Gamma-ray energies from the reactionCl35(n,γ)

A two-axis flat-crystal spectrometer has been used to measure accurately gamma-ray energies up to 2 MeV from the reaction ${}_{}{}^{35}{}_{}{}^{}\mathrm{Cl}$(n,γ). This represents a fourfold extension of the range of direct optically based gamma-ray energies. The crystals and spectrometer have performed in a manner which demonstrates that sub-ppm measurements are possible at energies ≳2 MeV. The reported transition energies (in eV) are 517 077.41±0.23, 786 311.32±0.38, 788 437.43±0.44, 1 164 885.74±0.48, 1 951 197.06±0.58, and 1 959 413.45±8.45. The sum rule is satisfied by three of the lines (786 keV+1165 keV=1951 keV) within an uncertainty of ∼1 ppm.