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

The binding energies of Si-29, S-33, and Cl-36 have been measured with a relative uncertainty of < 0.59x10(-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(-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.