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At least 487 records · Page 27

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NASA NTRS1974

A burst of energetic gamma rays

A burst of gamma rays with energies greater than 1 MeV occurring on May 14, 1972, at 201247 UT (151247 local time) was detected during a balloon flight from Palestine, Texas, at a float altitude of 4g/sq cm residual atmosphere. The detector was a tank of liquid scintillator 1m x 0.5 m x 15 cm surrounded by a 0.6 cm plastic scintillator in anticoincidence. The signal was 60 standard deviations above a steady background of 600 counts/sec. The flux was 0.12 (+0.07 or -0.04) gamma/sq cm, and the time integrated flux 20(+11 or -7) gamma/sq cm. Only one such event was seen during the 8 hours of observation in the daytime on May 14 and 15. Two sub-flares in H alpha occurred during the burst, but not coincident with the start time. A detector on the Solrad satellite observed X-rays on all channels 2 minutes after the gamma ray start time. This event is similar to three earlier reported events.

Koga, R.↗

NASA NTRS1974

Cross correlation between cosmic-ray fluctuations and interplanetary magnetic-field fluctuations

Study of the cross-correlation between cosmic-ray intensity fluctuations and the interplanetary magnetic field, using the low-frequency limit of the theory of the interplanetary scintillations of cosmic rays. Cross-spectral analysis of the flux of the Alert neutron monitor and simultaneous values of the interplanetary magnetic field components are presented which support the theory. A model of cosmic-ray fluctuations is described, with effects of gradients and interplanetary sector structure dominating for very low frequencies (less than or about equal to .000005 Hz) and magnetic-field induced interplanetary scintillations of cosmic rays dominating for higher frequencies.

Jokipii, J. R.↗

NASA NTRS1974

The use of global ionospheric irregularity models for satellite communications

Scintillation data obtained in the VHF region were used by Fremouw to develop a global scintillation model. An attempt has been made in the present study to improve this model in several respects. One of these is to modify the high latitude term in the model to better represent data obtained in the northern high latitude regions. Another improvement is the extention of the frequency region of validity to the L band and microwave regions. This attempt is based on certain theoretical considerations regarding the effects of distribution in irregularity sizes. Recent satellite in situ measurements indicate that the ionospheric irregularity description is functionally different from that assumed in the past. These satellite measurements are used in connection with the theoretical development to improve the model.

Pope, J. H.↗

NASA NTRS1974

Burst-error characteristics of the equatorial transionospheric channel

Analyses of AGC analog data from the Small Astronomy Satellite (SAS) at VHF (136 MHz) have shown amplitude fluctuations in the signals received at several equatorial tracking sites operated by NASA. Errors in data are shown to increase markedly for nighttime satellite passes around the periods of the two equinoxes as compared to the errors observed during other periods. Qualitative and quantitative correlations are established between the ionospheric scintillation phenomenon and the occurrence of errors. Strong time and geographic cause-and-effect relationships are established by determining the statistical correlation between scintillation indices and bit error rates. Detailed analyses of the AGC fading statistics and the fine grain error statistics, such as the block-error distribution and the bit-error autocorrelation function, establish the strong correlation between deep fades and their effects on the burst error structure associated with the transionospheric channel and the communication receiver being employed.

Blank, H. A.↗

NASA NTRS1975

Large area double scattering telescope for balloon-borne studies of neutrons and gamma rays

A large area double scattering telescope for balloon-borne research is described. It measures the flux, energy and direction of 2-100 MeV neutrons and 0.5-30 MeV gamma rays. These measurements are made using time-of-flight and pulse height analysis techniques with two large tanks of mineral oil liquid scintillator. Results from Monte Carlo calculations of the efficiency, energy resolution and angular resolution are presented and the electronics implementation for the processing of 80 photomultiplier tubes signals will be discussed. The detector weighs 800 kg with a large part of this weight being the liquid scintillator (320 kg). It will be flown at 3 mbars for flight durations up to 40 hours. The first flight is planned for Spring, 1975.

Zych, A. D.↗

NASA NTRS1976

Improved collimator for imaging system

System's collimator, consisting of metal plate with many small-diameter holes and fiber optics scintillator, can increase system resolution to 1 mm and reduce scintillation loss to 25 percent.

Holladay, A. M.↗

NASA NTRS1975

The isotopic composition of cosmic rays with 5 is less than or equal to z which is less than or equal to 26

Results obtained from a high altitude balloon flight from Thompson, Canada in August, 1973 are reported. The instrument consisted of a spark chamber, a Lucite Gerenkov counter and thirteen layers of scintillators. For heavy particles the Cerenkov-range method of analysis was used to determine the mass of particles energetic enough to produce a Cerenkov signal and then stop in the layered scintillators. The data appear to be consistent with current cosmic-ray propagation models. Using a simple exponential path length propagation model this data is extrapolated to the cosmic-ray source and some implications of the data are discussed as to the nature of the source.

Fisher, A. J.↗

NASA NTRS1975

A cosmic gamma-ray burst on May 14, 1975

A cosmic gamma-ray burst is reported that occurred at 29309.11 s UTC, May 14, 1975. The burst was detected at an atmospheric depth of 4 g/sq cm residual atmosphere with the University of California double scatter gamma-ray telescope launched on a balloon from Palestine, Texas at 1150 UTC, May 13, 1975. The burst was observed both in the single scatter mode by the top liquid scintillator tank in anti-coincidence with the surrounding plastic scintillator and in the double scatter mode from which energy and directional information are obtained. The burst is 24 standard deviations above the background for single scatter events. The total gamma-ray flux in the burst, incident on the atmosphere with photon energy greater than 0.5 MeV, is 0.59 + or - 0.15 photons/sq cm. The initial rise time to 90% of maximum is 0.015 + or - 0.005 s and the duration is 0.11 s. Time structure down to the 5 ms resolution of the telescope is seen. The mean flux over this time period is 5.0 + or - 1.3 photons/sq cm/s and the maximum flux is 8.5 + or - 2.1 photons/sq cm/s.

Herzo, D.↗

NASA NTRS1976

Near threshold response of a wave shifted Cerenkov radiator to heavy ions

The response of Pilot 425 to heavy ions with energies less than 600 MeV/amu beta approximately 0.8 is examined both theoretically and experimentally. Measurements are presented from an experiment which employed a Ne-20 beam at many energies below 575 MeV/amu. The signal is assumed to come from three sources: (1) Cerenkov light from the heavy ion, (2) Cerenkov light from secondary electrons, and (3) scintillation of the radiator. It is found that the effective index of refraction is 1.518 and that scintillation is present at a level of approximately 2.7 percent of the Cerenkov signal for beta = 1 for Ne-20. The first of these values differs from values previously quoted in the literature.

Ahlen, S. P.↗

NASA NTRS1975

Instrumental technique in X-ray astronomy

A detailed review of the development of instruments for X-ray astronomy is given with major emphasis on nonfocusing high-sensitivity counter techniques used to detect cosmic photons in the energy range between 0.20 and 300 keV. The present status of X-ray astronomy is summarized together with significant results of the Uhuru observations, and photon interactions of importance for the detection of X-rays in space are noted. The three principal devices used in X-ray astronomy (proportional, scintillation, and solid-state counters) are described in detail, data-processing systems for these devices are briefly discussed, and the statistics of nuclear counting as applied to X-ray astronomy is outlined analytically. Effects of the near-earth X-ray environment and atmospheric gamma-ray production on X-ray detection by low-orbit satellites are considered. Several contemporary instruments are described (proportional-counter systems, scintillation-counter telescopes, modulation collimators), and X-ray astronomical satellite missions are tabulated.

Peterson, L. E.↗

NASA NTRS1976

An investigation of high-multiplicity gamma events in pp collisions with c.m. energies between 22 and 62 GeV

An experiment was conducted at the CERN intersecting storage rings using colliding proton beams to investigate high-multiplicity gamma-ray events. The objective of the study was to reveal certain features of multiple pion production as well as other possible mechanisms of gamma-ray production. The detector system consisted of ten planes of spark chambers, three scintillation counter hodoscopes and two arrays of lead-glass Cerenkov counters, the first array containing 16 counters and the second, 60 counters. The event trigger was obtained from the Cerenkov counters, and the energies in all the Cerenkov counters after trigger, as well as the information on all the charged particles given by the scintillation counters and spark chambers were recorded on magnetic tape. The relationship between the number of gamma-rays per event and the number of Cerenkov counters triggered by a neutral secondary was established by means of a Monte Carlo calculation.

Dell, G. F.↗

NASA NTRS1975

The detection of high charge cosmic ray nuclei

A large-area, light-weight electronic particle telescope was flown on a high altitude balloon in the summer of 1974 to study the heavy nuclei in the cosmic radiation. This telescope consisted of a double Cerenkov-double scintillator array composed of four 1.22 m diameter disk radiators mounted in light diffusion boxes, each looked at by multiple photomultipliers. The impact point of each particle on the scintillation radiators was determined by studying the relative signals observed by three equally spaced peripheral photomultipliers and one mounted at the center of the diffusion boxes. This telescope was flown in a configuration having a geometric factor of 0.45 sq m sr and observed some 5 x 10 to the 4 nuclei with Z exceeding 14 in a 11 hr exposure. The response and sensitivity of this telescope are discussed in detail.

Scarlett, W. R.↗

NASA NTRS1976

The irregularity spectrum in interstellar space

Published data on the interstellar scintillations of three pulsars are analyzed using a theory based on the Markov approximation for strong scintillations. The data are found to be consistent with either a Gaussian or Kolmogorov-like power-law irregularity spectrum for the interstellar material. For two of the pulsars, application of the Kolmogorov power law suggests the presence of regions of larger than normal electron density between us and the pulsar. The parameters of the deduced power-law spectrum are considered with independent measures of the large-scale structures of the gas and indicate the possibility of a broadly turbulent interstellar medium with a Kolmogorov-like spectrum.

Lee, L. C.↗

NASA NTRS1976

The specific light output of cesium iodide crystals

Large area ion chambers for a high energy cosmic ray experiment, scintillating plastic fibers as light pipes for a cosmic ray hodoscope, and an evaluation of clad scintillating light pipes were considered.

Gregory, J. C.↗

NASA NTRS1976

Large area ion chambers for a high energy cosmic ray experiment

High resolution measurement of the iron group nuclei was performed with the intention of determining individual abundances in the cosmic ray flux at the earth of particles with z = 22 to 30. Of the three types of dE/dx detectors used in the experiment, pulse ion chambers, Cerenkov radiators and scintillators, the first has the best z resolution over a wide range of particle z and energy. The plastic scintillators define the particle acceptance cone of the telescope while the Cerenkov detector aids in rejection of low energy particle background and measurement of particle velocity.

Source record↗

NASA NTRS1976

Plasma irregularities in the comet's tail

Scintillation theory is invoked to explain fluctuations in radio intensity observed during occultation of the extragalactic radio source PKS 2025-15 by the plasma tail of comet 1973 XII on Jan. 5, 1975. Plasma irregularities and turbulence in the tail of the comet (Kohoutek 1973f) are fitted to a Gaussian spectrum and to a Kolmogorov power-law spectrum in analyzing the scintillation data. The rms fluctuation of electron density in the cometary tail is reported at 80 electrons per cu mm, the inner scale of the fluctuation at 800 km, and the largest scale of fluctuation at possibly 400,000 km. A hump in the comet power-law spectrum is noted. Use of the power spectrum of electron density fluctuations to predict the power spectrum of magnetic field fluctuations for irregularities associated with hydromagnetic turbulence is recommended.

Lee, L. C.↗

NASA NTRS1976

Wavelength-shifted Cherenkov radiators

The scintillation and Cherenkov responses of plastic Cherenkov radiators containing different wavelength-shifting fluors in varying concentrations have been studied in beams of low energy protons and pions. For cosmic ray applications, where large Cherenkov to scintillation ratios are desired, the optimum fluor concentrations are 0.000025 by weight or less.

Krider, E. P.↗

NASA NTRS1977

Compensated time of flight telescope for spaceborne cosmic ray measurements

A large area time-of-flight telescope has been studied for future application in space-borne cosmic ray experiments. A new compensation technique for propagation delays inside the scintillators has been applied, which is operative in two perpendicular directions. This technique, superior to conventional one-dimensional compensations, allows high rejection probability for upward moving single particles at very short counter distances. Besides mechanical advantages a short counter distance is desirable because it permits a large field of view for the detector. A measurement of light transit times in scintillators is presented and based on it, directionality for shower events is discussed.

Rothermel, H.↗