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.
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.
Click the Schematic to Enlarge
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
mnemonic area thickness
***************** 3uM AL collimator
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
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.
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
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
| 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
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.
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.
.25 mm tungsten absorber
.56 mm tungsten absorber
1.12 mm tungsten absorber
1.60 mm tungsten absorber
2.03 mm tungsten absorber
2.34 mm tungsten absorber
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",
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.