The California Institute of Technology/Goddard Space Flight Center
Cosmic Ray Subsystem (CRS) experiment on Voyager
consists of three types of solid state detector telescopes:
The HETs and LETs are redundant and are designed to complement each
other and to cover a broad range in energy, intensity, and charge
spectra. Click the Space craft image to go to instrument webpage at the Jet Propulsion Labortory.
High Energy Telescope (HET)
Each High Energy Telescope consists of a multi-element stack
of solid state detectors. 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
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.
Low Energy Telescope (LET)
Low Energy Telescope. This detector was designed to measure
low-energy solar flare particles in the 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). The LET is a double dE/dx vs. E
solid state detector. To enter this telescope a particle 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 thick
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
The LET geometry factor is nominally 0.440 cm2-steradian.
LET Thickness and Delta Z Corrections
The Electron Telescope (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.
For more technical information on the Cosmic Ray Subsystem telescopes
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.
