconvolution calculation extrapolated to the top of the atmosphere are presented for the most abundant nuclei; it is found that the spectra are not amenable to representation by spectral indices, so the relative spectra of the different elements are compared by evaluating the charge ratios as a function of energy. The results show that secondary/primary ratios decrease with increasing energy, while primary/primary ratios are constant for Z of 6 to 10 and 14 to 26 but vary for Z of 10 to 14. It is concluded that the data seem to indicate more than one cosmic-ray source region.

Maehl, R. C.↗
NASA NTRS1977

Radio-emitting electrons and cosmic ray confinement

Evidence from radio data obtained at frequencies of 10 to 8000 MHz for steepening of the observed background-radio-continuum spectra in the directions of the galactic Anticenter (A) and Halo Minimum (H) is used to deduce quantitative information on the variation of the magnetic field with distance from the galactic plane. The radio data are analyzed in the framework of the cosmic-ray diffusion model developed by Bulanov and Dogel (1975), and some inferences are drawn regarding the injection spectrum of cosmic-ray electrons as well as their propagation in the Galaxy. The results indicate that: (1) radio-spectrum steepening is centered around 200 MHz in the direction of H and around 330 MHz in the direction of A, implying a lower mean magnetic field toward H and supporting the existence of a radio halo; (2) an injection electron spectrum with a single power law up to the lowest energies cannot explain the radio observations satisfactorily in terms of the diffusion model; and (3) the observed spectral steepening can be satisfactorily understood as being due partly to the deviation from a power-law injection spectrum below a few GeV and partly to the first break arising from electron energy losses in approximately the same energy region.

Badhwar, G. D.↗
NASA NTRS1978

The charge and energy spectra of heavy cosmic ray nuclei

A charged particle detector array flown in a high altitude balloon detected and measured some 30,000 cosmic ray nuclei with Z greater than or equal to 12. The charge spectrum at the top of the atmosphere for nuclei with E greater than 650 MeV/n and the energy spectrum for 650 less than or equal to E less than 1800 MeV/n are reported and compared with previously published results. The charge spectrum at the source of cosmic rays is deduced from these data and compared with a recent compilation of galactic abundances.

Scarlett, W. R.↗
NASA NTRS1977

Cosmic ray measurements on board Helios 1 from December 1974 to September 1975 Quiet time spectra, radial gradients, and solar events

The considered time period is characterized by a general decrease in solar activity towards a minimum which occurred in July 1976. The relatively quiet solar conditions facilitate the separation of the gradually varying galactic cosmic radiation from superimposed events of different characteristics. The inspection of neutron monitor data shows that the period is characterized by a slow increase of the high energy galactic cosmic radiation at a relatively constant rate. Attention is given to the instrumentation employed, intensity time profiles and preliminary radial gradients, and quiet time energy spectra. The solar particle events discussed include the January 5, 1976 event, the March 3, 1975 event, and the March 19/20, 1975 event.

Kunow, H.↗
NASA NTRS1977

Charge composition and energy spectra of cosmic-ray nuclei at energies above 5 GeV per nucleon

A scintillation-Cerenkov counter telescope, with three gas Cerenkov counters for energy determination between 5 and 90 GeV per nucleon, has been exposed for a net total of 4.5 sq m sr hr in two balloon flights in 1974. The measurement yields the chemical composition and energy spectra of cosmic-ray nuclei in the charge range 5-28. The differential spectral indices of oxygen and of the iron group are measured to be 2.67 plus or minus 0.04 and 2.5 plus or minus 0.08 above 5.4 GeV per nucleon, respectively. The results are interpreted in the context of the 'leaky-box' model of cosmic-ray confinement and propagation.

Caldwell, J. H.↗
NASA NTRS1977

Observations of galactic cosmic-ray energy spectra between 1 and 9 AU

Detector systems onboard Pioneer 10, Pioneer 11, and Helios I have collected data on the variation of the 5-500 MeV per nucleon cosmic-ray helium component between 1 and 9 AU in order to evaluate the properties of low and medium-energy galactic cosmic rays. At 9 AU new spectral features are found for helium nuclei below 60 MeV per nucleon, while at energies above 100 MeV per nucleon the radial gradient is found to be much smaller than theoretically predicted. The conventional modulation theory can be made consistent with these observations. The study is applicable to investigations of particle acceleration, injection, and interstellar propagation.

Mcdonald, F. B.↗
NASA NTRS1977

Cosmic diffuse gamma rays from 2 to 25 MeV

Results are reported for measurements of cosmic diffuse gamma rays performed with a double Compton scatter gamma-ray telescope flows aboard a balloon at 3.5-g/sq cm residual atmosphere. The operation and calibration of the telescope are briefly reviewed, unwanted backgrounds are identified, and the only significant background for the telescope used is shown to arise from the interaction of albedo neutrons with hydrogen and carbon in one of the liquid scintillators. The fluxes of cosmic diffuse gamma rays with energies of 2 to 3, 3 to 5, 5 to 7, 7.5 to 10 MeV are listed, and upper limits are provided for energies of 10 to 15 and 15 to 25 MeV. These data are compared with numerous previous measurements, and no indication is found that the diffuse radiation is statistically different from isotropic. Upper limits are placed on the gamma-ray fluxes (mainly 3 to 25 MeV) from various localized sources.

White, R. S.↗
NASA NTRS1978

Effects of particle drift on cosmic ray transport. II - Analytical solution to the modulation problem with no latitudinal diffusion

An analytical solution to a model of the modulation of galactic cosmic rays in the presence of particle drifts is presented and discussed. The solution assumes an energy-independent radial diffusion coefficient proportional to distance and no latitudinal diffusion, and includes energy-independent particle drift velocities similar to those expected in a Parker spiral magnetic field with an equatorial current sheet. The solutions clearly demonstrate the large effects of drifts on the modulated cosmic-ray intensity. For values of the radial diffusion coefficient and particle drift velocity which are plausible for 1-GV-rigidity protons, the logarithmic radial gradient in the inner solar system is reduced by more than a factor of 5 over the value calculated in the absence of drifts. It is found that even for much smaller values of particle drift velocity and radial diffusion coefficient, such as might be expected for protons with energies of the order of 10 MeV, the effects of the drifts can be substantial.

Isenberg, P. A.↗
NASA NTRS1977

Neutral particle background in cosmic ray telescopes composed of silicon solid state detectors

The energy loss-spectrum of secondary charged particles produced by the interaction of gamma-rays and energetic neutrons in silicon solid state detectors has been measured with a satellite-borne cosmic ray telescope. In the satellite measurements presented here two distinct neutral background effects are identified: secondary protons and alpha particles with energies of about 2 to 100 MeV produced by neutron interactions, and secondary electrons with energies of about 0.2 to 10 MeV produced by X-ray interactions. The implications of this neutral background for satellite measurements of low energy cosmic rays are discussed, and suggestions are given for applying these results to other detector systems in order to estimate background contamination and optimize detector system design.

Mewaldt, R. A.↗
NASA NTRS1978

The cosmic ray record in the San Juan Capistrano meteorite

Measurements of cosmic ray track densities, rare gas concentrations, and radioisotope activities on the same sample of the San Juan Capistrano (SJC) meteorite (March 15, 1973) were combined in order to obtain a consistent picture of the irradiation history of the meteorite. The latter was recovered in two fragments weighing 50.5 and 5.5 g, respectively, which were then sampled according to the objectives set forward. The preatmospheric size of SJC and the depth occupied by the sample in the preatmospheric body were determined within narrow limits. In addition, the study compared estimates of the cosmic ray exposure age as determined by various techniques and evaluated the amount of ablation undergone when SJC penetrated the earth's atmosphere.

Finkel, R. C.↗
NASA NTRS1978

The isotopic composition of cosmic-ray helium from 123 to 279 MeV per nucleon - A new measurement and analysis

A description is given of an experiment which was designed to measure the spectra and composition of cosmic-ray hydrogen and helium isotopes in the interval 120-280 MeV per nucleon to compare with the recent values observed at low energies and also with the only earlier measurement in this high-energy regime. The results presented were obtained during a high-altitude balloon flight from Thompson, Manitoba, in 1973 August. This flight occurred during the period in which the presence of the anomalous component in the helium spectrum became apparent, and provides the opportunity of determining whether this component extends to higher energies than those studied by satellite experiments. The results place an upper limit on the flux of 'anomalous' He-4 (which appeared at low energy in 1972) of at most 15% in the energy range of this experiment, and combined with the low-energy observations of the Chicago group, show an energy dependence of the average ratio of the helium isotopes in the modulated cosmic rays which is difficult to reconcile with current modulation models.

Leech, H. W.↗
NASA NTRS1977

A hard X-ray imaging instrument for solar and cosmic sources

A hard X-ray imaging instrument is described which is capable of high-resolution imaging of solar and cosmic hard X-ray sources between 2 and 80 keV during Shuttle sortie flights. The properties of solar burst sources and the resulting instrument requirements are discussed. The instrument envelope of 1.2 x 1.2 x 3.0 meters includes a tungsten multigrid collimator which has 4-arcsec resolution, a 40-arcmin response envelope and a point-source effective area of 26 sq cm. A combination of periodic fan beams and nonperiodic pencil beams enables a unique deconvolution to be achieved within a 128 x 128 arcsec field without mechanical scanning. The detector system is a set of direct-readout 40 atm-cm xenon-filled proportional counters designed to minimize background. The instrument is capable of refurbishment to optimize the collimator configuration for specific solar or cosmic scientific objectives, to upgrade the angular resolution, or to extend the high-energy response.

Hurford, G. J.↗
NASA NTRS1978

Ames collaborative study of cosmic ray neutrons - Mid-latitude flights

Three aircraft flights at 12.5 km have yielded data on cosmic-ray neutron-flux densities, neutron dose equivalent rates, and exposure rates for ionizing radiation. The data, collected at 45, 38, and 48 degrees N, indicate: (1) neutron dose equivalent rates of 0.20, 0.14, and 0.22 mrem/hour, (2) exposure rates from the ionizing component of 0.37, 0.31, and 0.41 mR/hour, (3) that the dose equivalent from 3-13-MeV neutrons is 30% of the total for all neutrons, (4) that exposure rates decrease exponentially with decreasing pressure altitude with a 140 g/sq cm attenuation length at 43 degrees N geomagnetic latitude, and (5) that the ionizing component of cosmic ray secondaries is less sensitive to latitude changes than the neutron component.

Hewitt, J. E.↗
NASA NTRS1978

ISEE-C HKH high energy cosmic rays

The paper describes the ISEE-C multidetector cosmic ray telescope experiment. The HKH particle identifier sensor array is designed to identify the charge and mass of incident cosmic ray nuclei from H-1 to Ni-64 over the energy range of approximately 20 to 500 MeV/nucleon. Particle identification is based on the multiple energy loss technique. The scientific aspects of the experiment are briefly reviewed and consideration is given to the flight hardware, including sensors, event encoding, buffer memory, redundancy and commandability, and packaging.

Greiner, D. E.↗
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

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

The charge and energy spectra of heavy cosmic-ray nuclei

A charged-particle detector array flown on a high-altitude balloon has detected and measured some 30,000 cosmic-ray nuclei with Z of at least 12. The charge spectrum at the top of the atmosphere for nuclei with energies greater than 650 MeV/n and the energy spectrum for energies between 650 and 1800 MeV/n are reported and compared with previously published results. The charge spectrum at the 'source' of cosmic rays is deduced from these data and compared with a recent compilation of 'galactic' abundances.

Scarlett, W. R.↗
NASA NTRS1979

The energy spectrum of cosmic ray electrons between 9 and 300 GeV

The high-energy cosmic-ray electron spectrum between 9 and 300 GeV has been measured using an instrument consisting of a combination of a transition-radiation detector and a shower detector. The instrument has been calibrated at accelerators over the energy range 5-300 GeV and has been exposed in a balloon flight for 9.3 sq m sr hr. The design of the instrument and the data analysis procedures are described. It is found that the electron spectrum is significantly steeper than the proton spectrum. If the spectrum is fitted to a single power law, a spectral index of 3.35 is obtained. This suggests the influence of radiative energy losses on galactic electrons at low energies. The results are interpreted in the context of the homogeneous model for galactic cosmic rays.

Prince, T. A.↗