Abstract
DuMond-type curved-crystal γ-ray spectrometers have been constructed and installed at the High Flux Reactor in Grenoble. They are used for the measurement of low energy γ-rays up to about 1500 keV emitted by an in-pile target after neutron capture. The target is located in the center of the tangential throughtube where the flux of thermal neutrons is ∼ 5.5 × 10 14/cm 2s. Two separate spectrometer systems, one of focal length 5.76 m (GAMS 1) and the other of focal length 24.0 m (GAMS 2/3) view the source from the opposite ends of the beam tube. The GAMS 1 spectrometer is designed to operate in the γ-ray energy interval 20 ⪅ E γ ⪅ 400 keV. Angular resolution as small as 1.1 arcsec have been achieved with this instrument. The GAMS 2 3 sysmt em consists of two spectrometers on top of each other, operating at +θ Bragg and −θ Bragg, respectively. The GAMS 2 3 diffractome ter is designed to cover the energy interval 200 ⪅ E γ ⪅ 1500 keV. Minimum line widths of ∼0.8 arcsec have been achieved. In routine measurements the detection sensitivity for neutron capture γ-rays is ∼1 mb, for GAMS 1 between 80 keV and 300 keV and for GAMS 2 3 from 300 keV to 800 keV. Both spectrometer systems allow for source migrations due to heating effects in the beam tube. The reflection angles in the spectrometers are measured with Michelson-type angle interferometers. The spectrometers serve mainly for nuclear structure studies.
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