The GAMS4 flat crystal facility

A high-resolution flat-crystal gamma-ray facility, GAMS4, has been constructed at the high-flux reactor at the Institut Laue-Langevin (ILL), Grenoble, France. The facility is located at the exit of a through-tube equipped to place sources in a neutron flux of ≈5.5×1014 n cm−2 s−1. Considerable care has been exercised to provide a precision gamma-ray metrology station including vibration isolation, temperature control, environmental monitoring, background suppression, and remote and automatic spectrometer control. The diffraction angles are controlled and measured interferometrically and absolute angle calibration is established with a relative uncertainty of ≈3×10−7. The crystals are nearly perfect specimens of Si and Ge whose lattice spacings are measured in meters and have a relative uncertainty of ≈5×10−8. The resolution obtained with this facility closely approaches dynamical diffraction predictions. Examples of measurements performed using this facility include (1) absolute wavelengths standards and neutron binding energies, (2) lifetimes of nuclear exited states, (3) determination of interatomic potentials, and (4) crystal structure factors. GAMS4 is a scheduled ILL instrument with beamtime being awarded through the ILL proposal process.