ERS 17 & 18

Environmental Research Satellites 17 & 18

Environmental Research Satellites 17 & 18

Gamma Ray Counters

The Cosmic Gamma-Ray Experiment on ERS-17 measured incident gamma-ray flux in five energy bands from 30 keV to 10 MeV, as well as cosmic ray particle flux above 10 MeV. The single detector unit consisted of a large NaI(Tl) crystal, 5.04 cm in diameter by 5.72 cm long, enclosed in a 0.3 cm thick NE-102 plastic scintillator. This assembly was optically coupled to an RCA 4461 photomultiplier tube. Events arising from the NaI(Tl) produced scintillations with a long rise and decay, whilst events in the plastic exhibited much faster decay times. Gamma-rays were discriminated from charged particles by electronic circuitry that required the presence of a long pulse and the absence of a fast one. The rates were collected in five energy bands: 33-75 keV, 75-365 keV, 0.365-1.07 MeV, 1.07-3.54 MeV, and 3.54-10.3 MeV. Events above 10.3 MeV were also monitored and represented cosmic rays.

ERS-18 carried two gamma-ray detectors: one shielded with graphite to stop low energy protons and electrons and providing a measurement of gamma-rays in the 1-3MeV range, and a variation of the ERS-17 system with a separate photomultiplier viewing the plastic scintillator. The Shielded Gamma-ray Counter consisted of a 1.91 cm long by 1.91 cm diameter NaI(Tl) scintillation crystal within a carbon cylinder 1.75 cm thick. The NaI(Tl) crystal was viewed by a RCA 4460 photomultiplier. The Dual Gamma-ray Counter consists of a 7.62 cm long by 6.72 cm diameter NaI(Tl) crystal viewed by a RCA 4461 photomultiplier. Surrounding the NaI(Tl) crystal on all but the side attached to the photomultiplier is a bucket of NE-102 plastic scintillator viewed by a separate RCA 4461 photomultiplier. Events in the NaI(Tl) seen simultaneously by the plastic scintillator were rejected as due to charged particles. This anticoincidence function was regularly switched on and off to allow for monitoring of its efficiency at charged particle rejection. Cosmic gamma-ray fluxes were measured in five energy ranges: 0.250-0.600 MeV, 0.6-1.0 MeV, 1-2 MeV, 2-3.7 MeV, and 3.7-6 MeV.

ERS 17 & 18 Information

Mission Objectives
Spacecraft
Gamma-ray Counters
Scientific Results
Publications