Jacques L'Heureux

Energy spectra and composition of primary cosmic rays

New results are described on the energy spectra and relative abundances of primary cosmic ray nuclei from carbon to iron. The measurement was performed on the Spacelab-2 mission of the Space Shuttle Challenger in 1985, and extends to energies beyond 1 TeV per amu. The data indicate that the cosmic ray flux arriving near earth becomes enriched with heavier nuclei, most notably iron, as energy increases. Extrapolating to the source, with a simple leaky box model of galactic propagation with rigidity-dependent containment time, relative abundances of the elements are obtained that are quite similar to those reported at lower energy. In particular, the depletion of elements with high first ionization potential relative to the local galactic abundances, seems to persist in the cosmic ray source well up to TeV energies. A single power-law energy spectrum about E exp {minus}2.1 provides a good description of the observed spectra of most elemental species. 33 refs.

Relative abundances of secondary and primary cosmic rays at high energies

New results on the energy spectra of the cosmic-ray nuclei boron, carbon, nitrogen, and oxygen up to energies around 1 TeV per amu are described. The measurements were performed on the Spacelab 2 mission of the Space Shuttle in 1985. Carbon and oxygen are essentially primary cosmic rays, while boron is purely secondary, and nitrogen has secondary as well as primary contributions. Therefore, the relative abundances of these nuclei provide sensitive information on the propagation of cosmic rays through the Galaxy. It is found that the flux of the secondary cosmic rays continues to decrease relative to that of the primaries over the energy range covered with this observation, and that the mean escape length near 1 TeV per amu is about 1 g/sq cm. 36 refs.

Elemental abundances in the local cosmic rays at high-energies

We discuss recent measurements of cosmic-ray fluxes at high energy. The energy spectra of heavy nuclei determined on the Space Shuttle and on HEAO 3 are considered in the context of a simple leaky box model. A fit to this model requires a source energy spectrum of the form E −2.2 for all nuclear species, which is slightly steeper than our previous estimate. We represent these data in terms of total energy per particle to make a direct comparison with the observed all-particle spectrum of cosmic rays

The Primary Cosmic Ray Electron Spectrum near Solar Minimum

Primary cosmic ray electron flux and energy spectrum near solar minimum compared with nonthermal radio emission from high galactic latitudes

A detector for cosmic-ray nuclei at very high energies

Abstract We discuss the design and performance of a detector system that was developed to measure the elemental abundance distribution of cosmic-ray nuclei with energies up to several TeV/amu. The low flux of high-energy cosmic rays requires an instrument with large geometric factor, but of reasonably low weight to be carried on the Space Shuttle. To meet these conditions we designed a counter telescope with gas Cherenkov counters and transition radiation detectors for particle energy measurements. Scintillation counters determine the particles atomic number. We describe design and performance of these individual detectors and their interplay in the instrument. The instrument was flown for eight days in the Spacelab-2 configuration on the Space Shuttle in July/August 1985.

The quiet-time spectra of cosmic-ray electrons of energies between 10 and 200 MeV observed on OGO-5.

Measurement of spectra of cosmic-ray electrons of energies between 10 and 200 MeV over a one-year period starting 1968 March. The measurement was made with a detector system on board the OGO-5 satellite. The instrument consists of a solid-state dE/dx detector, a total-energy CsI detector, a gas Cerenkov threshold detector, and two scintillation guard counters. Time periods during which no solar-flare events were recorded were selected for the study. It was found that during these quiet periods there were numerous intensity variations of the electron flux. These variations, which are seen only below 25 MeV, do not show marked correlation with any solar or interplanetary-medium parameters. The flux of the electrons of energies above 25 MeV, on the other hand, showed a gradual decrease over the one-year period, paralleling the neutron monitor intensity. The parameter describing this long-term modulation is almost independent of the rigidity of the electrons in the reported energy range. The physical implication of the finding is discussed.

Energy spectra of cosmic-ray nuclei from 50 to 2000 GeV per amu

A direct measurement of the elemental composition of cosmic rays up to energies of several TeV/amu was performed during the Spacelab 2 flight of the Space Shuttle. Results on the spectral shape for the elements C, O, Ne, Mg, Si, and Fe, obtained from this experiment, are presented. It was found that the C and O energy spectra retain a power-law spectrum in energy with an exponent Gamma of about 2.65. The Fe spectrum is flatter (Gamma of about 2.55) up to a particle energy of about 10 to the 14th eV, indicating a steady increase in the relative abundance of iron in cosmic rays up to this energy. The energy spectra of Ne, Mg, and Si are steeper than anticipated. This behavior is unexpected within current models of cosmic-ray acceleration. 12 references.

Quiet-time increases of low-energy electrons: The Jovian origin

With a detector on board the OGO-5 satellite, the flux and energy spectrum of electrons in the 10--200 MeV range has been continuously measured from 1968 to 1971. Sudden increases in intensity by factors of up to 300 percent have been observed during solar quite times. We show that these increases are nearly independent of energy up to approx.25 MeV and disappear rapidly above that energy. The frequency of the increases peaks every 13 months at a time following the crossing by the Earth of the interplanetary magnetic field line which passes the vicinity of the planet Jupiter. Most of the increases occur in a 3--5 month period following this crossing, and often appear to be 27 days apart. A Jovian origin for these electrons and their mode of transport to the inner solar system are discussed. (AIP)

Measurements of X-ray transition radiation from plastic fibers☆

Abstract Test measurements are presented on a new kind of radiator material for generating X-ray transition radiation by the passage of relativistic charged particles. This material consists of mats of thin polyolefin fibers which, when combined with multiwire proportional chambers, can be easily made into large area (several m2) detectors. Fibers of different thicknesses can be combined to give a response over a wide range of Lorentz factors, 500 ⪅ γ ≲ 15 000. The application of this material in a large detector for cosmic ray nuclei is discussed.

Cosmic gamma-ray burst detected with an instrument on board the OGO-5 satellite

Gamma-ray bursts of cosmic origin have recently been detected by instruments on the Vela satellites. We now confirm the detection of the June 30, 1971 event with an instrument on board the OGO-5 satellite. The intensity of this burst is calculated to be approximately 100-200 photons per sq cm/sec for photons of energy greater than 150 keV with an upper limit of 50 photons per sq cm/sec for the intensity above 5 MeV. An upper limit of one-third of the intensity of the June 30, 1971 event is set for 10 other events studied.