  The performance of germanium detectors for high-energy $\gamma$-rays was
evaluated using a 992-keV resonance in the $^{27}$Al(p, $\gamma$)$^{27}$Si
reaction. The measurement was conducted at the RIKEN tandem accelerator. The
energy of the excited state from the resonance was evaluated as 12540.7(2) keV.
Using newly evaluated excitation energy, an energy calibration function and the
photo-peak efficiency of Ge detectors up to 10.8-MeV photon were deduced. The
energy accuracy is achieved at 0.3 keV for the overall energy region. This
reaction provides reliable energy and efficiency standards for high-energy
$\gamma$ rays.
