Precision measurement of the {sup 29}Si, {sup 33}S, and {sup 36}Cl binding energies

The binding energies of {sup 29}Si, {sup 33}S, and {sup 36}Cl have been measured with a relative uncertainty of <0.59x10{sup -6} using a flat-crystal spectrometer. The unique features of these measurements are (1) nearly perfect crystals whose lattice spacing is known in meters, (2) a highly precise angle scale that is derived from first principles, and (3) a {gamma}-ray measurement facility that is coupled to a high-flux reactor with near-core source capability. The binding energy is obtained by measuring all {gamma}-rays in a cascade scheme connecting the capture and ground states. The measurements require the extension of precision flat-crystal diffraction techniques to the 5- to 6-MeV energy region, a significant precision measurement challenge. The binding energies determined from these {gamma}-ray measurements are consistent with recent highly accurate atomic-mass measurements within a relative uncertainty of 4.3x10{sup -7}. The {gamma}-ray measurement uncertainties are the dominant contributors to the uncertainty of this consistency test. The measured {gamma}-ray energies are in agreement with earlier precision {gamma}-ray measurements.