CRS INSTRUMENTS

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.

Voyager Spacecraft Gif

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.