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Instrument Information

INSTRUMENT_TYPE Cosmic Ray Detector
  Instrument Overview
    As its name implies, the Cosmic Ray Subsystem (CRS) was
    designed for cosmic ray studies [STONEETAL1977B].  It consists
    of two high Energy Telescopes (HET), four Low Energy Telescopes
    (LET) and The Electron Telescope (TET).  The detectors have
    large geometric factors (~ 0.48 to 8 cm^2 ster) and long
    electronic time constants (~ 24 [micro]sec) for low power
    consumption and good stability.  Normally, the data are
    primarily derived from comprehensive ([Delta]E[1], [Delta]E[2]
    and E) pulse- height information about individual events.
    Because of the high particle fluxes encountered at Jupiter and
    Saturn, greater reliance had to be placed on counting rates in
    single detectors and various coincidence rates.  In
    interplanetary space, guard counters are placed in
    anticoincidence with the primary detectors to reduce the
    background from high-energy particles penetrating through the
    sides of the telescopes.  These guard counters were turned off
    in the Jovian magnetosphere when the accidental anticoincidence
    rate became high enough to block a substantial fraction of the
    desired counts.  Fortunately, under these conditions the
    spectra were sufficiently soft that the background, due to
    penetrating particles, was small.
    The data on proton and ion fluxes at Jupiter were obtained with
    the LET.  The thicknesses of individual solid-state detectors
    in the LET and their trigger thresholds were chosen such that,
    even in the Jovian magnetosphere, electrons made, at most, a
    very minor contribution to the proton counting rates
    [LUPTON&STONE1972;].  Dead time corrections and accidental
    coincidences were small (< 20%) throughout most of the
    magnetotail, but were substantial (> 50%) at flux maxima within
    40 R[J] Of Jupiter.  Data have been included in this package
    for those periods when the corrections are less than ~ 50% and
    can be corrected by the user with the dead time appropriate to
    the detector (2 to 25 [micro]sec).  The high counting rates,
    however, caused some baseline shift which may have raised
    proton thresholds significantly.  In the inner magnetosphere,
    the L[2] counting rate was still useful because it never rolled
    over.  This rate is due to 1.8- to 13-MeV protons penetrating
    L[1] (0.43 cm^2 ster) and > 9-MeV protons penetrating the
    shield (8.4 cm^2 ster).  For an E^-2 spectrum, the two groups
    would make comparable contributions; but in the magnetosphere,
    for the E^-3 to E^-4 spectrum above 2.5 MeV [MCDONALDETAL1979],
    the contribution from protons penetrating the shield would be
    only 3 to 14%.
    The LET L[1]L[2]L[4] and L[1]L[2]L[3] coincidence-
    anticoincidence rates give the proton flux between 1.8 and 8
    MeV and 3 to 8 MeV with a small alpha particle contribution (~
    10^-3).  Corrections are required for dead time losses in L[1],
    accidental L[1]L[2] coincidences and anticoincidence losses
    from L[4].  Data are given only for periods when these
    corrections are relatively small.  The energy lost in detectors
    L[1], L[2] and L[3] was measured for individual particles.  For
    protons, this covered the energy range from 0.42 to 8.3 MeV.
    Protons can be identified positively by the [Delta]E vs.  E
    technique, their spectra obtained and accidental coincidences
    greatly reduced.  Because of telemetry limitations, however,
    only a small fraction of the events could be transmitted, and
    statistics become poor unless pulse-height data are averaged
    over a period of one hour.
    HET and LET detectors share the same data lines and pulse-
    height analyzers; thus, the telescopes can interfere with one
    another during periods of high counting rates.  To prevent such
    an interference and explore different coincidence conditions,
    the experiment was cycled through four operating modes, each
    192 seconds long.  Either the HETs or the LETs were turned on
    at a time.  LET-D was cycled through L[1] only and L[1]L[2]
    coincidence requirements.  The TET was cycled through various
    coincidence conditions, including singles from the front
    detectors.  At the expense of some time resolution, this
    procedure permitted us to obtain significant data in the outer
    magnetosphere and excellent data during the long passage
    through the magnetotail region.  Some of the published results
    from this experiment required extensive corrections for dead
    time, accidental coincidences and anticoincidences
    [GEHRELSETAL1981]).  These corrections can be applied only on a
    case-by-case basis after a careful study of the environment and
    many self-consistency checks.  They cannot be applied on a
    systematic basis and we have no computer programs to do so;
    therefore, data from such periods are not included in the Data
    Center submission.  The scientists on the CRS team will,
    however, be glad to consider special requests if the desired
    information can be extracted from the data.
    Principal Investigator: R.E.  Vogt
    The preceding section on instrumentation has been extracted
    from the NSSDC documentation for the Voyager Cosmic Ray
    Subsystem (Reference_ID = NSSDCCRS1979).
REFERENCE_DESCRIPTION Gehrels, N., E.C. Stone, and J.H. Trainor, Energetic oxygen and sulfur in theJovian magnetosphere, J. Geophys. Res., 86, 8906, 1981.

Lupton, J.E., and E.C. Stone, Measurement of Electron DetectionEfficiencies in Solid-state Detectors, Nucl. Instr. and Meth. 98, 189,1972.

McDonald, F.B., A.W. Schardt, and J.H. Trainor, Energetic Protons in theJovian Magnetosphere, J. Geophys. Res. 84, 2579, 1979.

Data and instrument description document provided by the NSSDC for dataset 77-048A-08A, Voyager 1 and 2 Cosmic Ray Subsystem Description ofJupiter Encounter Data. 1979.

Schardt, A.W., F.B. McDonald, and J.H. Trainor, Energetic Particles in thePre-dawn Magnetotail of Jupiter, J. Geophys. Res., special Voyager issue,1981.

Stilwell, D.E., W.D. Davis, R.M. Joyce, F.B. McDonald, J.H. Trainor, W.E.Althouse, A.C. Cummings, T.L. Garrard, E.C. Stone, and R.E. Vogt, The VoyagerCosmic Ray Experiment, IEEE Trans. on Nuclear Science, Vol. 26, p. 513, 1979.

Stone, E.C., R.E. Vogt, F.B. McDonald, B.J. Teegarden, J.H. Trainor, J.R.Jokipii, and W.R. Webber, Cosmic ray investigation for the Voyager missions;energetic particle studies in the outer heliosphere--and beyond, Space Sci.Rev., 12, No. 3, 355-376, Dec. 1977.

Vogt, R.E., W.R. Cook, A.C. Cummings, T.L. Garrard, N. Gehrels, E.C. Stone,J.H. Trainor, A.W. Schardt, T. Conlon, N. Lal, and F.B. McDonald, Voyager 1:Energetic Ions and Electrons in the Jovian Magnetosphere, Science, 204, 1003,1979.