Voyager 1 Jupiter Cosmic Ray Subsystem (CRS) Derived Proton, Ion, and Electron Fluxes, Version 1.0, 15 min Browse Data

* Data Set Overview\n* =================\n\n+------------------------------------------------------------------------------------------+\n| Data Set Characteristics          | Value                                                |\n--------------------------------------------------------------------------------------------\n| Instrument Principal Investigator | Rochus E. Vogt                                       |\n| Data Supplier                     | National Space Science Data Center                   |\n| Data Sampling Rate                | Variable (1 hr for FPHA Data, 15 min for all others) |\n| Data Set Start Time               | 1979-02-28T00:00:00.000Z                             |\n| Data Set Stop Time                | 1979-03-21T23:45:00.000Z                             |\n+------------------------------------------------------------------------------------------+\n\nThe following Description has been adapted from NSSDC CRS, 1979:\n\nAs its Name implies, the Cosmic Ray Subsystem (CRS) was designed for Cosmic Ray Studies (Stone et al., 1977b). It consists of two High Energy Telescopes (HET), four Low Energy Telescopes (LET) and The Electron Telescope (TET). The Detectors have large Geometric Factors (about 0.48 cm^2 sr to 8 cm^2 sr) and long Electronic Time Constants (∼24 µs) for low Power Consumption and good Stability. Normally, the Data are primarily derived from comprehensive (δE[1], δE[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.\n\nThe 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 and Stone, 1972). Dead Time Corrections and accidental Coincidences were small (<20%) throughout most of the Magnetotail, but were substantial (>50%) at Flux Maxima within 40 Rj 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 δs to 25 δs). 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 MeV to 13 MeV Protons penetrating L[1] (0.43 cm^2 sr) and >9 MeV Protons penetrating the Shield (8.4 cm^2 sr). 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 (McDonald et al., 1979), the Contribution from Protons penetrating the Shield would be only 3% to 14%.\n\nThe LET L[1]L[2]L[4] and L[1]L[2]L[3] Coincidence-Anticoincidence Rates give the Proton Flux between 1.8 MeV and 8 MeV and 3 MeV 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. In addition to the Rates listed in the Table, 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 MeV to 8.3 MeV. Protons can be identified positively by the δE versus 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.\n\nHET 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 s 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.\n\nSome of the published Results from this Experiment required extensive Corrections for Dead Time, accidental Coincidences and Anticoincidences (Vogt et al., 1979a, Vogt et al., 1979b, Schardt et al., 1981, Gehrels, 1981). 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.\n\n* Description of the Data\n* =======================\n\n(1) LD1 RATE gives the nominal >0.43 MeV Proton Flux (cm^2 s sr)^-1. This Rate includes all Particles which pass through a 0.8 mg/cm^2 Aluminum Foil and deposits more than 220 keV in a 34.6 µm Silicon Detector on Voyager 1 (209 keV, 33.9 µm on Voyager 2) Therefore, Heavy Ions, such as Oxygen and Sulfur are also detected, however, their Contribution is believed to be relatively small. Only a small Percentage of the Pulses in this Detector are larger than the maximum Energy that can be deposited by a Proton. Heavy Ions would produce such large Pulses, unless their Energy Spectra were much steeper than the Proton Spectrum. The true Flux, F(t), can be calculated from the Data:\n\nF(t) = F/(1-1.26x10^-4 F)\n\nand Corrections are small for F<1000 (cm^2 s)^-1.\n\n(2) The LD2 RATE is not suitable for an Absolute Flux Determination and is given in counts per second. The Detector responds to Protons and Ions that penetrate either (a) 0.8 mg/cm^2 Aluminum plus 8.0 mg/cm^2 Silicon and lose at least 200 keV in a 35 µm Si Detector (1.8 MeV to 13 MeV) or (b) pass through >140 mg/cm^2 Aluminum. For an E^-2 Proton Spectrum, the Contributions from (a) and (b) would be about equal, however, the Proton Spectrum is substantially softer throughout most of the Magnetosphere and the Detector should respond primarily to (a). Dead Time Corrections are given by\n\nR(t) = R/(1-2.55x10^-5 R)\n\nwhere R is the Count Rate in counts per second. Thus, Correction to the supplied data are small for R<4000 counts per second, but become so large in the middle Magnetosphere that the Magnitude of even relative intensity Changes becomes uncertain.\n\n(3) LD L[1].L[2].L[4]. SL COINCIDENCE RATE gives the total Proton Flux (cm^2 s sr)^-1 between 1.8 MeV and 8.1 MeV with a small Admixture of Alpha Particles. Accidental Coincidences become subst

Tags: energeticparticles
Organization: National Aeronautics and Space Administration