Progress on the GAMS-6 double crystal γ-spectrometer

Measuring the wavelength of gamma-rays emitted after a neutron capture reaction allows a direct determination of the molar Planck constant N_Ah. Currently these measurements are realized using the high resolution double crystal spectrometers GAMS4 and GAMS5 placed at the high flux reactor of the Institut Laue-Langevin in Grenoble, France. So far it was possible to achieve a relative uncertainty of 4 times 10^-7. In this contribution we describe the progress in building a new generation crystal spectrometer, GAMS 6, which is meant to lower the uncertainty to the 10^-8 level.