[en] An efficiency curve was constructed for a large-volume Ge detector located at the thermal-neutron beam line of the JRR-3M reactor at the Japan Atomic Energy Research Institute (JAERI). The calibrations for γ-ray energies below 2754 keV were accomplished with a large number of radioactive sources and above 2754 keV with the ¹²C(n,γ) and ¹⁴N(n,γ) reactions. This detector and its efficiency curve were subsequently used to determine accurately the photon emission probabilities of γ rays from the decays of ⁵⁶Co (T_1/2=77 d) and ⁶⁶Ga (9.5 h) and from the ³⁵Cl(n,γ) reaction. These radiation sources can serve as secondary standards for efficiency calibrations