High accuracy, absolute wavelength determination of capture gamma-ray energies for E⩽5 MeV and the direct determination of binding energies in light nuclei

A substantially improved double flat crystal gamma ray spectrometer (GAMS4) has been put into operation as a joint NBS/ILL facility at the HFR, Grenoble. This facility has the capability of determining gamma ray wavelengths, in absolute units, with uncertainties on the order of 0.1 ppm in the energy range from 0.1 to approximately=5 MeV. This new facility incorporates a number of major improvements over the earlier double flat crystal spectrometer used to determine the n-p 2.2 MeV line with an error of 1 ppm (2 eV). The operation of the instrument and the nature of the improvements is discussed. Experimental results related to the direct determination of the binding energy of several light nuclei (for example D, ¹³C, ¹⁵N) are given. The implications of this work for the atomic mass scale and for the determination of fundamental constants is reviewed.