Engineering topics

Meyer, P.

Publications and source records attributed to Meyer, P..

At least 37 records · Page 2

NASA NTRS1985

Detectors for high energy cosmic rays on Spacelab

Two instruments designed to determine the spectra of the individual cosmic-ray components at very high energies are described. One of these (CRNE) uses a combination of gas Cerenkov counters and transition radiation detectors for the cosmic-ray nuclei lithium to nickel; the other (TRIC) is optimized for the light cosmic rays (electrons, protons, helium) and uses a transition-radiation/ionization-calorimeter combination. The CRNE instrument, constructed at the University of Chicago, was delivered to NASA for a first Shuttle flight on Spacelab-2 in summer 1985. Some of the technical and programmatic requirements encountered during the hardware construction and integration are discussed, and the expected scientific return and the prospects of using such instrumentation on the Space Station are considered.

Lheureux, J.↗

NASA NTRS1984

Electron-rich particle events and the production of gamma-rays by solar flares

The abundance of electrons of 5-50 MeV energies relative to protons of similar energy has been determined in a total of 49 particle events of apparently solar origin during the year 1980. Most events with high electron abundances appear to have been produced by flares which also produced observable fluxes of gamma-rays. The overall distribution of abundances is consistent with that measured in 1968-1970 at similar energies, but is systematically lower in electron content than abundance distributions measured at lower energies. Electron-rich particle events have harder electron spectra than more normal events, and are never accompanied by strong interplanetary shocks. Therefore, an investigation is conducted to decide whether observations are consistent with models in which energetic particles are accelerated by a shock produced at the flare site. It is concluded that, in such models, the variable nature of the interplanetary particle events must reflect some fundamental but variable property of the shocks - possibly their direction of propagation. An outward moving shock may produce a particle event in interplanetary space whereas a shock directed toward the sun may produce a flux of particles in the lower solar atmosphere which generate the gamma-radiation.

Evenson, P.↗

NASA NTRS1984

Relative abundance of the helium isotopes He-3 and He-4 in the cosmic radiation

The geomagnetic field near the equator is used to measure the He-3/He-4 abundance ratio near 6 GeV/nucleon. This ratio is found to be 0.24 + or - 0.05, under the assumption that the helium rigidity spectrum has the form dI/dR = about R exp(-2.65). If all He-3 is of secondary origin, this implies an interstellar mean escape-path length of about 15 g/sq cm, a value considerably larger than that determined from observations of heavier elements but compatible with measurements of the helium isotopic ratio at lower energies.

Jordan, S. P.↗

NASA NTRS1984

Solar modulation of cosmic ray electrons 1978-1983

The ISEE 3 spacecraft has provided over 4 years of continuous data from nearby interplanetary space. By using these data together with prelaunch calibration data and precise electron spectra from balloon flights in 1979 and 1982 at Thompson, Manitoba, Canada, the flux level of approximately 1 GeV cosmic ray electrons with 1 month time resolution is monitored. The step-like onset of modulation observed for positive particles in 1979 is also seen in electrons, confirming that the dominant modulation mechanism is not sensitive to the charge of the particle. Hysteresis effects observed in the previous solar maximum by Burger and Swanenburg (1973) are not reproduced at the present solar maximum. A return to the relatively higher electron/proton ratios of the 1960s is a strong possibility. Conclusions must be drawn with caution, however, since the overall time structure of the present solar maximum is significantly different from that of the previous one.

Evenson, P.↗

NASA NTRS1983

A quantitative test of solar modulation theory - The proton, helium, and electron spectra from 1965 through 1979

The predictions of a conventional, spherically symmetric model of solar modulation have been compared with the measured spectra of positively and negatively charged galactic cosmic-ray particles at 1 AU throughout the 1965-1976 solar cycle and through the enhanced modulation of 1979. For the proton/helium, proton/electron, and helium/electron flux ratios, there is remarkably good agreement between theory and experiment, except for small differences in 1965 and 1969. Possible systematic experimental errors are discussed, and it is concluded that: (1) the 11 year modulation process is largely independent of the sign of the particle charge; and (2) the assumption of steady state is a fairly good approximation for long term modulation.

Evenson, P.↗

NASA NTRS1983

Protons from the decay of solar flare neutrons

Fluxes of energetic protons in interplanetary space are observed which are interpreted as the decay products of neutrons generated in a solar flare on 1982 June 3 at 11:42 UT. Because of the particular geometry of this event the spectrum of neutrons escaping from the sun can be constructed with great accuracy in the kinetic energy range 10-100 MeV. The resulting spectrum places stringent constraints on the free parameters used in previously published calculations of neutron production in solar flares. An estimate is made of the diffusion mean free path of charged particles in the interplanetary medium in a new way.

Evenson, P.↗

NASA NTRS1983

The isotopic composition of helium at high rigidities

The isotopic abundance distribution of the cosmic radiation at energies beyond 1 GeV/AMU can at the present time be determined only with the geomagnetic method. A balloon-borne instrument was flown for 12 hours near the geomagnetic equator to measure the relative abundance of the helium isotopes He-3 and He-4 around 12 GV rigidity. The sharp rigidity cut-off at equatorial latitudes permitted separation of the two isotopes using a high-resolution-gas Cerenkov counter. The experiment thus confirms the predicted sharp cut-off at those latitudes and demonstrates the potential for isotopic separation of other elements, once flights of longer duration can be made.

Jordan, S. P.↗

NASA NTRS1983

Solar flare neutron fluxes derived from interplanetary charged particle measurements

The first observation of interplanetary protons produced by the decay of solar neutrons made by Evenson et al. (1983) after a solar flare which occurred on June 3, 1982, is expanded, extending the measurement of the spectrum of the decay protons to higher energy. The spectrum of the decay protons for the June 21, 1980, neutron event observed by Chupp et al. (1982) is also determined. The measurements suggest that neutron emission from solar flares is isotropic and that different flares emit neutrons with similar spectra. The importance of such measurements in the study of interplanetary propagation of charged particles is discussed.

Evenson, P.↗

NASA NTRS1982

Solar flare shocks in interplanetary space and solar flare particle events

Data on particle events resulting from three solar flares are examined to determine the effect of shocks on the population of protons at energies not less than 30 MeV. The arrival of the shock is found to mark the start of the decay phase of the particle event, and changes in particle anisotropy are found to be related to features in the shock structure. Two distinct modes of particle propagation are found to exist: a direct component, and a second component which has a time scale of days and is seen in two of the flares which also produced interplanetary shock. In addition, a model is described in which the protons are accelerated by the shocks, and it is shown to be in agreement with observations.

Evenson, P.↗

NASA NTRS1982

Gamma ray lines from buried supernovae

An investigation is conducted concerning the possibility that supernovae (SN), located in dense interstellar clouds, might become the sources of gamma ray lines. The SN progenitor, in such a case, has to be an O or B star so that its evolutionary lifetime is short, and an explosion inside the cloud is still possible. It is shown that, in principle, a measurement of the abundances in the ejecta is possible. Attention is given to the characteristics of a model, the expected luminosity of gamma-ray lines, and the study of specific numerical examples for testing the feasibility of the considered mechanism. On the basis of the obtained results, it is concluded that gamma-ray line production by collisional excitation in confined supernovae remnants may be quite important.

Morfill, G. E.↗

NASA NTRS1982

The source abundances of galactic cosmic rays

The galactic cosmic ray source abundances have been determined from two complete datasets, one at low and the other at high energy. For both exponential and truncated exponential pathlength distributions (PLD), the two sets of source abundances show significant differences for the primary elements, i.e., the Fe/O ratio. An energy dependent PLD reduces but does not eliminate the discrepancy, and this may indicate an energy dependence in the source composition. New source abundances for Na, P, Cl, Ca, and Mn are derived.

Dwyer, R. D.↗

NASA NTRS1982

The primary cosmic ray electron spectrum 1978-1980

In August of 1978 the ISEE-3 spacecraft carried the University of Chicago electron spectrometer into interplanetary space. Strong intensity variations of Jovian electrons have been observed in the energy range from 5 to 25 MeV in conjunction with 3 Jovian seasons. The spectral shape of the extra electrons has a shallow maximum around 15 MeV. No measurable long term variation in the average electron spectrum has been observed since 1968 up to energies of about 50 MeV. However, strong solar cycle modulation occurs at energies around a few hundred MeV.

Evenson, P.↗

NASA NTRS1981

High resolution determination of elemental abundances for Z equals 8-28 at 1.2-2.4 GeV/n

Results are reported from a series of high-altitude balloon flights of a combination scintillator-double Cerenkov counter telescope to obtain abundances for the nuclei oxygen through nickel corrected to the top of the atmosphere. Over this charge range unambiguous element separation, including the rare element cobalt, has been achieved. Final results are presented of an analysis giving relative abundances over this charge and energy range and compared with other recent experiments.

Dwyer, R.↗

NASA NTRS1981

Unusual properties of particle events associated with solar flare gamma ray events

An attempt to establish a link between gamma rays observed at the earth with solar flare areas highly enriched with electrons is presented. Two hour averages of the counting rates of 5-100 MeV electrons and 25-145 MeV protons performed on the ISEE-3 spacecraft were correlated with solar flares with a maximum intensity of 6-11 MeV electrons and 25-44 MeV protons recorded by other observers. The coverage was part of the Solar Maximum Mission, which attained a 50 percent coverage. Gamma ray associated events showed high ratios of electrons to protons, about 0.2, and electrons with energies greater than 80 MeV were observed, which are values high enough to produce the highest gamma rays observed, 40 MeV. The available data for electron, proton, and rare isotope fluxes and the time histories of the fluxes are noted to provide a data base for further information on solar flares and particle acceleration mechanisms.

Evenson, P.↗

NASA NTRS1981

The relation of type II radio bursts to solar energetic particles observed at earth

Observations of particle events associated with type II radio bursts as recorded on the ISEE-3 spacecraft are reported. Data on burst events following flares of Sept. 23,1978 and Aug. 18, 1979 yield time histories of the particle fluxes, which exceeded 25 MeV energy. The profiles of the Category-1 type II bursts display a continuous release of particles, which was concluded by no decrease in the fluxes until after the passage of the shock. The continuous nature of the recorded events suggests that the secondary acceleration process associated with the type II bursts is maintained as the flare shock propagates through interplanetary space, and may be the source of the energetic particles which propagate with the shock.

Evenson, P.↗

NASA NTRS1981

The cosmic ray electron/proton intensity ratio between 1965 and 1979

In experimental investigations, differences have been found regarding the modulation of low-energy electrons and protons. These differences cannot be explained on the basis of conventional theory. Evenson et al. (1979) have attempted to relate the differences in the modulation of electrons and protons to the solar field reversal of 1969-1971. The analyses have been inconclusive due to lack of a long time base and to a scarcity of reliable electron data. The present study represents an extension of he investigation of Evenson et al. (1979) to the time period 1965-1979. New data obtained in 1977-1979 are added, 1965 electron data are reexamined, and the time behavior of the helium/proton ratio is considered. It is concluded that there was a systematic shift in the intensity ratio of low-energy electrons to protons in the time period around the reversal of the solar polar magnetic field, leading to a clear difference in the values of the ratio for the two consecutive solar minima 1965 and 1976.

Evenson, P.↗

NASA NTRS1981

The rigidity dependence of cosmic ray solar modulation

Continuous particle flux measurements above rigidity thresholds of 1.2, 2.2, 5.5 and 11 GV were made by using the thresholds of two Cerenkov detectors aboard the ISEE-3 spacecraft. The ISEE-3 was launched in August 1978, near the beginning of the current solar cycle's heavy modulation phase, and the data presented represent the first direct measurement made at these energies with such a long time base. The measured long term modulation rigidity spectrum is compared with other data and with the spectrum of Forbush decreases, and it is found that the agreement between electron and positively charged particle results must be considered a constraint on cosmic ray modulation models involving the mechanism of gradient and curvature drift in the interplanetary magnetic field.

Evenson, P.↗

NASA NTRS1981

A new transition radiation detector for cosmic ray nuclei

Test measurements on materials for transition radiation detectors at a low Lorentz factor are reported. The materials will be based on board Spacelab-2 for determining the composition and energy spectra of nuclear cosmic rays in the 1 TeV/nucleon range. The transition radiation detectors consist of a sandwich of radiator-photon detector combinations. The radiators emit X-rays and are composed of polyolefin fibers used with Xe filled multiwired proportional chamber (MWPC) detectors capable of detecting particle Lorentz factors of several hundred. The sizing of the detectors is outlined, noting the requirement of a thickness which provides a maximum ratio of transition radiation to total signal in the chambers. The fiber radiator-MWPC responses were tested at Fermilab and in an electron cyclotron. An increase in transition radiation detection was found as a square power law of Z, and the use of six radiator-MWPC on board the Spacelab-2 is outlined.

Lheureux, J.↗