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INSTRUMENTATION

The California Institute of Technology/Goddard Space Flight Center Cosmic Ray Subsystem (CRS) experiment on the Voyagers, with a mass of 7.50 kg and power requirement of 5.35 W, consists of three types of solid state detector telescopes mounted on the science boom.

Voyager Spacecraft Gif

On each space craft CRS consists of four low-energy telescopes (LETs), referred to as LETs A, B, C, and D (marked in the figure below); two double-ended high-energy telescopes (HETs) referred to as HET 1A, 1B, 2A and 2B (shown in the the figure below on the left and right); and an electron telescope (TET) located under LET A. These telescopes measure the energy spectra and elemental composition of nuclei from hydrogen through nickel over an energy range from 3-500 MeV/nucleon and the energy spectrum of electrons from 3-110 MeV.

Graphic of CRS Instrument Gif

Graphic of CRS Instrument Gif
Click the Schematic to Enlarge


LET

The LET is a double dE/dx vs E solid state detector. This detector was designed to measure low-energy solar flare particles in interplanetary space and trapped particles in the Jovian and Saturnian magnetospheres. Its geometry factor (4.4E-01 cm2-sr) allows measurement of fluxes as high as 5.0E+05/(cm2-s-sr).

A particle entering this telescope must first pass through a 3 micron Aluminum collimator which helps define the geometry and then two thin (2.8 cm2 by 35 microns thick) surface barrier detectors which provide a double dE/dx measurement. Two lithium drift detectors (4.5 cm2 by 450 microns thick) provide another dE/dx measurement and a total energy measurement. The LET covers the energy range 1.8 to 30 MeV/nucleon with charge resolution from Z=1 to 28.

                element
                mnemonic              area      thickness

                     *****************   3uM AL collimator
                                           light baffle

                  L1    ---------  2.8 cm**2 surface barrier 35 uM



                  L2    ---------  2.8 cm**2 surface barrier 35 uM

                  L3    xxxxxxxxx  4.5 cm**2 surface barrier 450 uM

                  L4    xxxxxxxxx  4.5 cm**2 surface barrier 450 uM

 

Library Document:  'SRL_Technical_Report_76-1.pdf' Page 11

LET   2) PHA, Discriminator Values

Detector     Threshold     Full Scale     Channel Width
             (MeV)         (Mev)          (keV)
L1,L2        0.2            307            75
L3           1.00          2048           500
L4           0.3             XX            XX

Slant
SL:      L1 + 0.42L2 + 0.20L3 + 9.6  (MeV)

L4:      10V preamp output for 25 MeV
         2:1 transformer is on output of L4 preamp.

 


HET

Each High Energy Telescope consists of a multi-element stack of solid state detectors and covers an energy range between 6 and 500 MeV/nucleon for nuclei ranging in atomic numbers from 1 through 30.

Particles can enter this telescope from both ends of this stack. The Two "A" elements (see diagram below) are single lithium drift detectors, 8 cm2 in area and .15 mm thick. The "C1" element is a surface barrier detector 8 cm2 in area and 3 mm thick. Next is an array of six "C" surface barrier detectors each 8 cm2 in area and 6 mm thick and finally two curved 8 cm2 by 2 mm thick "B" detectors are stacked to form a two-ended telescope.

For particles which come to rest within this stack (4 - 70 MeV/ nucleon) three measurements are made: energy loss (dE/dx), total energy, and range. For particles which penetrate completely through the stack of solid state detectors three separate dE/dx measurements are made. This multiparameter analysis reduces the back-ground level of spurious events to a negligible level. Charge resolution for penetrating particles is possible up to about 200 MeV/nucleon. It is estimated that the absolute uncertainty in the helium flux is about 7% at 400 MeV and about 5% at energies below 200 MeV.

                Element               area      thickness

                   A1      ---------  8 cm**2   0.15 mm



                   A2      ---------  8 cm**2   0.15 mm

                   C1      xxxxxxxxx  9.5 cm**2  3 mm
              G1
                |  C2a     xxxxxxxxx  9.5 cm**2  6 mm
                |  C2b     xxxxxxxxx
                |
                |  C3a     xxxxxxxxx  9.5 cm**2  6 mm
                |  C3b     xxxxxxxxx
                |
                |  C4a     xxxxxxxxx  9.5 cm**2  6 mm
                |  C4b     xxxxxxxxx
                            _______
                   B2     //       \\ 8 cm**2    2 mm  curved

                   B1     \\_______// 8 cm**2    2 mm  curved

 

Library Document:  'SRL_Technical_Report_76-1.pdf' Page 6

HET         2) PHA, Discriminator Values

                 |         High Gain          |           Low Gain            |
Detector         thresh     full     channel     thresh     full     channel     gain change
                            scale    width                  scale    width       factor
                 (MeV)      (MeV)    (keV)       (MeV)      (GeV)    (MeV)


A1,A2            0.1         188      46         0.5         0.94    0.23        5.
B1               0.3         730     178         1.02        2.50    0.61        3.42
B2               0.3         730     178         2.04        5.00    1.22        6.84
C1               0.5        1024     250         2.5         5.12    1.25        5.
C2, C3, C4       0.92         XX      XX         4.6           XX      XX        5.
C1 + C2 + C3     XX         3523     860          XX        17.61    4.30        5.
C2 + C3 + C4     XX         3523     860          XX        17.61    4.30        5.
G1               0.3          XX      XX         0.3           XX      XX        XX
G2               2.5          XX      XX         2.5           XX      XX        XX
G3               9.           XX      XX         9.            XX      XX        XX

Slants

SB:                       B1 + B2 + (2 + 3 + 4) = 60               (channels)
           Low Gain       B1 + 0.5B2 + 0.142(C2 + C3 + C4) = 36.6  (MeV)
           High Gain      B1 + B2 + 0.207(C2 + C3 + C4) = 10.7     (MeV)

SA:        Low Gain only  SA2:  A1 + 0.60A2 + 0.29(C1 + C2 + C3) = 24 (MeV)
                          SA1:  A1 + 0.60A2 + 0.02(C1 + C2 + C3) = 9  (MeV)
                          SA = SA1.SA2

Full Scale = 10V in preamp, 5v in ADC; coupling done with 2:1 transformer
G1, G2, G3:  10V preamp output for 396 MeV, not gain switched.
C2, C3, C4:  10V preamp output for 1.86 GeV in high gain, 9.63 GeV in low gain

The HET geometry factor varies from about .74 - 1.7 over the energy range covered by the telescope depending on whether the event is A Stopping, B Stopping, or Penetrating.

 


TET

The Electron Telescope consists of eight solid state detectors, each 3 mm thick and 4.5 cm2 in area. These detectors, with varying depth tungsten absorber between each element, are used individually and in coincidence as total absorption spectrometers.

                   D1      xxxxxxxxx


                   D2      xxxxxxxxx
                             .25 mm tungsten absorber
                   D3      xxxxxxxxx
                             .56 mm tungsten absorber
                   D4      xxxxxxxxx
                            1.12 mm tungsten absorber
                   D5      xxxxxxxxx
                            1.60 mm tungsten absorber
                   D6      xxxxxxxxx
                            2.03 mm tungsten absorber
                   D7      xxxxxxxxx
                            2.34 mm tungsten absorber
                   D8      xxxxxxxxx

                   Di detectors= 4.5 cm**2 Lithium drifted 3mm
                   tungsten absorbers are 18.0 g/cm**3

                   where cm = centimeters
                         mm = millimeter
                   where uM = micrometer

TET geometry factor varies from about .66 - 3.12 depending upon depth of penetration into the Di stack.

 

Library Document:  'SRL_Technical_Report_76-1.pdf' Page 16

TET    2) PHA, Discriminator Values

Detector     Threshold          Full Scale     Channel
             Lower     Upper                   Width
             (MeV)     (MeV)    (Mev)          (keV)
D1, D2       0.5       2.5      2.5            19.4
D3 to D7     0.5       8.0       XX              XX
D8           0.2        XX       XX              XX
GA, GB       0.2        XX       XX              XX

Preamp full scale  10V = 24.70 MeV
2.47 MeV = channel 127 of ADC


CRS Instrument Issues


For more technical information on the Cosmic Ray Subsystem telescopes please refer to the following documents:

D.E.Stillwell, 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 Voyager Cosmic Ray Instrument", IEEE Transactions on Nuclear Science, Vol. 26, 1979, pp. 513

E. C. Stone, 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 Science Reviews, 21, 355-376, 1977.

 
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